Low oil pressure or bad sender?
07-02-2011, 05:24 PM
#31
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My GTS has the metal pins in already when we changed the cams.
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Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission?
George Layton March 2014928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
07-02-2011, 09:45 PM
#32
Three Wheelin'
Paul, I wish I had a GTS with S3 Cams, and if I did, I would probably listen to the the other people who do and utilize their experience......and follow their advice. All Porsche manuals and literature aside, there have been obvious miscalulations and/or design issues as a result of the original engineering on these automobiles such as: water pumps, timing belts/tensioners, torque tube clamps and.........oil delivery. Dontcha think that if after 100K+ miles by other enthusiasts and vendors, that the general consensus says 20w50 is the best choice; that you oughta just change your oil and and probably enjoy your GTS longer instead of defending 25 year old factory literature? This was not meant to be personal, just sayin.
07-02-2011, 11:35 PM
#33
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Paul, I wish I had a GTS with S3 Cams, and if I did, I would probably listen to the the other people who do and utilize their experience......and follow their advice. All Porsche manuals and literature aside, there have been obvious miscalulations and/or design issues as a result of the original engineering on these automobiles such as: water pumps, timing belts/tensioners, torque tube clamps and.........oil delivery. Dontcha think that if after 100K+ miles by other enthusiasts and vendors, that the general consensus says 20w50 is the best choice; that you oughta just change your oil and and probably enjoy your GTS longer instead of defending 25 year old factory literature? This was not meant to be personal, just sayin.
At this point I am waiting for the mechanical gauge verification of actual oil pressure on the car, since I certainly have seen oil pressure sender problems in the past on 928s.
The main thing I'm defending the (actually 19 years old) literature from is potential out-of-context quoting on this thread. We've had people say it's different from the bulletin Z posted. It's not. We've had people say it lists certain oils first, when it does not. I'm pretty sure Roger and I are now in agreement that his feeling is that the car needs a 50W oil in hot weather regardless of what any of the Porsche recommendations say.
If the mechanical check shows the dash is underreporting actual pressure, I'll probably remove the sender mounting, clean it out, install a new sender, and see where things go. If the dash proves to be accurate, then I'll probably switch to a 15W50 synthetic instead and see how that goes.
In general, though, my first take is going to be to assume that the folks in Zuffenhausen are correct, until I have pretty solid proof otherwise... they did a LOT of testing and research before they printed their results. For all the complaints about the timing belt tensioners, for instance, the actual rate of failure on these 17 to 34 year old cars doesn't seem to be that high. The flex plate seems to be more of a problem, and Porsche made torque tube changes to later cars to try to mitigate that.
07-03-2011, 12:05 AM
#34
Team Owner
if you swap out the oil sender then swap out the oil thermostat and springs as well
07-03-2011, 01:43 AM
#35
Nordschleife Master
If the mechanical check shows the dash is underreporting actual pressure, I'll probably remove the sender mounting, clean it out, install a new sender, and see where things go. If the dash proves to be accurate, then I'll probably switch to a 15W50 synthetic instead and see how that goes.
If you're swapping the pressure sender, or "cleaning" it or whatever, take the extra few minutes to remove and examine the oil pressure relief valve - its above the sender and the sender must be removed to access it. If its stuck open, or has a broken spring providing less spring pressure, you will get low pressure.
Anyway - on the oil debate.. looking at the page you show I have a question for those who probably know more than me. If the second number is effectively the "hot" viscosity, why does the maximum recommended temperature vary between the 10W40 and 15W40?
07-03-2011, 01:49 AM
#36
Three Wheelin'
When there is a big difference between the first number and the second number, for example 5W40 to 20w40. The oil will lose its viscosity faster when it reaches operating temperature. They call it shearing. The second number is for when the engine is hot but if theres a big difference compared to the first number, its more likly for the oil to lose its viscosity compared to one with less difference when the engine is operating at extrem temperatures.
This is what I have read online, I dont stand behind it. But something to research about.
This is what I have read online, I dont stand behind it. But something to research about.
07-03-2011, 03:09 AM
#37
Rennlist Member
Sure, whatever you say. And please don't take this unkindly, but you also are looking at this from just one point of view.
But tell me, please, where does the word "recommended" appear in ANY of this?
The word that Porsche uses repeatedly is "approved".
There is no question that Porsche "approved" 5W-40 oil, that is not the question. You came here complaining about an oil-pressure warning with 5W-40 oil at high temperatures. A number of folks pointed out that heavier-weight oils were listed in the owner's manuals, and did not exhibit the same low-pressure/high-temperature problem.
Now let me ask another question: How long has it been since the engineers made the business decisions at Porsche? (Or any car company? Or anywhere?)
The reality is that the business and regulatory priorities are governing most decisions these days. If a car company can eke out another 0.1 mpg and cut CO2 emissions (a big deal in Europe) then they will do what they need to do.
Here's another question, admittedly a bit cynical: Why does any car company care about the long-term durability of an engine? (Past the warranty period, that is). Isn't it in the best corporate interest to minimize warranty cost (and any pre-paid maintenance) and then optimize new-car sales? And isn't any corporation obligated, by law, to do whatever is in the best interests of its shareholders?
If you do a bit more research you will find that VW and Audi have been busy writing their own oil standards, because simply relying on the SAE standard for lightweight, fuel-efficient oils does not adequately protect the engines against early failure. (We're talking warranty-period failures, not long-term). The principal issue is the HTHS spec (high-temp/high-shear, the oil's shear-strength at high temp's). VW/Audi have established a minimum standard of 3.5 cP-- which many 5W-40 "fuel efficient" oils do not meet. Hence the VW standards, and which I suspect is also the reason that Porsche, in the past, has maintained its "approved oils" list. Most of the popular oils available (Amsoil, Mobil, Redline, Valvoline) are not listed. Amsoil publishes their HTHS numbers, their 5W-40 "Euro" oil is 3.8 and the 20W-50 is 5.0. Heavier oils have higher HTHS but don't flow as well when cold, don't use a 20W-50 oil in the winter in Salt Lake City. But as I said before, in your climate I think a single oil for year-around use is not realistic.
The conundrum is this: Regulations and market forces, here and in Europe, have put a lot of pressure on manufacturers to improve fuel economy and CO2 emissions. Thinner oils have less friction for the light-load running that makes up 98% of the average auto use, but they also offer less protection for high loads at higher temp's. Companies are motivated by survival and profits, and they are walking a tightrope between regulations and warranty costs. And the decisions are being made for business reasons, not engineering reasons. So yes, of course 5W-40 "fuel efficient" oils are "approved".
Personally, I would happily trade a bit of fuel economy for longer engine life. Our GT just turned 189K, AFAIK it has always had 15W-50 or 20W-50, we change it every 5-7K and do a lab report every time we change it. You might say we are silly, but that all seems pretty darned cheap to me. And we've never seen less than 2.0 bar at idle, even stopped in traffic in 100F temps with the A/C on full in BFE. But those are our personal choices, and we're happy with them, as you are with yours.
Peace, brother.
But tell me, please, where does the word "recommended" appear in ANY of this?
The word that Porsche uses repeatedly is "approved".
There is no question that Porsche "approved" 5W-40 oil, that is not the question. You came here complaining about an oil-pressure warning with 5W-40 oil at high temperatures. A number of folks pointed out that heavier-weight oils were listed in the owner's manuals, and did not exhibit the same low-pressure/high-temperature problem.
Now let me ask another question: How long has it been since the engineers made the business decisions at Porsche? (Or any car company? Or anywhere?)
The reality is that the business and regulatory priorities are governing most decisions these days. If a car company can eke out another 0.1 mpg and cut CO2 emissions (a big deal in Europe) then they will do what they need to do.
Here's another question, admittedly a bit cynical: Why does any car company care about the long-term durability of an engine? (Past the warranty period, that is). Isn't it in the best corporate interest to minimize warranty cost (and any pre-paid maintenance) and then optimize new-car sales? And isn't any corporation obligated, by law, to do whatever is in the best interests of its shareholders?
If you do a bit more research you will find that VW and Audi have been busy writing their own oil standards, because simply relying on the SAE standard for lightweight, fuel-efficient oils does not adequately protect the engines against early failure. (We're talking warranty-period failures, not long-term). The principal issue is the HTHS spec (high-temp/high-shear, the oil's shear-strength at high temp's). VW/Audi have established a minimum standard of 3.5 cP-- which many 5W-40 "fuel efficient" oils do not meet. Hence the VW standards, and which I suspect is also the reason that Porsche, in the past, has maintained its "approved oils" list. Most of the popular oils available (Amsoil, Mobil, Redline, Valvoline) are not listed. Amsoil publishes their HTHS numbers, their 5W-40 "Euro" oil is 3.8 and the 20W-50 is 5.0. Heavier oils have higher HTHS but don't flow as well when cold, don't use a 20W-50 oil in the winter in Salt Lake City. But as I said before, in your climate I think a single oil for year-around use is not realistic.
The conundrum is this: Regulations and market forces, here and in Europe, have put a lot of pressure on manufacturers to improve fuel economy and CO2 emissions. Thinner oils have less friction for the light-load running that makes up 98% of the average auto use, but they also offer less protection for high loads at higher temp's. Companies are motivated by survival and profits, and they are walking a tightrope between regulations and warranty costs. And the decisions are being made for business reasons, not engineering reasons. So yes, of course 5W-40 "fuel efficient" oils are "approved".
Personally, I would happily trade a bit of fuel economy for longer engine life. Our GT just turned 189K, AFAIK it has always had 15W-50 or 20W-50, we change it every 5-7K and do a lab report every time we change it. You might say we are silly, but that all seems pretty darned cheap to me. And we've never seen less than 2.0 bar at idle, even stopped in traffic in 100F temps with the A/C on full in BFE. But those are our personal choices, and we're happy with them, as you are with yours.
Peace, brother.
07-03-2011, 03:59 AM
#38
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The Porsche approved oils list that I posted is four years old, not twenty five, and it covers all cars being discussed here.
Questions for some of you to think about:
Since the engine operates at basically the same temperature all the time when it's fully warmed up, why are there different oil weight recommendations for different ambient temperatures?
When does the majority of wear in an engine occur, and why?
Where is the oil pressure sender located in the oil path through the engine, and what does that mean as far as oil flow and pressure throughout the engine goes? What does the oil pressure gauge really tell you about the oil going to all of the bearings along the oil path?
What are the effects of temperature and oil flow in an aluminum engine compared to a cast iron one?
If the xW-40 oils are too thin, why didn't Roger's engine have the low pressure warning issue with that weight of oil when he first got the car, and the warning started after using the 15W-40 for several years?
Why are there a lot of 928s out there who are using the thinner oils and are not having the low oil pressure issues that some others are, even when the cars are in the same climates?
What weights of oil were being used in engines where people have experienced bearing failures, and were they getting low oil pressure warnings before those bearing failures occurred?
Did any of the people reporting low idle oil pressure have the engine fail from it? (Not counting situations like an oil pump failure causing no oil to flow and being the reason for the oil pressure warning, low oil level, someone forgetting to put oil in the engine, etc. )
Why would a 928 engine in good condition require thicker oil than is used without problems in other engines, including ones that are also aluminum, making more power, and in some cases also spinning to higher RPM, and that are lasting for hundreds of thousands of miles like that with the thin oils?
What are the consequences of an oil being too thick, too thin, and which components would be most affected by each scenario?
Why did some auto manufacturers stop putting oil pressure gauges in cars? (There's more to it than cost, and those of you with oil pressure gauges in your other cars might be interested in what pops up when you Google fake oil pressure gauge)
Here's another question that may be easier. Why do some used car dealers use thick oil in some of the cars that they're trying to sell?
I think that once you think about some of those questions, and know the answers to them, you might have a much better understanding of why Porsche has the oils on their approval list that they do. Some of you with low oil pressure issues may also start to get a better idea of why that might possibly be.
I don't know when the low oil pressure issues started for the three cars mentioned in this thread so far, but I couldn't help but notice that all three are GTS cars with non-stock cams in them. Are people checking cam "bearing" clearances when changing cams?
Questions for some of you to think about:
Since the engine operates at basically the same temperature all the time when it's fully warmed up, why are there different oil weight recommendations for different ambient temperatures?
When does the majority of wear in an engine occur, and why?
Where is the oil pressure sender located in the oil path through the engine, and what does that mean as far as oil flow and pressure throughout the engine goes? What does the oil pressure gauge really tell you about the oil going to all of the bearings along the oil path?
What are the effects of temperature and oil flow in an aluminum engine compared to a cast iron one?
If the xW-40 oils are too thin, why didn't Roger's engine have the low pressure warning issue with that weight of oil when he first got the car, and the warning started after using the 15W-40 for several years?
Why are there a lot of 928s out there who are using the thinner oils and are not having the low oil pressure issues that some others are, even when the cars are in the same climates?
What weights of oil were being used in engines where people have experienced bearing failures, and were they getting low oil pressure warnings before those bearing failures occurred?
Did any of the people reporting low idle oil pressure have the engine fail from it? (Not counting situations like an oil pump failure causing no oil to flow and being the reason for the oil pressure warning, low oil level, someone forgetting to put oil in the engine, etc. )
Why would a 928 engine in good condition require thicker oil than is used without problems in other engines, including ones that are also aluminum, making more power, and in some cases also spinning to higher RPM, and that are lasting for hundreds of thousands of miles like that with the thin oils?
What are the consequences of an oil being too thick, too thin, and which components would be most affected by each scenario?
Why did some auto manufacturers stop putting oil pressure gauges in cars? (There's more to it than cost, and those of you with oil pressure gauges in your other cars might be interested in what pops up when you Google fake oil pressure gauge)
Here's another question that may be easier. Why do some used car dealers use thick oil in some of the cars that they're trying to sell?
I think that once you think about some of those questions, and know the answers to them, you might have a much better understanding of why Porsche has the oils on their approval list that they do. Some of you with low oil pressure issues may also start to get a better idea of why that might possibly be.
I don't know when the low oil pressure issues started for the three cars mentioned in this thread so far, but I couldn't help but notice that all three are GTS cars with non-stock cams in them. Are people checking cam "bearing" clearances when changing cams?
07-03-2011, 06:46 AM
#39
Nordschleife Master
Thanks Z for persisting with this - its appreciated. I know we all feel like this has been done to death and people have become attached enough to their respective opinions that they will fight to the internet-death to defend their position.
In my experience, used-car dealers usually use thick oil to stop cars smoking due to burning oil - presumably due to blocked rings (carbon) or worn valve guides allowing oil into the combustion chamber, or preventing it from draining out when scraped by the rings? (these are guesses on my part) Not sure what that would have to do with oil pressure however?
Interesting question about cam clearances - hadn't occurred to me to measure, but I will when I'm ready to fit some to my S4's.
On possible causes for intermittent low oil pressure - as far as I can tell from my knowledge of 928's, it comes down to these: (and I could be missing some? also note I'm ignoring non-intermittent causes like the pickup seal)
1. Sludge build-up occluding oilways (and possibly causing oil check/relief valves to stick open?)
2. Fatigue in springs (head check valves, and oil pressure relief valve)
3. Leaking oil pump seals/o-rings
4. Increased bearing clearances due to wear
Funnily enough, all the above factors have a significant time element to them. I'd imagine dirty grounds and poor wiring could also result in warnings and gauge readings?
1 should be taken care of by using a good engine flush (e.g. Lubro-Moly) with each oil change, and changing oil frequently.
2,3 and 4 can all be addressed with parts - (didn't Brad in Canada do the main bearings from underneath?).
Now I guess the real interesting data would come from comparisons of actual oil pressure readings from another location in the oil system, comparing 5W40 and 20W50 pressures both before and after doing 2/3/4 above - preferably on a 100k+ mile 928. If anyone has such data, I'd expect it to be the green bay guys?
I suspect that springs, pistons/*****, seats etc. on check and relief valves should be considered wear items, and have a couple of sets for my cars when I get around to the work. Oil pump seals are part of the TBWP for me - at least when I don't know when/whether they were replaced last.
In my experience, used-car dealers usually use thick oil to stop cars smoking due to burning oil - presumably due to blocked rings (carbon) or worn valve guides allowing oil into the combustion chamber, or preventing it from draining out when scraped by the rings? (these are guesses on my part) Not sure what that would have to do with oil pressure however?
Interesting question about cam clearances - hadn't occurred to me to measure, but I will when I'm ready to fit some to my S4's.
On possible causes for intermittent low oil pressure - as far as I can tell from my knowledge of 928's, it comes down to these: (and I could be missing some? also note I'm ignoring non-intermittent causes like the pickup seal)
1. Sludge build-up occluding oilways (and possibly causing oil check/relief valves to stick open?)
2. Fatigue in springs (head check valves, and oil pressure relief valve)
3. Leaking oil pump seals/o-rings
4. Increased bearing clearances due to wear
Funnily enough, all the above factors have a significant time element to them. I'd imagine dirty grounds and poor wiring could also result in warnings and gauge readings?
1 should be taken care of by using a good engine flush (e.g. Lubro-Moly) with each oil change, and changing oil frequently.
2,3 and 4 can all be addressed with parts - (didn't Brad in Canada do the main bearings from underneath?).
Now I guess the real interesting data would come from comparisons of actual oil pressure readings from another location in the oil system, comparing 5W40 and 20W50 pressures both before and after doing 2/3/4 above - preferably on a 100k+ mile 928. If anyone has such data, I'd expect it to be the green bay guys?
I suspect that springs, pistons/*****, seats etc. on check and relief valves should be considered wear items, and have a couple of sets for my cars when I get around to the work. Oil pump seals are part of the TBWP for me - at least when I don't know when/whether they were replaced last.
Last edited by Hilton; 07-03-2011 at 08:21 AM.
07-03-2011, 07:20 AM
#40
Nordschleife Master
Doesn't help the OP - but it just occurred to me that I can use my digital-dash readings to compare before and after oil pressure readings when I get around to replacing some of the parts in items 2/3/4 in my previous post.
If there's a difference in the dash diagnostics value for the sender output (rather than the needle which can be read incorrectly), it'll be interesting to see. Shouldn't be too hard to do back-to-back readings without changing other parts of the "system".
Oh well - not something I'll be doing soon, but I'll try to remember to do so when I'm ready to change those parts.
If there's a difference in the dash diagnostics value for the sender output (rather than the needle which can be read incorrectly), it'll be interesting to see. Shouldn't be too hard to do back-to-back readings without changing other parts of the "system".
Oh well - not something I'll be doing soon, but I'll try to remember to do so when I'm ready to change those parts.
07-03-2011, 11:07 AM
#41
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I think everyone has a good point here on this thread and I am pursuing it because I am interested in the conclusion. I am not an expert and have been careful to state that I am basing my facts on actual findings with mine and other cars.
My car started showing lower oil pressure long before I had the cams installed.
So WHY are cars showing lower hot idle pressures – seems to be GTS 5.4L cars in particular.
Is my car about to die? Performance has not changed, oil consumption has decreased slightly. Prior to the cam install I would say the car performed better than it did when I first bought it.
Can’t you interrogate the digital dash and see actual pressures and temperatures?
Has anyone seen it on earlier digital dash equipped 5.0L cars?
Why is it not a problem with all my other 78 to 87 cars – low and high mileage cars in the same ambient temperatures in the same traffic conditions. I never see a low pressure light in any of those cars ever.
For the time being I will run the 15W50 as the pressure issue has gone away.
Maybe I need to swap out the thermostat and springs.
My car started showing lower oil pressure long before I had the cams installed.
So WHY are cars showing lower hot idle pressures – seems to be GTS 5.4L cars in particular.
Is my car about to die? Performance has not changed, oil consumption has decreased slightly. Prior to the cam install I would say the car performed better than it did when I first bought it.
Can’t you interrogate the digital dash and see actual pressures and temperatures?
Has anyone seen it on earlier digital dash equipped 5.0L cars?
Why is it not a problem with all my other 78 to 87 cars – low and high mileage cars in the same ambient temperatures in the same traffic conditions. I never see a low pressure light in any of those cars ever.
For the time being I will run the 15W50 as the pressure issue has gone away.
Maybe I need to swap out the thermostat and springs.
07-03-2011, 12:30 PM
#42
Rennlist Member
Roger,
The digi-dash will show oil pressure in the readout with a jumper the diagnostic connector. But not oil temperature, and that would be a key thing to know.
The oil-pressure sensor is on the main gallery near the pump, basically measuring the back-pressure from flow to the various bearings. If the pump-output is high and flow through the bearings is low (thick oil, tight clearances) then pressure will be high. The relief valve only comes into play if the pressure would otherwise exceed 8 bar, it basically provides a large "leak" to limit pressure to 8 bar.
If the pump-output is low (e.g. idle), and the flow through the bearings is high (thin oil, large clearances) then the pressure will be low. If the bearings are lightly loaded then this is not a problem, if loaded (i.e. put your foot in it from idle) then it can result in metal contact and accelerated wear.
Personally I think the under-mount oil cooler (used from '90 on??) may be a key piece of the puzzle. It works great on the highway and unloads some of the heat from the main radiator, but it is ineffective at low speeds. I would expect that to lead to higher oil temps, which will further thin any oil. I think GB's hose kit to use both the under-mount and radiator coolers is a terrific idea for the warmer climes.
Mike, you pose some excellent questions. The answer to when the wear occurs, is "it depends".
I have one data-point that I can contribute: For our GT engine, lead (the major bearing-wear metal) is very consistently 1ppm per 1K miles with mixed driving, including lots of short (5-10 mile) trips around home. That's the same number that Doug Hillary reported here many years ago (using mostly 5w-40 as I recall).
We've also done two 6-to-7K-mile road trips, with an oil fill pretty much just for those trips. The report on those samples was different: lead was about half the usual rate, 3 ppm/6K miles or 0.5 ppm per 1K miles.
So for our typical use, start-up wear is about half of the total. For folks who drive longer distances after warmup, it will be less.
And why did Porsche include 20W-50 (or 40 single-weight) at all, in the owners manuals? I don't think they did that for other engines at that time, and I don't recall seeing oils that heavy in the BMW manuals at that time. The 928 bearings are pretty large in diameter compared to other V8's, how do clearances compare?
Certainly the oils -- and especially multigrades-- have gotten better, but there are still other factors at play now, that were not issues in the past.
Jim
The digi-dash will show oil pressure in the readout with a jumper the diagnostic connector. But not oil temperature, and that would be a key thing to know.
The oil-pressure sensor is on the main gallery near the pump, basically measuring the back-pressure from flow to the various bearings. If the pump-output is high and flow through the bearings is low (thick oil, tight clearances) then pressure will be high. The relief valve only comes into play if the pressure would otherwise exceed 8 bar, it basically provides a large "leak" to limit pressure to 8 bar.
If the pump-output is low (e.g. idle), and the flow through the bearings is high (thin oil, large clearances) then the pressure will be low. If the bearings are lightly loaded then this is not a problem, if loaded (i.e. put your foot in it from idle) then it can result in metal contact and accelerated wear.
Personally I think the under-mount oil cooler (used from '90 on??) may be a key piece of the puzzle. It works great on the highway and unloads some of the heat from the main radiator, but it is ineffective at low speeds. I would expect that to lead to higher oil temps, which will further thin any oil. I think GB's hose kit to use both the under-mount and radiator coolers is a terrific idea for the warmer climes.
Mike, you pose some excellent questions. The answer to when the wear occurs, is "it depends".
I have one data-point that I can contribute: For our GT engine, lead (the major bearing-wear metal) is very consistently 1ppm per 1K miles with mixed driving, including lots of short (5-10 mile) trips around home. That's the same number that Doug Hillary reported here many years ago (using mostly 5w-40 as I recall).
We've also done two 6-to-7K-mile road trips, with an oil fill pretty much just for those trips. The report on those samples was different: lead was about half the usual rate, 3 ppm/6K miles or 0.5 ppm per 1K miles.
So for our typical use, start-up wear is about half of the total. For folks who drive longer distances after warmup, it will be less.
And why did Porsche include 20W-50 (or 40 single-weight) at all, in the owners manuals? I don't think they did that for other engines at that time, and I don't recall seeing oils that heavy in the BMW manuals at that time. The 928 bearings are pretty large in diameter compared to other V8's, how do clearances compare?
Certainly the oils -- and especially multigrades-- have gotten better, but there are still other factors at play now, that were not issues in the past.
Jim
07-03-2011, 10:01 PM
#43
Under the Lift
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Man, I can't answer any of Z's questions. I just know that the one time I used 10W40 synthetic (Castrol) I got a low oil pressure warning when my engine was very hot and I pulled over at the end of an open road race in the Nevada desert during July. The pressure guage was below 1 bar at idle. I immediately stopped the engine. Once the engine cooled down, the pressure was higher and the warning did not appear. I went back to 20W50 M1 after that. Never seen a pressure warning with it. The pressure sensor is right after the pump and not in the galleys or the head. I think pressure is lower in the galleys and heads, but I'm not sure. I'd rather not see a low oil pressure warning again even if I'm not entirely sure what it means.
07-04-2011, 02:59 AM
#44
Rennlist Member
Paul, I have a 93 GTS 5-speed with GT cams (not S3). As Roger pointed out I was getting low oil pressure warnings (both the digital dash and the oil press light) I also have an oil temperture gauge installed (see avatar). I was ONLY getting the warnings when the ambient temp was 100 Deg. F or higher and only at idle when the car was hot (oil temp above 210). This was occuring with Mobil 1, 15w50, Brad Penn, and Royal Purple. After shark tuning and raising the idle speed to the GT spec I have not had a problem. Now even at 100F+ temps the oil pressure gauge never goes below 1.5 Bar. I do plan to add the water/oil cooler in the radiator but only as extra protection.
07-04-2011, 10:13 AM
#45
Drifting
Hi SQLGuy, the Porsche owners manual year type I was looking at was a 1994 928GTS , interestingly there was no reference to the 20w-40 at all in that owners manual vis chart , so the first cab off the rank in the shaded "Look at me" section of the oil vis chart was 20w-50, however looking at a few more 928 owners manuals I noticed that the reference of a 20w-40 came in around 1989 and then disappeared around 1993 or so and the 20w-50 came back to the top spot in 1994 , just a bit of trivia .
Regards
Bruce Buchanan
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Bruce Buchanan