ROG100

On the digital dashes I have a seen a lot where the oil pressure reads 4 to 4.5 bar and never higher. As mine does - remember the gauge is not that accurate. For low pressure if you see the warning light come on then that is accurate.

High ambients - wrong oil - that is your problem on the GTS.

I am pretty sure Motorsports SLC would have installed the cams correctly.

jcorenman

Paul,

I would urge you to take another look at your owner's manual. The oil chart does not list 5W-40, the closest 5W oil is 5W-30 which is rated to about 32F (!). The 10W-40 is rated to around 90F but that would NOT apply to a 5W oil. The "5W" is the base oil, the 40-weight is viscosity-improver's-- thickeners, not lubricants. Synthetics are better in this regard than dino oil, but still...

You live in an area that goes through large temperature swings, summer to winter. I don't think it is realistic to expect a single oil grade to be suitable for 100F in the summer down to 10F in the winter. It seems to me like you are risking engine damage by running oil that is clearly too thin in the summer, with what benefit? Motorsports knows what they are doing, but it sure seems like they must have grabbed the wrong oil chart. Or maybe they are trying to save you the cost of a seasonal change. Or something, but I would change it, now, to a 20W-50.

Z

In my opinion, quite a few people with problems "fix" them by just putting in a thicker oil, then claim that the engines need to use thicker oil. When the Porsche approved oil list is pointed out, consisting of almost all thinner oils, it's usually ignored, or discredited.

I know it won't do any good, so I'm really not sure why I'm even bothering to post it, but directly from Porsche in their service information on changes to the '93 GTS:

BC

Z- older engines do sometimes see benefit, at least in terms of viewable pressure - when using the thicker oils. Obviously the usage would need to be determined. As you can imagine, different oils can be utilized in different engine operational parameters.

SQLGuy

Thanks Z.

I dropped the car off at my mechanic this afternoon for him to do a bit of a post-purchase inspection. One of the things he's going to check is actual oil pressure with a gauge. Should have some results on this early next week.

SQLGuy

Hi Jim,

Just checked my owner's manual. The last item listed in the chart on page 66, in the category of approved Fuel Efficient Oils (synthetic), is SAE 5 W-40 / SAE 5 W-50. This is shown as applicable for the entire temperature range from below -20F to above 110F.

Cheers,
Paul

Hilton

I figured Motorsport SLC would know what they're doing - but it was worth asking as even experienced builders make the odd mistake. Good to rule out the cams as the issue.

Actual oil pressure readings will be good verification - the pressure relief valve opens at 10bar, so readings should be in the range from about 2.5-10 bar depending on rpms and engine temperature.

jcorenman

I saw that also, but it is completely inconsistent with everything listed above that. Why would a 10w40 oil be rated only to ~90F, yet a 5w40 is rated to >100F? That makes no sense to me.

SQLGuy

Probably because the 10W40 is conventional and the 5W40 is synthetic. They specifically call out the "Fuel Efficient" oils as synthetic in the description of the types.

I use only Amsoil in my motorcycles because the info I've seen on temperature-related breakdown show the better synthetics lasting MUCH longer under the conditions found in an air cooled bike engine in summer.

JET951

Hi Z , If you go to the oil viscosity page in the 928GTS owners manual ( that came with the car), printed by Porsche ,the first cab off the rank in the owners manual shaded "look at me section" in the ambient temp range of }

Minus 10 deg cel ( aprox 14 deg F ) to Unlimited high temp = 20W - 50 oil viscosity

I have found ( working on Porsche's for the past 34+ years) in high ambient temps ( summer + traffic conditions= high core temp ) oil pressure insufficient warning at idle is very common if the engine oil vis is too low in these conditions ,( meaning 5w-40 or even 10w-40 ) which also translates to too lower oil pressure all the way through the rev range as well which is not desirable at all .
The other bonus of a 20w-50 is they generally have decent levels of ZDDP( less prone to restrictive emmission protocols) , so the combination of 20w-50 + decent levels of ZDDP = high oil film strength , which is very important for longer life of cam lobes , lifter faces , timing chain sprockets( part of the cams) , thrust bearings , etc etc



Regards
Bruce Buchanan

SQLGuy

What year GTS manual are you looking at?

In the 1993 one I have (early '93 production - so actually 1992), it's 20W40 first in the shaded region and with the temp range you describe. 20W50 is second.

Reading through the whole page, though, I really get the impression that this is a generic page Porsche probably used in the manual of every model they made in 1993. They describe oils but don't make any specific recommendations other than, "Your Porsche dealer will be glad to advise you on the correct type of oil for your engine." Z's GTS-specific factory bulletin seems to me to be the more authoritative reference here.

Z

The Porsche approved oils list:

ROG100

In my manual - 1993 GTS - it quotes both 20W40 and 20W50 as the correct oil for the temperature experienced in my area – Texas.

If I were to use the later Porsche recommended oils – added by Z – I would experience very low oil pressure warnings at idle. I am not disputing the information provided but stating reality.

20W50 allows me to run my car in traffic – stop and go – ambient up to 110F – with no low pressure warnings.
Jim Mayzurk has exactly the same issues on his early 93 GTS.

Other customers with GTS’s have the same issues.

Why would you want to put in a lower grade of oil and risk damage to the engine.

Bruce you are 100% right in my book.

SQLGuy

Roger,

The only thing that's going to make a difference at the high temp end of the spectrum is the second number. 5W40 and 20W40 are both going to act like 40 weights when hot. A synthetic xW40, though, is going to act like 40W when hot a lot longer than a convention 40W will.

Is your point that, regardless of what Porsche says in manuals and bulletins, 928's need something that acts heavier than 40W when hot?

The other part of the question is, why, if heavier weights are always better and safer, would Porsche be recommending, and shipping with, a 5W oil in the later 928's? In fact, they ship current production vehicles with 0W multi-grade synthetics. At the least, I'd expect you're losing a bit of power and bit of fuel economy due to the hydraulic "drag" of heavier base weight oils, and that's probably part of their motivation (EPA requirements), but will there also be situations where some parts of the engine aren't getting enough oil immediately after startup because it takes too long to get the thicker oil to them?

Edit: BTW, just so we're all on the same page (literally), here's the page from my '93 GTS manual I'm talking about.

P.S. Note that, in the manual, all 40W and 50W oils, single or multi-grade, are rated to over 110F. The low oil pressure warnings I was seeing was in about 85 degree weather, and, again, I am (apparently) running synthetic 5W40 that's only a couple of months and a few hundred miles old. I suppose it's possible Porsche was that off on the oil recommendations, or that GTS tolerances loosen up a lot over 100K miles, but I also wonder whether I might just be covering up a different problem by "fixing" things with a thicker oil that was originally recommended.

ROG100

Paul,
Exactly what I am trying to say. Just stating reality.

This is only a problem with the GTS or 89+ cars with the digital dash. Maybe someone else can jump in and pass comment on hot idle oil pressures in the 5.0L 89 to 91 cars – this would indicate whether it was a gauge issue or if the 5.4L is only effected.

On all my other cars – I do have an 89 with Digital dash but not currently in use – idle oil pressure is absolutely no problem and most have 15W 40 synthetic in them.

When I first bought my GTS about 8 years ago and at 60K miles never a problem. Same conditions here in Texas. Over the last 3 to 4 years, slowly, the idle oil pressure started to fall from 2bar to 1.5bar on the gauge. Occasionally, after a very spirited run, the warning light would come on indicating low pressure at idle – IIRC that is in the 1bar range. I realize that 14psi at idle is probably fine but if Porsche set a warning light they had a reason. At that time I was running Mobil 15W40. To try and alleviate the symptom I moved to 15W50. The issue became a non issue.

Jim Mayzurk had exactly the same issues. He was seeing more frequent warning lights but maybe that was because his car being a 5 speed runs at a lower RPM at idle.

What has changed – my car has about 130K miles – so maybe this is a wear issue. Car runs perfectly and performance is awesome. Car uses less oil than it did when I first got it. Usage has gone from a quart every 500 to 600 miles to a quart every 700 to 800 miles. Depends how I drive.

Here in Texas hot idle pressure concerns me more than cold starts. To help even further we are both going to fit the combined oil cooler (below rad) and drivers end radiator cooler to better cool the oil.

Bruce in Australia has to be one of the most knowledgeable 928 mechanics that I know and has worked on more 928’s than I have hot dinners so I take his advice as the best there is.

I guess the change in oil could be masking a problem but it seems to be a GTS problem that we are all suffering from.

Roger