hacker-pschorr

Damn you Doug - now my head is spinning & it's not from the beer.

What was worrying me the most is the brief 0 rpm when coming from high rpm (no load, blipping the throttle at idle) was triggering the "no oil pressure" lamps. My car has never done this before. Even when I had the vacuum limiter on with no idle switch, the car would often try to die, oil pressure always lingered.

Call me paranoid - changed the rod bearings last summer so I'm a bit touchy with this engine at the moment. I'm so close to getting my 944S back on the road, somethings always gets in the way (that something is always the 928 barfing up a part). Something tells me she (928) does not want the 944S back in the garage.

Any 928 voodoo experts out there?

123

I remember reading that auto manufacturers were starting to do away with oil pressure gauges in new cars more and more, and only have low oil pressure warning lights. The reason given was because of people being overly concerned with gauge readings and what they thought were problems because of those gauge readings.

Why are you seeing zero RPM? Zero RPM would mean the engine isn't turning. The engine not turning means the oil pump isn't turning, so a low oil pressure light would be what I'd expect, regardless of what oil you had in there. Of course I'd also be thinking that if the engine was at zero RPM, there couldn't be any engine wear, even with no oil pressure.

Bill Ball

This is a tough one for me. When the low OP light came on, something I had never seen on my car before, like Hacker, despite several years of racing and driving with M1 15W 50, I wasn't about to wait very long to determine if it was transient or not. With your knowledge you are probably comfortable that the Syntec 5W 40 was OK at idle despite the desert heat and the very hot but not overheated engine.

slate blue

Another interesting post, as Doug knows I used to run Castrol synthetic R 10w60 in my original 2 valve engine. Oil pressure was always good, never below 2 bar on the guage in the car and the oil pressure light was never triggered. Also the oil pressure was never excessively high and when the car warmed up oil pressure stayed around where it is now just over 2 bar.

The oil I'm using now is Caltex Delo Gold 15w 40 , I thought this would be a good running in oil, a mineral oil I believe. Well oil pressure is good, the temperature of the engine is good, remember the engine has crank scrapers, new GT radiator, new Porsche thermosat and S4 thermo fans, these do not trigger until 2/3 on the guage is reached. It sits just over the 1/3 mark on the cruise say 70 MPH or 110 KPH. So it not getting hot while running on the highway. So I believe I have a good enviroment to assess oil pressure.

After all this debate I think I will go back to the Castrol oil after this engine is run in because as Doug says, the oil pressure will be lower with the synthetic and this should allow better protection of the camshaft lobes because of the higher viscosity.

I must admit I think oil pressure is an important factor in avoiding wear not just flow , I believe there is a trade off, too much pressure is a bad thing, not enough is a bad thing, so if I can get the guage to be where it was with a mineral oil but with a synthetic and hopefully its superior protection against wear I think that is a good thing. I also know that people have had trouble on hot track days with Delvac, noisy lifters etc.

This is a pet topic for me being a two valve man who is going to run high lift cams. I need a decent hydro dynamic wedge between my lifter and my cam lobe. No place in the engine has as much friction, in fact I'm told that I will save 2% in losses when I go to DLC coatings on the lifters.

If I'm missing something here I am happy to listen, more than happy to listen, I can tell you that my engine before it was sold was in excellent order is still going great according to the new owner. I wonder if there is any HP difference between the Delo Gold and the Castrol synthetic R, both leave a very big hole in your wallet I know that. The other oil I was tempted to try was fully Synthetic Valvoline 15w 50.

Cheers Greg

AO

I'm not an engine builder and consider myself as a complete n00b when it comes to the inner workings of an engine, but do the items that get lubricated in an engine require pressurized oil to get lubricated? I thought the idea was that they get coated with oil and the oil passages help direct the flow to vulnerable areas. To this extent, I always thought oil FLOW is more important than oil PRESSURE. But like I said, I'm a novice in this area.

hacker-pschorr

Don't get Todd started on this one. You will learn everything you ever wanted to know about rod clearance & Oldsmobile engines
It's actually pretty interesting (might be Buick, dunno) back in the day, one of the GM branches were seeing blown engines left and right on the track. The fix was to widen the rod clearance gap to lower oil pressure.

Todd is also playing with this idea on the 928 engine in regards to the rod bearing issue.


Under throttle everything is fine. Problem is I’ve been under the impression a failing rod bearing will start to show up as low idle pressure before you see anything under load.

So I guess at this point, if something is starting to fail the oil weight is not going to make a difference. Maybe I should grab a beer, fire up the car in the garage for a few hours and see if anything hits the fan.

Does anyone have a known plug & play solution for an aftermarket oil pressure gauge? I’d like to throw one in ASAP as a secondary guide.

ROG100

Am I right in saying that Delvac syn is only available in 5w 40?
I'm with Andrew as a complete noob when it comes to the inside of the engine - but like Andrew learning fast.
1) Listening to the experts the Delvac formulation is better than the Mobil 1.
2) The Delvac is a thinner oil and therefor will be even thinner at high operating temps - ie TX.
3) Thinner oil means less pressure?
4) Thinner oil means that it can reach those "important little places" better and faster.
Am I making any sense????

I have seen a slight decrease in oil pressure - down 7 psi. Is that directly related to viscosity?
Oil pressure is supposed to be 73.5 psi at 5k - is that irrespective of the viscosity of oil used.
If you used a very thin oil would you still reach 73.5psi?

My head hurts

hacker-pschorr

Do our cars have an issue with oil starvation in these little important areas? No, we have issues with rod bearings. So my #1 concern is my bearings are getting the oil they need.

Correct me if I'm wrong, oil pressure is really created in the crank as the oil tries to squeeze it's way through to the bearings and up in the lifters.

My lifters have been clanking off / on with the 5w-40. Either that or a rod bearing is clanking off / on, not 100% sure.

928autobahndreamer

Now I am really confused.

I have been a little worried about my hot oil pressure in stop and go driving. The oil pressure light has never come on, but pressure at idle will drop to 1-1.5 when hot.

I am due for an oil change and was all ready to put in Delvac 1 or maybe Rottela if I can't find the Mobile 1 Diesel Truck 5W-40. With my oil pressure being what it is should I stick with a "thicker" oil? I am worried that if I get another 0.5 bar drop with the Delvac that will be too low. Would maybe the hydrocracked synthetic (Shell Rottela) be a better option being just a little thicker? Or should I stick with the old tried and true? (Any recommendations?)

I know this topic has been discussed to death (I know because I have read and re-read all of them) but I am just hoping that some other nugget of knowledge may be out there that helps me make a decision on what to do.

As a side note, I do not know what oil is currently in my engine. I just bought this car a couple of months ago and do not have record of what oil was used. Anyway, thanks for listening.

ROG100

Delvac 1 5w 40 and Mobil 1 diesel & truck 5w 40 are the same oil.

928autobahndreamer

Sorry, I wasn't clear. Delvac 1 is not available in the US, so I was going to see if the US version Mobil 1 Diesel Truck 5W-40 was still available. I simply used the two interchangably in the same sentance.

AO

Hacker-
Riddle me this? How does oil pressure affect the rod bearings? Aren't they just swept throught he oil bath and dripped on from above? Or is there a pressureized passage that pump oil to them?

hacker-pschorr

What are you using now?
If a rod bearing is gone, oil pressure will drop since a gap was created in that area, pissing oil out the side of the bearing - correct? That is what happened on my 944S except it was sudden, in traffic under load I watched the oil pressure fall from 5 bar to 1bar then.... knock knock knock......I never paid attention to my idle oil pressure in the 944S & always ran 5w-50 Castrol or 15w-50 Mobile 1. So now I'm paranoid.

So I'm not worried that this low oil pressure will kill a rod bearing (well, not toally) I'm more worried this low oil pressure is a sign I have a bearing waving goodbuy. Does that make more sense? But, if pressure is low not due to a bad bearing but maybe oil is pissing out some wide clearance in my motor because it's too thin, could oil not be getting somewhere else (like the last bearing or some lifter)?

So in my half-assed way of seeing things, if I go back to 15w-50 & my oil pressure goes up and stays there.......my rod bearings are ok afterall? It seams cheaper & easier to do an oil change than pull the pan again.

I'm confusing myself now.

Kevin in Atlanta

I know very little about all this, but you what they say about opinions.

Like fingerprints, I think no two engines are alike. Not sure comparisons are valid from car to car.

Also, I think that relying on what the engine temp gauge says may lead to false comparisons.

That said, when I had issues with low oil pressure issues with my 86.5 when running hot with the AC on, I pulled the intake, replaced all the gaskets, o-rings, vacuum lines and elbows, rebuilt the injectors. I also re-did the entire A/C system front and rear. I found after that my car's oil pressure and temp were no longer an issue. In my case I found antifreeze leaking from the big o-ring at the bottom of the coolant crossover, so my system was not fully presurized.

This may not be the case for you, but I wonder if the cars are actually running hotter than the temp gauge would indicate.

FWIW, my GTS in the Atlanta heat with the temp mark nearly at the last white mark holds oil pressure about the 2.5~ bars at idle. I am now using M1 15-40, I think. Normally I can count on losing a quart between fill ups, but I drove to and from SITM without adding a quart and no black smoke under hard acceleration.

928drvr86.5

There are passages for the main journals and the rod pins. The crank is not swept thru a bath of oil, this would aerate the oil and cause severe foaming issues