DLadner

I had a scary drop in oil pressure earlier today.

I took my 928 out on a spirited drive, and had been driving for around an hour. The car had been running like a champ - and I had been running it hard (running it up to red line for first and second gears a few times). About a block from my house, I noticed that the valve lifters were suddenly clattering very loudly (loud enough to hear over the stereo). I looked down at the oil pressure gauge and saw that it was pointing straight down at zero (no warning lights were on though). I immediately killed the engine and coasted over to the side of the road. I popped the hood and checked for any oil leaks or obvious signs of trouble in the engine bay. Everything looked fine. I thought about leaving the car there, but it was stopped in a bad spot, and I was only a block from home, so I decided to take a chance and I started the motor up to see what would happen (figuring that I'd just kill it again immediately if the oil pressure still read zero). The engine fired up like normal, and the oil pressure came up to around 3 bar like it normally does on a warm engine. The noise on the valve lifters was down to their normal "sewing machine" levels as well. I drove the car home, parked it and checked everything over more throughly. Everything still looked fine in the engine bay, there are no obvious leaks, and the oil level reads full on the dipstick.

So was this just a fluke, or the sign of oncoming trouble? Is there a specific part on the engine I should look at? I've always been careful to not romp on the engine until the car was up to operating temperature.

I had last changed the oil about 800 miles ago, and on this last change, I changed oil weight and brands over to Lubro-Molly 5W-40 full synthetic. Prior to that, I had run Mobil-1 15W-50 full synthetic without issues. My car is a 1985 USA 928 5-speed manual. Stock, except for a Motorsport cross-pipe and a Porken EZF chip. The engine has around 160,000 miles on it.

Thank you for any help and advice.

Hilton

Given that the gauge was accompanied by noise, I wouldn't drive the car until you've thoroughly checked it out.

First step would be to remove your oil filter, and cut it open to inspect the filter material for metal. If you're lucky, then it'll be clean and you didn't suffer actual damage - but you'll still want to find out why you had no pressure at all, and the noise.

WallyP

Some odd things going on...
- The gauge said that you had no oil pressure.
- The lifters apparently lost oil pressure - perhaps not down to zero, but very low at least.
- The oil pressure warning light did not come on.

Some possibilities:
- Low oil level.
- Temporary blockage at the pump inlet.
- Temporary air bubble at the pump inlet.
- Temporary sticking of one of the spring-operated valves in the oil system, such as the oil pressure relief valve. This would be my first guess.

I am not familiar with the oil that you used, but I am not much of a fan of "boutique" oils. I prefer to use a product that has some serious research behind it. I'm not saying that your oil is no good, or the cause of the problem - it is just an additional complication in the issue.

Vlocity

+ 1

I would then go back to a known "good" oil.

I hope this is nothing major for you. How long did the car cool down before you refired and drove home?

If it was just minutes the oil would not have cooled enough to return the viscosity. Then the question is was there a blockage of some sort to the pickup and the pan refilled and allowed the pressure to also return.

Weird.

Ken

DLadner

Re Vlocity: The car was shut down for about 3 minutes before I fired it back up again.

Re Wally: I've been inclined to blame the recent change in oil weight and brand as well. The reason I changed over is because Dave at Motorsport SLC recommended the oil to me, and he said that they now run it in all of the 928s that they service. I'm going to ask his opinion on my glitch as well on Monday since I need to order a new filter to replace the one I'm going to cut open this afternoon ...

FWIW, I had never heard of Lubro-Molly either until talking to Dave. They sell it at my local NAPA auto-parts, and it claims to be a premium German brand. Still, if my filter shows up clean, then I think I'll change back to Mobil-1.

Thanks for the info guys. I'll let you know what I find in the filter.

hacker-pschorr

Check the teeth on your timing belt. When my oil pump locked up it shredded every tooth in half on my belt.
There was a lot of smoke though from the belt burning.

Much to my surprise the cam gears never skipped a tooth.

Lizard928

did it hurt to pull that horseshoe out?

M. Requin

Dollars to donuts this had nothing to do with the oil itself - something in the lubrication system momentarily failed, and that you were able to drive home indicates that it was "reversible". In other words, not a TB failure, not the oil, but a valve, the pump itself (I think I might have a look at the keyway on the pump drive sprocket), a relief valve, or the filter (assuming you replaced it with the oil change). In any case please let us know what you find!!

DLadner

Well, I have discovered three new findings since my last update:

1) My oil level was actually low. The last time I changed the oil, I tag teamed the work with a buddy that has an 87 S4. We accidentally got the dip sticks mixed up, but assumed at the time that they were the same - a dangerous assumption. Now that I put them side-by-side, it's obvious that the 85 dip stick is shorter than the 87 dip stick, so my oil is under filled, and his oil is over filled.

In the end, I estimate that I was running about 1-1/2 to 2.0 quarts low (it took around that much from a 5 quart jug to bring it up to the full mark). I don't know if that's enough to explain my temporary drop in oil pressure, but it's definitely a possibility.

2) I cut open the oil filter and inspected it, and everything looks fine - no signs of mettalic flakes or debris. Just to be 100% sure, I'm going to send the oil that was inside the filter off for an oil analysis.

3) I checked the timing belt visually, and everything looks okay. No signs of stripped teeth or belt stretching.

So for now I think I'm going to put on a new filter, top everything off again, and go for a cautious drive this upcoming weekend. I've got my fingers crossed that everything will be okay.

Thanks again for the advice!

slate blue

By DLadner

Check your owners manual, that oil weight 5w-40 I believe is not recommended oil from the manufacturer, many 928s are having their engine's destroyed by this, I have seen a couple of late, that Mobil 1 15w-50 was in the last one, (91 S4) owner didn't listen to me about the mechanic or the oil, result, new engine needed. Only took 10,000 kms too. Thrust bearing failure, previously it has knocking noises around the camshaft area, I presumed this to be tappet related. None of the warnings meant anything to the owner till it went furbar. That engine had a genuine 30K miles on it.

That oil is SM rated that you are using, that's a worry for a start, it has low extreme pressure wear agents like ZDDP, you are better off with an oil like Amsoil 20w-50 or Royal Purple 20w-50, your engine will last a lot longer. There are other oils they sell here in Oz that are much cheaper that may fit the bill too, Valvoline Classic 20w-50 is made for vehicles like ours that have a cam lobe lifter interface. You won't have any oil pressure problems with the proper weight oil. The advantage the more expensive oil I mentioned may have is better anti foaming ability. Always best to ask the manufacturer when in doubt.

Greg

Darklands

I´m german and I don´t know Lubro-Molly.Liqui molly is a known brand here.

hacker-pschorr

I completely missed that tidbit from the opening post.
A couple of years ago I reported a low / no oil pressure incident after switching to Mobil 1 Delvac 5w-40 in my 81. Andrew Olson had a similar experience with 5w-40 Shell Rotella.


First off, I would do some more research on Royal Purple before recommended it to anyone. I was a "fan" of their oil until I recently saw the aftermath of a few high performance cars using it. I have also seen oil analysis reports from RP that shows less than stellar ZDDP numbers. This is from their street oil, not the XPR racing blend.

As for Mobil 1 and ZDDP, they are one of the few motor oil manufactures that openly shares their ZDDP levels:

http://www.mobiloil.com/USA-English/...duct_Guide.pdf

Assuming this is the same for all markets.

As you can see, 15w-50 is SM rated and has over 1100ppm/1200ppm phosphorous and Zinc (two main properties of ZDDP).
The "new" standard that yanked some of the ZDDP out of oil is GF-4, which is the environmental stamp. GF-5 is currently in the works and I've read the ZDDP level may go down even further. Looking at that chart you can see all GF-4 oils have 800ppm/900ppm of phosphorous and Zinc.

I'm leery of any oil claiming to have high ZDDP yet will not release specific numbers. Valvoline has the numbers posted on their site for 20w-50 which is why I switched over this year.

ptuomov

I understand that the low ZDDP level is a concern, but please explain to me why 5w-40 viscosity is a problem? I think that the higher than 40 hot viscosity will protect bearings when the car is under high load, especially if combined with higher bearing clearances. But the low-rpm oil pressure dropping simply because of lower hot viscosity sounds to me like it's not the complete story. Is the oil pump not feeding enough or is there something else going on?

hacker-pschorr

It's my complete story and I doubt Andrew is holding anything back. I went from using 15w-50/20w-50 for years to 5w-40. The first hot day not only did my oil pressure drop to almost zero my lifters were clicking away. I immediately changed back to 20w50 without any issues to report since. Yes I know the gauges are not 100% accurate, my ears did not imagine the lifter noise.

One theory is even on a hot July day, driving around the city will not fully heat up 10 quarts of motor oil.
Just for the sake of this discussion, lets assume my oil temperature was 85 degrees Celsius when this happened. This is a very plausible theory since I have a 75 degree thermostat in my car and the coolant temp was below the first tick mark on the dash (where it normally is). Actually, the oil temp is probably below the coolant temp, but that can be another discussion.

The second number in multi-weight oil is the equivalent viscosity protection at 100 degrees Celsius. The true viscosity of the oil is the first number. So even if we were comparing 5w-50 to 15w-50 in the "conditions" set above, running engine oil at 85 degrees, the 5w-50 will be "thinner" than the 15w-50. The standards for oil viscosity are only for the two extreme's, hot and cold. There is no standard for in-between.
So now we drop it down to 5w-40........ see where I'm going here? At 85 degrees or there abouts the "working" viscosity of the oil in my car could have very well been 20 where as the 15w-50 might be closer to 35 or 40...... These numbers are all speculation since not even two different brand 15w-50's "ramp up" the same.

ptuomov

Interesting. By complete story I didn't mean you making other changes but all the conditions.

Did this happen after the car had been stopped for hours or after hard driving? What I am trying to get at is whether the oil had air mixed in it or not at that point. From your description it sounds like air being mixed in is not a possibility.

Your guess is that it's the oil being still cold. I am wondering why the problem showed up on a hot day then?

The low temperature can be a possibility. Just a question: Does it make sense to run a 75 degree thermostat in the car? Wouldn't the car be better off running hotter? Don't know the answer, just asking.

I've been reading all the oil related stuff, both on RL and in the library. It's safe to say that I am not "getting it," at least not yet.