Crisis

Something new to worry about. For the first time ever today, I was experiencing low oil pressure (< 1 Bar and warning light on) while idling with a warm/hot engine. Even under load the gauge wasn't pegged at 5 Bar, as per usual. I let the car sit for a couple of hours and cool down and just recently fired it up again. This time on a cool engine, it was reading about 3 Bar at idle. I took it for a 10 minute drive to get the engine up to normal operating temp. By the time I was done the gauge was at approx 1 Bar when idling in gear and at about 1.5 Bar in Park (higher idle).

Searching old posts, it would appear that it's not likely the sending unit, as both the gauge and warning light came on and they are served by separate sensors. My diagnosis is an oil thermostat failure. Before ordering up the thermostat kit (and waiting 3 weeks for arrival), I was just hoping to get some opinions as to whether or not that is the likely culprit.

Any input is greatly appreciated.

Thanks in advance,

heinrich

i think you need to consider the possibility that you in fact suffer from low oil pressure, and that can be a result of bearing failure.

danglerb

Measure the oil pressure with a real gauge.

Pull the oil filter and cut it open.

Tails

+1 on a calibrated oil pressure gauge.

Have you checked the engine cooling water temperature, is it above normal?

The most expensive way to repair a 928 is by replacing new parts for good and correct operating parts. Always undertake some fault finding/trouble shooting before getting out the credit card.

Identify the problem and then repair it.

Tails 1990 928S4 Auto

Marine Blue

What weight oil are you using and when was the last time you changed it?

Not that this is a problem but it helps to have all of the info up front when trying to diagnose.

mj1pate

The manual states that under load, the gauge should read 5 bar. *IF* you come upon or decide to buy a manual oil pressure rig to hook up, perhaps we could share the cost. Read my current post, and I have the same investigative step ahead, before I pull the engine.

My tests suggest that the sender includes both an analog pressure sensor for the gauge and contact closure for the light. Someone like ALAN :-) could shed light on this.


The springs and plunger are cheap. It takes a minute or sixty to fit the thermo housing up into the block, but I would certainly try this. Any of the major suppliers can send these parts overnight.

Mrmerlin

A quick test , pull the dipstick and drip the oil onto a black piece of cardboard, go into the sun and look at the oil looking for metallic particles, if you find metallic particles in the oil then there is some sort of failure.
If no particles change the oil to 15W50 and change the oil filter

Crisis

Further info: running Castrol 10W40 (relatively cool climate) that was changed approx 2000 miles ago, though that was approx 1 year ago. Coolant temp seems fine - running mid level on gauge.

This morning's commute (15 minutes) yielded similar results to last night's test drive: 3 Bar at startup idle. Just above 1 Bar at idle in parking lot at work.

Keep the input coming, I will do some further investigation this weekend.

Mrmerlin

change oil and also change the brand............. I suggest that you use Valvoline.
I have had a few viscosity breakdowns with Castrol non sysn oil.
Usually a fresh oil change will restore performance also change out the filter

Chuck Schreiber

Royal Purple 20w50 ought to do the trick if it's an oil issue.

heinrich

Chuck, Stan, if the oil he uses works for others and worked for him, what changed? I wouldn't use the oil he's using, but .... if Royal Purple 20/50 will fix the issue I'll eat my hat. Anyway then any 20/50 would do

Chuck Schreiber

Like I said Heinrich in my above post. RP 20w50 should do the trick "IF" it's an oil issue. But yes, if it started happening suddenly, probably not an oil issue.
And NO, I'm not gonna eat your shorts either!

I will tell you that Roger and Jim M. here in DFW land started using the Shell Rotel (Spelling??) and they had oil pressure issues that sound very similar to what Crisis is going through. Low oil pressure/warning light issues at idle, etc.

Crisis, do a search on oil pressure issues, you can probably find a few posts here.

Mrmerlin

I have found that viscosity breakdown is real and i have had issues with Castrol in particular after getting hot, that oil pressure has dropped on the gauge and its noticeable.
Thats why I recommend swapping the oil and the MFG and the filter, but check for metal first

Hilton

I see from your sig you have a '90.

First off - I wouldn't drive or run the engine until I'd checked the oil and oil filter for metal particles. If the pressure was fine previously on this oil, then chances are something in the engine has changed. If it was viscosity breakdown it'd be more gradual than your post indicates.

If your oil filter and oil don't contain metal particles, then start the engine and use your digital dash to get a more accurate reading from the oil pressure sender than the analogue gauge. Make a jumper and connect pins 5 and 13 on the diagnostic plug (under the trunk switch by the passenger sear).

There's a pdf that contains the diagnostic info from the digital dash.. called "Diagnosis of the Instrument Cluster" from 1989 about the digital dash.

If pressure is wayward, try changing to a cheap 20W50 oil and see what difference it makes - if it's better, then replace with decent 20W50 (e.g. Royal Purple). If no difference, then it's something mechanical or a sensor failure.

Other candidates on S4's include the oil plastic galley plugs in the heads - the plastic plugs warp and eventually open a galley causing loss of pressure. However, before chasing the gremlin, make sure your car isn't eating bearings.

Andre Hedrick

20-50W + 2 bottles of Lucas in the hot summer
10-40W + 1 bottle of Lucas in the cool winter