Strange Oil Pressure Problem

[shäferhunde]

I'm taking my '03 3.0 in to the local independent on Wednesday for this, but I thought I'd run it past you guys first. I've read through all the oil pressure threads I can find but don't see an obvious answer.

The problem is that I'm getting the flickering red oil light and the stop engine warning, but only after I let the car idle while in park for about ten minutes (the car was already at temp before the 10 min idle each time this has happened). After that, I'll get the flickering light when I put it in drive or reverse at idle. Of course when I accelerate or put it in neutral, the light goes out as you'd expect. The strange thing is that after driving a few blocks, the problem slowly goes away (first red light, the light will flicker a bit, second one a bit less, etc.) and won't reappear unless I park the car again and let it idle for another ten minutes.

I don't know of anything that would "re-pressurize" the system with driving, so I'm thinking that it has to be temperature related. The temp needle doesn't move when idling, so I assume that it's not the oil thats getting hot and thinning out. Outside temp has been around 80 when this happens, so not unusual. My best guess is that the ambient air around the pressure sensor gets hotter when the car is sitting and is causing it to fail. Then as I drive it cools down and starts working. Seems far fetched, but that's all I've got.

The car has been well maintained - a bit less than 100k miles and regular oil changes with Mobil 1, always do whatever maintenance is recommended, etc. I had the gasket on the oil filter housing replaced in December, but that's the only oil related work that's been done. I've got a small leak in the valve cover gasket but nothing major - oil level is good, filter is clean. Idles smooth and no engine noise or anything.

I also have no idea if this is something new or not, since it's only by chance that over the past few weeks I've found myself twice sitting in the parking lot of the grocery store while my wife ran in to get something. It could be a ten year old problem for all I know.

Any thoughts before I take the car in?

[JCL]

Your shop should be installing a pressure gauge and determining the actual oil pressure. Sensors can fail.

[shäferhunde]

Thanks, I'd hope that they would though I'm sure a lot of shops would just replace the sensor without checking.

Mostly I'm hoping someone can tell me if I'm off base thinking through this. I always hate going into the shop without being able to carry on an intelligent conversation about the problem.

[Doru]

Could be the oil pressure switch. Item # 12 in this diagram (p/n 12617568480 - easy to change)



This part has been used in BMW's for a long time, and there were many reported cases about that switch failing. Sometimes the connectors get corroded, and it will trigger the same warning. Here is a thread about a similar issue, with some good info about it. The part is cheap, and if I were you, I would attempt the repair myself. About 7-8 bux vs. 1 Hr labor + marked up part + diagnostic time at dealership.

[shäferhunde]

Thanks Doru - that's a good thread and I must have missed it in my search. Especially these two posts, as they point to an ambient temp problem also, and removing the extra flap on the aux fan seemed to do the trick...

Odd thing about this oil light flicker, it only happens once in a while. When sitting for a long time at idle with the air on and the car in gear, after a few minutes this will start to occur. I have remembered finally something I had been doing each year when the hot weather started to come around that I had not done this year. At the front of the car is the aug fan--or pusher fan. Down around 7:00 oclock on the face of the fan is a tab about 6 inches long and about 2 1/2 wide. It's there for the V8 engine models for the air snorkle going back into the air filter box. I removed that Tab. Along with that I removed the cap on the left side of the fendesr well where the air snorkle would come into the engine compartment. That has lowered the engine temp enough that the light doesn't come on now --not even a flicker. Along with that, the air conditioner fells like it's cooling the car more efficiently also. I don't know if this is a good fix, but it's working for now. I'm going to replace the pressure switch also, just to find out if that might be the real culprit. But the high 90 degree weather we are having now has driven the under hood temps right high. These cars need an oil cooler in my op, but that is another project maybe.

With the removal of the two plastic caps, I have let the car set at idle for some time now while in gear and with the air on and with the air off, the light has not begun to come back on. Thats telling me the heat has something to do with it. ... I'm by all mean going to purchase a new sending unit, and I'm of course closely montering what the extra area allowed for under the hood cooling might reveal also. I can say one thing --the car cools down in high heat right away now--LOL

I think I'll take your advice and postpone my appointment. I might try removing the tab on the fan first, since it's a simple thing to try; and probably replace that switch as well, even if the extra cooling does the trick on it's own.

[Doru]

I don't have the specs, but you could also measure the temp sensor and the oil sensor with a multimeter. You would need to search for the specs though.

[JCL]

Originally Posted by shäferhunde

Thanks, I'd hope that they would though I'm sure a lot of shops would just replace the sensor without checking.

Mostly I'm hoping someone can tell me if I'm off base thinking through this. I always hate going into the shop without being able to carry on an intelligent conversation about the problem.

Originally Posted by shäferhunde

I think I'll take your advice and postpone my appointment. I might try removing the tab on the fan first, since it's a simple thing to try; and probably replace that switch as well, even if the extra cooling does the trick on it's own.

Following on from your comment about thinking your way through this, the first step is to see what the oil pressure actually is. Not to try and divert cold air to blow on it, that is a band-aid at best. The light is there for a reason, to tell you you have low oil pressure. The absolute first step is to check and see what the oil pressure really is, not to decide that it is in fact fine and just a problem with the light. It may be, but only after you rule out an oil pressure problem. A sensor will only be a few dollars, but replacing the sensor without checking the actual pressure is bad practice.

That is because many things can cause low oil pressure, and all of them get much more expensive if left longer or until failure. A clogged filter, a failing oil pump, engine bearings, wrong oil viscosity, all can cause this situation, and all will be temperature dependent since oil viscosity varies with underhood temperature. You just appear to be at the borderline for low oil pressure.

So first, determine actual pressure compared to spec. If it is fine, then replace the sensor, because that is the cheapest and most likely, apart from inspecting the wiring harness. If oil pressure isn't fine, diagnose the problem. That is the conversation to have with your shop.

Good luck.