Hi,
Had a question about my wife’s car. She has a 1992 VW Cabrio 4-cylinder; manual transmission; full set of gauges-the Germans like 'em that way, I guess. Anyhow, the oil pressure gauge, when the engine is cold, shows normal oil pressure. However, when the engine is hot, the oil pressure, as measured by the gauge, drops to near zero - has been this way for about six months - Yikes! Our mechanic changed the oil - put in a thicker(?) grade oil; changed - I guess there are two sensors for the oil pressure gauge - he first changed the inexpensive one - no difference. He then, with our go-ahead, changed the more expensive sensor - no difference. At this point, he doesn’t know quite how to proceed. He says that he could change the oil pump, but can’t guarantee that will solve the problem. Recently, I had my other car - a 1994 Olds Ciera Wagon - towed in - another mechanic had not tightened the oil filter sufficiently after changing the oil. They fixed it and, needless to say, I am not going back to that - second - mechanic for service any time soon. I’m lucky my car runs <groan…> after blowing out all its crankcase oil. Anyhow, back to the VW. While I was getting towed in, the tow truck drive said: “Nah, it’s not the oil pump - that would cost about $400, but that ain’t gonna solve the problem.” He said the problem was with what he called the engine main bearing - still said that it would cost about $400, but that was the issue, not the oil pump. Not sure what to do. She’s (the wife) been driving it and we’ve been crossing our fingers, but I would really like to resolve the problem, if possible. At this point, I really - with the economy, both she and I are working multiple part-time jobs - can’t afford to replace the VW, but I can’t afford to lose it, either. If I knew that resolution of this presumed engine ‘main bearing’ issue would resolve it, I would do so in a heartbeat. Any thoughts and/or ideas for a fellow Institute grad (Course XV - 1974 S.M, which is why I’m not the most mechanical guy, for sure).
Would appreciate any help that you might be able to provide in this regard.
IHTFP!!!
Thanks and best regards,
Dan Deren
It shouldn’t be too hard for your mechanic to put a manual pressure guage on the car to see what the actual oil pressure is at specific rpm, say idle, 1,500, 2,500, and 3,500 rpm; was this test done and what are the results? If there is pressure then the oil pump is OK, if not then the pump is bad.
If the pump is OK pressure may not be getting to the entire motor due to sludge and gunk clogging the internal passages in the motor. In you heart you can have great blood pressure but if your coronary arteries are blocked no blood is flowing to you heart.
Your motor is sick and continuing to drive it without figuring out and fixing the problem is going to kill the motor. You should not expect the car to last much longer, either get it fixed or get the funds together to replace it.
Is the thing making noise? How’s the pressure when driving down the road?
It can be a fouled or scored relief valve on the pump. That would provide decent pressure cold and it would degrade to sub normal hot.
Main bearings would be rumbling or giving you some other indication besides pressure.
How is the consumption? General performance otherwise?
A 5w-40 oil would be my choice. A 15w-40 would be my choice in a conventional. I’d also do an Auto-Rx treatment (google) to assure that no fouling of the relief valve is causing this.
I have to agree with the tow truck driver. I’ve seen a lot of engines display this symtom and it usually turns out to be worn out main bearings.
Tester
In addition to what others have said, does this engine have a turbocharger? Turbo bearings can wear out and cause oil pressure to drop drastically too. Usually you’ll see quite a bit of smoke out the back if this is happening though.
Unfortunately it probably is worn main or connecting rod bearings though.
A couple of key facts are missing…How many miles on the engine, exactly what grade of oil is being used?? AND, is the oil pressure RPM sensitive? As long as you have 10 psi per 1000 RPM you are good to go…Oil pressure at idle is no that big an issue…
200K+ miles. I will check on grade of motor oil - not certain. Oil pressure is ABSOLUTELY RPM-sensitive and shows as at least 20 - 30 bars on the oil gauge at, I believe (it’s been a while since I’ve driven her car) at 1000 - 2000 RPM. The low oil pressure occurs when the engine is hot and exclusively at idle, such as when my wife is idling in neutral at a stop light or similar signal. Thanks for your help, by the way. Right now, with the economy, we can’t afford to replace either of our older vehicles. We do have the funds to repair them, however, if this needs to be done.
My mechanic whom, as far as I can tell, is usually very good, has not put a manual pressure gauge on the car - he has indicated that is difficult to do, as the problem - low oil pressure exclusively at idle - only occurs when the engine is hot and that it is difficult to attach the pressure gauge when the engine is hot - which, even I have to admit, with my limited mechnical skills, sounds as though it should have been done. I will certainly take your advice and go back to him to make sure that this is done. One other bit of information that my wife shared with me this evening - I had thought that this was a recent occurrence - we moved to Florida four years ago; she moved down first; I followed - and that this oil pressure issue is a recent phenomenon, dating back about six+ months or so. Upon discussing this with my wife today - I work part-time nights over the weekend; so this was late in the day today - she indicated to me that this situation has been going on for some time - and that she discussed it with our former mechanic up north of Boston years ago and that he had, at that time, changed the oil pump and it hadn’t made any difference. I understand and agree with the possibility that sludge and gunk is clogging up the internal passages in the motor. I will indeed go back to my current mechanic and insist that he test the oil pressure with a manual gauge. Thanks for your help. While I can’t afford right now to replace this vehicle, I can afford the appropriate repair - hopefully, depending on the cost - as soon as we can determine what that repair should be. Thanks again!
No unusual noise. Oil pressure is fine driving down the road - although it seems a ‘bit’ low still as RPM increases, but still steadily and linearly increases as RPM increases. As RPM increases, the oil gauge shows 2 - 3+ bars of oil pressure. The issue occurs only when the engine is hot and only at idle - such as when she is idling in neutral at a stop light, stop sign, etc. Oil consumption seems relatively normal, give that the car is getting a bit ‘long in tooth’ - i.e., 200K+ miles on the clock. General performance appears fine. I will also take your suggestion and do the Auto-Rx treatment (google) to assure that no fouling of the relief valve is causing this. Thanks for your help - I appreciate it.
Why do you think the oil pressure is too low? Just because the indication is low on the dash gauge doesn’t mean that is TOO low. And, dash gauges aren’t THAT accurate, anyway.
What standard units of measure is used on the oil pressure gauge? Is it kPa? 101 kPa is equal to 15 psi.
For many engines, the minimum oil pressure at idle is allowed to be 10 psi (maybe 15 psi), with the engine hot. Then, at 3,000 rpm, look for a value of 35 psi, or higher. Your mechanic needs to obtain the oil pressure specifications. It might take a little searching. So?
A direct-indicating oil pressure test gauge can be installed on a COLD engine. The engine can be run until it is hot, and then, the oil pressures can be read at idle; 1,000 rpm; 2,000 rpm; and 3,000 rpm. The test gauge can be removed when the engine cools.
I don’t think there is a problem; or, if the oil pressure is a LITTLE low, it can be liveed with. Just, don’t push the engine hard. Keep acceleration loads at a moderate value.
With that mileage and those symptoms, it is almost certainly the result of worn bearings. Don’t waste your money on a pump. I have never seen, or heard of, one failing in that way.
As mentioned, the first step should involve verifying the pressure with an auxilliary guage, not throwing senders (or pumps for that matter) at the problem.
The pressure developed is a function of the pump speed, oil viscosity and the system restriction. Your bearings are worn so the restriction is lowered. When the oil thins with temp, the pressure goes down.
I personally think some people do more damage than good when they use heavy weight or wide range multi-vis oils in the quest to increase low pressures at idle. Heavy weight oils do not circulate well until warm. Wide range, multi-viscosity oils have polymers that provide the range enhancement but those parts of the oil are not lubricating. So you end up with less lubricating qualities but good pressure.
The tow truck driver is quite likely correct.
The problem would more than likely not be confined to a worn main bearing; it would be to all of the main bearings and rod bearings due to wear.
Replacing an oil pump to cure low oil pressure is what I would consider a misguided process that has been around forever. The oil pump is the first part in the chain to get the oil out of the oil pan and if someone is going to assume the oil pump is worn badly enough to cause low oil pressure they should assume the crankshaft bearings are even worse.
What could be done is to drop the oil pan and remove a few bearing caps located the fartherest away from the oil pump as these are the last in the chain so to speak.
If they’re badly worn and the crankshaft journals are not scored, etc. it’s at least possible to replace all of the rod/main bearings without further engine disassembly and give that a go.
The mechanic states that he can’t attach an external gauge due to the engine being hot. Well, how about connect the gauge when the engine is cold, allow the engine to warm up, and then see what the pressure is doing. I don’t understand his logic here at all and if it comes to an expensive sending unit the oil. press. should be tested first before throwing a pricy part at the problem.
And my memory is very fuzzy here on one this old but I thought the oil pressure sending unit screwed into the end of the cylinder head near the camshaft; which means it’s easy to access a pressure port.
Hope some of that helps you out.
Move up one viscosity number and see how that works. Try using 10-40 and in the summer, 20-50
Just closing the loop on this thread. We have changed mechanics and our new mechanic did indeed put a manual oil pressure gauge on the gauge and determined, among other things, that the oil pressure at idle was fine. We will continue to maintain this vehicle and will hope that this car lasts as long as possible; but, in the meantime, it appears that oil pressure, as measured by the manual oil gauge, at idle, especially (which is where our concern was) is more than adequate. Thanks and best regards, Dan Deren
Just closing the loop on this thread. We have changed mechanics and our new mechanic did indeed put a manual oil pressure gauge on the gauge and determined, among other things, that the oil pressure at idle was fine. We will continue to maintain this vehicle and will hope that this car lasts as long as possible; but, in the meantime, it appears that oil pressure, as measured by the manual oil gauge, at idle, especially (which is where our concern was) is more than adequate. Thanks and best regards, Dan Deren
Just closing the loop on this thread. We have changed mechanics and our new mechanic did indeed put a manual oil pressure gauge on the gauge and determined, among other things, that the oil pressure at idle was fine. We will continue to maintain this vehicle and will hope that this car lasts as long as possible; but, in the meantime, it appears that oil pressure, as measured by the manual oil gauge, at idle, especially (which is where our concern was) is more than adequate. Thanks and best regards, Dan Deren
Just closing the loop on this thread. We have changed mechanics and our new mechanic did indeed put a manual oil pressure gauge on the gauge and determined, among other things, that the oil pressure at idle was fine. We will continue to maintain this vehicle and will hope that this car lasts as long as possible; but, in the meantime, it appears that oil pressure, as measured by the manual oil gauge, at idle, especially (which is where our concern was) is more than adequate. Thanks and best regards, Dan Deren
Just closing the loop on this thread. We have changed mechanics and our new mechanic did indeed put a manual oil pressure gauge on the gauge and determined, among other things, that the oil pressure at idle was fine. We will continue to maintain this vehicle and will hope that this car lasts as long as possible; but, in the meantime, it appears that oil pressure, as measured by the manual oil gauge, at idle, especially (which is where our concern was) is more than adequate. Thanks and best regards, Dan Deren
It’s good that you have found a mechanic who verifies assumptions, in at least one instance. The original assumption was “low oil pressure”.
Gauges are inaccurate at their low ranges and their high ranges. Dash gauges aren’t the best quality; so, they need to be backed up by a better gauge.
As you saw, the VW dash gauge showed low on its scale; but, it wouldn’t accurately show that the oil pressure was below the minimum of 15 psi, at idle, would it?
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