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AudiGuru, Master Guild Audi Technician
Category: Audi
Satisfied Customers: 371
Experience:  Master Guild Audi / Master ASE Tech incl. L1 Advanced Level Diagnosis
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low oil pressure..New oil pumps fitted both times.

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My 5 cylider 2.5 motor has recurring low oil pressure after complete overhaul. Motor opened twice alraedy. New oil pumps fitted both times. Main and bigend bearings renewed.
Have you confirmed the low oil pressure with a oil pressure gage besides the one in the vehicle?
Was the motor overhauled because of sludge or low oil pressure?
Have you replaced the oil pressure sensor?
Customer: replied 8 years ago.
Low oil pressure has indeed been verified with additional instrument and sensors check out correctly too. Motor was overhauled because of high oil consumption and was rebored (20 thou) and honed to VW specs. Oil consumption now ok. Low oil pressure was assumed to be a consequence of high mileage (about 200000 kms). However, excessive oil consumption seemed to be only because of cylinder walls being "glazed" by possible use of additives to cure oil consumption.

Excuse me for the way this sounds but it has been a while since I have worked on these motors.


By the front of the oil pan there is a bolt that looks like a drain plug but when you pull it there is a spring behind it. This I believe controls a check valve that controls oil pressure.


Does this sound familiar to you?


If that spring is weak or broken this may be a problem or the valve itself.



Customer: replied 8 years ago.

This is the oil pressure relief valve and the uncompressed spring length is 53mm in the new oil pump body. Being new, everything is spick and span unblemished. (Plunger falls out of oil pump body cleanly with out sticking).

Is it possible that oil pressure to the cylinder head is restricted at some point (in the engine block or cylinder head) so that a lesser flow of oil is supplied to the moving parts in the cylinder head? I am thinking that an excessive oil flow to the head could detract from the pressure in the main oil galleries.

So the head wasn't rebuilt?


Are you familiar with BG engine flushes?


They have a product that Audi / VW use to desludge their motors if they are having oil pressure problems. It works great.


If you have a blocked oil passage this will clean it.

You would have to call a rep to get the product.

Customer: replied 8 years ago.

Sorry, should have mentioned that too. Head has been rebuilt with new valves and guides and seals. But this head rebuild only done on second round of engine rebuild. Oil pressure has been low from the start and before any work was done by me. Bearing in mind that earlier history on this motor is an unknown factor because the vehicle was bought second hand and no history is available. It is therefore conceivable that cylinder head has been worked on before.

It seems to me that present oil pressure is low due to a large outflow of oil at a point where a restriction should be in place. Is this excessive flow perhaps in the cylinder head at the camshaft or via the hydraulic lifter channels?

I agree with you. But at this time I don't have any suggestions on where to look.


I can check some repair manuals tomorrow and do some research and get back to you.


Are you OK with this? Let me know because I can opt out and let another expert try and help you. It is your call.



Customer: replied 8 years ago.
I would like you to go ahead please. We're at out wits end here. Please see what you can find in the manuals. Thank you very much. Good night!
I will see what I can find.

One last thing. Are you checking oil pressure at the oil filter or sensor location?
If you are checking at the sensor with the oil filter on, I have had an aftermarket oil filter cause low oil pressure once. Very odd I know but I won't forget because it took me awhile to figure it out. Just something else to check.
AudiGuru and other Audi Specialists are ready to help you
Customer: replied 8 years ago.

The oil filters have been changed. Some were after-market ones but the present one is a genuine VW filter. We are measuring the oil pressure at one of the two sensor points. Actually at the upper oil gallery where the white coloured sender unit is normally located. A tee piece routes the oil to both the oil light sender unit and the electric VDO guage sender unit. I have the same set-up on a second similar 2.6 litre vehicle where it works fine.

Customer: replied 8 years ago.

Good morning,


I couldn't sleep, so I got to thinking that maybe the oil supply to the engine's cylinder head is fed from the block along one of the head bolts and into the head galleries.

Now if this particular head bolt has a damaged head or bolt seating face, then oil under pressure could escape there and cause a loss of pressure in the whole system.

If VW is using this principle of oil supply, which cylinder head bolt is the one that handles the oil feed into the head? My guess would be the centre one on the oil pressure sender side of the block. How is that for reasoning? Please check the manual for special precautions when tightening up this bolt and advise. Thanks, XXXXX XXXXX Pretoria S. Africa.

Customer: replied 8 years ago.

Hello again,


The vehicle in question has just blown its engine about 700km from here. Yes, we let the owner go away to the coast for the weekend with his family, thinking the engine would probably survive an open road situation. However I will be going to tow the vehicle back to our workshop now and will be away from the internet for about two days.

I look forward to your findings on my return...



I hate to hear the bad news.


This is what I found so far.


When the vehicle comes back you will know if you lost oil pressure to the top end if so check to make sure if you have the right head gasket.


I can not find anything about the head bolts and oil pressure. Just the torque spec.

Just checking to see how things are going?
Customer: replied 8 years ago.

Hi there Audiguru,


We have towed the vehicle back from the coast to our inland workshop in Pretoria.

We have not dismantled the motor yet due to work pressure from other customers.

The observed symptoms are that a piston has collapsed because the engine runs unevenly with light-coloured smoke from the exhaust. We will probably do a compression check tomorrow to confirm the failure of power from one cylinder.

The conclusion so far is that the low oil pressure was not the cause of this failure but that the reconditioned (skimmed) cylinder head has probably raised the compression pressures to beyond the available fuel octane ratings. The engine failed running on 93 octane when it approached sea level atmospheric pressures. It might have survived on the available 97 octane used at the coast. Sparkplug heat-range NGK BP6ES might also be little on the HOT side. aswell and pre-ignition is also a possible cause for failure.

Intermittent raised water temperatures were observed before failure. I will try to give you the final verdict via this forum as soon as we have lifted the cylinder head to check damage. The oil retention valve has not been checked at this stage but a new valve is on order from the VW agency. Will let you know about this as well. Regards,Customer


Customer: replied 8 years ago.

Hello AudiGuru,


Just some more feedback on the low oil pressure and the "blown" 5 cylinder VW motor; When the cylinder head was lifted on this motor, the pistons on cylinders 2 & 3 were found to be seriously damaged with the top rims partly broken away and the top piston rings visible. Strangely enough, the piston fragments escaped down the exhaust system with no associated damage to the cylinder head. This damage is in line with our theory of detonation caused by excessive compression ratio. As far as the low oil pressure goes, the oil retention valve which you identified as being installed in the main oil gallery WAS MISSING from this engine. I will be conducting further tests on the rebuilt engine as to the effect of this valve on oil pressure both when fitted and removed. Will let you know what happens... Thanks again,Customer

Hey thanks for the update. Most people don't come back and I am always wondering about the outcome.


It sounds like you are right about the detonation and it seems we are on to something with the oil retention valve.


Keep me posted and if I can help any further let me know.

Customer: replied 8 years ago.

Hi there again AudiGuru,


I will certainly keep you posted on the outcome.