Too much oil pressure, no compression, AFN engine

Hello everyone,

I bought a Golf 3 TDI AFN with 254,000 km, manufactured in October 1997. I've noticed the following issue: If I rev the engine too high too quickly, it stalls and loses compression. It also doesn't start immediately; it takes about 10 minutes to start again. However, once it's warm, you can accelerate as much as you want.

I suspect the following:
- The oil pump generates too much oil pressure when the engine is cold, which pressurizes the hydraulic lifters and then causes a loss of compression!

What do you think about that? Have you ever experienced anything like this before?

I would now add an engine flush and then replace the oil pump.

Best regards,
Michael.

Hello!

Okay, I already checked, there's too much oil pressure.
With the VR-6 engine, there were then problems with the chain tensioner. Because he pressed down too hard.

It's fundamentally possible, as you suspect.
I've already read about such strange things.

I would advise you to measure the oil pressure using a pressure gauge.
The maximum permissible pressure for the Corrado was 5.5 bar.
There's a pressure relief valve stuck in the oil pump. As far as I can remember, that was then fixed by an improved oil pump.

I would start by changing the oil filter and filling the engine with oil that meets the VW specification 50500 (50500 should also be suitable for the AFN engine).
hg
Herbert.

. If that doesn't help, I would first check the hydraulic lines for leaks, or perform an oil pressure measurement, if you have the appropriate measuring device available.

I just spoke with the owner before the previous owner... He also experienced the same issue at 150,000 km. He has already tried many different oils that were approved. However, it didn't bring any improvement...

I'll check the oil pressure in the next few days and see what the gauge reads when the problem occurs... Should I measure the temperature at the head, the oil filter housing, or both?

Thank you in advance.

Don't forget to check the bypass valve. Similarly, relay "109".

The achieved oil pressure should ideally decrease as the pump gears wear out. Increasing axial and radial clearance leads to increased leakage towards the suction side.
Therefore, the suspicion is either an unsuitable oil or a clogged filter.
To measure the oil pressure, you need to remove one of the oil pressure switches.
Was there ever any work done on the valve lifters (or camshaft)? (e.g., replacement, aftermarket parts).
Given the mileage, I would replace the hydraulic lifters anyway.
hg
Herbert.

berger20000 wrote:

Hello everyone, then replace the oil pump... Best regards, Michael

That's probably the problem, as the pressure relief valve is likely stuck. It's quick and easy to change the cross-flow air filter.

I had the same issue with my 1Z engine once; the pressure relief valve was defective, resulting in over 7 bar of pressure in a cold, idling state. Changing the filter and doing an oil change didn't help. And that was in the middle of summer, with temperatures exceeding 30 degrees Celsius in August 2003!
"At the time, I installed a used pump including an overpressure valve, and the problem disappeared! I measured the oil pressure at the oil pressure switch on the oil filter housing." I would start by checking the oil pressure – it provides clear information.

dieselschrauber wrote:

Don't forget to check the shut-off valve.

There isn't one in my AFN in the G3.
Are there any AFNs (presumably referring to a type of firearm) with a closing valve?

Greetings, Klaus.

Klausel wrote:

Do not forget to check the dieselschrauber wrote: shut-off valve. There isn't one in my AFN in the G3. Are there any AFNs (presumably referring to a type of firearm) with a closing valve? Greetings Klaus

Hm, right? I probably confused it with the "newer" ALH/AHF engines, which have a vacuum-operated shut-off valve located on the intake manifold.

Hello everyone...

Just measured the oil pressure at the head while the engine was cold; it was 6 bar until it dropped and there was no more compression.
"When it's warm, it has 3 bar of pressure and runs normally!"

Okay, I understand. Please provide the German text you would like me to translate into English. I will only provide the translation.
Michael.

Both are perfectly healthy values.

Quote:

Just measured the oil pressure at the head while it was cold, 6 bar until it drops and there is no more compression...

I have no idea how much oil pressure he (the engine) loses in the cold state before reaching the last bearing point in the cylinder head.

I would first check the oil pressure again at the oil filter housing. If it exceeds 7 bar, that's too much.
The pressure relief valve should open between 5.7 and 6.7 bar.

The AFN should have the same test values as the 1Z.
The measurement is taken using the oil pressure switch, with the engine warm, at an oil temperature of approximately 80°C.
- Oil pressure at 2000 rpm: at least 2.0 bar;
- Oil pressure at higher RPM: max 7.0 bar.

Measurements without reference to speed are not meaningful.
Where at the ZK did you measure something, and with what?
hg
Herbert.

So, the specified oil pressure is the maximum value.

When cold, the oil pressure is 3.5 bar at idle and 6 bar at 4000 rpm.

And warm, 0.5 and 3 bar.

Measured with an analog pressure gauge on the right-hand side, where the oil pressure switch is normally located.



I won't be able to take another measurement at the oil filter housing until next Saturday! Since it has to be cold.