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[BazaJT]

As I understand it[and I could be wrong here]they can leak from the oil cooler cover plate,by-passing the oil cooler will not stop a leak occurring here as the coolant pressure would still be there.

I hope that makes some kind of sense.

[Andy H]

I wouldn't mess around with the oil cooler until the source of the leak is identified.

Inlet plenum off. Plug the two little pipes that go to the throttle body and then pressurise the cooling system to 15 psi / 1 atmosphere.

With a cold engine you can climb over it and waggle things around to see if any coolant leaks out. If you have one you can use a vacuum pump to operate the HBV to see if it leaks when it is operated.

To see the cover on top of the oil cooler you will need to remove the lower part of the inlet manifold.

Read Pressure testing cooling system which shows how you can modify a header tank cap to make a test cap.

[MartinV6]

today we removed the plenum to see what's happening underneath....  everything seemed fine!  the HBV valve is working accurately and has no leaks what so ever, the hoses around also... the complete back of the engine is dry, so no leaking from the cooler then....
the reason we want to bypass the oil cooler is to stop letting oil in the coolant system, because it constantly get clogged somewhere and that leads to overpressure and air bubbles... today after refitting the plenum, the car had some leaked coolant underneath, but that may have been due to the work we had done... we left the car running, it heated normally, fan on, then revved it quite a bit - no leaks.... we left it to cool for a good half an hour - no leaks.... we drove it 20kms - no leaks! normal heating in cabin, normal running temperature... hasn't lost any coolant. Also all the hoses are firm and warm, as it should be.
   I will not drive it until we bypass the oil cooler and flush the cooling system - after we make sure that is operating correctly and makes the right working pressure, then we check for leaks - if no such, than I will be happy.... in the spring hopefully I will get to the point of bypassing the coolant part of the cooler too and probably make a outside aftermarket cooler with a thermostat.

so puzzled today again... two days ago, before we discovered the clogged lines in the cooling system, the leak underneath the car was like you left the sink running slowly! ...

[Andy H]

Did you pressurise the cooling system?

Did you move the HBV from open to closed while the system was pressurised?

[mantaray]

I may be wrong, but I have been told that the "oil cooler" is in fact a heat transfer unit.
It is not there to cool the oil, it is to allow heat transfer between the oil and water  to bring the engine up to operating temp. quickly.

[powerslinky]

I may be wrong, but I have been told that the "oil cooler" is in fact a heat transfer unit.
It is not there to cool the oil, it is to allow heat transfer between the oil and water  to bring the engine up to operating temp. quickly.

Cannot see that one  . . clue is in the title  "oil cooler" surely .   But you never know  . . . no doubt more knowledgable Oofers will confirm

[Bojan]

Every cooler or heater is a heat transfer unit.
Oil cooler on our V6s is designed to help heating up the oil to the operating temp when the engine is cold, because coolant heats up faster than oil.
When all is on operating temp, oil is hotter than coolant, so the oil cooler cools down the oil.

[mantaray]

I was sort of right.

So it is advisable to remove the cooler and fit an external one?

It would keep the oil cooler when the engine is at operation temp, but would take a lot longer to get the engine up to temp, as you are not only, not getting the coolant heating the oil but you are also cooling the oil with the external cooler.

[MartinV6]

Did you pressurise the cooling system?

Did you move the HBV from open to closed while the system was pressurised?

I did not understand what you meant - the hbv valve is working, since there is normal heat in the cabin... and after cleaning and unplugging of some hoses, we managed to achieve pressure in the cooling system, but there still may be air inside... I suspect I have been driving the car with air in the coolant for quite some time and at one point the blockages caused it to overpressure and leak somewhere - thats when I saw the gauge go up to 100 and more degrees and the leak was found - more likely it was there before and lost coolant, and that is why it went up to 100 degrees

the other day we drove the car - it heated up fine, turned the fan on and off as normal, no leaks underneath and no coolant loss.... we well test again after we clean, drain, flush and seal the cooling system, if there are leaks after that...