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The modeen is a small factory oil cooler bolted to the block .

Its not really a high performance oil cooler just a water jacket round the outlet oil pipe from the block and is designed to keep the oil temperature sensible .

If the oil pipe cracks/splits inside the modeen when the oil gets hot the crack/split gets a little bigger. Because the oil is at pump pressure it is pushed out of the split into the jacket and because water isnt under the same pressure it doesnt get back into the oil system.Obviously with a high power oil pump it will be worse

As the split is usually small the above only happens when the oil gets hot and this can make it hard to diagnose.

As the oil is lighter than water it goes round the system with the water but tends to get stuck in or at the top of the rad

I have never ever seen the oil/water cooler split in working on these cars for nearly 20 years.

We repair the head on site , can turn then around pretty quickly. But the head needs strip right down to a bare head.

We had some many people think that the oil in the water is a head gasket problem , oil/water cooler problem but it is always the caracked head problem.

The blocks only crack externally , which is normally above the ridge by the starter motor area. a lot of 1996 onwards blocks go porous around the oil feed connection on the turbo side thou.
 

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I have never ever seen the oil/water cooler split in working on these cars for nearly 2 years.

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Mine did hence the post .

Swopped it and all was fine and still is .

And yes I agree its very rare which is why I went to great pains to say this .

and I think you mean 20 years not 2 :chuckle:
 

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i would just like to add my situation to this discussion,could even be an alternative.five years ago had to do a rebuild(33 gtr)had oil in the water exactly the same symptons as reported here,eventually a coolant pipe burst(under the plenum)and i had overheating issues.took the oppurtunity to upgrade engine to run 500/550 bhp upon rebuild.had the head tested and was told it was no good,so bought brand new head for the rebuild.the block was rebored ready for the rebuild but upon inspection it was found to have hairline cracks between the water jacket and head bolt holes.after speaking to a few people about this and being advised this wouldnt be a problem the engine was rebuilt.engine was run in and then mapped to 452bhp(wheels)and has been running this power for the last five years.however the engine still loses a small amount of oil into the water(maybe not as much as before the rebuild)this with new head and all gaskets,oil/cooler was checked during the rebuild.ive always thought the oil/water problem to be the cracks between the water jacket and head bolt holes this is assuming that the oil around the head bolts is under pressure.can anyone confirm that the oil around the head bolts is under pressure.ive also found out ive got a porous block with the coolant leaking out around the turbo oil feed.knowing all this and with a careful eye on oil/coolant levels ive been running this car for all this time without any major issues,so its possible to live this with problem and run a decent amount of power.obviously if i had to do another rebuild i would change the block for a known good one.
 
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