This post is about my experience fixing the classic oil-in-coolant problem that many Td5 owners run into. This happened some 2-years ago, but finally going out to the press.
It all started with the usual oil stain in the expansion tank (aka coolant reservoir). It did not take very long for the stain to become a 1/8" thick oil film on top of the coolant which forced me to tackle the problem immediately. According to RAVE and own measurements oil pressure peaks at ~3 bar (when engine cold) whereas maximum coolant pressure is set by the expansion tank relief valve at about 1.4 bar (engine hot). The leak path is then obvious, engine oil goes into the coolant and not the other way around.
After draining all engine coolant took out viscous fan, poly-v belt, turbo hoses, turbo and exhaust manifold. Released A/C compressor and carefully moved out of the way (piping still attached). Then did away with oil filter & housing and centrifugal filter & housing, and finally removed the oil cooler assembly.
At first sight I could not see where the leak was coming from, so undid the (2) hollow bolts that hold the heat exchanger on to the cooler housing to further investigate. Immediately noticed that the heat exchanger o-rings where deformed (flattened) and hardened, and also that there were oil marks in the oil cooler casing areas against which the o-rings seal.
The heat exchanger did not seem to be leaking at all, but wanted to have assurance around that. Based on the numbers above, the maximum pressure differential that the element sees is when the engine is started from cold, i.e. 3 bar inside the element and ~nil on the outside (assuming all relative pressures).
To have the test done, sourced bolts identical in size/thread as those used to attach the heat exchange on to the oil cooler housing. The bolts I could get my hands on were longer than needed so had to cut them back to the required length; in addition one of them was drilled through and tapped to a 1/4" NPT (F) thread.
Using hose and various compressed air type fittings, rigged the following up:
The heat exchanger element was then successfully tested to just above 3.5 bar (thought about going higher but did not want to push my luck).
More testing: with new o-rings on the heat exchanger and using the specially developed bolts, tested sealing integrity of the 'radiator' against the housing (I know... only partially valid as bolts have to come off).
Regrettably, I did not take note of either bolt or o-ring sizes. The o-rings I was able to source at that point were not Viton (FKM) as they should be for this kind of application (hot hydrocarbons), but regular Buna rubber ones (aka Nitrile or NBR). In all honesty I was expecting that they would not last long and that I would soon be dealing with this issue again thus having a chance to check o-ring sizing, but today some 70K later they are still going.
I suppose I was lucky in that there was nothing wrong with my 'oil radiator' since these were hard if not impossible to get a hold of back then, and needless to say a replacement oil cooler assembly was and still is worth a small fortune. The blue brand with the bad name now sells the heat exchanger as a separate part (p/n DA1127) although they don't come cheap either.
Regards
Matt
It all started with the usual oil stain in the expansion tank (aka coolant reservoir). It did not take very long for the stain to become a 1/8" thick oil film on top of the coolant which forced me to tackle the problem immediately. According to RAVE and own measurements oil pressure peaks at ~3 bar (when engine cold) whereas maximum coolant pressure is set by the expansion tank relief valve at about 1.4 bar (engine hot). The leak path is then obvious, engine oil goes into the coolant and not the other way around.
After draining all engine coolant took out viscous fan, poly-v belt, turbo hoses, turbo and exhaust manifold. Released A/C compressor and carefully moved out of the way (piping still attached). Then did away with oil filter & housing and centrifugal filter & housing, and finally removed the oil cooler assembly.
At first sight I could not see where the leak was coming from, so undid the (2) hollow bolts that hold the heat exchanger on to the cooler housing to further investigate. Immediately noticed that the heat exchanger o-rings where deformed (flattened) and hardened, and also that there were oil marks in the oil cooler casing areas against which the o-rings seal.
The heat exchanger did not seem to be leaking at all, but wanted to have assurance around that. Based on the numbers above, the maximum pressure differential that the element sees is when the engine is started from cold, i.e. 3 bar inside the element and ~nil on the outside (assuming all relative pressures).
To have the test done, sourced bolts identical in size/thread as those used to attach the heat exchange on to the oil cooler housing. The bolts I could get my hands on were longer than needed so had to cut them back to the required length; in addition one of them was drilled through and tapped to a 1/4" NPT (F) thread.
Using hose and various compressed air type fittings, rigged the following up:
The heat exchanger element was then successfully tested to just above 3.5 bar (thought about going higher but did not want to push my luck).
More testing: with new o-rings on the heat exchanger and using the specially developed bolts, tested sealing integrity of the 'radiator' against the housing (I know... only partially valid as bolts have to come off).
Regrettably, I did not take note of either bolt or o-ring sizes. The o-rings I was able to source at that point were not Viton (FKM) as they should be for this kind of application (hot hydrocarbons), but regular Buna rubber ones (aka Nitrile or NBR). In all honesty I was expecting that they would not last long and that I would soon be dealing with this issue again thus having a chance to check o-ring sizing, but today some 70K later they are still going.
I suppose I was lucky in that there was nothing wrong with my 'oil radiator' since these were hard if not impossible to get a hold of back then, and needless to say a replacement oil cooler assembly was and still is worth a small fortune. The blue brand with the bad name now sells the heat exchanger as a separate part (p/n DA1127) although they don't come cheap either.
Regards
Matt
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