Oil cooler or O-ring replacment interval?

Hi everyone, just curious if while I am at it for the AOS swap...is it worth doing the oil cooler as a replacement; or even just the O-rings? I wasn't sure if these where ever culprit to issues or problems and if anyone felt it was good measure to just replace unit when the engine is being serviced. 40th AE & 42K miles... Thanks! Chris

Sounds like you are planning to change out your AOS, now that is good and I guess not a bad idea for preventive maintenance purposes. Unless your AOS unit actually failed, at which case it would be a must remove and replace then. As far as the oil cooler, I don't think there would be a need for that unless you had an oil leak or were experiencing oil over temp conditions. The cooler sits high up on the motor and is protected from road debris. So to answer your question if there was an active oil leak, oil and coolant mix or something physically wrong with the cooler unit or an oil overheating condition I wouldn't even consider replacing the oil cooler. As far as the O-rings I don't believe there is a service interval. But the O-rings between the oil cooler and the engine block, I would consider replacing due to age of car if the O-rings were originals and only if I actually dropped the entire motor. MHO.

If the water pump impeller disintegrated and you failed to retrieve all the broken pieces, they are probably in the heat exchanger. That is the best reason to r&r. You will loose coolant so there is the whole airlift chore. The "O" rings are a tricky part unless you buy from a reputable source. The thickness is critical. Mine were part of a complete conversion set from Parts Container. The oil(not coolant) O rings leaked all over my newly rebuilt engine at start up.The fasteners were correctly torqued . I removed them and checked the thickness - significantly under-size ! The coolant "O" rings were correct. I replaced them with OEM parts (as recommended by JFP) from Pelican . Perfect. So measure the thickness of any replacement "O" ring against spec before you fit them ! Here is my old post on the subject that may help "The Pelican rings are HNBR.Odd that the stock spec calls for 4mm thick coolant rings but thinner 3mm oil rings.The annular grove for the coolant seal is 3mm. For the oil is 2mm. So less than 1 mm of compression to seal. Hence the importance of the thickness dimension I mentioned earlier.The Parts Container oil "o" rings are too thin !Yes, they are thinner than the specified 3mm. The Pelican part is a full 3mm. Just like JFP said , the OEM seals worked perfectly. The ones from Parts Container leaked immediately. The issue was below spec thickness of the oil "O" rings from Parts Container. As I mentioned ,these came as part of a large engine rebuild kit that I used. Now I am wondering about the other seals and parts. The Heat Exchanger seals was a relatively easy fix. Other parts would be much more difficult and potentially destroy a newly rebuilt engine. To be clear, the issue in this specific case was not HNBR/Buna/Viton. That is only because the engine has zero miles. The oil seals leaked when the engine started for the first time after the rebuild.And yes, of course the 4 bolt were torqued correctly and the base of the HeatX is flat. As my measurements above showed, if you have an undersized thickness of the "O" rings and the factory machining allows for a max of 1mm of seal compression, it will leak. I was lucky to catch it before any damage occurred. I hope this helps others with the same issue or choices in sources for seals. " Here are the part numbers for the convenience of others. 999-707-389-40 999-707-409-40

Thanks for the reply gentlemen. Device2 yes, I am going to be in there for IMS solution/RMS/clutch/AOS…no issues just want to tackle everything that ‘could’ be potential down the road. The car has no leaks at all, don’t know if that’s considered lucky but everything underneath is completely dry – better stay that way once I am done! If the cooler is protected, that rules a lot out in my paranoia right there. Schell, thanks for the detailed response. I recall reading a lot of your informative posts from the Garage Journal year’s back – nice to see you here also! The water pump to my knowledge at this point is fine, but also getting replaced. I will be sure to check for any impeller breakage. Wonderful feedback on the O-rings. Thanks for the details, I will be sure to order those part numbers and make sure to measure. I have actually been through something like this similar in the past but thankfully not nearly ending up to the headache I think you have experienced. I have a W140 S600 I got to learn a lot of the German car quirks on and the O-rings in the cooling system (and no space to work) sound all too similar with the 996. Parts Container is not a valued source in my opinion. I went through them once and was not impressed from there business practice all the way to the shipping results and how the package was delivered. Everything was just poor. I will never order from there again, I think they just buy and resell…meaning; they have no technical support or service. I am still in the air if I am going to lower the engine or just work from underneath with all this but I am on the way to getting as much knowledge as possible before tackling all the work. Thanks again! Chris