C4 100s AAH Oil pressure questions

[JC390]

Long time enthusiast (1.8t and 2.7tt), first time messing with a 12v V6. Car in question is a 1993 100s 2.8 12v V6 AAH 5spd, rust free minus paint peel on roof. Car came from DE. From what i understand the car sat for 5 years before i purchased it. I purchased the car not running. Upon inspection, R bank headgasket was bad, to which i assume is the reason it stopped being driven. Tore apart, took both heads to machine shop, replaced all gaskets and timing components, car now runs great. Fires up and idles, sounds amazing. Now, the dash gauge upon starting spikes over 5bar. Which thru what ive read is far to high. Removed valve covers to double check oil flow to heads, oil flows and drains fine. When cold, there is no issues. Once the car starts to warm up, the O-ring between the oil cooler and flange will leak. Ive already replaced the oil cooler itself when doing the oring the first time. Ive looked thru various forum posts and found varying torque specs for said oil cooler nut, and have tried most of them. So, im assuming the pressure bypass valve/s arnt working correctly. Ive also read the switch could be bad. Im currently waiting on another o-ring so i can hook up my mechanical gauge to see with the switch value is seeing without a concern of the current seal being an issue, just looking for input from those with more expierence with these engines. Seems most of the info i can find between a few forums is more related to the later AFC engines, and from my understanding they changed quite a bit between the AAH and AFC engines when it comes to the oil system.

Also another issue ive noticed, and will be addressing at the same time, coolant doesnt seem to be flowing from the back of the heads. I did flush the motor after putting it back together and didnt notice any blockages, but my dumba** didnt replace the thermostat while i was in there, so ill be taking it apart again to replace that incase thats the issue. Ive also read the water pumps on these can be an issue, so ill double check that as well. Most ive gotten so far out the coolant hard pipe bleeder (back of L head), is steam, and have gotten no liquid from the bleeder under the rain tray.

Any input is greatly appreciated. Im super excited to finally be able to drive this car, and these seem to be the last issues until i can do so.

[JC390]

Despite the dead thread, im still trying resolve this issue. Finally was able to check pressure at switch site, which shows 75-80psi at cold idle. I do believe the switch is incorrect, however it doesnt seem to be having bypass valve issues which is a huge relief. So onto my next thoughts. I replaced the oil cooler itself with a Nissens (?) product from FCP Euro. It is no longer mixing coolant and oil, however the o-ring behind it is indeed still leaking once it gets hot. Goin to be ditching the WIX filter ive been using, and get my hands on some OEM filters. Also, been using Castrol 10w-40 Euro for oil. Anyone have a torque spec for the oil cooler nut? Ive tried snug, snug plus half a turn, and finally 30NM, all of which will leak once the car heats up. Unsure if theres something else going on or what. Hoping i can get some people to chime in, otherwise this will just serve as documentation for future reference.

[ShelbyM3]

No experience, just willing to engage with you. I found the torque spec to be 25Nm when doing my 2.7. It was in a random YouTube video off a 2.8 car. Should be in that neighborhood as the pan is aluminum and that’s usually the most torque when going into that material, I’ve found on these.

If you’re able, I’d pull it all apart and inspect it. Other ideas: Maybe the threaded rod isn’t seated into the pan well or it’s loose and leaking? Maybe there’s something on the mating surface of the new cooler or the o-ring was boogered up and the knubs got twisted? Are you positive it’s not the upper pan seal? Or maybe one of the cooler lines is weeping once warmed up?


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[JC390]

I did pull it apart again, im going to pick up some aluminum polish and try just polishing the surfaces as there doesnt seem to be any damage to the sealing surfaces. Thinking about trying another brand of oil cooler, just out of curiosity. The leak is defiantly the oring between the cooler and block flange. When i replace it, which i have done 4 times now chasing and trying different things, it wont leak until hot. Once hot, the seal becomes deformed and leaks. Every seal ive removed so far has been deformed. I hadent considered the pipe, i will inspect that. Im also going to remove the lower oil pan and just inspect whats going on in there for curiosities sake. Not thinking its a cooler line as it not leaking coolant, only oil from back of the cooler mating surface.

I did find the 30NM spec in another thread on audiworld, but that has also leaked. So theres gotta be another reason why it keeps leaking on this specific seal. No other oil leaks ive noticed, either hot or cold. Atleast externally anyway.

[ShelbyM3]

Odd. You’ve clearly had enough hands on time to understand it all. Checking the rod can’t hurt, but I’m doubtful. Have you tried torquing it once it’s warm? Couldn’t hurt unless an oil change isn’t in the near future.

Also, looking back at my 2.7 pan, there isn’t much to see with the lower pan off. You just see the passageways for the oil pump tubes. I bet yours is similar.

Pics to reference what I’m seeing/saw.

How my OE one sat.

My Nissen

Upper Pan



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