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Old 06-09-2019, 08:33 PM
ngoma ngoma is offline
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When you remove the flange you will see there is a recess cut out of the edge of the hole in the engine where the o-ring seats. Very similar to the relief the thermostat o-ring sits in, but smaller.

The o-ring for the heater coolant flange in the rear of the head measures 22 x 3mm. I didn't measure the one for the rear of the block. That one may be larger because the hose that connects to that flange is 7/8" as opposed to 5/8" for the one on the head.

Sorry, no good access for taking photos because they are right up against the firewall.

Maybe I will experiment with viton next time because I recently had to replace a somewhat fresh (1 year old?) leaking nitrile one, no overheats in that time period.

Did your car suffer overheat condition or oil-in-coolant condition?

If it wasn't leaking, and if I wasn't replacing the heater hoses I wouldn't replace the o-rings just to replace them. If it goes, it won't be a catastrophic huge leak (you will see coolant slowly dripping off the bellhousing and it will stay that way for a long time).

Difficult access, hard to turn a wrench in there, hard to get your hand in there to seat the o-ring properly. Better to expend the energy inspecting (and replacing as necessary) the coolant hoses under the IP which are subject to fuel leaking from the IP or injector spill lines. If those let go, that definitely has potential to cause a catastrophic overheat condition. Sudden loss of coolant.
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1985 744 gle d24t
1985 745 gle d24t
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