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AON Club Member Christina
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Hey guys,

Seems there’s oil mixing in with the coolant on my Astra H (1.8 Z18XER). It appears it’s transmission fluid. The automatic trans oil coolers seem to be known to fail in the rad.
Anyways, flushed coolant to remove the oil and the oil came came back ( not as much, car wasn’t driven just ran to circulate the coolant so that confirmed the Rad failure. I decided to put in a coolant flush with the distilled water after draining the system. Was just flushing that stuff out and this little gasket came out of the rad as It was draining.
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Any idea where it’s from? Seems there may be another one the same or similar size that’s failed/failing from the little extra piece that also came out. The other one seems to be whole.

Thanks a bunch!
 

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There are two major coolant mixing failures for the Astra AFAIK. I don't know which you faced.

1. The popular z18xer automatic transmission failure is from the combined oil/engine radiator failing and mixing the two liquids.

2 .A different failure is the engine oil cooler (located behind the exhaust manifold).

After my z18xer automatic experienced a failure of the radiator, we had some bits like that in the coolant tank but maybe the o-ring was a bit bigger. Also the coolant turned milky brown.

First obvious o-ring failure was the coolant reservoir tank cover (that is typically yellow). Then the thermostat. I don't know what size o-rings those items might have in Europe but you can check photos on-line. You see, in North America we have different thermostats and coolant tanks (different emissions and lower operating temps on same engine).

Are there o-rings on the radiator drain valve that size? North American radiator is slightly different.

The o-ring looks smaller than the 55353328 in the engine oil cooler and I don't see how that o-ring would get into the coolant. It is #13 on this diagram so you might look for leaks around there I suppose if you can see it.

FYI -
My mechanic said that oil inside the coolant could damage some hoses and some o-rings. The hoses might become swollen and oily but I don't know if that is a good signal they will fail.

So we added a separate transmission oil cooler. Replaced all the coolant hoses. The o-rings on the coolant tank and thermostat failed shortly afterwards, so we replaced those too. Oh...had to replace the automatic transmission too. You might be lucky with a superflush of the transmission and cooling circuit...

If this is the engine oil cooler (behind the exhaust manifold) that is a different fix. . .
 
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