HI All
Thanks in advance.

I have a 95 940 N/A with 150k miles on the clock.

Tonight I changed the crank position sensor because I was getting fluctuating tach readings and did some other maintenance: oil change and filter, air filter, cleaned the flame trap, and cleaned the throttle body. I noticed in the coolant expansion tank there was a small quantity of a dark build-up on the bottom of the reservoir and a build-up of film on the top, although it was not as apparent as the bottom. It doesn’t really have any discernable color to it, other than being darker than the coolant.

I flushed the coolant about 2 months ago with the last oil change, and I also replaced the coolant reservoir with a new one. At that time, there was no mystery material in the coolant as I flushed it. The last coolant flush was when the water pump was changed about 2.5 years ago.

I checked the oil for any signs of coolant as I changed it, and there was none apparent. Checked the ATF on the dipstick, no coolant. Decided why not drain the ATF to see if any coolant seeps out. None.

Next, I did a compression test and received readings ranging from 170 - 176 PSI. Spark plugs were clean. No signs of coolant on them.

I scraped the top film from the expansion tank and wiped it on a paper towel. It was brown/black.

Do I have a head gasket leak even withstanding the great compression readings I have?
Any ideas? Any further tests to try… (I called around looking for a coolant pressure tester, but no parts store had the adaptor for a Volvo—only G.M.)