Dear Fellow Brickboarders,

May this find you well. A friend, vastly experienced in engine rebuilding (not Volvos, mostly heavy equipment) looked at the engine on this 940.

While it was running, he removed the oil filler cap. He put his hand over the opening, and then asked me to do so. There was a fair amount of "air" exiting the oil filler opening.

He thought that this was the result of the "oil" ring on one or more pistons being clogged, as a result of the previous owner's failure to get the oil changed often enough.

As a result, there was excess "air" pressure in the head.

As a result, the ventilation system (flame trap) could not vent all of it.

As a result, an oil mist was being blown past the filler cap.

As a result, the cooling system was inhaling this mist through its filler cap.

As a result, there was an oil film on the coolant inside the overflow tank.

Does this make sense?

If so, what is the best way to unclog the oil rings?

I put in Mobil 1 as soon as I got the car. I do not leave Mobil 1 in more than 3K.

I have heard of oil system cleaners. Do they work? Are they safe, or can they damage things?

By way of further updating, I see no signs of headgasket failure:
- there are no clouds of steam at any point, not even at start up.
- the coolant is not discolored (apart from the oily film atop the coolant)
- the engine has plenty of pep, even with 87 Octane fuel
- there is no "foam" inside the oil filler cap
- there is no discoloration visible at the oil dipstick.

When I remove the coolant system filler cap, there is a slight "phhffttt". There are no bubbles welling-up and bursting (a sign of exhaust gas in the coolant).

I welcome your suggestions and thank you for them in advance.

Yours faithfully,

spook