http://www.brickboard.com/AWD/index.htm?id=589578

In the linked thread, what I was talking about is far different from the pics shown here showing a "milkshake" effect. That's a whole different situation than what most people here are always bringing up about the "mayo" type stuff they're seeing on their dipsticks (sometimes oil fill caps too).

The oil that looks like a milkshake when drained (doing an oil change) indicates a severe problem where coolant is mixing with oil, a very serious situation in comparison. In my many years as a Volvo tech, the only times I've seen that was after an engine was severely overheated and the cyl head warped badly. It's far from common or normal. A bad t-stat doesn't do that either.

Now.....back in the old days when I was a Datsun tech, I'd see that fairly often as old Datsuns ate head gaskets, often every 40K miles in their pushrod type engines (F10s, 310s, 210s).