I checked out my Volvo 4.3L (275 hours) for the first time this
season. Ran the engine for a few minutes and checked the oil. It was
milky white, apparently mixed with water. The last thing I did at the
end of the season was change the oil, haven't run it since then.

Changed the oil, ran for a minute, checked again. Milky white.

My guess is something froze over the winter. Is there anything I can
check that I could possibly fix myself, or should I just bite the
bullet and take to a mechanic?

A friend suggested a running compression test. It's too dark now, I'll
do that in the morning.

Any other diagnostic suggestions?

Thanks,

Terry