Overheating and oil press drop, head gasket or water pump?

[captainrawmeat]

A couple of days ago I noticed that the oil pressure guage slowly got lower at idle, at one stoplight it got so low that the oil light came on. At the same time, I noticed the temp guage get really high, almost off the scale. I took the car out later that night and coolant started streaming out of the expansion tank (thankfully when I pulled into the driveway.) I troubleshot the overheating and here's what I found:

Upper radiator hose gets hot, so t-stat is good,

Radiator temperature gradient from top to bottom is correct, so radiator is not clogged,

I can hear what may be a low howl from the water pump area, but since I'm new to DSM's, I don't know if this is normal. If it were not overheating, I would not be suspicious.

My next thought was a bad head gasket, this would explain the oil press drop and the overheating. I did a compression test and got 160psi in #1, 150 in 2, 170 in 3, and 172in 4. The service limis is 133, but the difference between cylinders should be 14 max. Does this tell me that the head gasket is blown? I left the tester on #2 and it stayed at 150 for 10 minutes. I don't know if it would eventually drop? I don't notice white smoke out the tailpipe, or milky residue in the oil.

I think I'm on the right track with the head gasket, but I wanted to get some feedback before I tore the engine apart. Thanks in advance!

 

[TotalEclipse21]

Sounds like something as deep down as a head gasket. You can hope it's just a head gasket but don't be surprised if either head or block is cracked along the oil and coolant galleries.