'91 legacy potential headgasket failure

[saw]

Have a '91 legacy with 196K on it. Other than a lot of front axle replacements for torn CV joint boots, been a great car.

Over the past few months, have had occasional overheating troubles.

The first occurrence was after a 2 mile (one way) jaunt to the local store. The car was cold and ran fine to the store. Upon return, however, the temperature guage began to elevate. Because of the short distance back, everything remained under control. An inspection of the radiator overflow bottle showed it to be full. After cooling, transferred liquid back into radiator and allowed system to run & burp with radiator cap off.

Everything's been fine for the past month. This past weekend drove the car for ~ 20miles at 65mph. Switched to some back roads, and after about 5 miles, it started to overheat again. Made it to my destination and checked radiator overflow bottle; once again it was full. After about 5 hours, returned to car to find all liquid had been drawn back into radiator. Returned home with no problems.

Upon startup, haven't noticed any excessive smoke emanating from the exhaust. Vehicle runs fine. Have noticed some mild clatter coming from the driver side of the motor when under load - typically when first releasing clutch. Don't know if there could be a tie in or not with overheating problem.

Checked sparkplugs this afternoon and they all seem to be burning similarly. Looked into radiator overflow reservoir while engine was running, and noticed some bubbling - possible indication of compression leakage?

Any comments, advice appreciated. Thanks.

[Manarius]

Thermostat before assuming HG's. If there's no mixing or leaking going on, it can't be the HG's.

[OB99W]

[...]

Am going to remove sparkplugs this afternoon and inspect electrodes for dissimilarities.[...]

Expect to see differences, even if nothing is wrong. The "wasted spark" ignition causes two of the plugs to have ignition voltage polarity opposite that of the other two; there should be more-evident center electrode wear on half the plugs.