Since there is not Subaru sub forum yet...

My backup car (2004 Subaru Legacy Wagon) has started overheating when cruising. Under load, the temps drastically drop. But when leveling out and just idling/cruising it will increase. I changed the thermostat and seal and it persists. I don't notice any leaking anywhere (but will be monitoring soon). I changed the oil today, no coolant is mixed in.


I am still selling camera gear to cover the costs of labor to get my Miata's oil leak diagnosed and am starting to get tired of constantly repairing cars... Is this tell tale sign of head gasket failure?

Might just donate the wagon or sell it cheap, but that puts me out of transport completely until the Miata comes home.

 

Do "the block test"

 

Also check out your coolant overflow tank, you can sniff in there after opening the cap to see if you smell exhaust, also look with your eyes to see if it is bubbling steadily when at full temp, which is another sign of HG.

Of course the "block test" negates the need to do this, it's just a poor mans way of looking real quick.