Before I begin I’ve already had the heads and the radiator tested. I have a 1997 Subaru Legacy 248,000miles with a 2.2L engine. I’ve replaced 3 thermostats, new radiator cap, flushed the system, all new hoses, bleed the system, new water pump, and a new timing belt. Now here’s the issue. It has over heated in the past which has led to all of these replacements but now its overheating again. Got it back from the mechanic that ran all the tests said it was fine drove it around for a couple of hours was going up a hill and it started over heating again. Could it be the heator core? Local mechanic wants over 800 to fix that!! Any ideas would be great.
Probably a head gasket. A small leak is hard to detect by any means.
Sounds to me like a crack between a water journal and a cylinder in your engine block.
I have seen these occur and not burn or use coolant, but instead feed cylinder compression into your cooling system.
The heater core wouldn’t cause that but a partially plugged radiator would. At 20 years old it’d be the next thing to replace.
combustion gas is forming an “air” pocket that impacts coolant flow? causes an air pocket in the vicinity of the coolant temp gauge? coolant level is fine so no coolant is being pushed out of system.