Hello - My 89 does not produce sufficient heat. At 90 degree setting it is just luke warm. I replaced the thermostat with the factory 195 degree, coolant level is ok, and the air mix valve is full hot position. Bottom heater hose going into the core is warm, top hose is cool, blower working fine. Engine coolant temp is right at the center of the scale. I'm out of ideas at this point. I am thinking of replacing the thermostat with a higher setting, maybe 210. Any help would be appreciated Thanks - John
From EVERYTHING in your Post I would suspect a stopped up Heater Core, have IT backflushed INDIVIDUALLY, & then possibly the entire Sysytem - I would NOT up the Thermostat - Typically a car pumps Hot Coolant to the Heater Core even when the Thermostat is CLOSED - It's possible therefore to drive around in REALLY COLD weather NEVER opening the Thermostat & using only your Heater Core as the "Radiator" - good luck
The best way to proceed is to remove both hoses from the heater core at the engine piping, and alternate back and forth between those two hoses until full flow is restored. It takes some time and patience, but they can be flushed out this way even if completely clogged when you start as long as you keep alternating back and forth.
I disconnected the heater core hoses at the engine (a bit challenging to get to the lower clamp!) and backflushed the core. I was amazed at what came out. I alternated between the 2 hoses until water ran clean. It worked great - I now have good heat! Thanks again for the great advice - John