Lukewarm heat in car (idle, versus, engine, replace)

[steel7]

When my 85 olds delta 88 is warmed up good the heater blows out lukewarm heat.

I think i may need a new thermostat (its old).

Do you agree & if yes, what temperature ?

My radiator & heater core is good & i flushed my radiator last year.

[Drover]

Does it have a temp gauge? Does the needle barely move past the "cold" reading, esp. at highway speed? If so, then indeed you need a new thermostat.

[steel7]

Originally Posted by Drover

Does it have a temp gauge? Does the needle barely move past the "cold" reading, esp. at highway speed? If so, then indeed you need a new thermostat.

The car has a dummy light.

UGH !

[square peg]

You might also have a problem with your heater temp control. And if it's the thermostat, the hotter the better.

[Drover]

What if the car has just been sitting at idle for a while? Does the heat coming out of the vents feel warmer versus when it's moving?

Without anything more specific than an idiot light to go by, one way to check is to take it to a shop that has one of those infrared gun thingies they can point at the radiator neck to get a temperature reading.

[steel7]

Since i live in a mild climate ill most likely leave it alone cause i rarely drive at night (when its the coldest) & the winters are short here.

My car would be worthless in a cold climate.

Its a gas guzzler so i only drive it when i have to such as getting to work, grocery shopping & va hospital.

I only get 15 mph combined (city/highway).

[steel7]

Originally Posted by Drover

What if the car has just been sitting at idle for a while? Does the heat coming out of the vents feel warmer versus when it's moving?

Without anything more specific than an idiot light to go by, one way to check is to take it to a shop that has one of those infrared gun thingies they can point at the radiator neck to get a temperature reading.

The heat is is the same (lukewarm) after sitting idle for awhile.

No heat comes out hot & toasty.

I just turn it off after awhile cause its useless.

It did almost the same thing last winter.

[Lux Hauler]

Without a gauge it is hard to tell. Heater cores WILL gradually degrade as build up collects on the tube walls and effectively inhibits heat transfer. You should REVERSE flush the heater core coolant circuit, this will break loose most of that build up. Another thing is the mixer door for directing flow could be getting stuck prematurely.

However, the first and easiest thing is to do is replace the thermostat. If it's old it should be done anyway. They are very cheap and accessible for that engine.

[steel7]

The heater used to work really good but not anymore.

Yrs back i owned a 78 mustang & the thermostat stuck so the car over heated. I replaced the stat & then shortly thereafter the heater core leaked.

I disconnected the heater hoses & had no heat for a few yrs. It wasnt too bad unless the front window fogged up.

It rarely gets below freezing here & thats at night. The coldest daytime highs in winter may peak in the mid 40s but not often.

Avg winter highs is 60-70 degrees.

[Deez Nuttz]

Lukewarm heat could mean a thermostat that's stuck open all the time.

Lukewarm heat could also mean the flap on the door for the hot/cold selector isn't fully opening to allow the heater core to be fully exposed.

Lukewarm heat could also indicate a restriction in the heater core. aka plugged up. Especially if you've ever used that radiator stop leak crap in your cooling system.

I'd pull the t stat 1st and see if it's open when the engine is cold, and if in doubt replace it, they're not expensive. Then make sure the flap on the hvac box is opening all the way.