So I have a 2001 jeep Cherokee sport. I've been having problems getting regular heat in this car. The vehicle seems to get up to temperature and it stays just below the 210 degree level and never moves. When I turned the heat on after the car has reached temperature I will get an initial blast of hot air but as time passes that heat slowly becomes cool air. If I turn the heat off again and wait a while then turn it back on I will have the same thing where I get an initial blast of hot air which turns to cool air. I've checked the blend doors and they seem to be functioning properly. I've read some things regarding a malfunctioning thermostat, A clogged heater core, and a few other odd things. Where should I look next and what would be causing this problem. Any help would be great and thanks.

Jim

 

If heat comes and goes, my guess is u can eliminate a t-stat and coolant flow thru the heater core problem. Those items either work/flow or they don't vs sometimes work/flow then not. Sounds more like a under the dash blend door issue.......vacuum leak or blend door actuator problem.

 

Well, OP said blend doors are fine. Have you checked your coolant level? Probably would not hurt to flush your core either. I had the same issue in mine and it turned out to be low coolant secondary to a blown head gasket.

 

"I've checked the blend doors and they seem to be functioning properly."

Are you sure it is still attached to the actuator and not simply flopping around? Have you checked the circuit for - / + voltage to the motor?

 

I removed the motor that turns the blend doors and manually turned it from side to side. The door turns easily from side to side and does not seem to get stuck. When turned all the way to the side that closes off the cold air, I still only get cool air.

I'll attempt to flush the core just to eliminate it from the equation. As far as the TStat is concerned, would an open Tstat cause low coolant flow to the core? Top heater hose is always hot... return hose not so much.

If I were to start with vacuum issues, or any other in dash issues, where would I start?

Do any of this info help you guys with diagnosis? Or at least where to look next?

Jim

 

I agree with the check coolant level idea. If its normal I would take it to a shop (I know you'd rather do it tourself but....) and have them do a coolant flush because the machines they use to do it pressurize the system vs draining then filling it back up with no pressure on the system...also they usually use a chemical that breaks up any poo that may be in the system.

My .02

 

I assume a full system flush would include the core as well. Correct?

 

Yes as long as they have the heat running it will because the lines have to be opened. They should do that as long as they are a decent experience level mecahnic. I learned that you have to do that on my first flush I did. I know longer work in the car business but that is the one fluid change I believe in letting the "pros" do. Everything else can be done just as well by shade tree bob...

Hope it works for you

 

I'll give it a shot. Hopefully it works.

 

"Top heater hose is always hot... return hose not so much."

Plugged heater core more than likely. What does the coolant look like? Any evidence of some type of "stop leak" product being used?

 

So I finally had a chance to get I'm there yesterday... Back washed the heater core and replaced thermostat for good measure. Antifreeze didn't look as filthy as anticipated but there was a clog. Heat works like a charm again though!

One thing I did notice... An oily residue on the bottom of the radiator cap. Almost like a dirty vasoline. Any thoughts?

 

BARS LEAK

 

whats a bars leak!?

Oily residue on the bottom of the radiator cap could mean oil has been mixing with the coolant, which could mean more serious trouble. Oil and coolant circuits are seperated, so mixing means one leaks into the other (for instance an cracked head or gasket leak).
Remove your oil filler cap and shine a light in there, looking for moisture/coolant drops.
another way is draining some oil after its been sitting overnight and collect the sample in a glass jar. Let is sit for a while and if oil and coolant have mixed, it will layer out (reason why you just collect the first sample is that coolant is heavier than oil, so in the oil pain, theoretically will drain out first).

 

Bars leak uses a water soluble oil in its sealing mixture that turns a nice creamy tan/whitish color when not contaminated. It will appear as a sludge ring around your radiator cap seal.

 

He better has that, because if not, that nice creamy brown stuff sure is engine oil mixed with coolant