UConnJack

So my heater hasn't worked right for a few years. It would only blow hot air when the engine was revving/driving, back to cold when idling. It was a nuisance, but I tried a few simple things based on advice here including flushing and burping the system of possible air pockets. I also ended up replacing the radiator due to a leak over this time, and then flushed and burped the system again. After all this, the hot air seemed hotter, but it would still go cold at idle.

Fast forward to this fall, and now I am getting no heat at all, revving, idle or otherwise. I made sure coolant was topped off and burped again, but no dice. Based on searches of the forum, it seems like the main culprits would be:

1) A blocked heater core. This intuitively makes sense, that it may have been partially blocked before, but only a revving engine could force fluid past the partial blockage. Wrinkle is, when I feel the heater hose going into the firewall, they are both warm/hot, implying that hot fluid it going through the core.

2) A faulty thermostat. However, the engine/fluid warms up normally, and does not seem to run to hot or cold.

3) A faulty air mix motor/valve. Could be, would make sense now with no heat at all, but why would a revving/idle engine have made a difference in the past.

Opinions?

Are there any possibilities I have missed?

Is there anymore easy troubleshooting I could do before I start ripping the dashboard out to check the air mix and core?

Thanks!

BTW, it is a 2000SE 5sp with manual climate controls.

00Lightsout

your water pump is bad, and your thermostat is fine I bet

UConnJack

But if the water pump was bad, wouldn't I have overheating problems?

DennisMik

iTrader: (2)

Here is a checklist. If you have done some of them, fine. There is no particular order to this list.

Engine coolant level - When the engine is cold, take off the radiator cap. The top tank of the radiator should be completely full.

Thermostat - Start car and drive. Observe engine temperature gauge. Needle should move to normal operating temperature spot. Stop driving and let car idle for maybe 5 minutes and then rev engine. Temperature gauge should not fluxuate at all. Another way is to remove the thermostat and put it in hot water and see if opens at the correct temperature. It should open at 180 degrees and the amount of movement that it opens should be .4 inch at 203 degrees. The thermostat should close at 9 degrees below the opening temperature.

Heater core - Remove hoses from engine and reverse flush with a garden hose. Word of warning. Household water pressure can be as high as 60 psi. The cooling system operates at around 14 psi. If there is little or no water flow, don't keep the garden hose turned on or the heater core may rupture.

Air mix door - With ignition switch in "ON" position (engine does not have to be running), move the temperature control lever back and forth from hot to cold while watching the air mix door motor. The arm on the motor will move when you slide the lever back and forth.

If any of these items aren't as they should be, you have located the problem area and need to either further diagnose or repair.

jgilbs

I second the coolant level. My radiator was leaking and I had the same symptoms. New radiator fixed that right up. However, I had copious amounts of residue all over the engine bay, so if you dont have that the issue might be something else

00Lightsout

great advise DennisMik!! check the checklist before you perform any repairs.

well, you have a newer radiator...I wonder if you have a coolant leak out one of the head gaskets or in a harder to locate area :/ lets hope not

UConnJack

Thanks everyone.

Coolant level has been OK. Like I said, I have flushed, changed the radiator, refilled, burped, and watched coolant level, and it didn't seem to make a difference with the revving/idle problem I had previously. Coolant temp seems to behave normally too. Only thing that seems to be left for the rev/idle issue is the core itself.

That said, I think my current problem with no heat at all is unrelated to the previous issue, but is with the air mix. I contorted my body to get view under the dash, and the door does not seem to move when the heat is toggled. I tried to move it manually, but I cannot get it to move. I am going to try and disconnect the arm so I can move it manually to check.

ColtMax

I went through the same issue. Did the same testing / replacements... to find out that:

Bad Radiator Cap allowing air in the system. The air gets trapped in the heater core creating a pocket that disturbs the normal flow of coolant.

Change you cap, refill your coolant reserve, give it 2-3 days of hot / cold cycles and it should be good.