OT auto repair OT

[Terry Coombs]

Hey at least it ain't politics !

Our '99 Toyota 4Runner has a heater problem that's driving me (more) nuts . The heater apparently isn't getting enough coolant flow , and isn't putting out enough heat . I've checked all the hoses from the motor thru the valve and heater core and back to the engine , hoses are OK and the core isn't plugged . I've also flushed the entire system , all hoses and the core and associated plumbing . After flushing it out it'll do OK for a short time then it's back to not enough heat . Pertinent info - the water control valve is cable operated from the dash along with the gating for airflow in the heater box . I don't think there's a t-stat type device in there for temp control , but if there is one and it's malfing that might explain it . The coolant level is up , and circulating when observed in the radiator . This has really got me stumped , and the wife is getting pretty hot herself about it - we're getting into the cold season here and she's the main driver . -- Snag

[trader_4]

Does the car have a temp gauge? Any chance the problem is the engine is running cold due to a bad thermostat?

[DerbyDad03]

Are you sure that the blend doors are opening and closing properly?

I've had them fail on various model cars. Until recently I had a 2002 Mitsubishi that sometimes would not produce heat after the temp knob was moved from full cold to heat. Turned out that the blend door actuator would get intermittently get stuck in the fully closed position. I followed the cable down to where it entered the duct work and installed a small block of wood to prevent the cable from being moved to the fully cold position. The difference was maybe a 16th of an inch at the knob end.

Car had heat for 3 winters until other issues signaled it's demise.

[Mr.E]

Feel the heater hoses with the heat working and note the approximate differences. Do the same when the heat has malfunctioned. If the hoses to and from feel the same or hotter when it quits, you may have a mixer door air flow problem.

[Stormin Mormon]

Years ago, my Mom had similar problem. The mechanic found a lot of leaves in the box with the heater core. Some times the leaves would rise up, cover the fins and block the air flow.

Is there a temp gage on the insturment cluster? Might be thermostat sticking open. Did you check the temp at the Tstat with a non contact thermometer while this problem is occuring? I had to change the thermostat on my newer vehicle.

Who knows....

[Stormin Mormon]

Quit reading my mind!

BTW, all those images of naked women ren't really there.

[DerbyDad03]

Speaking of leaves, have you checked your cabin air filter recently?

Having bought 4 used cars in the past 3 years, I can attest to the fact that the cabin air filter is a highly neglected item. Leaves, bees, rocks (rocks?) and all manner of debris can be found embedded in the cabin air filter.

One car I bought was so clean it practically glowed. The engine air filter looked like it had been changed the day I test drove the vehicle. After I bought it I pulled the cabin air filter. It was so dirty I'll bet it was the original.

[Terry Coombs]

Not a chance , the motor temp is where it shouild be - and it does work well for a short time after flushing .

[Terry Coombs]

Not the problem , I can observe the mechanism moving when I move the control knob . Unless there is a t-stat in there that controls them and the cable only signals it for heat .

[Terry Coombs]

I have done so , and when it works right both hoses are hot to the touch . When it's not working right the exit hose is noticeably cooler , that's why I think it's a coolant flow problem .

[Terry Coombs]

I didn't know there was a filter ... but if it was plugged wouldn't I be seeing a reduction in airflow ? It blows a good air stream , it just ain't warm enough .

[bob_villa]

Is there coolant in the expansion tank...could air be in the system?

[Stormin Mormon]

When I replaced vehicle, I checked the main air filter. Pretty bad, so I kept the one off the older vehicle. As to cabin air filter, I did ask at a parts house, and they were unable to find any such listed.

Rock auto (dot com) also does not list such a part.

Good advice for all concerned. Thank you.

[Stormin Mormon]

Strike that one off the list of possible problems.

[DerbyDad03]

My response wasn't to you, it was to Stormy. The cabin air filter will not cause the problem you are describing. It was just a comment on the neglect of the cabin air filters.

I believe that the 4Runner started to use cabin air filter in 2003, so no, you don't have one.

[Terry Coombs]

Yes , the exp tank is full , and the rad is up to just below the neck .

[bob_villa]

There may be an air-bleeder on the T-stat housing...

[DerbyDad03]

What mechanism can you observe move? On the Mit, I could see the cable move a nylon connector over it's full range of motion as observed from outside the blend door housing. However, the blend door shut motor itself is inside the housing and that was what was intermittently failing in the fully closed position - by design.

If you fast forward to 7:00 in the following video, you'll see what I mean.

What I did was keep playing with the control knob until the shut motor activated and opened the doors. I then physically prevented the cable from ever moving to the fully closed position, thereby "eliminating" the shut motor from the system.

My Dad has a mid-2000's Mercury Sable. He had poor heat also. He had a blend door issue, but it cost him $800 to fix. It was mostly labor because half the dash board had to be taken apart to get to the problem.

Blend door issues are a common cause of no/low heat.

[Tony Hwang]

Sure you burped the system free of air pocket? Sure rad. thermostat is good?

[Tony Hwang]

When it does not work feel two hoses going to heater core. Do you feel heat?