heater problem?

Recently my heater has not been working, well at least most of the time, if I try to run the defrost or other heater function with the heat on it just blows cool air. a few times when i turn it on my "check gauges" light comes on because the temp. is running too hot, which goes to normal when I put the heat to Off!, I am blown away, not even sure where to start, I would be grateful for any help, Happy New Year, Ryan!

Please note: coolant system problems that are not corrected can cause MAJOR ENGINE problems. So it is very wise to check yours out.

1. First (and easiest) check your radiator fluid. If your fluid is real low, you might notice cold air through the heater. Top off your fluid as needed.

2. How does the radiator cap look? Is it loose? Has it been a while since it was replaced? Radiator caps should hold 15 lbs pressure. Replace the cap when you flush your radiator each year. Heck they are cheap! While you are at it, give your upper and lower radiator hoses a squeeze.

3. Your problem could be as simple as a thermostat stuck closed . If the thermostat is stuck closed you may also have overheating problems as the fluid will not cycle through the radiator (causing engine overheating) nor the heater core (causing no warm air in the passenger compartment). The engine may not overheat in cold climates even with a stuck thermostat. But you WILL notice the cold air. :eek:

Disconnect the thermostat housing and drop the thermostat in some 195 F water (use your wife's candy thermometer) and see if it pops open. If it fully opens at ~195 F, then your thermostat is fine. Thermostats are said to last 60k miles or so.

You will need to scrape off the themostat housing surface smooth and replace the gasket. Use some Permatex Water Pump & Thermostat Housing RTV Silicone (Autozone = $2.99) on the gasket.

3. It could be your heater core is clogged. This is common especially when people use "stop leak" in the radiator. I don't like the "stop leak" stuff having had to replace two heater cores after the stuff was used...
If your radator is leaking, then just replace it. It is TEN TIMES easier to replace a radiator than a heater core.

The heater core is pretty easy to check. First locate your heater hoses. Most heater cores are located under the dash of the passenger side. So the heater core pipes will be sticking through the engine compartment on the passenger side. The black heater hoses are attached to the heater core pipes. One hose goes to the radiator and one goes to the engine.

You might want to drain a little radiator fluid before you disconnect the heater hoses. Also get some towels ready to catch the fluid.

Once you have located your heater hoses and drained a little raddy fluid off, then disconnect both heater hoses from the heater core pipes. They are different diameter hoses so you don't have to worry about where they go when you replace them. GM uses the squeeze clamps on the hoses. Personally I prefer the screw clamp, so I replaced all my clamps with screw clamps.

For my 94 Jimmy, the molded hose goes to the engine. Yours may be different depending on model/year.

If your hoses are in good condition (they don't "crackle" when squeezed and the interior is not deteriorating) then you can reuse them. You will have to work them off the heater core pipes.

If you are going to replace your heater hoses, then what the heck! Cut the hoses off and save time.

With your heater hoses off and towels in place (to catch fluid), try blowing some compressed air into one of the heater core pipes. Since it is only supposed to be fluid in there, it should go through really easy. Don't have a air compressor? Get a turkey baster and drop some fluid in the pipe and squeeze the bulb. If you put the a turkey baster full of radiator fluid tight into one of the heater core pipes, just queezing the bulb should force fluid out of the other pipe in a healthy heater core.

Does the fluid come out the other pipe easy? Or does it get stuck?

Note what the fluid looks like. Is it all rusty looking? uh oh...:uhoh:

If the fluid looks nice and clean and comes out easy when blown with some compressed air, then let out a big sigh of relief: your heater core is not the problem. Reattach your heater hoses and look elsewhere for the problem.

If the fluid is rusty and/or gelatinous, or if the fluid cannot be blown/forced through, then your heater core is probably clogged and will need to be replaced.

I just had to replace mine and it is a major pain in the butt. $20 for the part. 20 hours of my time... The repair guides say 7.2 hours of labor.:sly:

Simpler way to check if your thermostat (DOH!) is stuck closed: at normal operating temperature feel the upper raddy hose. If it is warm, then your thermostat is opening (it may be stuck open, but that is kind of rare as I understand it). But if the upper raddy hose is cold at normal engine operating temperatures, then your thermostat is probably stuck closed. This will cause engine overheating and you won't get warm air through the heater vent.

If your coolant is flowing through the return hose (upper raddy hose), then your thermostat has to be opening or is stuck open (not as serious of a problem as being stuck closed).

Test the thermostat as described in the above post.

You can do the same thing with your heater hoses. If the heater hose going to the radiator is cool AND your upper radiator hose is warm at normal operating temperature, then your thermostat is working, but your heater core is prolly clogged. uh oh.

At normal op temps, both the heater hoses and the upper raddy hose should be nice and warm.

Once you understand the flow path of the coolant, diagnosing these problems becomes pretty easy. Fixing them can be another matter...:icon16: Actually everything except the heater core is pretty easy.