Author Topic: No Heat? (Read 13295 times)

KenC · « **on:** October 16, 2008, 01:57:40 PM »

I'm totally stumped on my cooling/heating system.

I have bled it about three times now, and I still can't get it to function properly.

Symptoms:
Heat only works while the car is moving and rpms above 2500. Blows cold air while idleing.

Any ideas?

ak96ss · « **Reply #1 on:** October 16, 2008, 05:14:42 PM »

Thermostat in the right way? Check the coolant lines from the block to the firewall, do either of them get hot when the engine is hot?

Jack the front end up, bleed at a high idle. You do have the interior heater set all the way to hot and the interior fan on when you bleed it, right?

RED IS 91 · « **Reply #2 on:** October 16, 2008, 05:18:45 PM »

What is the history ?
Has it always done this ?Did you do something recently?
Check you belt ? Make sure it's tight .
Might be the pump......
Might be the heater valve.....
Might need bleeding ............
Might be thermostat...........
Really need to know what led up to this to do a diagnosis

good luck

KenC · « **Reply #3 on:** October 16, 2008, 05:26:05 PM »

I've bled it three times with the front end elevated every time. And yes, with the heater and blower both on high.
Although I haven't checked the heatercore lines for temperature, every time I've bled the system, the radiator return line has been warm so I'm assuming that coolant is flowing through all of the lines.
A cool output line would indicate a clogged heatercore?

How do I check the heater valve?

New thermostat and water pump didn't fix the issue. Pump is brand new, thermostat has about 5k on it.

Thermostat is in the right way (longer portion into the head) per Bentley manual.

EN318isPDX · « **Reply #4 on:** October 16, 2008, 06:15:57 PM »

Quote from: KenCopperwheat;58699

I've bled it three times with the front end elevated every time. And yes, with the heater and blower both on high.
Although I haven't checked the heatercore lines for temperature, every time I've bled the system, the radiator return line has been warm so I'm assuming that coolant is flowing through all of the lines.
A cool output line would indicate a clogged heatercore?

How do I check the heater valve?

New thermostat and water pump didn't fix the issue. Pump is brand new, thermostat has about 5k on it.

Thermostat is in the right way (longer portion into the head) per Bentley manual.

I had this problem but my fan was completely missing and it had similar symptoms. My guess is the valve.. its under the center console by the gas pedal. You have to pull the shifter console out to see it. You could cross wire it so hot coolant is always going through the heater core.. this is not so good during the summer

quinn11m20 · « **Reply #5 on:** October 16, 2008, 07:31:56 PM »

I have that same issue. I just deal with it. Um. Thinking about it... Its been that way as long as i have owned the car. Since 97. I have replaced the thermostat twice and did a complete coolant changeover , like hoses and radiator.

Is... the long side of the thermo goes toward the cockpit right? Thats the way mine is.

KenC · « **Reply #6 on:** October 16, 2008, 07:46:04 PM »

Would replacing the entire heatercore possibly fix this? Or would it just be easier to replace the valve? Is there one or two valves in the heatercore? I'd rather not just "deal with it."

EN318isPDX · « **Reply #7 on:** October 17, 2008, 02:53:28 AM »

Quote from: KenCopperwheat;58713

Would replacing the entire heatercore possibly fix this? Or would it just be easier to replace the valve? Is there one or two valves in the heatercore? I'd rather not just "deal with it."

lol he lives in florida not portland, the valve is an easy job.. entire heater core is not worth it unless you have a leak.

KenC · « **Reply #8 on:** October 17, 2008, 04:15:12 PM »

Is there just the one valve? Or are there two?

monty23psk · « **Reply #9 on:** October 17, 2008, 05:12:29 PM »

I believe there should be 1, at least from the bentley. If the valve is not working, not hot coolant will enter the heater core. Unlike the e28, if the valve is not working, it will not close and only hot coolant will enter heater core, which causes a premature leak.

RED IS 91 · « **Reply #10 on:** October 17, 2008, 05:34:30 PM »

Check your radiator hoses to make sure they both get hot when engine is at operating temp.
Start your car cold and wait for the thermostat to open .When it does you should feel the hot water circulating around through the radiator hoses.They both should get hot.
good luck

monty23psk · « **Reply #11 on:** October 17, 2008, 07:47:03 PM »

I believe your hoses should get hot no matter if your heater is working. Once engine gets hot, thermo opens, then allows coolant to enter radiator for extra cooling. If your heater valve is stuck close, you should not get heat. But you said you get heat when driving, this cold just be non-ac air entering cabin, which would seem warm. Currenlty on my car, I get no heat, but I dont care living in Miami. But when I fixed it in my m5, the heat was so hot I could not leave my hand in the way, almost burning heat. I remember taking the temp and it was over 120 degrees F.

Here is a pic of the coolant flow from the repair manual:

RED IS 91 · « **Reply #12 on:** October 18, 2008, 06:27:21 AM »

Does the car run Hot ,What does your temp needle indicate?
Is the problem just no Heat coming out when you turn the heater on or does the car run hot or cold?

KenC · « **Reply #13 on:** October 18, 2008, 08:59:34 AM »

Quote from: RED IS 91;58795

Does the car run Hot ,What does your temp needle indicate?
Is the problem just no Heat coming out when you turn the heater on or does the car run hot or cold?

It doesn't get that hot. The needle will fluctuate a little below and a little above the center hash depending on the heater settings.

Wise Old Dog · « **Reply #14 on:** October 18, 2008, 09:16:43 AM »

It sounds like everything is working except that it is not flowing hot water through the heater core as it should. 3 causes for this:
Air bubble in the system preventing full flow.
Improperly functioning heater valve.
Clogged heater core.

Mercedes recommends a citric acid flush for their cooling systems. I just finished doing this on mine, and if there's crud in the core the flush procedure should clear it. It is pretty involved, and will kill an afternoon doing it, but it is effective. Info is on the MB mechanic board.