I have No heat after a coolant change... - PeachParts Mercedes-Benz Forum

Two560Two · #1 01-28-2006, 11:11 PM

I just acquired a 91 560sel with 124k miles. It seems as if the PO just recently did a collant change to zerex? Well, I have no heat! The engine is at full operating temp but the heat doesnt come through. Only cool air blows through. The A/C works fine and was able to test that today since it was 60 deg. Now its a bout 39 deg and I get no heat. I ran the defrost on high thinking there was air in the system but still no luck. I did that for about 5 minutes though. I am thinking that i need a new heater core? There are no leaks or coolant anywhere. Please help

t walgamuth · #2 01-28-2006, 11:15 PM

chance your hvac controls are messed up.

tom w

Two560Two · #3 01-28-2006, 11:17 PM

well, all the buttons function as they should. the A/C works. blower works in all settings

Brian Carlton · #4 01-29-2006, 12:21 AM

Start with the basics.

Open up the monovalve and check the condition of the diaphragm. 90% of the problem with "no heat" is caused by a tear in the monovalve diaphragm.

If the diaphragm is torn, replace it and you're done.

If the diaphragm is good, put it back together and unplug the monovalve and drive it. See if you then have heat.

stevebfl · #5 01-29-2006, 10:30 AM

Quote:

Originally Posted by Brian Carlton

Start with the basics.

Open up the monovalve and check the condition of the diaphragm. 90% of the problem with "no heat" is caused by a tear in the monovalve diaphragm.

If the diaphragm is torn, replace it and you're done.

If the diaphragm is good, put it back together and unplug the monovalve and drive it. See if you then have heat.

Yea, that is exactly what I would do.

If that didn't solve it I would put a pressure tester on the radiator and open the return line from the core. I would plug the engine side and I would pump the system and see what came out (the valve should be open if the key is off). You might be able to do this without the pressure tester by just reving the motor with the engine side off and something to collect the flow. Doing it that way of course empties the system rather tahn bleeding as the pressure tool woul allow.

Brian Carlton · #6 01-29-2006, 10:38 AM

Quote:

Originally Posted by stevebfl

Yea, that is exactly what I would do.

If that didn't solve it I would put a pressure tester on the radiator and open the return line from the core. I would plug the engine side and I would pump the system and see what came out (the valve should be open if the key is off). You might be able to do this without the pressure tester by just reving the motor with the engine side off and something to collect the flow. Doing it that way of course empties the system rather tahn bleeding as the pressure tool woul allow.

Could the shadetree mechanic accomplish the same thing by putting a garden hose to the core supply side and watching the return line from the core to ensure a proper flow?

whunter · #7 01-29-2006, 05:31 PM

Quote:

Originally Posted by Two560Two

I just acquired a 91 560sel with 124k miles. It seems as if the PO just recently did a coolant change to zerex? Well, I have no heat! The engine is at full operating temp but the heat doesn't come through. Only cool air blows through. The A/C works fine and was able to test that today since it was 60 deg. Now its a bout 39 deg and I get no heat. I ran the defrost on high thinking there was air in the system but still no luck. I did that for about 5 minutes though. I am thinking that i need a new heater core? There are no leaks or coolant anywhere. Please help

Best guess:
#1. The system has air trapped.
#2. The bypass/bleed tube (block to head) is plugged.
#3. The thermostat bypass is plugged, and/or thermostat is junk.