help needed, My 92 Benz has very little heat on either heat or defrost,and less on the passenger side,the engine gets up to temp fine ,and the heater hoses are hot going into and coming out of the firewall,I changed the control in the dash with one thought to be good …no difference it will be warmer for a few seconds when you first turn it on any help is greatly appreciated Sean
@bambamss IMO you have the classic symptoms of a plugged heater core.
Flush that sucker out!
There is a sensor in the panel which contains the sunroof switch and a light up on the forward edge of the headliner. It has a hose connected to it. It’s for the temperature sensor that tells the system to add heat or add cool. It snaps into place. Check the hose connection first. I had to replace it on one of my Benz 300Es of that era.
thank you both ,if the core is plugged ,possibly from some additive (I hear they had head gasket trouble) would a Prestone type flush work ? or something more aggresive ? I wondered that but thought if heated water was moving slowly through core it would extract all the heat ,and not head back to the engine hot
It could be the blend door not opening properly.
With all due respect to the other responses, I still believe flushing out the heater core is the easiest thing to try, and IMO should also be the first thing to try.
Remove both heater hoses and flush it out from both sides. I use something similar to this.
Here’s another reason I believe the heater core is plugged. OP’s statement that “will be warmer for a few seconds when you first turn it on” PERFECTLY matches the symptoms of cars that I’ve worked on that had plugged heater cores.
FWIW . . . all of these cars had heater cores because the coolant had NEVER been changed, and the cars were at least 10 years old with some miles.
@bambamss What does “I hear they had head gasket trouble” mean?
Another FWIW, those M103 inline 6 cylinder engines are known for head gasket issues. Usually, the only real problem is seepage near the back of the head. But occasionally, the head gasket will split. Usually, this is very obvious because the coolant reservoir will have oil in it and the oil itself will look like mocha frappuccino
Another BTW you may also want to replace the thermostat and coolant pressure cap if it’s been awhile. I don’t believe that is your problem here, but it’s cheap insurance against future troubles.