Mercedes-Benz Forum banner

1 - 7 of 7 Posts

·
Registered
Joined
·
49 Posts
Discussion Starter #1
I posted another thread a week or two ago about how I'd drained the coolant to top up the antifreeze in my E200 wagon. The temperature gauge is now showing just under 90 deg when running, but the heater inside the car is barely waming up & seems to be just luke warm at best. At the moment it's minus 8 deg outside & I really need to get the temperature inside the car warm again. It used to get lovely & warm inside within a short distance, but now regardless of how long it's driven it still doesn't get hot inside. Sometimes, first thing in the morning after a cold night, it's got ice on the inside of the windows & the heater doesn't melt it.:confused:

Anyone have any ideas what could be wrong??

cheers...Nige
 

·
Premium Member
About a dozen 1988, 1989, 1990, and 1991 sedans, wagons, 4Matics and 1 coupe
Joined
·
5,466 Posts
When you drained the coolant, air entered the heater core and when you refilled the system the air became trapped there.
We have no 4 cylinder 124s here in the USA so I'm not familiar with the layout. Does the M102 head have an air bleed plug like the M103 does? If so you need to loosen that to vent the air bubble in the head.
Does your car have an auxiliary coolant pump (electric) mounted to the frame rail below the surge tank? Is it running?
Have a helper raise engine RPMs to about 2k, twist teh heat control to max, and then use your fingers to squeeze the hose walls together near the pump and restrict coolant flow. You'll feel air bubbles passing through the hose and then the hose will get too hot to squeeze. That's how you know you're done.
Recheck the coolant level again and you're done.
 

·
Registered
Joined
·
49 Posts
Discussion Starter #3
When you drained the coolant, air entered the heater core and when you refilled the system the air became trapped there.
We have no 4 cylinder 124s here in the USA so I'm not familiar with the layout. Does the M102 head have an air bleed plug like the M103 does? If so you need to loosen that to vent the air bubble in the head.
Does your car have an auxiliary coolant pump (electric) mounted to the frame rail below the surge tank? Is it running?
Have a helper raise engine RPMs to about 2k, twist teh heat control to max, and then use your fingers to squeeze the hose walls together near the pump and restrict coolant flow. You'll feel air bubbles passing through the hose and then the hose will get too hot to squeeze. That's how you know you're done.
Recheck the coolant level again and you're done.

Thanks for the advice but I've already bled the system (numerous times :() to make sure it wasn't air trapped in the matrix. When I re filled the radiator I did it with the engine running, squeezing the hoses as I filled it & left the cap off the expansion tank overnite. All the hoses are the same temperature & when it's hot you can't hold them for too long. I don't think the car has an auxilliary coolant pump but will check in daylight tomorrow to be sure.

I can't find a bleed screw anywhere on the car, but have loosened off the top hose with the engine running, squeezed it & got air out of the system that way. Again, I've done this numerous times & now no air bubbles come out, but the heater is still barely luke warm.

Thanks...Nige
 

·
Premium Member
About a dozen 1988, 1989, 1990, and 1991 sedans, wagons, 4Matics and 1 coupe
Joined
·
5,466 Posts
The bleeder fitting on the M103 is on top of the cylinder head near the oil dipstick. See the pic. It has a 13mm hex head and there's a copper sealing washer against the head. Your method of bleeding air out of the system may work fine but I haven't tried it so I can't say for sure. It sounds too messy to me.

I'll include a pic of the aux coolant pump too. From personal experience I can say that heater output is very poor at idle when the aux pump dies. Once you're moving heater output improves. From your description the aux pump (if installed) maynot be the problem.

I do still suspect that the heater matrix is air-locked. Have you unplugged the mono- or duo-valve connector to insure that the controls are working?
 

Attachments

·
Registered
Joined
·
49 Posts
Discussion Starter #5
Have you unplugged the mono- or duo-valve connector to insure that the controls are working?
Thanks for your help it's really appreciated, what do I need to do with the duo valves to see if they're causing a problem??

Thanks...Nige
 

·
Registered
Joined
·
49 Posts
Discussion Starter #6
An update on this, I've checked the car after a long run in minus 4 deg temperature today & found that the water in the rubber pipes seems to be warm up to the auxilliary heater pump, but the two hoses coming from the duo valves are cold.

I can't hear a buzzing noise from the pump, or feel any vibration, should I be able to with the engine running & the heater controls on full/hot?


Could this be a faulty pump, if so how do I check it, are they dismantleable to clean? Is the pump fused & could this maybe have blown?

If so where are the fuses?

Is this pump supposed to help circulate the flow of water through the heater matrix?

There's virtually no heat coming from any of the vents in the car (minimal at best compared to really warm before).

Do these symptoms point to pump or duo valve problems?

Sorry for sooo many questions but I really need some help witht his as it's down right uncomfortable to drive now as the windows inside are icing up as I'm driving.

Thanks in advance....Nige
 

·
Premium Member
About a dozen 1988, 1989, 1990, and 1991 sedans, wagons, 4Matics and 1 coupe
Joined
·
5,466 Posts
It sounds like you're close to finding the source of the problem.
On US cars Fuse #7 in the underhood box is responsible for getting power to just about all of the climate control system including the monovalve, the aux coolant pump, the interior temp sensor, etc. If that fuse is blown you'll definitely have cabin temp control problems. Check #7 immediately.
Don't just look for a blown fuse. Spin the fuse in the contacts to make sure that good contact exists between the fuse ends and the fuse block strips.
The aux cooloant pump is there *specifically* to aid coolant flow through the heater matrix. On M103 cars the pump is necessary at idle but not once the car is moving. Maybe M102 cars need the aux pump to work all the time. If fuse #7 isn't the problem look closely at teh aux pump. If the temp dials are set to max and the engine is running you should be able to feel the pump running if you wrap your hand around it. Typically the seals fail and coolant seeps into the electric motor causing the armature to seize.
The duo valve fails "open" causing max heat so I doubt it is the problem. Everything points to the aux pump, possible lack of power to it.
 
1 - 7 of 7 Posts
Top