Overheating w123 - Page 11 - PeachParts Mercedes-Benz Forum

dieseldiehard · #**151** 06-01-2013, 11:38 AM

Quote:

Originally Posted by funola

yes, if the heater temp wheel controls a valve (which I am not sure about). I don't think it does, i.e. coolant is flowing through the heater core all the time. But to be safe as far as getting the air out, turn the heat on.

Edit: I forgot the monovalve controls heat on /off so there is a valve. so turn heat on.

OK, my 20-cents here.
1) The 123 diesel should not overheat, provided the radiator isn't calcified (a can of Prestone cleaned is worth a shot as a cheap remedy for that!) and of course you need a decent water pump and changin that would be my last resort.

I believe the monovalve default is open so water should get into the heater if you disconnect it. There is however a screen in the monovalve that will fill with crud and block or restrict flow.

Also, the small pump that supplys the heater may not be working, they tend to short and cause damage to the control panel climate control on the dash. A resistance check of the pump is a good idea if you have an Ohmmeter. I recall its around 50 Ohms normal, 2 Ohms shorted. Add a 1A inline fuse at the pump also if you have time (later, after this problem is solved).

When you fill the cooling system do you attach a hose to the head?
On the Rt side just near the rear of the head an S shaped heater hose going to the firewall, running very close to the lid of the OF cannister, is where you should first put water (or coolant) as that is behind the thermostat and will fill the head and part of the cooling system, then you fill the expansion tank after reattaching the heater hose to the head. That esentially burps the system by backfilling the cooling loop. I always use this technique on the 123 and 126 diesels.
DDH

dieseldiehard · #**152** 06-01-2013, 11:42 AM

Quote:

Originally Posted by digieditny

Ran the car on a hill (not extremely steep). Coolant level dropped slightly, refilled and I hope it burped. I don't see that much difference in temps. Will drive the car again sometime today and see if there's still a lot of air build up.

As I was getting my teeth drilled at the dentist last night, I remembered the conversation we had about the thermostat maybe not opening till around 90c. Like you saw, if I don't turn on the air, the car stays at around at 90c but will overheat with the AC. Is it possible it's another issue? Can the ac clutch be going and causing too much load on the car causing it to overheat? Not even sure if that's possible. Remember you felt the car idle roughly with the AC on? Just a thought...

The first thing that should have been done is to replace the thermostat, but I have known of a brand new thermostat that wasn't opening at the rated temp, just a thought. If a new thermostat was installed and things are not significantly different than move on to the rest of the cooling system. I still don't know if the radiator was replaced thats always the critical element in a cooling system! If its even partially plugged it can't efficiently remove heat from the water and you will find the car runs hot or hotter than it should with symptoms like getting over 90 with the AC on, etc.

Ndralle · #**153** 09-04-2013, 06:01 PM

i dont mean to reboot this thread, and i stopped reading after page 6 so i dont know if this was suggested...

get a new radiator/reservoir cap. if the system is not keeping pressure at the cap the water can start to boil due to a lack of "atmospheric pressure." this is not always caught im a pressure test because the tech hooks up to the cap fitting.

also check the water pump for side to side play. this is the sign of a bad bearing and if the pump isnt toast it will be soon.

pull the radiator and have it tested at a radiator shop. they will test the back pressure and test it for leaks. they can also reverse flush it with compressed ari/water. i have don this and it only cost me 10$+tip at the local guys garage shop. it also make my 190td run 10c cooler.

My last comment is that i have always been told that the tstat is critical in our engines to keep back pressure on the radiator thereby keeping the water in it longer and cooling it more efficiently. when removed it leave a large hole and less back pressure. i have seen many people remove the guys of a tstat (spring looking thang) and use just the surrounding plate. in theory this would make the system work as if the tstat is fully open at all time. I don't recommend it but ive seen it work.

cya