240D Overheating - PeachParts Mercedes-Benz Forum

benallenh · #1 03-14-2007, 01:54 PM

My 1977 240D with 260,000 miles, which ran wonderfully up to the point where I decided that I need get the green stuff out, now has overheating issues. I replaced old coolant with the Zerex GO-5 per numerous reference on this forum and other sources. While changing over I also back flush the cooling to confirm that all of the old coolant was completely removed. After purged the system of air through the bleed screw in the top of the thermostat housing and running the heater, I thought I was back on the road as good as ever. The car began gradually getting running hotter while sitting idle in traffic. So I thought it might be a good idea to do the citric acid flush. This did nothing to improve the temperature problem and now the car was running hotter than normal a freeway speeds. Since I wasn't sure of how to fix the problem I began throwing money at it by way of a new thermostat, radiator, and water pump. During the process of replacing these parts, I also adjusted the valves in the hope that that might have some positive effect. Now I can't purge all of the air out of the cooling system and it overheats within just a few minutes of driving.
It appears that I may have a leaking head gasket but I hope that isn't the case. There is no water in the oil or vice versa but the air/heat has to be coming from somewhere. I'm planning to check the compression today as a final test of the head gasket. I assume that this should give me some indication of leakage from the combustion chamber into the water jacket.
Does anyone have any suggestions to what maybe causing this overheating besides the head gasket? If I do need to change the gasket I'll probably bite the bullet and get the heat reconditioned. I've read that Metric is good but appears to be expensive and Mark DeGroff's Cylinder Head Service was mentioned. What are your experiences with these and other shops in Southern California?

rrgrassi · #2 03-14-2007, 03:49 PM

Sorry, can't help you, but someone should chime in that lives in SoCal

Stevo · #3 03-14-2007, 04:50 PM

I'm guessing you did't get all of the air out of the system when you drained the block. How did you bleed the system?

benallenh · #4 03-14-2007, 06:55 PM

The final time I tried to bleed the car, it was parked on a hill so that the radiator was above the engine. At which point I added coolant to fill the radiator. Then I opened the heater valve and pulled off one of the hose going to it to confirm that there was coolant in the heater core. Once again I topped of the radiator. With the engine running and the radiator cap off, I could see large burps of air began rising up to the neck of the radiator. I believed that this was an indication that the air was being purged from the system. The large size of the bubbles and the absence of froth lead me to initially think that the head gasket wasn't the problem and it just need to get all of the air out to cool properly. However the bubbles never quit coming and the the heater eventually stopped producing heat. All this happened while the car was park on the hill running at high idle. Although I had a new thermostat that was confirmed good by a hot water test, I decide to try a second time without the thermostat. I had no better luck without the thermostat.

Stevo · #5 03-14-2007, 07:11 PM

Getting all the air out can be a bugger especially after you drain the block, I think thats your problem. Having the front of the car up is good, then disconnect the heater hose from the fire wall side and wire it up. (the hose from the head to the firewall, driver side) Then disconnect the upper radiator hose at the eng and pour coolant in till it comes out the heater hose you have wired up. hook things back up. Running at a fast idle have the heater on full and when you get heat coming out, your home free. The temp will get up high but shouldn't get into the red, don't let it do that.

maddogg20 · #6 03-14-2007, 08:24 PM

whats up bro. I live in rancho cucamonga in so cali. Yea my cars been running hot as hell too lol.

Mojool · #7 03-14-2007, 08:28 PM

is it possible that you dislodged some sludge or sometihng...kinda like a heart attack in a human...i know it sounds dumb...but couldn't it be clogged somehow??

cgunderm · #8 03-14-2007, 09:40 PM

Quote:

Originally Posted by benallenh

Does anyone have any suggestions to what maybe causing this overheating besides the head gasket? If I do need to change the gasket I'll probably bite the bullet and get the heat reconditioned. I've read that Metric is good but appears to be expensive and Mark DeGroff's Cylinder Head Service was mentioned. What are your experiences with these and other shops in Southern California?

I had exactly the same symptoms, and for more than a year I did everything that you did, new radiator (twice!), new thermostats, three times, new waterpump, new heat sensor, everything. It would only run hotter and hotter, hardly ever come down from 100C. You know what solved the problem? I sanded the surfaces on the thermostat housing and put some red silicone sealer on it, and voila, running at just over 80C after bleeding. There must have been air getting sucked in at the surface of the housing. The problem had started after I changed the thermostat for the first time because the car was running too cool. I also started thinking, maybe head gasket, but it didn't have any other symptoms. Also, 617s rarely have any head gasket or head issues. (It's the 1985 300D)
Check it out, maybe this is your solution, too....

t walgamuth · #9 03-14-2007, 10:01 PM

sorry to be mr obvious but are you sure you don't have the stat in backwards?

it is pretty easy to do and it will get hot in a hurry if it is.

tom w

log673 · #10 03-14-2007, 10:50 PM

I just flushed my cooling system. However, I haven't brought it out on the highway yet, so the temp is staying at just above 80C for now anyway. I never read about bleeding the air out of the system in any of the coolant flush posts. How do I do this?