Thermostat / Radiator Woes - PeachParts Mercedes-Benz Forum

jpmaynard · #1 01-06-2005, 07:00 AM

not exactly the time of year to have this thread but it is what it is.

so i noticed that my thermostat was stuck open b/c i could never get up to operating temp when it was cold. but during summer would stay around 90c. decided to change the thermostat. put new one in, burped system and now running at 100c on guage. went out and bought a behr 78c thermostat from indy and put the NEW NEW one in. STILL running at 100, but it kinda looks like its the gauge that is flakey. sometimes it will flick between 90 and 100.

AND now i appear to have a radiator leak!

i've had the top hose off and im getting water into the radiator and its not backing (not due to leak, only seems to leak under pressure) up in the radiator so i assume that the thermostat is opening and sending it through when warm.

is there a way of testing to see if i need to replace the instrument cluster?

how much of a PITA is it to replace the instrument cluster?

can someone help me sort this out!?!?!? because im

SD Blue · #2 01-06-2005, 08:53 AM

Your guage problem is more than likely not the instrument cluster. There are a few things to check before doing anything drastic. The sensor for engine temp is between the middle glow plugs. Check for a snug connection and even wiggle it a little in case there is a little corrosion in the contact. Also, check your grounds especially, both battery to chassis and chassis to engine. On mine, a loose bracket on the engine ground caused fluctuation and false readings.

Don't suspect a leak right off. As most here will attest to, these engines are really hard to "burp". Run the engine to operating temp. then place your heater on high. Even after all of this, I have had to top the coolant after driving it a few times.

Pete Burton · #3 01-06-2005, 09:01 AM

Quote:

Originally Posted by SD Blue

Your guage problem is more than likely not the instrument cluster. There are a few things to check before doing anything drastic. The sensor for engine temp is between the middle glow plugs. Check for a snug connection and even wiggle it a little in case there is a little corrosion in the contact. Also, check your grounds especially, both battery to chassis and chassis to engine. On mine, a loose bracket on the engine ground caused fluctuation and false readings.

Don't suspect a leak right off. As most here will attest to, these engines are really hard to "burp". Run the engine to operating temp. then place your heater on high. Even after all of this, I have had to top the coolant after driving it a few times.

beat me to it, couldn't agree more. Suggest you put your model, year, engine type in your signature.

boneheaddoctor · #4 01-06-2005, 09:05 AM

I had a pinhole leak in my thermostat housing last year that I had to replace......... and a clogged bypass tube on the waterpump might make it harder to burp also.

jpmaynard · #5 01-06-2005, 11:01 AM

its a 240D.

its a new (as of this summer) temp sensor in the block. will check the grounds, thanks for that tip. would that also make the fuel gauge wacky? (i replaced the fuel tank sender w/a junkyard one and still get the same bouncing of THAT gauge when i get below 1/2 tank.....)

i know the radiator is leaking because coolant is coming from where the solid part of the top radiator connects to the fins!

man, and im trying to get out of town this weekend!

jpmaynard · #6 01-12-2005, 07:33 AM

o.k. replaced the radiator that had a large crack in the top tank.

removed and filed off corrosion off grounds and put dialectric grease on all of it and refastened.

drove around and still gets almost up to 100! but as i was driving around defeated last-night, it looked like the gauge all of a sudden was driving right where i like it ~90ish. drove it up to 65 mph for a while and didnt move (same course that previously would bring it up to 100) and so i figured the system burped itself or the gauge sorted itself out.

Drove it in this morning to work and popped onto the highway for about 5 miles and then it steadily climbs to around 105. when i knock the gauge, it appears to drop to 95 sometimes and but immediately flicks back up to 105.

Got to work and turned the car off and felt that the radiator was warm up top but cool to the touch down low and the lower pipe was cool to the touch. is that normal? i would expect it to be a bit warm on the return.

the entire cooling system is basically new. new radiator, new water pump, new temp sensor, hoses, thermostat. the radiator cap tested OK by the radiator shop. the only thing left would be the instrument cluster....

Should i keep trying to burp the damn thing or replace the cluster or throw a match to the friggin thing!!!!!!!!?!?!?!?!?!??!?!?

Any and all advice appreciated. :wtf:

Pete Burton · #7 01-12-2005, 08:52 AM

It does seem strange that you say the lower hose is cool after running - but if it's working well (even though the gage disagrees) and it's cold outside, this could be the case. Try draining some fluid when it's hot into a styrofoam cup and check with a thermometer. Also, try to use something like ox-guard for coating grounds - it's a conductive corrosion preventative. Dielectric grease is good for distributors, spark plugs and the like - thousands of volts which will pass through the dielectric. I don't use dielectric on my diesel wiring. It's also possible that the thermostat is sticking/binding, but I really doubt it. You can tell if the temp is much over 100C as the system will be pressurized. Maybe your gage is a problem. Run a super ground like a jumper cable from the body of the sender unit right to the negative terminal of the battery. Does the readout change? Lastly, do you know that the impeller in the water pump is good? I've heard of some "rebuilt" units with substandard impellers. Good luck