1970 280SE coupe overheating again!!!!! - PeachParts Mercedes-Benz Forum

Sheila Taylor · #1 05-16-2004, 11:03 PM

hey all,
I am new to all this ,so bear with me.
My 1970 280SE is overheating again! Last year I had a new radiator put in over 1000.00 bucks. had the timeing checked,They checked the heads no cracks,Even put in some water wetter.She ran just great this winter. the first hot day,80s,sitting at stop lights the temp went up and it started jumping and bucking, acting like it was going to shut off. As soon as I took off,It cools down.
If anyone has any Ideas on what is going on,Sure would like some input!!!!!!

Thanks,
Sheila

wbain5280 · #2 05-17-2004, 12:27 AM

The first thing that comes to mind is the viscous coupling in the middle of the fan. If the fan does not turn fast enough at idle, the fan will not draw enough air to cool the engine. It's hard to describe, but the fan should rotate by had, engine off of course, and have a slight resistance to the touch. If it spins freely, it may need to be replaced or have its internal fluid, silicone I think, replaced or added/topped up.

Mayby another poster can provide a better descripition.

Here is a pic from Fastlane, available on this website:

Tomguy · #3 05-17-2004, 02:46 AM

If you're low on coolant AT ALL, even if it's not much at all (like 1 qt), you WILL overheat! Check the coolant level, it should be up to the bump inside the rad, if not, ADD SOME! Otherwise, check your fan clutch as suggested. I think mine needs silicone too, can anyone (Peter or Peter? Chuck or Chuck? Mike? Anyone?) tell me how to go about this?

cth350 · #4 05-17-2004, 07:28 AM

- Thermostat replaced lately?
- Water pump operating well?
- Reclogged your radiator?
- Clogged a block passage?

Does turning on the head dramatically help or only a little?
-CTH

kpb · #5 05-17-2004, 08:15 AM

I think Chuck's last post references "heat" rather than "head."

(My 280 does not have a head which I can turn on)

ctaylor738 · #6 05-17-2004, 08:21 AM

If the problem is only happening at idle, then it is probably the declutching fan. But some other stuff to check:

- if the car came with a fan shroud, is it in place?

- if there is an auxiliary fan, is it coming on per spec?

- radiator cap the right version and in good shape?

- coolant mix right (too much antifreeze inhibits cooling)?

- was the system "burped" (lots of posts on this)

Tomguy - As far as I know, you need to replace the fan hub. Never heard of anyone adding silicone to one.

tosbt · #7 05-17-2004, 10:41 AM

As Chuck said, BURPING . . is a must everytime you change coolant. I replaced my radiator a few months back and the tech did not know this car needed burping. after I got home I did the 'BURP' job myself and reduced the temp by 10 degrees.

(1) I placed the car at the edge of the driveway droping the rear a few inches.
(2) I removed the cap and the top radiator hose. Placed a sock in the hole were the hose went keeping as much coolent in radiator as possiable.
(3) Put a water hose in the upper hose to the thermostate and block and slowly let the water circulate until air came out of the cap hole.

The car must be burped. Good luck!

I am making the assumption that you car is a V8.

j9fd3s · #8 05-17-2004, 12:13 PM

both my 300sel 3.5 and my moms 95 e320 do the exact same thing, over 80 degrees outside and you're stopped the water temp goes up.

i'm kinda thinking, in my case its the fan clutch, ive never heard the fan come on. also at a stop theres no air circulation thru the radiator, thats the fans job. mine runs 1 tick over the 175 line if you can go faster than 20mph.

i've just been thinking this is normal, cause the 95 does it too!

mbz72 · #9 05-17-2004, 01:40 PM

tosbt, The burping, did you do that with a runing engine or did you force the water through the system with the water hose and shut off engine?

cK

tosbt · #10 05-17-2004, 02:53 PM

mbz72, I did it with the engine running, also shake the car to force air movement.

Sheila Taylor · #11 05-17-2004, 04:29 PM

Thanks for all the info!
Tuesday I will check fan and water,the last time I checked, a month ago it was fine. The info on burpping my car(I Knew it was like a baby to me) I read that before but did not know how it was done. The 280SE is a 6 cyclinder,If that makes a difference.
My Chris-Craft has a head and works fine,the MB,well still looking,maybe in the trunk!
Why would the car buck and vibrate so bad when it gets hot?
I would like to know more about the fan and the fluid you should put in that.
This is a nice group and very informed on mercedes.
Thank you.
Sheila

ctaylor738 · #12 05-17-2004, 07:53 PM

A guy on the mercedes-veterans list had the same sort of problem with the car running badly when it got hot. It was a 3.5 but FWIW, here are some of the suggestions:

1. Sounds like something is screwed up with the idle circuit. Is the throttle body setup properly? The throttle should be fully
closed at idle and the electronic position sensor needs to be reset. On my 3.5 the throttle was not closing and someone tried to compensate by making other adjustments. This really screwed things up until everything was reset to factory specs.

2. I had similar problems in a 300SE L 3.5 sedan once. The car
bucked and stalled when it was first driven in warm
weather. That was eventually diagnosed as overheating of
the Crane breakerless ignition module. My mechanic
relocated it to a cooler part of the engine bay and I never
had that problem again.

In your case, it sounds like you have an electrical glitch
that could be due to bad trigger points, a faulty temperature probe, or a distributor problem. Could also be a wiring short in the ignition wires that is triggered at high operating temperatures.

3. Well, that car has temperture sensors for the air and fuel. You may try testing the resistance on the water temp sensor. and sometimes you can unplug the air sensor on the air filter housing. That will lean out the mixture a bit.

wbain5280 · #13 05-18-2004, 09:37 PM

It's a 6 cyl with mechanical FI. Never adjust the stops on the injection pump or throttle body.

autozen · #14 05-25-2004, 11:30 AM

Chuck gave you an excellent list of things to check for over heating, however, the bucking and snorting may or may not be mechanical. It is possible that the underhood temp is going extremely high, because of the high engine temps. I suspect the points or the ignition module. Try cleaning the points with the folded end of a clean piece of paper. These first transistorized ignitions had very little current flow through the points, and it didn't take much to make them fail. I woildn't suspect the mechanical injection to be affected by heat. I've made my 230SL into a route 66 Corvette and have driven it all through the mountains at high altitudes in over 100 deg weather without incident. The only time I had trouble is when I shut it down at 4000 ft in extreme heat to enjoy a view. When I tried to leave the, car was vapor locked and wouldn't start. The nearest town was an hour away on mountain roads and had no phones or electricity. I simply soaked a wash cloth in the cooler ice water and laid it on the injection lines. After about a minute it fired right up.

If nothing else corrects your heating problem, you may be stuck. If memory serves me the only way to solve the problem on 70 and 71 cars was the installation of a special MB kit that ran a cooling water pipe around the back of the engine. I'm sure the kit is no longer available. The 1969 was the absolute best year for those cars, because you got the upgraded steering wheel, headrests, standard ignition, and you didn't get the modified combustion chamber head which were a problem from the start. The heads were modified in 70 to reduce hydrocarbons by removing combustion area where the flame front could be quenched, and leave unburned fuel.Although I have never seen documentation, I believe MB had a manufacturing problem with these heads, because they were replaced at a rate never seen before on any other MB engine.

Peter

ctaylor738 · #15 05-25-2004, 07:20 PM

Here's some good information from the SL Forum on the silicone trick. Don't know if it will work on your car, though.

Viscous clutch/fan repair