300e Overheating but not losing coolant... - PeachParts Mercedes-Benz Forum

DEPRIEST · #1 11-21-2006, 02:15 PM

Hi All,
I've been doing a little reading of some previous posts, but I can't seem to find anything to address my specific issue...

My '86 300e is over heating in traffic. If let sit, it will get damn hot. If I'm moving, it's fine. If I turn the heater on, that will cool it quite a bit, but that's no kind of solution. It is not losing coolant. There is plenty of coolant and plenty of oil in the car and neither is mixing with the other.

So, after doing a little head scratching, I decided it must be the radiator. So just now, I changed the radiator and the hoses. My logic for this was... If the water pump was failing, it wouldn't send water through the heater core which in essence, helps to cool the car. Water pump (to me) seems to be in order. Also, if it were the thermostat, same problem... No water could get through, therefor, the heater core trick couldn't help with cooling the car. That leaves the radiator.

So I just changed it. (the radiator that is) Now, I added a bunch of Mercedes Fluid and water... and the car is still over heating when idle. Keep in mind, it's not losing water, so that must not be the issue.

So, I'm lead to believe one thing... Either I need to bleed the water with that 14mm bolt on the block. (how do I best do that again?) OR the little water pump's internal fan/propeller thingys are worn down and simply not moving enough water fast enough. The fan is spinning fine.

So, this is where I need your help. The termostat is easy, I *COULD* change that. The water pump looks hard. Is it? (btw, the radiator was a piece of cake thanks to the DIY section of this site) Based on the symptoms, is there anything else I should do before I tackle this water pump?

I appreciate your mental energy in helping me solve my issues.
-Kyle

Rob Pruijt · #2 11-21-2006, 04:11 PM

If it is not overheating while driving the water pump and radiator are fine. Most likely the fan clutch is not working like it should. Even if it seems to spin fine it may be spinning to slow, getting enough air though the radiator takes a lot of force.

A264172 · #3 11-21-2006, 04:19 PM

Quote:

Originally Posted by Rob Pruijt

.Most likely the fan clutch is not working like it should. Even if it seems to spin fine it may be spinning to slow, getting enough air though the radiator takes a lot of force.

I agree that the fan clutch is probably bad.

You can test it by: when it is 'overheating' (up over 110 C) stop the car, pop the hood, and see if the fan (inward or the radiator) spins easily. If it has no resistance it is bad.

Also sounds like your auxiliary fan may be bad.

How hot does it get in traffic?

gmercoleza · #4 11-21-2006, 04:40 PM

You can also do the broomstick trick. Be careful!

bpaz_ph · #5 11-21-2006, 07:01 PM

don't replace the fans yet. check the temp switches first if they're working.

Rob Pruijt · #6 11-21-2006, 07:37 PM

Replacing expensive parts is never a good way to diagnose a problem.

Diagnosing a failing fan clutch is easy. Let the engine running until it is above normal operating temperature (not to hot). Stop the engine with someone watching the fan. If is does not stop immediately if the engine stops it is defective (or the bold that attaches the fan to the clutch is loose).

Never stick something in a running fan, that is very dangerous, the fan will break and parts will fly out.

You may also check if the fan cowl (the plastic thing around the fan) is properly seated, if air can enter between the radiator and the cowl cooling is dramatically reduced.
If you do not know the history of the car check also for the less obvious mistakes in the past, like mounting the fan the wrong way. If it tries to blow the air towards the front cooling will not be as effective.

carnut · #7 11-21-2006, 07:44 PM

Please define "overheating" by that I mean what temperature does it stabilize at while driven and what temperture does it go to prior to turning on the heater?

DEPRIEST · #8 11-21-2006, 08:49 PM

Hi all,
Thanks a million for your answers.

When I say Hot, I mean, while driving, at speed on the freeway, it runs at about 85 degrees. Normal, right (?) When I'm stopped, the tempature begins to climb. When it gets to 100 and things aren't looking to start moving soon, I turn on the heater. That can usually keep it around 105/110 depending on the tempature outside. My wife would drive it and it would get up to the 125 mark. (no, she isn't driving the car anymore until this is fixed)

So I did the "Try to stop the fan" trick very very carefully with one of the used radiator hoses. It stopped easily. Now, the Visco Clutch (spelling?) I guess has fluid in it that expands outwards when the car is running hot(?) I didn't think there was a switch that would make it come on is there? The AUX fan is a different story. I'll look into that one soon.

The fan spinning backwards. Interesting. I'll look into that one. That is possible. I wonder...

Ok, I'll keep you posted. The Visco Clutch is looking suspect. Any other ideas? I was able to bleed the radiator fluid... Good tip, I never would have known about that one.

A264172 · #9 11-21-2006, 09:03 PM

Quote:

Originally Posted by DEPRIEST

...So I did the "Try to stop the fan" trick very very carefully with one of the used radiator hoses. It stopped easily. Now, the Visco Clutch (spelling?) I guess has fluid in it that expands outwards when the car is running hot(?) I didn't think there was a switch that would make it come on is there? The AUX fan is a different story. I'll look into that one soon...

The aux fan is electrical and should kick on above 115 C to cool back down to 105 C. There are a couple of points at which it can fail but the most likley is the 105/115 temp sensor on top of the block (2 pin I believe) You can test it by bridging the two wires that run into it while the ignition is in the 'on' position... this should activate the fan... also temps above 115 C should activate the fan... You can also jump the fan to the battery to see if the fan's motor is shot.
The visco fan clutch is a tricky system. A broken fan shroud/a partly blocked radiator/ or a bad fan clutch can all cause that fan not to function. Usually the fan clutch and radiator being covered in oliy gunk is a good indicator of a fan clutch that has 'leaked out'.