optimizer

hi there - i'm hoping to get some help with an overheating issue (i've read lots of posts but not sure if any match my issue...). i'm driving a 1993 w124 (300ce).

i replaced a stuck thermostat about 2 months ago to fix a previous cooling issue and it worked like a charm..

now it seems like the issue is back again, so yesterday i popped the hood open and noticed that the pipe that goes from the radiator to the thermostat (circle in pic) was pinched shut, obviously from some kind of vacuum created internally!!!

after about 30 mins the vacuum went away but i also turn the car on (not the engine just to the first key stop).

appreciate to hear your ideas on what this could be!

optimizer

i'm wondering if there's a blockage somewhere like in the radiator?? any easy way to check this kind of stuff?

PaulX608

When you changed the thermostat, did you purge ALL the air from your system? If not, this could certainly contribute to cooling problems and hose collapse. When the air finds a high point in your hose there, it collects and contracts as it cools to draw the hose walls in.

whipplem104

Its nothing to worry about. The radiator cap is supposed to let excess pressure out and then when the system cools it should allow the air back in. As far as overheating goes it could be the radiator, fan or worse. Since you did the themostat already two things to check. First see if the heater is on full if this helps. Second does it overheat on the highway or just slow traffic. If the heater does not work you have something major like no flow. If on the highway it is cool then try the fan clutch first. Also, if it is actually not hot but coolant comes out mostly after you turn it off, this is just the cap. If on the highway it still overheats then it is radiator, water pump, or headgasket.
If it is the radiator then it will be cold or have cold areas. If it is the water pump then the radiator will be cold all over. You just have to try something.
It also could be a combination of things.
Just for info. Other than leaking, or bearing failure, I have never seen a water pump fail. 11 years as mercedes tech. I would check the fan clutch and then if thats not it repl. the radiator.

PaulX608

True, the cap should allow air past in a vacuum situation, but into the tank on the right fender. There shouldn't be any air in the system itself, it should be purged and the tank kept filled to the specified level to prevent air from getting into the rest of the system.

YNVDIZW124

Go to a mechanic that has a tool to pressurize the system. Paul and whipplem104 are correct. You might have to remove the hose and check that there isn't any debris blocking a core in the radiator.

optimizer

thanks whipplem104, all the cooling pipes are hot and the car stays cool on the highway. i checked the rad fan today and you're right, the fan clutch is pretty much worn i can stop the fan with my hand!!!

the radiator cap is probably causing the vacuum, but the clutch fan probably explains the overheating?? thoughts??

ronald7410

Hey guys. I'm thinking I have the same problem. Never really opened the hood to feel the problem though, just saw the hose collapsing. The hose was the one from the water pump, the thick one that points upward.

Am I in the same boat?

optimizer

Hmm not sure its the same hose that's collapsed in mine.. actually I had the car out for a country drive yesterday and checked every so often and didn't notice the hose getting sucked in again.

I pulled off the radiator cap to inspect and not sure what could go wrong with it? The rubber seal could go maybe? It seems to contract ok...

Still doesn't explain the overheating problem tho - sometimes it will get to 100 / 110 in city / stop n go traffic.

PaulX608

If you're reaching 100-110 or so in stop and go, especially with the a/c running, that doesn't sound too unusual. Are your auxillary fans coming on at 107 or so as they should? If so, then I wouldn't worry about it. This is simply the high end of the operating temp range, and not necessarily overheating. Real overheating would be indicated by overpressurization causing the cap on your expansion tank to spew coolant. We've had 4 MB vehicles, 2 v8s, 1 v6, and 1 supercharged i4. All of them have run in the 80-90 range when rolling down the road and hit 100 or so on hot days in traffic with the a/c running.

karugs

Probably a combination of a bad fan clutch and a bad radiator cap. Cap is the easier of the two. Replace it and if it still overheats in traffic then the fan clutch is next...