I have a 300e that just in the last 2 days has started running really hot. hotter than usual. there has always been an issue with the car running hot when stopped running at idle for too long, but when you get going down the road, it would cool back down to around 80 degrees. now, its running up to 120 degrees, and staying there. every once in awhile, you'll hear bubbling in the dash, and the temp will drop to about 100, but then it will go back up. I thought maybe the thermostat was stuck, so i removed it just to see, but it still does it. there does not seem to be any circulation in the cooling system. the car can be reading 120 degrees on the temp gauge, and hoses hot, but i can physically put my hand on the radiator, and it is cool. I am assuming that the water pump has gone bad. the coolant is still green, and the radiator does not appear to be plugged. Anybody got any ideas?

 

Update: Well, I got to looking around under the hood, and it seems the serpentine belt was loose. Looser than it should be. Apparently the tensioner isn't functioning properly. The water pump appears to move water when you spin it by hand. I got a new belt, but like i said, the tensioner just won't adjust the threaded rod is all the way at the top of the adjustment range. Is there any way to tell when these things are bad? it doesn't look like there's anything wrong with it other than it seems like its all the way at the end of its travel, and the belt is still loose.
Any advice would be appreciated.

 

You prabably have a bad tensioner. There is a pointer on the tentioner along with a picture that looks like this > (a ramp) If the pointer is at the top of the ramp or past it. Then its time for a new tensioner and shock.. Does the tension move a lot or make noise while the engine is running? As for the cooling, is the clutch for the fan enguaging?? Upper and lower radiator hose hot? Heater work properly?

 

Thanks for your reply.
I haven't really checked the fan clutch, i was afraid to get the car too hot. the upper hose was hot, and the lower hose wasn't checked. the radiator was cool when i put my hand on it. the heater was not blowing hot air.

Once I saw the belt was really loose, thats what i figured. We had been having problems with the battery not getting enough charge, and then the overheating started. My immediate thought was the belt, but seeing it still on, I didn't really think about it. I guess i figured that if it was still attached it was ok. The thing that really got me thinking about the tensioner, was coming here and reading these forums, and I started looking at it again, and noticed the pulley was at its topmost position, really just under the water pump pulley. then i tried to adjust and found that it just wouldn't adjust anymore. so i removed the old tensioner assy and replaced it yesterday, but i ran out of daylight. so today i plan to put the rest of it back together, and see if its gonna solve the problem. I guess i probably could have replaced the water pump while i was in there, but it seems rather simple to disassemble to get to it, now that i've done it.
When these pumps start going bad, do they leak first?

 

Update: So I got everything back together, and the damn thing still overheats. I went and bought some radiator flush, and ran the car for a good 1/2 hour or more. temp stayed below 100, but its still gurgling in the heater box, and pushing water out the evap hose. Heat coming out the vents is intermittent. upper and lower rad hoses are hot. I can feel the water boiling in the heater hose into the heater. all the fans work. the fan clutch does not seem to have any difference in resistance between when the car is cold or when it is hot.
I'm seriously at my wits end with this car.

 

Maybe somebody can give me an idea of the way the coolant is supposed to flow.
From what i can see, it goes into the thermostat housing at the top house, and then out the bottom hose into the radiator.
Also, when I disconnect the upper hose, and turn on the car, shouldn't the water be coming out of the radiator? at least once the thermostat opens up?

 

Yes the water should come out of the top hose to the rad cool out the bottom and backto the engine. Not sure on your car but could it be possible the belt is on wrong. Just a question. Also any thermostat I put in I drill a 1/8" hole in the outter plate. Reason this aids in refilling the coolent even if the thermostat is closed the air can pass. Even in winter the hole is small so the car still warms up normal, but will allow some water to pass to aid in over heating. Most of all it helps get air pockets out of the system. I read one artical were he drilled a few larger holes to keep his 300E from over heating, but changed it to 1 hole for winter in Ga. Make sure all of your cooling componets are good and clean. From what I've read overheating is a issue for the 300E's for theirs no extra cooling for them. Good luck and don't burn it up

87 300D
205K

 

Update: I replaced the water pump, thermostat, stat housing, bypass hose.I flushed out both the inside of the radiator with a hose, and hosed out the fins as well. Now the car runs at about 80 degrees, up to the next line if i turn on the AC, and when I hit the gas, the temp goes back down. I think the car runs cooler now than it did when i got it 2 years ago. I got the new housing because the old one didn't have the bleeder hole, and between having the bleeder hole, and drilling the 1/8 hole as suggested, I barely had any air in the system.
Thanks for the advice!

 

Thats good to hear.

87 300D
205K