1994 E320 water pump impeller
 

My 94 E320 is running slightly warmer than it should. Seems to warm up when sitting at idle, then returns to normal at higher engine RPM. All the standard items have checked good. (hoses, thermostat, fan clutch, aux fans, radiator.......)

At the end of last summer, I experimented with a thermostat rigged full open with a small brass bushing. Result was car ran very cool even in 90 degree heat with AC on. From this I conclude system cooling capacity is adequate. Tried two different new thermostats and symptoms returned. Checked thermostats in pan of hot water and noticed neither opened quite as far as the one I rigged full open with the brass sleeve.

I'm beginning to think I may have a partially damaged pump impeller. Could coolant flow be sufficient with thermostat rigged slightly past full open but not with standard functioning thermostat? Seems a damaged impeller might explain this.

Anyone ever have a pump impeller partially fail on a 104?

I'll probably just remove the pump and have a look........

Thanks for reading.

J. M. van Swaay

I have 93 with M104 (3.2L). A few years ago, same thing happen to my car, not over heat but run a little hotter than it should be. Without AC and traffic, a little over 100 C. With AC and traffic, a little over 105-110 C. If the car moving, it seemed to be OK. I know it's not water pump or thermostat cause did replace them a year ago. Thought it's a fan clutch but before I could have time to replace it, heard the noise and check it. Turn out to be the bearing of fan clutch bracket gave up. Change the bracket and have no problem after that ( now about 90 without AC). hope it help.

How warm?

I use an Arthur Dalton resistor to bring the fan on a bit sooner.... these cars seem to run hotter than those with the 103 engine

Creeps up to 105ish..... Last summer during very hot weather (100 F) with AC on and at highway speed, my temps would creep up to between 100 and 110.

I know that a properly functioning cooling system will keep the needle splitting the top circle of the 8 on the temp gauge regardless of OAT or vehicle speed. My system seems to have lost some efficiency, but I can't figure out the cause....

Might have to try throwing parts at it.........

I have the resistor also, but that won't help if there is a problem with coolant flow.

I had a similar problem, a new clutch fan fixed it.

It does sound like a fan clutch issue.

I initially thought this was a fan clutch problem as well. I did the "newspaper" test--couldn't stop it when coolant temp in the 100 degree range. Could stop it when engine first started cold.

I have a couple old fan clutches laying around in my shop. Maybe I'll rig one permanently engaged, install and see what happens......