engine temp high - blown fuse
 

89 420 sel with 195k

Engine will heat up at idle (stop light and/or traffic) and typically gets to around 90+ but goes back down upon movement. I let it run in the drive and it went to 120 and I shut it down. Checked the fuse box and found the #1 fuse blown. Replaced and ran again - same thing - temp. ran to 120 and the #1 fuse was blown. AC has been running recently - it was checked earlier this spring with regards to refrigerant and it was fine.

I don't have a diagram for the fuse box and only found specific references to fuses based on circumstances in the forum. Does this relate to the auxiliary fan? I found several posts relating to checking this but am not sure that it's related.

The thermostat is about 2 years old. Recently removed the radiator to replace the timing chain/ rails/etc. so the system was flushed and filled with mb coolant (50/50 mix).

Any help would be appreciated.

*Is this a mistake or what about the AC?

Does that engine have to be "Burped" via a bleed port anyone? Could have air in the system.

The viscous fan clutch could need replacing.

Thermostats can fail, too. That's what caused my recent overheat issue.

There have been some discussion about methods of testing the water pump. do a search.

I'm not too well versed in V8s but I saw no one was replying so...

Good luck
-Tom

Hi - yeah, it definitely sounds like the auxillary fan issue. I had this issue with my old '85 380SE. The aux fan fuse would blow. I could not run the A/C in town.

how old is the radiator?they are made of plastic and aluminium and as they age the aluminium shrinks and it won't flow enough coolant at idle,then when you put your foot on gas and engine speeds up[and water pump]the temp gauge immediately starts to come down.

radiator
 

The radiator is about a year old - the last one broke off where the top hose connects (fortunately close to home) and I had to replace it.

I pulled the high temp sensor (from reading other posts, it was supposed to cause the auxiliary fan to operate on high speed) but it didn't move...

Can you pull the power source and connect it to a 12v battery to see if it will run on its own?

Thanks for the response.

Yes
 

12 volts direct to the Auxiliary fan will tell you if it's good or not.

If you pulled the electrical connecter off the blue coolant temp sensor and the high fan did not come on (ignition ON), the fault could be in the sensor, the CCU, the aux fan relay, the fan motor itself or the wiring in that circuit. Bring a jumper from + battery to the 2-wire terminal of the pre-resistor (R15) for high fan (ignition OFF). Jumper to 1-wire side gets low fan. That'll help rule out bad fan motor, and potentially pre-resistor, wiring and relays. But I'm not sure if that will explain why you're blowing #1 fuses.

#1 fuse on that car IS for the aux fan.

Most likely a bad motor.

<<Bring a jumper from + battery to the 2-wire terminal of the pre-resistor (R15) for high fan (ignition OFF). Jumper to 1-wire side gets low fan. >>

That test sounds familiar....:).....but put an in-line fuse in the jumper. I would use same value as F1.
If that fuse blows, you have found the problem ,being a bad fan motor.

See if the fan can be spun freely by hand.

aux. fan
 

Results:

tried the 12v battery - it didn't run

the fan did not spin freely

Ordered a new fan - put it in and it works really well

thanks for the help