HappyAndy Dork
June 25, 2012 11:23 a.m.

So my wifes BMW E34 525i just had a bad engine swapped for a low mileage (hopefully) good engine.

Yeah ; my first engine R/R on a car! Done all by myself too.

BOO; It overheats! It has a new T-stat, the radiator and all the hoses were recently replaced by the PO. I filled and bled the cooling system according to the instructions in the Bentley manual that came with the car.

The engine runs hot, but not in the red when driving at moderate speeds, but as soon as I stop and let it idle it goes into the red and the dash display gives the over-temp warning. Running the engine at a high idle does not help cool it at all.

I checked the fan clutch when it was in this over-temp state, and it was free wheeling just like a cold engine. Thats bad right?

I know the fan on my work truck howls when the engine temp is high and the clutch is either locking up or at max resistance. Should the fan on this Bimmer do the same? .

Tom Suddard SonDork
June 25, 2012 11:29 a.m.

Yes, that's bad. It needs a new fan clutch. A surefire way to tell if it's shot is to stick a screwdriver in the fan when it's hot. If the fan stops, the clutch is bad. If the fan throws the screwdriver back at you, then the clutch is good.

N Sperlo PowerDork
June 25, 2012 11:35 a.m.

The fan should move freely by hand when the vehicle is off. Any strong resistance means its locking up. Thats when they get noisy. This has been my experience with locked up fans only. That shouldn't really effect heat, so it didn't sound like you locked er up.

HappyAndy Dork
June 25, 2012 11:42 a.m.
N Sperlo wrote: The fan should move freely by hand when the vehicle is off. Any strong resistance means its locking up. Thats when they get noisy. This has been my experience with locked up fans only. That shouldn't really effect heat, so it didn't sound like you locked er up.

But when its boiling hot the fan should have a lot of resistance or be locked up right? Or does it need the centrifugal force of actually running to have the resistance?

N Sperlo PowerDork
June 25, 2012 11:52 a.m.

I believe it needs centrifugal force, but when they lock up, you can hear the fan from about a block away when you get on it, like you said when your work truck howls.

Tommy may have experience with dead clutches while move is with locked. The dead clutch sounds more likely.

The heating issue sounds like when my escort's electric fan locked up.

Kenny_McCormic New Reader
June 25, 2012 11:56 a.m.

You could try locking it manually with some zip ties.

Cone_Junky Dork
June 25, 2012 12:03 p.m.

How's the water pump? Most of that generation of vehicle have plastic impellers that break loose. If the water pump isn't pumping hot coolant into the radiator, then the fan clutch won't get enough hot air to lock up.

Make sure there is a steady stream of coolant coming through the bleed line when the car is running. Just pull off the radiator cap and look for a strong/steady stream of coolant shooting across the fill neck from that bleed line.

Ranger50 SuperDork
June 25, 2012 12:12 p.m.

You could always do the old piece of paper in front of the radiator trick to see if you have airflow into the radiator..... If it stays, you have some flow. If it doesn't, "UT OH, Spaghetti-o's!"

HappyAndy Dork
June 25, 2012 12:15 p.m.

In reply to Cone_Junky: WP is brand new with a metal impeller.

N Sperlo PowerDork
June 25, 2012 12:16 p.m.

Try Tommy's suggestion. See if you can stop it with a long screwdriver. Don't hurt yourself.

Dr. Hess UltimaDork
June 25, 2012 1:04 p.m.

Fan clutch is a good guess with your observations. If that doesn't fix it, then new radiator time. And I think you will probably need a new radiator anyway. The getting warm at reasonable highway speeds thing kinda indicates to me that the radiator is getting plugged.

Gets hot when in stop and go traffic: Fan issue.
Gets hot out on the highway cruising: Radiator issue.

iceracer UltraDork
June 25, 2012 5:01 p.m.

Engine cold and off. If you can spin the fan freely, it is bad.

If good there will be considerable resistance.

HappyAndy Dork
June 25, 2012 7:11 p.m.

I just replaced the fan clutch, I used the skanky looking one that was attached to the replacement engine. After driving the same route as yesterday, with the AC blasting, it never touched the red zone on the gauge, in fact it barely went past the middle. Problem solved!

The funny thing is, the resistance that I can feel by hand between the two clutches is negligible. But with the engine warmed up and running, I can feel and hear a difference. I didn't want to use this particular clutch because it eas attached to a broken fan ehen I picked it up from the junk yard. .

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