Overheating: Fan failing newspaper test with new clutch(s)

[jrsaucke]

I'm having overheating issues with my m20. The cooling system has been refreshed (water pump, hoses, fan clutch, old radiator), but it is still overheating. The fan fails the newspaper test even though the clutch is a brand new Behr unit. Initially I thought I received a defective part, so I got another one and the result is the same. When the temperature gauge is up over half, the fan spins very weakly and I can stop it with a rolled up newspaper.

My thoughts

• I was thinking the temperature gauge might be wrong, but it seems to be working to me. I keep an eye on the temperature if I'm not moving and switch on the heat and the A/C fan if its getting too warm, but that obviously shouldn't be necessary.
• The clutch isn't getting hot enough to engage for some reason? I'm unclear as to whether its conducted heat from the water pump hub that triggers it, the temperature of the air off of the radiator, or a combination of both?
• ???

Not sure what is going on here.... Anyone have any ideas?

Thanks

[YosemiteSam]

Sounds like your radiator is not getting flow, when your temp gauge is reading normal operating temperature how hot is your radiator? Can you touch it with your bare hand for more than a second? Did you do the thermostat when you did the cooling system refresh? If so I'd bet your thermostat is installed backwards (it should be installed with the springy thing toward the head). If not it is possible your thermostat has failed. Regardless, a check of your radiator temperature at normal operating temp will say a lot.

[jrsaucke]

I did replace the thermostat and it is functioning. The top radiator hose gets hot when the thermostat triggers. I've checked it with an ir thermometer and it was reading close to the thermostat temp.

I'll check the temperature of the radiator tonight. That's a good point. I guess the hot air coming off the radiator is the main source triggering the fan clutch (not conduction through the water pump). The radiator just may not be working all that well. It was a junkyard pull and looked fairly new, but that doesn't mean too much. It's a behr.

I'll check it out. Thanks

[jrsaucke]

I used an it gun to measure the upper radiator hose, that radiator, and lower radiator hose with the car stationary and the fan spinning weakly.

Upper was 201
Radiator around 200
Lower 196

Not sure how accurate. I'm not sure how much of a drop in temperature there should be when no air is flowing through the radiator?

Upper hose was firm, lower hose seemed soft, but I'm not sure how much of a drop there should be across the radiator.

[YosemiteSam]

Interesting, there should be much more of a drop than that, at least 10-15 degrees but that assumes there is air flow through the radiator which requires the fan to be working when not moving. That high of numbers means that your radiator is getting flow though.
To be honest, I think you may have just been super unlucky and received two bad brand new fan clutches. Even with the engine at the low end of normal operating temp the main fan should be pulling in enough air to make a larger temperature drop than that. Also, you have a fan shroud, right?

[jrsaucke]

I'm thinking it might just be how the BEHR fan clutches function. I found the thread linked below and another that said something similar. I'm going to grab a SACHS clutch and see if that works right. Hopefully I can return one of these BEHR clutches...

http://www.m5board.com/vbulletin/e28...buy-sachs.html

[jlevie]

Given the small difference if upper/lower temps and the fact that the lower hose was soft, my bet is a well clogged radiator. The fan clutch is engaged by hot air from the radiator. If the radiator is clogged, the air moving through it won't be hot enough to engage the clutch.

[jrsaucke]

Given the small difference if upper/lower temps and the fact that the lower hose was soft, my bet is a well clogged radiator. The fan clutch is engaged by hot air from the radiator. If the radiator is clogged, the air moving through it won't be hot enough to engage the clutch.

I'm not sure if I was getting a great measurement but a cheap IR thermometer on the radiator was reading within several degrees of the inlet temperature.

In my limited experience of feeling radiator hoses I'm not sure what to really qualify as soft. The lower hose was certainly softer than the upper, but there should be some amount of pressure drop across the radiator.

That said... I am slightly suspicious of the radiator as well. I might just grab a Nissens replacement for $120 from rockauto.

Any thoughts on the BEHR vs Sachs fan clutch Jim?