Lazy fan clutch?

[Rus]

Hello everyone!

My E34 has recently given me some trouble with its cooling system, and I think I've resolved those issues (such as the radiator failing at the top hose connection). The problem that I am experiencing now is that the fan clutch seems to be late to engage. While on the freeway the engine temperature is shown to be comfortably below the middle mark (about 5mm) which in my opinion is normal. Once in traffic, the engine doesn't overheat, but the temperature needle goes just barely over the 12 o'clock mark. This I am not used to and thus am worried about it. I've noticed that even when the temperature goes up to this point, the engine fan isn't fully engaging. What's even more puzzling is that the fan clutch is brand new. Has anyone received a defective fan clutch before? I'm pretty sure its not an issue with coolant flow since the thermostat is new (actually changed twice to verify that it wasn't it) and so is the radiator. As far as I can tell, as soon as I get moving the temperature drops to or below 12 o'clock.

Recent work done on car:
Changed coolant hoses
Changed radiator and thermostat
Flushed system and refilled w/ BMW Blue
New radiator cap

No noticeable loss of coolant or any signs of problems. Bottom hose on radiator gets hot, so coolant is flowing.

So, what are the chances that I scored a defective fan clutch? The brand is Behr.

[winfred]

the temp should hit the middle line and pretty much stay with in about a needle width of it, i've gotten bad clutches out of the box but it's very rare with behr, after a run on the road after a few minutes of idling should get it mostly engauged, sometimes you need to turn off the ac to get the clutch to lock up as the electric is keeping the temp just below the fan's engaugenent point, several minutes of idling after a run should get you atleast a short howl when you blip the throttle, if not give it a few more minutes if the temp gauge is not climbing, the gauges are so dampened they are just about as useful as a dummy light

[Rus]

Winfred,

The gauge basically hovers a tick over the middle and when I let the car idle at this temperature for a long time, the fan doesn't engage to the point of being audible. So far I've witnessed it fully engage once, which to me seems abnormal (even if the engine maintains the "just over the middle mark" temperature). Does this sound like a defective clutch to you?

[winfred]

if it's not needed it won't kick in, double check that the electric isn't kicking on early and floating the mechanical fan, seen it happen a few times and had to unplug the electric to test the clutch

[Ross]

I see you have replaced the t-stat twice , this would have been my first inclination.
The fluctuations are not normal, even if it's not overheating.Your temp needle ought to remain dead center or very close.
I wonder if air is present in system causing the pump to cavitate a bit at slow speed?
I like Winfred's idea about the elec fan coming on, the cruising temp is too low. It's easy enough to unplug and watch the result.

[nirvana19]

My systems doing the same thing, just replaced fan clutch twice (first WAS defective behr, just last week). I think the new fan clutch is working as before the temperature would start to rise well past the center mark when idling for a long long time. Now the temperature is basically staying at just a little above center, although as I was JUST driving at highway speeds I saw it go BELOW the center line. t-stat for me I guess but our symptoms are EXACTLY the same so I'm wondering.

[whiskychaser]

Just posted reply to this so if this is a duplicate, sorry. Thought my fan clutch was playing up some time ago. After a lot of searching found a very good test method but cant find the link now. Its 2 pages of pdf so a bit big to post here. Anyone wants it is welcome or you can just tell me where to stick it:-)

[Rus]

@Ross:

The thermostat was first replaced with an 80 degree C unit. Suspecting that the temperature going above the middle mark was a failing fan clutch, I changed the clutch. When the problem continued, I changed to a 71 degree T-stat. I am used to seeing my temperature range between ~5mm below center (at highway speed) and dead in the middle (for traffic). What I see right now is normal highway temperatures, but slightly higher traffic temps. I also think I bled the system pretty thoroughly, but knowing these cars, I'll probably do another round of bleeding. Also, as far as pump cavitation, I noticed today (when I let the car idle for ~15 minutes), the fan did finally engage on and off, and when it was engage the temperature pretty quickly dropped below the middle mark, so I think I'm getting good coolant flow, but lower than desired air flow. It seems that the fan engages at a temperature that is higher than I expect, and effectively disengages once it cools the engine down a bit. So I see this fluctuation of temperature as the fan goes through its cycle.

@Winfred:
Thanks for the heads up on the electric fan. I forgot that there's a temperature switch for it in the radiator (would disconnecting the switch disable the coolant temperature switch only, or both that and the A/C function?)

[winfred]

if the pisser line into the tank is flowing the system will purge any air on it's own, unplugging the temp switch on the rad will just kill the electric fan's ability to help on engine temp, you should only need to idle 5-10 minutes for the fan to lock up after a drive, you could also just look through the grill and see if the fan is running, id do this test without the ac

[Rus]

if the pisser line into the tank is flowing the system will purge any air on it's own, unplugging the temp switch on the rad will just kill the electric fan's ability to help on engine temp, you should only need to idle 5-10 minutes for the fan to lock up after a drive, you could also just look through the grill and see if the fan is running, id do this test without the ac

This morning, after my commute, the fan seemed to engage (lock) and disengage during a 15 minute period where I just idled the engine. I know my pisser line is clear (new tank too), so it should then purge the air from the radiator if any is present. I checked the auxiliary fan after a drive at the max temperature the engine reaches and it was off. I think I'll grab my IR thermometer and check the temperatures around the thermostat housing, top hose, radiator, bottom hose, and possible fan clutch itself. Perhaps the sensor is going nuts and nothing is wrong?