M5 aux fan running at idle even with AC off?

[itsbrokeagain]

Finished up a 'restored back to stock' E39 M5 from an old customer of mine. Was formerly a BaT car, PO hacked the crap out of it and just did all new stock suspension, stock mufflers, new OEM bumper and all undertray bits, Clutch, and fixed some coolant leaks.


I was letting it run to charge the battery yesterday and I noticed even with the AC off, the aux fan kicked on to keep the temps in check. Im not familiar with the S62s but do they run hot like the M62s? His clutch fan doesn't seem to really make any noise like it's engaging but it still has resistance when I spin it by hand. I know what a dead fan clutch feels like, but Im second guessing myself here.

Car has 70k on it. Thinking about just changing it out for good measure anyway.

[TerraPhantm]

S62s don't run as hot as M62s. Either way, it's normal for the aux fan to run with the AC off.

[edjack]

Break down and buy a smart battery charger that can deliver at least 6 A.

Did you monitor the coolant temp via the cluster? An engine running stationary at idle will heat up enough to engage the aux fan.

On later models, the DME monitors the coolant outlet temp, and will engage the fan as it sees fit, as Terra mentions.

[itsbrokeagain]

Good to know. I have a battery charger at home but in this case it was at a shop and for the most part it had to be parked outside due to the other cars needing work during the week. It's an overflow shop for my friends bodyshop and they are restoring a 67 Shelby GT500 so that kinda take priority being inside lol.

[edjack]

So, get an extension cord.

[Mike WW]

His clutch fan doesn't seem to really make any noise like it's engaging but it still has resistance when I spin it by hand. I know what a dead fan clutch feels like, but Im second guessing myself here.

Car has 70k on it. Thinking about just changing it out for good measure anyway.

Most bad fan clutches I've seen have felt just fine with moderate resistance to spinning. If there's a better test than the newspaper test for a fan clutch I don't know what it is. Low tech, but effective.

[edjack]

Most bad fan clutches I've seen have felt just fine with moderate resistance to spinning. If there's a better test than the newspaper test for a fan clutch I don't know what it is. Low tech, but effective.

What? This is the aux fan.

[itsbrokeagain]

Edjack, that would have been one long extension cord and it would have gotten trampled everyday by traffic in the lot. She sits at home on a tender so I'm not really worried about it.

For everyone else asking about the paper test, yes I know about that but the reason I asked about the aux fan is that my 528 aux fan has come on once in it's life during the summer...the clutch fan engages and does the majority of the work idling in the heat, whereas the M5 doesnt and kicked the aux fan on idling in 65 degree weather. My question was do S62s run hot enough to warrant that action, or do I have a failing/bad fan clutch that's attributing to it.

Since most everyone here said it's normal operation, that's how I'm leaving it

[Mike WW]

What? This is the aux fan.

I know it's the aux fan that's running, but if the engine fan clutch isn't working the aux fan is going to be running more than it normally would.

[DIRTe39]

I've had an aux fan issue lately. It seems to be running more often but at the same time, I hadn't really kept tabs prior to when the aux fan gave out. So long as I'm not overheating, I'm not fretting to much about it for now.

[edjack]

Wait for a traffic jam on the 405!

[Santaclaus4]

Wait for a traffic jam on the 405!

Won't have to wait much longer. Traffic is coming back with a vengeance.