Coolant temp / Fan question

[JGood]

Finishing up a 24 hours of lemons build, looking to get the engine fan sorted.

We removed the mechanical fan, and I mounted the stock aux fan in the core support in front of the radiator. Deleted the (broken) 1k ohm resistor, and hard wired around it. The fan still wouldn't kick on, so I tested the radiator mounted switch, it wouldn't engage either pin at 200+ degrees. So I bought a new one, tested it prior to install. First switch pin comes on at the specified 191 F, second pin came on at specified 210 F.

I only have one power wire running to the fan, so I can choose which engagement temp I want. Which one of those would be recommended? I don't want it to be on the whole race, just when we slow down/stop for caution/pits. 191 seems a bit low, but 210 seems awful hot for an m20. Will the coolant temp at race speed stay below 191? And/or will the m20 be OK running up to 210 in pits/caution laps?

[irish44j]

I'd have to check with the guys, but I'm pretty sure we run at around 205 degrees in our Chump ETA when on the track, with the fan off. Fan is switched on all the time in the pits or during cautions, but I assume we have a 210 auto-switch as well. I know the switch in my M42 rallycross car is at 210 as well.

[MX339]

210 shouldn't be an issue. I remember the some Spec E30 guys telling me they were almost getting into the 220's in race conditions when it was super hot last August during nationals. I don't believe my stock temp gauge starts to tick over the middle until my VDO gauge hits 220.

[JGood]

Thanks guys!

[Axxe]

We run a 80/88 deg temp switch to the stock dual speed fan. It only kicks on when pulling into the pits after a hard run (176 F), never when it's running. Remember that the temp in the rad while moving will be significantly lower than the head when you have airflow. Can't really confirm it's not running when the motor is at full chat but it distinctly kicks in every time I come into the pits and get the egg timer. I would start at the lower temp and see how it works for you, I haven't heard the fan go into high yet.

[TobyB]

The low temp.

It's measuring temperature a good ways from the hot water inlet to the rad, so it won't
kick on until the rad's mostly heat- soaked already.
The extra 15 amps won't
cost you a position if it comes on too early.

The blown head gasket most certainly will if it comes on too late!

That said, easy enough to move if you find it's getting hyperactive.

But you won't

t

[JGood]

Thanks guys. Good call on the fact that the temp switch is located on the cold side of the radiator, I didn't really consider that.

Going to wire the fan to the 91C side of the switch, and put the 99C side on a toggle switch for manual control. That setup will get us through the first race one way or another, then I can adjust from there if needed.

Wasn't so much worried about power draw as I was with making a 20+ year old fan last as long as possible haha.