Fan switch in lower radiator hose?

[Valiant100SM]

This came up on another board I'm on, but one of the guys says that having the fan switch in the lower radiator hose really helped keep the fan (and engine temps) from cycling as wildly as they would with the switch in the intake manifold water passage. I'm talking small block Mopar, here. On one hand, I can kind of see how that might work, but on the other, I can't see where you'd A) find a switch that would kick on at seriously low temps, and B) wouldn't require a good bit of tweaking to sort out what temp that would be.

Anyone else heard of this location for a fan switch? I'm using the Painless 210/180 switch now, and with my 180 t-stat in the intake, it NEVER turns off once the engine is up to operating temp. I don't want to run lower than 180, and may go up to a 190 once I get my new cooling system sorted out.

Thanks,
Clair

[protour_chevelle]

My fan temp probe its designed for the upper rad neck...

-Matt

[CarlC]

I had mine in the return tank using a 165*off / 185*on switch. The problem that I had was that the engine temp would be 210* before the fans turned on, and then turn off around 195*. I could not find a switch with and On/Off temp range that would allow for a lower temp range and fit a standard NPT thread.

There are engine mounted switches with a 195*on/185* off range. I believe Painless offers these.

For me, the best option is the DC Controls variable speed controller. Rock solid 180* engine temps. However, my car has excessive cooling capacity, both radiator and fan, so keeping the engine cool is no problem. Since the fan speed varies with the temperature, wild engine temperature fluctuations are minimized.

[Valiant100SM]

My Painless fan switch is set up for the water passage near the t-stat, so same kind of situation. Is there any real advantage to running the switch in the already-cooled coolant in the lower hose?

Clair

[CarlC]

After dealing with the return tank arrangement (same as lower hose), IMO, no.

There is some +/- temperature error in the switch, and +/- error in the thermostat. You may have a combined error that is not allowing the fan to turn off. Moving up to a 195off switch, or trying another thermostat, might help. Any NAPA store will have a catalog of available switches with temperature and thread listings.

If you have access to an infrared temperature gun it will help to diagnose what's going on. You can monitor the engine temp as it warms and note when the fans turn on in relation to the thermostat opening temp.

[CFster]

I have a switch in the lower hose - works great turning on my dual Spals.

[Valiant100SM]

Carl, CFster, thanks for the info. I think I'm just going to bite the bullet and get the DC Controls unit. There was a similar controller that came on the Volvo fan I'm using, and i like the concept much better than the light switch function I've lived with until now. Besides, I need to free up a port in my manifold for the heater core return line, anyway.


BTW, it's sure strange seeing about 50 of the same names on several different boards. Between here, CC, and a few of the Mopar boards I'm on, I'm wondering if it isn't just the same 50 folks that ever do anything with their cars...

Clair