What temp of radiator fan switch?

[shortboxin]

I've got an '84 C10 that I'm just getting around to installing an aluminum radiator and electric fan in post 5.3 LS swap last September. From the sounds of it, guys are recommending using an external fan switch rather than rely on the PCM to control the fans for numerous reasons.

I would like to mount a switch in the radiator in an available port in the upper portion of the passenger radiator tank. The factory temp for the thermostat is 186°. Based on what I've read, you need to factor in that the water temperature will be lower than 186° due to the fact that it is mixing with other lower temp water. Then again, I probably don't want it turning on at the thermostat's opening temp, so maybe the 186° range in the tank will mean the water coming in is actually 195°? to get 186° at the switch?? I'm not actually sure this is even a viable option, but otherwise, I've got to go to the passenger rear head port or make something to go inline on the lower hose. Neither of which is a "good" easy option.

Anyone with engineering background that has some experience with this? All help is much appreciated!

[SunSoaked]

You don't need an engineer but from experience I can tell you the water temp in the heads runs about 10 degrees hotter than at the radiator inlet.
Most folks want to know what temp the hottest part of the engine is running at. You can use whatever temp switch you want and just do the math in your head.
I use a Dakota digital fan controller that's fully adjustable. I love it. Just my .02$.

[shortboxin]

Originally Posted by SunSoaked

Most folks want to know what temp the hottest part of the engine is running at.

If the heads run 10° hotter, then they would be at 196° with the engine operating at thermostat opening temp. Unless you want the fans running 100% of the time, I would think you wouldn't want them to come on until probably 200° or so at the head.

Originally Posted by SunSoaked

I use a Dakota digital fan controller that's fully adjustable.

Glad you like that. I prefer to use OEM replacement parts when possible because they're easy to repair anytime/any place.

Anyone out there that's done it with a switch and relay setup? Be surprised if no one has. I've seen guys discussing it on hot rod forums, but most guys were going into the head. I can do that if need be, I just thought since the radiator had an available port...

[Rich84]

What are the reasons to not use the PCM? It works fine.

[Dead Parrot]

IIRC - the temp on a thermostat is the temp it begins opening at. Normal running temps once everything is warmed up is 10~20 hotter then opening temp. So your 185 t-stat would give an engine temp of 195~205 at the thermostat housing once things are fully warmed up.

[shortboxin]

Originally Posted by Rich84

What are the reasons to not use the PCM? It works fine.

I haven't verified it yet, but the PCM is a 2002 and according to what I've read online, the DBC Tahoe model that it came from did not have it switched on in the code due to it running a mechanical fan.

[shortboxin]

Originally Posted by Dead Parrot

IIRC - the temp on a thermostat is the temp it begins opening at. Normal running temps once everything is warmed up is 10~20 hotter then opening temp. So your 185 t-stat would give an engine temp of 195~205 at the thermostat housing once things are fully warmed up.

More to consider. Thanks for the info.

[hatzie]

VAG Gruppe vehicles from the 70's & 80's switched the radiator fans on when the radiator temp reached 205°F.

If the heads are 10°F hotter then you want a thermal switch in the heads to switch somewhere between 215°-220°F.

You also want to switch the fans on with the AC compressor.

50:50 Coolant mix at 0psi boils at 220°F. With a properly sealed system and a 16psi cap it boils at 250°F.

[shortboxin]

Originally Posted by hatzie

VAG Gruppe vehicles from the 70's & 80's switched the radiator fans on when the radiator temp reached 205°F.

If the heads are 10°F hotter then you want a thermal switch in the heads to switch somewhere between 215°-220°F.

You also want to switch the fans on with the AC compressor.

50:50 Coolant mix at 0psi boils at 220°F. With a properly sealed system and a 16psi cap it boils at 250°F.

Thank you. That's the kind of info I was looking for.

[Ziegelsteinfaust]

Remember if you lower your t-stat temp lower the fan settings.

On my Camaro project I got a fancy adjustable model from summit. Have not tested it yet as work is well making me work.

[SunSoaked]

I got a 160 stat and 2 row aluminum radiator. Today only got to 57 degrees here in Southern Arizona. Damn thing wouldn't get above 163 degrees. Heater not worth a damn! Guess a 180 stat is getting swapped in.

[shortboxin]

Originally Posted by SunSoaked

I got a 160 stat and 2 row aluminum radiator. Today only got to 57 degrees here in Southern Arizona. Damn thing wouldn't get above 163 degrees. Heater not worth a damn! Guess a 180 stat is getting swapped in.

I stuck to stock temp thermostat as I figured even here in"Phoenix", vehicles do not overheat provided there isn't a problem with the cooling system. Although, the Civic we bought used last year doesn't heat up much either. I've been thinking either someone put in a lower temp thermostat or it's stuck open.