engine and drivetrain fan switch in radiator plug topic again

[jimk]

Is the lower hose getting Hot? perhaps your T-stat is not working properly. i have the 85c switch in the bottom of the rad and it switches fine when engine is in the 185-190 range.

It seems that if the switch was in the top hose area, the fan would come on early and OFTEN.

Your t-stat should be opening or closing first, at what ever temp it is, then when the Rad gets hot the fan should switch on. by the way what is the T-stat rated at? Have you tested that?

Have Fun

This is correct. The fan is to cool the radiator, not the engine. The coolant cools the engine, the radiator cools the coolant, the fan cools the radiator. Puttin the switch in the head outlet will keep it cool alright, but the fan will run all the time. Might as well leave the mechanical driven fan on with it in the head outlet.

Finkbuilt is right about the grounding and with the switch he is using, a flat gasket washer is used to seal, not teflon tape. Finkbuilt, be sure to have a diode in the circuit to stop the reverse emf from eating up the switch contacts!

[Squatch Pads]

I have a brass push through temp sensor/switch that is in the top of an IE aluminum radiator. I'm running a 21lb cap and my electric fan doesn't come on until 230. This of course is at an idle. I've got a M10 motor which is stroked and running 40mm side drafts. My trusting friend and mechanic tells me not to worry, because really that isn't too hot for the fan to come on. Mine might be a special case though. My sensor is at the top of the radiator near the hose. Freaky seeing the needle close to the red at idle.

[M3M3]

Puttin the switch in the head outlet will keep it cool alright, but the fan will run all the time. Might as well leave the mechanical driven fan on with it in the head outlet.

not correct. it depends on what temp the switch is set for. a correctly spec'd switch will only turn the fan on when the temp coming out of the head is too hot. it is a closed system. if the water coming out from the bottom of the rad is too hot, it will be even hotter coming out of the head than it should be. a correct switch threshold will only cycle when needed. i have the switch in the head outlet. it works perfectly. fan does not run all the time.

[jimk]

Puttin the switch in the head outlet will keep it cool alright, but the fan will run all the time. Might as well leave the mechanical driven fan on with it in the head outlet.

not correct. it depends on what temp the switch is set for. a correctly spec'd switch will only turn the fan on when the temp coming out of the head is too hot. it is a closed system. if the water coming out from the bottom of the rad is too hot, it will be even hotter coming out of the head than it should be. a correct switch threshold will only cycle when needed. i have the switch in the head outlet. it works perfectly. fan does not run all the time.

How hot is too hot? What is a "correctly spec'd switch". What's your criteria? The water will be tstat setting + 10F nominally most of the time and maybe +12F if run hard.

If water coming out of the radiator is colder than the tstat setting, the tstat closes and the engine outlet recycles to the tstat inlet. If you switch based on the water leaving the engine is too hot, it is too late! Sensing on the radiator bottom avoids the overtemp condition.

Anything colder than the tstat setting is a waste of effort because the tstat closes. Water temp coming out of the head is controlled by the tstat, not the fan. If the tstat is wide open and the water passing thru the tstat is hotter than the tstat setting, the radiator/fan is not big enough or the fan should be on and isn't.

There is a FAQ on cooling system. It is consistant with a switch in the radiator outlet.

[Harv]

I use a VW fan switch. If you find a crappy / broken rad from a VW, you can dig out the fan switch mounting bung and have it soldered to your 02 rad. i had this done to the lower left (facing forward). That was the wrong place as it's one of the coldest areas. I recently had the rad redone and had them move the switch to the output side. I figured, if the rad is putting out coolant that is too hot, it's time for the fan to turn on. No ground is required because the switch has an in and out terminal.

Sorry no pictures.

As was said, with Megasquirt, you can trigger it from the ecu.

John