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I just installed an aluminum radiator and electric fan in my truck and I'm having a little difficulty getting the thermostat to stay open. With a 195 deg on / 175 deg off thermal switch installed in the water jacket on the head to operate the fan the 180 deg thermostat is constantly opening and closing. I know that I need to change the switch out to a hotter one, but how much hotter?

By the way, I'm running a bone stock 230 in front of a T-5 and 3.73 rear end. At 70 MPH I'm running ~ 2000 RPM and the temp varies between 160 and 180. The thermostat opening and closing is very distinct on the gauge. I only have to live with this for a few months until I swap in a 350 so I might just put a toggle switch in line with the thermal switch to turn off the fan while I'm in cruise mode, but if someone else happens to drive the truck (which happens on rare occasion) that is not familiar with the toggle I'm afraid that they would burn up the motor. Thoughts?

Texmo,

I wonder if a temporary, or experimental approach would be to drill a substantial hole in the thermostat flange to help smooth out the temperature 'ripple'. It wouldn't cost much to try it.

My son has a Jeep with the fan setup, and he mentioned that a adjustable set-point switch is available.

Stuart

I think the fan thermal switch should be on the radiator side of the water flow thermostat to keep it from cycling needlessly. The water flow thermostat is operating normally, but the fan running at the wrong time exaggerates its action.

just some thoughts when i read this question .......

engine (head) water sensor:
I have no fan blade run off the pulley.
when i installed my new water temperature thermostat sensor in the head I was sold a newer sensor which is the replacement for my old. this newer sensor has a smaller pipe thread, so i had to use an adapter bush to reduce the 3/4' to 1/2''. Because of this i ended up chucking the bushing on my lathe and shaving off some threads and also cutting a couple more threads on to the new sensor. this now allows me to thread the new sensor further into the bush and now allows the water @ the head (temp) to reach the flow of water that flows past it to get a better reading on my gauge. if i did not do this a false sensor reading happens in that 'dead zone' around the reducer bushing because of the reduced (lack of) water flow. this senses the temp in the block, the blocks temp trips the stat to open.

fan sensor::
i put my pusher fan's thermostat sensor on the lower side of the thermostat housing , below the thermostat, along w/ the water to my carb-(tap ... split intake and exhaust systems) and the water to the cab's heater-(tap). so i had to drill an extra hole because my two available ports were used. I have recently seen the inserted into the radiator fins sensor, and that's worth some investigation.
i know this may not be the case w/ you Tex but others may read this thread and it may give raise to some thought.

i also am using two relays to power my pusher fan because of the greater amount of draw during fan start up mode. the fan can run easily on one relay but that start is what might kill your systems fan. you will also have a higher temp reading at idle and after you stop the engine. that gauge will rise just a bit, which is normal because of the no air flow mode.


When selecting a fan switch, seems The Fan Man Switch kit works great. For a 160º thermostat, use an 185º or 195º switch. For an 180º thermostat, use a 195º switch. For a 195º thermostat, use a 210º switch.

The trick is to move the switch. The fan switch should go on the radiator side of the thermostat, not in the block. You want the block/head to always be at 180, this is what the thermostat is for. Adding a fan switch that only comes on at 195 means the water in the head has to get up that hot.

Move your switch so it senses the temperature of the radiator water. Either drill and tap the water neck on the radiator side of the thermostat (some housings already have a hole here) or the radiator itself.

I use a radiator mounted fan switch that has a probe that attaches to the top tank. It works great.

I'm using a sensor that pushes thru the fins on the radiator. I am running at a constant 190 and the fans never go on unless I am in stop and go traffic.

Thanks all for the response. Right now the fan switch is on the head and temp sendor is on the thermostat housing...I think what I'll do is swap the temp sensor and fan switch for the time being and see how that works.