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Spal Fan Questions AGAIN


Roy M

Recently I asked several questions about the dual Spal fan set up and received good information. I am now back to ask more quetions.
My water temperature gage is mounted in the head between Nos. 1 & 3 cylinders. When I got the fans, I told them that the only place I could mount the temperature sensor was in the thermostat housing so I was sent a 1/2" pipe threaded sensor.
No problem getting everything hooked up after asking a few questions.
My problem now is that I have a 180 degree thermostat [modified to let coolant flow through 3 small holes constantly]. The sensor that I have for the fans is suppose to energise the fans on at 185 degrees and shut them down at 165 degrees.
I can start the car and the temperature will get to 200 degrees [this reading is through digital gage and has been checked with thermal gun to be accurate] before the fans will kick on and they will kick off when the temperature gage is somewhere around 195 degrees.
I called the company I purchased the fans from and they thought that I might have a defective sensor so they sent a new one and the problem is still there.
It would be my thoughts that the temperature of the water at the termostat housing would be as hot or hotter than in the head where the temperature gage is located.
Has anyone experienced such a problem or do you have any ideas as what might be wrong or what I might do to correct this problem.

Roy M

It sounds like your controlling the fans by sensing the water temp ahead of the thermostat. Your radiator cools the water very quickly, most likely to the correct value, and shuts off your fan. However the engine remains at much higher temperature because it is being regulated by the thermostat. Sounds like the fan sensor is working correctly. Also if your engine swings to 200 before the thermostat opens you may want to replace it.
I would think that the thermostat housing is the worst place to mount the sensor (this should be the coldest). The next best place would be in the water passage of the intake manifold. The best place would be in the heads (should be the hottest and is where your temp gauge is mounted).

If you can measure the difference between the heads and the thermostat housing then you could get a sensor of the correct value (if they make one.)
Okay, now that I have a couple of replies, they bring up some questions. 1st - I was under the impression that the water was returning to the radiator when it passed thru the thermostat housing. Am I wrong here?? I can not mount in the intake, it is a Edelbrock for the Vortec Heads and has only one plug and that is directly under the radiator hose about an inch from where the hose attaches to the thermostat housing. Just no room here unless I go with some other type hose.
2nd- It is a Stewart Stage II water pump and a modified Robert Shaw thermostat [by this I mean that I get constant flow thru 3 3/16" holes} until the temperature sensor reaches 180 degrees and then the thermostat opens fully. It is working properly and my temperature gage is correct on the temperature in the heads. That has been checked with a thermal gun.
Just got back in from looking at the car and I could possibly mount the fan sensor in between Nos. 6 and 8 cylinders. That is the only possible place that I could mount it but honestly I still can not understand why it would not work at the thermostat housing. Guess that I am still missing something in my little feeble mind.
Thanks for the replies.
Roy M,

Hot water enters the radiator via the pump discharge to the bottom of the radiator. You can prove this with your heat gun by seeing the temperature difference between the upper and lower hoses. The thermostat modulates so the flow across the radiator is not constant except during high engine load and warm air temperatures. If the fans are cycling, and the engine temperature is constant then I don't see a problem. If you intend to shut off the fans at 165 then the sensor is in the correct spot. If you use the cylinder head for a sensor mount the fan will never shut off as the thermostat is maintaining 195 degrees regardless of water temperature at the radiator.

That's why I said the thermostat housing is the worst place to mount the sensor. The best place to mount the sensor is in the head. I was told the fans should shut off about 5 deg above your thermostat rating and come on at 205-210 deg.

If you have an adjustable sensor then it should be easy. If not, look at the PAINLESS kits (SUMMIT, JEGS) that have sensors. For example: If your thermostat is 180deg then get the sensor that is 185 on and 205 off. These are 3/8"-NPT threads and should work in your right head. If the hole is 1/2"-NPT then get a reducer from a hardware store.
KenSny is exactly right. A head mounted sensor w/the on off settings 5 & 10 degrees above your thermostat setting will work very well. Both left and right cylinder heads should be tapped to accept a sensor.

Just a quick update on my problem for anyone interested. Since I have digital gages from Nordskog, I thought I would call them and see if they had any ideas. I explained the problem and they had me to run a test on the temperature gage and it turned out to be bad. Now I have to take out the whole instrument cluster and send to them for a chip replacement. Plus side is that the gages have a lifetime warranty. They promised a quick turn-around. So much fun taking all the gages out but hopefully this will solve the problem.

I have the Performer intake for vortec heads and there is another place to mount your fan sensor. At the very front of the intake just above the water pump facing towards the front of the engine is another port in your intake. You may not have noticed it, but it should be there. This is where I am mounting my fan sensor.



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