Radiator Thermoswitch

Dimi Terleckyj

Lifetime Supporter
All depends on if you have a fixed temp switch or if you use an adjustable temp switch such as the Craig Davies series.

The adjustable are the only choice IMHO as you can set the on temp according to you engine requirements.

Dimi
 
Dave,

I was wondering that myself. I tend to agree and disagree with Steve. It does seems to activate the cooling fans at 95C but, the sender for the temp gauge is typically in the intake manifold and the switch is in the radiator. So I'm thinking that the switch might be set to come on at a lower temp. Would think the coolant in the engine is hotter than that in the radiator. Just a thought.

John
 

Steve C

Steve
GT40s Supporter
John,

I agree wiith your logic but, I believe Dave was looking for a gauge reading not the actual trip point of the radiator thermal switch.

Steve
 

Jack Houpe

GT40s Supporter
I noticed that the thermostatic switch for the fans is on the wrong side of the radiator, look at your car, its on the output of the radiator which is sencing the water after it has been cooled. On all other cars I have its on the input side or even the block where it sences the block temp not the water that has already been cooled. I put a electronic adjustable temp switch on the output of the block and used the Brown Black wire which SPF gives you in the engine compartment to turn the fans on remotely, now they kick on at 90 C and off at 85 C. You can buy it from Summit Racing. The way they have causes the engine to heat to very high limits when just idling before the fan kicks on.

One more thing, I use a electric 55 GPM water pump hooked to a time off relay that activates when the engine is over 80 C, then it stays on for 1 minute after you turn your car off so it removes the heat from the heads and engine.

To answer your question on my car the fans USE to come on at 97 C.
 
Last edited:

Tim Kay

Lifetime Supporter
Anyone know the part number, where to buy, this radiator thermal switch? Mine is not operating and since I'm going to install a new one I would like to have one that turns the fans on\off at the same temps as Jack Houpe's car.

If in fact the thermal switch is on the wrong side of the radiator as Jack suggest then installing a lower temp sensor would solve that, no? Or an adjustable type so you could set at the temp you decide according to your temp gauge at the dash?

Tim
 
The advantage to having the fans activate on the output side of the radiator is that they will not be on when the car is moving (unless AC is activated). The temp leaving the engine will always be hot if you have a thermostat in it so the fans can run when they are not needed.. My CAV had the fan sensor by the engine and it always offended me but it worked fine too, neiher car ever had a heating problem.
Dave
 

Tim Kay

Lifetime Supporter
Hi Dave, makes perfect sense when explained that way. BTW, nice to hear you chime in more often, you always offer up valuable information and I look forward to your comments.

Tim
 

Jack Houpe

GT40s Supporter
The purpose of the fans is so the engine doesn't over heat, if your fans kick on at 200 degrees on the output of the radiator then what would the temp be at the engine? I monitor engine temp to activate the fans and care nothing about radiator temp, all the modern cars use this method to activate fans and most use pulse width modulation which run the fans at different speeds according to the degrees of engine temp, I haven't seen a switch in the radiator in years.
 

Tim Kay

Lifetime Supporter
Wow, I feel like a blind lesbian in a fish market who can't make up her mind :confused: Jack makes a great point too, what is one to do :shrug:
If I'm not mistaken, my thermoswitch is operating the fans, like David says, at the output of the radiator but my temp gauge reads at the output of the motor. So logic tells me if utilizing the thermoswitch at the radiator simply install one with a setting that takes into account the temp delta between the radiator output and motor output.

I'm stilling wondering if anyone has the thermoswitch part number so I can go buy a new one. I'd prefer to get the part first rather than disassemble it then run into a problem locating one.
 

Seymour Snerd

Lifetime Supporter
So logic tells me if utilizing the thermoswitch at the radiator simply install one with a setting that takes into account the temp delta between the radiator output and motor output.

I'm stilling wondering if anyone has the thermoswitch part number so I can go buy a new one. I'd prefer to get the part first rather than disassemble it then run into a problem locating one.

I think the intellectual objection to that scheme is that delta temp of water leaving the block to water leaving the radiator is not fixed; it's influenced by the absolute water temp, the air temp, and air velocity through the radiator.

Regardless of that, if we just knew the thread of the thermoswitch it probably wouldn't be hard to find one with a different trip point. I'd go yank mine and look, but I really hate draining and refilling that cooling system.... Maybe it's NPT and you could estimate with a pair of calipers? Put a pan under it, unscrew it enough to expose some threads, quickly measure and retighten? 3/8" NPT seems to be by far the most common thread for these sensors. See

http://www.summitracing.com/search/part-type/fan-switches-thermal

The approx. OD of male 3/8" NPT is 0.675", and it's 18 threads/inch.

Failing that, I've seen kits that use a sensor that slips into the end of the rad hose and the radiator spigot. I've seen one that included a kind of double-wedge shaped rubber "spacer" for lack of a better word that fits between the hose and the spigot and provides a roundish shape so the hose doesn't leak. This link
Derale Adjustable Fan-Control Thermostat with Radiator Hose Probe Derale Radiator Fans D16769
implies you can insert the probe of Derale #16769 into the hose like this. As a temporary measure there are a lot of fan controllers that use "radiator probes" that you kind of shove through the radiator which is a mounting method that scares me. But I suspect with some cleverness you could slip any of those through the hose-spigot interface. Another advantage of this scheme is that you can put the sensor on either side of the radiator. Furthermore, some of those come with sophisticated adjustable controllers.

According to my notes our radiator spigots are 1-5/8" (41 mm) OD so maybe one of these adapters can be made to work:
http://www.summitracing.com/search/part-type/temperature-sender-fittings

BTW, regarding Jack's comment about modern PWM fan control, I just noticed Painless makes a nice looking dual-fan controller:

Painless Performance: F5 Dual Fan Controller

This assumes a 3/8" NPT sensor bung is available. I had always planned to use something like that in P2160 and will get to it eventually. They want you to put the sensor in the water jacket in the head, and to put it on the radiator only as a last resort.
 
Last edited:

Tim Kay

Lifetime Supporter
Thanks Alan and no need to drain your system just to inspect the sensor for my benefit but thanks for the generous offer non the less. Good info but I'll keep is simple and leave the system to it's current design right or wrong.

We've had some pretty hot days around here lately and the cooling system on this car is very stable. It'll hit 92-95c in stop and go traffic and with the fans on it stays right there. Can't complain.

I just have to remember to turn the fans on manually, due to the thermoswitch not operating, otherwise it will rise in temp.
 
I don't have a computer in my GT and as long as the coolant leaving the radiator, going into the engine, is cool that is fine with me. A lot of this seems to be over thought for a simple beast like the GT40. I do have an electric water pump but it is not computer controlled either.
 

Jack Houpe

GT40s Supporter
On this particular part of my install I'm not using the EFI computer to control the fans, its a variable fan control that uses a thermistor (sold through summit racing) installed in one of the ports on exit of the engine. I didn't have enough general purpose outputs on the old electromotive TEC2 to control the fans.
 

Tim Kay

Lifetime Supporter
I love the idea of cooling the water after shut down for a short bit to reduce the heat soak. Can an electric water pump be installed/operated without removing the water pump on the motor?

BTW, I installed a lower temp thermoswitch and the fans still don't come on, I took the motor temp up to 96c. Keeping in mind that the thermoswitch is on the exit side of the radiator, it seems the temp drops considerably, even without the fans. As an afterthought, I put a heat gun on both sides of the radiator shortly after shut down and they are at least 20 degrees F different.

I guess I'll lower the thermoswitch again. The new one is supposed to be a 180F so it should have triggered the fans. I'll double check the switch to make sure it's lower than the one it replace (should've done that before the install)
 
Last edited:
Back
Top