Over-temperature switch - how hot is too hot?

Competition engines and ancillaries - general discussion
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Paul Eustace
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Over-temperature switch - how hot is too hot?

Post by Paul Eustace » Mon Jul 29, 2013 9:28 pm

I am soon to run a GC competition 2 litre 8V in a mid engined Lancia Beta replica for road and track day use.

I have a 74C in head thermostat, Pro Alloy radiator with 2 Spal electric fans and Laminova oil/water heat exchanger.

The 8V engine has a in-head over-temperature coolant switch that closes at 115C and I intend to connect this to a big red, impossible to ignore, LED on the dashboard. However, with the coolant at 115C I will be very unhappy.

Question 1: Can anyone recommend a lower temperature switch? I am aware of a 100C switch from a Volvo 460 and I can obtain an adaptor to match the Fiat/Lancia M16*1.5mm thread but I was hoping for a 90C switch to give me time to react.

Question 2: Any recommendations on coolant temperature I want the switch to alert me to?

Paul #332
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fingers99
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Re: Over-temperature switch - how hot is too hot?

Post by fingers99 » Mon Jul 29, 2013 11:04 pm

Check at what temperature your cooling fan triggers. That'll be about the right temperature and give you some margin.

Remember that coolant in a pressurised system boils at a much hotter temperature. My guess is that if you set it at 90C you'll have that light on almost all the time.
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Paul Eustace
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Re: Over-temperature switch - how hot is too hot?

Post by Paul Eustace » Tue Jul 30, 2013 11:37 am

Good point about radiator fan switch threshold. With a 15psi cap on the expansion tank the water will not boil until 120C unless I am at the top of a mountain but at 120C the engine is well outside the ideal operating temperature!
My radiator sensor is mounted at the mid-point of the radiator. The fans will start at by 87C and stop at 77C. If the car is stationary the engine temperature will be in excess of 87C before the fans start. I am wondering if this is too high a start temperature as the fans could more sensibly trigger at 80C if I am to maintain the optimum engine temperature.
Essentially if the car is stationary the fans will run and maintain the optimum operating temperature. I will investigate a lower temperature range radiator switch but I am keen to hear of the forum's experience of over-temperature warning light thresholds.
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Guy Croft
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Re: Over-temperature switch - how hot is too hot?

Post by Guy Croft » Wed Jul 31, 2013 2:32 pm

Forget reliance on automatic switches.

Fit a fan bypass switch wired to the dash via relay and warning light to tell you when it is on.

GC
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Rallyroller
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Re: Over-temperature switch - how hot is too hot?

Post by Rallyroller » Thu Aug 01, 2013 2:38 pm

Hi

I agree with Guy. In my last rally car (124ST) we would get to the start of a stage- sit in a queue and the temperature would start to rise. The fan would cut in at the normal temperature (too hot?) just as we were about to start the stage, so the engine started hot before nay action!.

I fitted a manual switch and warning light so that the temperature would be kept down while in the queue. I also added another feature where a momentarya push button would stop the fan. This is used by the co driver as we entered water splashes to stop the electric fan. The twin cams are great for throwing water up onto the inside of the bonnet then filling all the plug recesses with water and cutting the engine out. ( Not something you would get on a track day though)

Nigel.
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Guy Croft
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Re: Over-temperature switch - how hot is too hot?

Post by Guy Croft » Thu Aug 01, 2013 3:10 pm

GOOD POINTS WELL DONE

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Paul Eustace
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Re: Over-temperature switch - how hot is too hot?

Post by Paul Eustace » Fri Aug 02, 2013 8:05 pm

Many thanks for the advice. I will definitely go with the over-ride switch approach. I will source a lower temperature radiator fan switch and use the over temp warning light as a last resort.

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timinator
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Re: Over-temperature switch - how hot is too hot?

Post by timinator » Sat Aug 10, 2013 5:03 pm

Hi Paul, I have a few comments regarding cooling. I use radiator caps that are rated at 22- 24 psi for race applicantions. Most caps lose 2-3 psi from their rating fairly quickly. Had to buy a pressure cap tester to find this out. I also connect a 1 gallon overflow can to the cooling system pressure release port. Then install a small clear plastic tubing up to the lower corner of the outside of the windshield. When you see steam on the windshield it does not mater what all the guages and warning lights indicate.

I try to run 85C water temp during races, so 80C tip in would seem close. Empi makes an adjustable sensor that is affordable. Having a manual override is required.

Having an oil temp guage is a much better way to know if your engine is up to temperature than water temp.

Tim

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