Radiator Thermostat Help

The thermostat on my kart is missing something and leaking, i noticed it had a hole in the back to put some sort of screw. Should i add a bolt or leave it open?

The hole is probably for a temperature sensor. Install the sensor or block with a screw. Don’t the size of the thread off the top of my head. Check the AiM web site.

What is the website link, i dont know the website and i cant find it.

@Richard_Jacques, can you point Lorenzo to some kart dealers locally and or online?

AiM Sensors (from the AiM-Sportsline Web page)

Coupler from Pegasus (This is what I believe you have)


Sensors on Pegasus (AiM sensors listed on the Pegasus site)


The thread sizes seem to be either M5x0.8 or M10x1.0 or 1/8 NPT. Good luck

Best place to get a sensor would be RAK track. Al Ain is closed still

If I need something urgent I’ll get it either from Al Ain Raceway or RAK Track, if CRG doesn’t have it here in AD. Non urgent kartstore.it but use shop n ship.

I’m not familiar with that t/stat - if it’s a standard metric size you could get away with a stainless bolt and copper washer from Ace if you just want to plug it. If it’s imperial will be more difficult, you might be better swapping it out with an IAME thermostat (50 deg) from RAK if that’s the case.

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Also, but this is just me, I’d relocate it away from the brake disc. I don’t like a coupling and potential leakage point above the brake rotor for obvious reasons.

I was just wondering, how does the thermostat know how much to open at the correct time? And the sensor doesnt give that information to the thermostat, it just gives the temperature on the lap timer.

It’s purely mechanical.

I saw this on this website saying that you need a bypass to let the fluid thats not meant to go into the engine back into the radiator

This is the website: http://www.risingsuncycles.com/tech_articles/Thereo_tech.htm

You’re thinking of a set up like this - it’s unlikely unless you have another open line back into the motor. Pretty sure it’s for a sensor - and I’m guessing the previous owner ran a datalogger which he took off before selling the kart? The sensor is part of the datalogger (Mychron, Unipro for example) not part of the kart, which might explain why it’s missing.

Ok, so i wont need to route another pipe into the engine or the radiator, i also thought it was for a data logger, but i was just making sure. So a bolt should do the job then.

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At the center of the thermostat is a wax filled plug and a pin coming out one side (engine side). As the water heats up from the engine, it melts the wax, expands it and pushes on the pin to begin to open the valve. The wax is tuned to begin to melt at a certain temp and fully melt/expand above a slightly higher temp. It could start to open at 40C and be fully open above 49C. This would allow engine to warm more quickly on cooler days, but maintain max temps on warmer days.

If you are not sure what the temp rating is for a given thermostat, you can test it. Boil some water. In a separate glass vessel, submerge the thermostat in room temperature water. Measure the temp of the water thermostat is in. Slowly add the boiling water while watching the thermostat valve. As the valve begins to move, note the temp at that point. Continue to add boiling water until the thermostat is completely open. Note that temp for your overall working range.

Warning, A thermostat that has been operated too high above its working range can alter the working range. Meaning, if it gets too hot, it may not begin to open until a higher temp than before. So if you ever have an incident of over heating, it is imperative to test the thermostat range again or just simply replace it.

Correct it is just a coupling to allow a water temp sensor to be used.
It is not a thermostat.

You beat me to it James.

Yep, i got it now thanks. I just put a bolt in it and its all good. Thanks everyone for the help.