Overheating..gauge or sensor?

[merc123]

For the past two weeks I've had what appear overheating issues. During the race the gauge shows 230*. The idiot light comes on around 250. I have a QuickCar gauge and sensor and they only have 225 or 235 sensors that come with their panels. It has a 22-24# cap and a few years old. I've pressure tested the radiator/cooling system and the cap. Cap blew air at about 20 PSI on the test but the cooling system held pressure for 15 minutes with no leak down so ruled out head gasket.

I raced most of the race at 250* (engine builder said run until it pukes no matter what temp says) but when I spun out it showed 270 and steamed.

So, is there a way I can test the gauge or the sensor to see which one I need to replace..maybe with a laser temp gauge on the radiator?

[cheaterleaddog]

For the past two weeks I've had what appear overheating issues. During the race the gauge shows 230*. The idiot light comes on around 250. I have a QuickCar gauge and sensor and they only have 225 or 235 sensors that come with their panels. It has a 22-24# cap and a few years old. I've pressure tested the radiator/cooling system and the cap. Cap blew air at about 20 PSI on the test but the cooling system held pressure for 15 minutes with no leak down so ruled out head gasket.

I raced most of the race at 250* (engine builder said run until it pukes no matter what temp says) but when I spun out it showed 270 and steamed.

So, is there a way I can test the gauge or the sensor to see which one I need to replace..maybe with a laser temp gauge on the radiator?

does the light come and gauge reading coinside with each other

[dirty white boy]

put gauge senser in a pot of water an boil it,..then youll know if its right

[merc123]

Even with a pot of water, you will still need a reliable thermometer, as the light will not come on right when the water boils. You could use a household thermometer, for meat, I suppose.

Are both the sending unit and gage on the intake, or is one in the head? That may make a difference in reading.

Also, I've had motors ran that hot, and they start noticeably bogging down after about 250*. They were hard to turn over and barely start once they pegged the gage over 260*. If your motor was truly 270*, I would expect similar issues.


I had an old oil temp gauge so I took the sensor out and put the gauge in. Both are in the intake. The oil temp one read faster than my water temp one but when they 'leveled' out they were both right on.

I didn't notice it losing power at 250 but it was definitely hard to turn over and get started. Usually with it sitting on 270 I can get it to push start enough to get the water flowing and bring the temp down to about 250 but if I shut it off it won't start back for about 15 minutes or so.

[merc123]

QuickCar is going to send me a new temp sensor since the light isn't coming on until 250 any how. Now to figure out the overheating.

[billetbirdcage]

Check your pulleys, grab the fan and see if you can turn the fan by hand? If yes, look at the lower pulley and see if the grooves are worn. This is a common problem with the cheaper non-anodized pulleys, they wear and the belt doesn't ride on the sides of the V but the bottom of the pulley and slips at RPM.

Hope that helps (assuming you have V belts)

[700horsepower]

If the radiator is more than one year old, replace it. You will instantly lower the water temp 20 degrees. You could also have a cracked head or gasket that is only leaking high temps. 250 degrees is way too hot to be stable and probably is down on power from the high temp.

[Egoracing]

Get a cheap plastic kids pool, take the radiator out and put it into the pool tubes up with the cap on it. Put 2-3 drops of Ivory dish soap in it. Fill the pool with water until it covers the radiator but NOT the tubes. Let it set for an hour or so, then go out and gently lift the radiator up and lower it back down several times and let is set again. After it sets remove the radiator and dump the pool out and do it again.

You will be AMAZED how much dirt and junk will come out in a few "baths". When you do this and do not get much dirt out replace the radiator and fill it with water and one bottle of prestone rust inhibitor to lube the pump and ease surface tension of the water to allow the engine to transfer heat better. See how it works, it will only cost you about $25-30 and it fixes MANY overheating problems.

[merc123]

Check your pulleys, grab the fan and see if you can turn the fan by hand? If yes, look at the lower pulley and see if the grooves are worn. This is a common problem with the cheaper non-anodized pulleys, they wear and the belt doesn't ride on the sides of the V but the bottom of the pulley and slips at RPM.

Hope that helps (assuming you have V belts)

I can turn it by hand. Someone made the comment the lower pulley looked worn out but I had just gotten it back from the builder and he made no mention of it. Only had maybe 45 laps on the pulleys. I'll double check it.


If the radiator is more than one year old, replace it. You will instantly lower the water temp 20 degrees. You could also have a cracked head or gasket that is only leaking high temps. 250 degrees is way too hot to be stable and probably is down on power from the high temp.

Only three races old. Motor felt flat the week before so I changed the plug out and seemed fine this past week. Any way to check it for cracked head or gasket at high temps?


Get a cheap plastic kids pool, take the radiator out and put it into the pool tubes up with the cap on it. Put 2-3 drops of Ivory dish soap in it. Fill the pool with water until it covers the radiator but NOT the tubes. Let it set for an hour or so, then go out and gently lift the radiator up and lower it back down several times and let is set again. After it sets remove the radiator and dump the pool out and do it again.

You will be AMAZED how much dirt and junk will come out in a few "baths". When you do this and do not get much dirt out replace the radiator and fill it with water and one bottle of prestone rust inhibitor to lube the pump and ease surface tension of the water to allow the engine to transfer heat better. See how it works, it will only cost you about $25-30 and it fixes MANY overheating problems.

I've got an old fuel cell (it's crashed up but holds water) that I'm going to cut the top of and do this. I used to always pull out the radiator and purple power and run the hose thought it, back to front. Got lots of dirt out of it last week.

I also went up on my jets 2 points and took the 3/4" restrictor out and put a 5/8" one in to see if that helps.

[crate late]

I can turn it by hand. Someone made the comment the lower pulley looked worn out but I had just gotten it back from the builder and he made no mention of it. Only had maybe 45 laps on the pulleys. I'll double check it.

Why did the builder have the motor back with only 45 laps on it?



I also went up on my jets 2 points and took the 3/4" restrictor out and put a 5/8" one in to see if that helps.

Ditch the restrictor all together