Temp gauge testing

[BennSport]

Yes, my reading of 130 ohms was from the disconnected sensor to ground. I was just wondering if my measurement from the wire to ground was important enough to mention. This all started because I had a slightly leaking head gasket, causing combustion gasses to leak into the coolant system causing me to overheat due to all of the air pockets.

You might try it again in the morning after the car sits all night, and compare your results to the ambient temperature.

Yes, i definitely will. I’m wondering if this whole time I thought I was overheating it was just due to a faulty sensor. in hindsight I should’ve been checking to see other symptoms of my engine running way too hot.

[Tom]

Yes, my reading of 130 ohms was from the disconnected sensor to ground. I was just wondering if my measurement from the wire to ground was important enough to mention. This all started because I had a slightly leaking head gasket, causing combustion gasses to leak into the coolant system causing me to overheat due to all of the air pockets.

You might try it again in the morning after the car sits all night, and compare your results to the ambient temperature.

Yes, i definitely will. I’m wondering if this whole time I thought I was overheating it was just due to a faulty sensor. in hindsight I should’ve been checking to see other symptoms of my engine running way too hot.

But you had coolant in the cylinders per your scope camera, no?

[BennSport]

Yes, but the drive I went on prior to taking those photos was quite short Im wondering if it could be condensation due to the engine not getting up to temp. If my coolant block sensor is also bad then that would be more evidence to that being the issue. I guess it’s wishful thinking too, hoping I don’t have to pull the head again.

[Tom]

Yes, but the drive I went on prior to taking those photos was quite short Im wondering if it could be condensation due to the engine not getting up to temp. If my coolant block sensor is also bad then that would be more evidence to that being the issue. I guess it’s wishful thinking too, hoping I don’t have to pull the head again.

Take it for a long drive to dry it out and recheck? Make sure there is no coolant in the spark plug wells before pulling the plugs. Coolant can get trapped in there from venting the cooling system and well you pull out the plugs the coolant drips down onto the end of the plug. I kind of doubt your temp gauge is off by more than a needle's width or two. Do the fans come on about when you'd expect from the gauge? Since they are controlled by a separate sensor/switch, that would be corroborating evidence...

[BennSport]

They fans don’t come on quite when I expect them to. Once the gauge hits the 3rd thin line it stays there for a minute, then the fans kick on. Another reason why I think its condensation is because I just recently changed my oil, and the black puddles im seeing on the top of the pistons are way too dark to be the oil I just changed out. So perhaps the water in the cylinder picked up all the soot from the combustion process.

[BennSport]

Well on a 63 degree day, my sensor is reading at 795-800 ohms. I don’t know how much deviation is normal, but it doesn’t seem as bad as I originally thought.

[Tom]

Well on a 63 degree day, my sensor is reading at 795-800 ohms. I don’t know how much deviation is normal, but it doesn’t seem as bad as I originally thought.

That's actually quite accurate for a 40 year old sensor. 800 ohms would be about 63.5F if you run the math, so pretty much exactly right.

[BennSport]

Well on a 63 degree day, my sensor is reading at 795-800 ohms. I don’t know how much deviation is normal, but it doesn’t seem as bad as I originally thought.

That's actually quite accurate for a 40 year old sensor. 800 ohms would be about 63.5F if you run the math, so pretty much exactly right.

Dang. Well before cracking into the motor I’m going to double check the accuracy of the gauge. Gotta make sure I’ve checked every other issue it could be before doing the head gasket again.

[Tom]

Well on a 63 degree day, my sensor is reading at 795-800 ohms. I don’t know how much deviation is normal, but it doesn’t seem as bad as I originally thought.

That's actually quite accurate for a 40 year old sensor. 800 ohms would be about 63.5F if you run the math, so pretty much exactly right.

Dang. Well before cracking into the motor I’m going to double check the accuracy of the gauge. Gotta make sure I’ve checked every other issue it could be before doing the head gasket again.

Clark's has a gauge testing procedure using a potentiometer, which is technically sound, but can trip up people who aren't real experienced with pots and multimeters. A much simpler and foolproof method is just to pull the connector off the sender and connector the wire to ground through a 68ohm resistor. The gauge should then be right around the first (80c) hash. If you wanted to double check you can then replace the resistor with a 39ohm resistor and the gauge should be right around the second (97/100c) hash. You can get resistor kits for cheap on Amazon, or ping me and I'll send you those two gratis.

[BennSport]

Well with Tom’s help, I’ll be able to test the gauge in a couple days. I was just wondering how likely it is for the gauge to be quite inaccurate after 40+ years? Since my thermoswitch is new, I’m kind of using it as a baseline for engine temp since I don’t yet know how reliable it is to use the gauge. And since the fans kick on incredibly late when referring to my coolant temp gauge, I’ve got my fingers crossed that it’s the faulty component in the system.