Water temp gauge not accurate

[cob427sc]

I have the gauge cluster option from FFR which includes the water temp/oil pressure/speedo/tach/volt meter all in one cluster. My problem is the accuracy of the water temp gauge. It will jump up to 260 degrees when the engine is warm, yet the engine does not overheat and actually no water even goes back to the overflow tank. I suspect that either the gauge or the sender is bad. I'd like to try either a new sender or if someone knows how to check the sender with a meter would work too. Not sure who FFR buys the senders from.

[egchewy79]

new sender would likely be the cheapest/easiest thing to look into initially. make sure there's no air bubble trapped under the sender in the intake.

[33fromSD]

FFR gets the gauge cluster from SpeedHut, I know this because I contacted FFR when I was doing my build to get a new GPS antenna and they sent me to SpeedHut and noted this was the same place they source the cluster from.

I have the same cluster (love it) and it's dead on. My guess is the sender may be flaky.

Jim

[Brave Salmon]

you can put the sending unit in a pot of water on the stove and heat it up. Hook your multi meter up to the top and to the side case of the sending unit and read the resistance. Watch it as the water heats up and you should see the resistance vary as the water gets hot. It should be a gradual change and should not jump around if you wiggle the thing while its in the pot. resistance will either rise or drop depending on the polarity of your hook up but it's the delta, or change, you're looking for. short story, it's probably either bad or you have it in an area that has inconsistent flow of coolant.

[33fromSD]

you can put the sending unit in a pot of water on the stove and heat it up. Hook your multi meter up to the top and to the side case of the sending unit and read the resistance. Watch it as the water heats up and you should see the resistance vary as the water gets hot. It should be a gradual change and should not jump around if you wiggle the thing while its in the pot. resistance will either rise or drop depending on the polarity of your hook up but it's the delta, or change, you're looking for. short story, it's probably either bad or you have it in an area that has inconsistent flow of coolant.

Yup, good test to do. The downfall is I don't think there is a way to correlate the resistance reading to an actual temp (I may be wrong about that). But fully agree this would at least help see if your getting erratic readings.

Another thing to check out on the car is run a temporary ground wire to the casing on the sending unit while still installed in the engine and then run the car. If the reading are more accurate than the sending unit is not grounded properly to the engine.

If teflon tape or teflon goop was used depending upon how much was used, I've seen where the threads on the sending unit haven't been able to cut through the tape or goop causing a grounding issue on the sending nit in which no signal or flaky signals were sent to the gauge.

One other question is where is the sending unit located? Most common spot is on thermostat housing and intake manifold for most accurate readings, but some folks have tried putting them in one of the drain ports on the block which could indeed result in readings in the 260 range due to added heat from the block while the actual coolant itself running through the engine is around the 190-220 range.

Jim

[wallace18]

Contact Speed Hut. They may offer info to check. The temp gauge in my wife's 33 runs about 20 degrees hotter than my 35 and both have identical drivetrains and cooling systems. My infrared heat gun verifies the sensor or gauge is off 10-20 degrees. Like you no overheating but 220+ on the gauge is uncomfortable at times. My 35 runs 190 in 95 degree temps with A/C on in FL summers. Both have the same gauge pod as you. Difference is about a year in production date.

[cob427sc]

I'm one of the odd ball guys running a 1958 Buick Nailhead engine instead of the common Ford or Chevy. The sensor is mounted on the water supply side of the radiator in the pump housing. The water flow is from the bottom of the radiator through the pump then into the block, back out through the heads into the top of the radiator. The electric fan sensor is located on the return side from the radiator and seems to function fine. I'll check the grounding of the sensor first, then Speedhut if necessary. I suspect it is the sensor as it originally didn't read high enough when a bad t-stat caused the engine to overheat.

[Fman]

I have the gauge cluster option from FFR which includes the water temp/oil pressure/speedo/tach/volt meter all in one cluster. My problem is the accuracy of the water temp gauge. It will jump up to 260 degrees when the engine is warm, yet the engine does not overheat and actually no water even goes back to the overflow tank. I suspect that either the gauge or the sender is bad. I'd like to try either a new sender or if someone knows how to check the sender with a meter would work too. Not sure who FFR buys the senders from.

I also had one of them fail already, the Speedhut took a dump last month. I had the same issues temps were jumping all over the place. I installed a new sending unit and it has taken care of the problem (for now). We will see how long this one does last, Speedhut did sent it to me free of charge.

Maybe it is my luck but I always have had better luck with mechanical gauges, electrical gauges always seem to have glitches in them.