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Discussion Starter #1 (Edited)
Hello all. Any suggestions would be much appreciated. A few days ago my temperature guage stopped working. I replaced the sensor with a new one from Advanced Auto Parts and after replacing I flushed the coolant and added with Prestone at about 60-40 coolant/water ratio. Now the guage works, but it quickly goes from completely cool to "hot" within a few minutes, even when driving on a 75 degree day. I replaced the thermostat last year or the previous year (can't remember) and before the guage stopped everything was fine. Bad sensor maybe? Or could have the flushing (used prestone coolant flush) maybe caused the thermostat to stick in closed position? During the flushing, as directed on the bottle, I set the heater to "high" for 10 minutes, then repeated with just water for 10 minutes and at these times the temp guage rose quickly to hot just as it did when running/driving. This is on a '69 Boss 302. Any thoughts?
Thanks!
Kevin
 

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Sounds like you got a sender that fits - but I bet it's not the right one. I know there are various ones that are for later models that will fit but don't have the correct reistance through the range your guage reflects.....unless it's actually right of course! ;>) Then you got other troubles....Not sure what the range is supposed to be but I'd find out if you can return it for a different one just for giggles (I know it's electric and they figure we aren't smart enough no to trash it....yada, yada) Have him look up others that are available at least
 

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Discussion Starter #3
Thanks. That was close to what I was thinking, and it could be a possibility. I thought maybe I just got a defective sensor, but what you said also makes sense. I'll try to find another somewhere else.
 

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Discussion Starter #4
I ordered a "premium" motorcraft sender from Mustangsunlimited to replace the cheapo from Advanceauto, and guess what? It's the same damn thing, only $25 more expensive. It looks like the same one, anyway, with the same markings and number on the end. Don't know if they tried to rip me off or an honest mistake or there is some difference I can't see. But it performs the same as the Advanceauto part (both worked, but guage ran to "hot" after about 10 minutes).

I did notice the one I removed from my Boss that wasn't working is about 3 grams lighter, and the end that goes into the manifold is a little shorter and fatter. Don't think I have a thermostat problem, but I'm not positive.

One question> what is an acceptable block temp after running for 10-15 minutes on a 80 degree day? I have a infrared thermometer that shows the temp at about 205-215, which fluctuates as I measure it. Is this too hot for a Boss 302? I think I put a 180 degree themostat in it a few years ago.
 

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What is your water temp on both sides of the radiator? I.E., in front of, and behind the thermostat, and then down at the bottom of the radiator, and at the water inlet? I LOVE the laser for just exactly this reason!
 

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Discussion Starter #6
Probably should just close this thread since the "running hot" thread seems to be very similar. But if it helps, my temp readings were 195 on radiator side, 200 the other side on manifold (my hose goes to manifold), and 175 at bottom of radiator. I bought one of the cheaper thermo gun, but it seems to accurate on other things, even though my measurements on the engine jumped around +/- to some degree, I guess from coolant running though the system. I'm near 100% positive it's my "new" temp sender. I now need to find one somewhere that's accurate. The 2 I tried so far are the same brand with the same readings. Tried Advanceauto and Mustangs unlimited with no luck.
 
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