View Full Version : great cooling or bad gauge???

July 11th, 2006, 20:23
ok i got the new engine in and everything hooked up and double checked everything and then tried to start it.

it started right away and sounded beautiful. but while letting it idle to burb the cooling system (started with clean empty engine and radiator) i noticed that the thermostat seemed to open properly and everything is working normal. BUT.....

my temp gauge only moved 1mm past 100degrees and didn't go any higher. i had it idle for about 20minutes and then high idled (1,500rpm) for about 5minutes.

so i hooked up my techmaster and checked the coolant temp through the computer and it was reading 208degrees.

i replaced that temp sensor that i asked about earlier ( http://www.naxja.org/forum/showthread.php?t=90833 ) with a brand new one, and i double checked to make sure it was pluged in.

any ideas where i should start with getting my temp gauge working again???

July 11th, 2006, 20:34
The gauge may be faulty like described. If you have a seperate coolant gauge handy(an aftermarket one that screws in the head or manifold), I would hook that up, and see what it reads and go from there.

July 11th, 2006, 20:40
oh i forgot to add. the gauge has always worked flawlessly. last time it worked was when i pulled the engine out to replace it.

so i'm not saying the gauge isn't bad, but it would seem weird that it went bad when it wasn't being used.

so other than trying a test gauge, any other ideas???

July 11th, 2006, 21:24
figured it out.......if you take the plug that connects to the sending unit, and ground the plug, it should send the gauge to all the way to hot. it did. so my gauge is fine, and the brand new sending unit is bad.

July 11th, 2006, 21:35
Did you try measuring the resistance across the gauge and comparing it to what the FSM says it should be?

July 11th, 2006, 21:38
you do that with a voltimeter right??? never did figure out how to use those things.....that's the only tool i don't have.

what would testing the resistance tell me???

July 11th, 2006, 23:43
Yup, a meter is what you want - one that can measure resistance or ohms. A decent basic one can be had for $20 at Sears or Radio Shack. Or $4 on sale at Harbor Freight. The resistance of the sensor changes with temperature, which changes the current flowing through the sensor and the reading on the dash guage. If the resistance isn't what the FSM calls for then the sensor is bad. If it is, then you've got a wiring or guage problem.

Your profile says a 95 XJ, so the sensor resistance should be around %10 of these numbers. If you have a bad connection, causing extra resistance then the guage will read low. Since you grounded the sensor wire and it pegged, I agree that you probably have a bad or incorrect sensor.

100*F 1365 Ohms
220*F 93.5 Ohms
260*F 53.1 Ohms

July 12th, 2006, 05:48
i see....cool thanks.