While driving home today i noticed that my stock water temp gauge was reading high. i get home and after the car cools down i check the fluid level in the radiator and the overflow tank, both are at normal levels. check color.....normal green color no sign of oil in the radiator fluid. i turn the car on and let it idle, will not overheat. i continue waiting, and the gauge is reading normal.

after about 20 minutes of watching the fan kick on and off and checking for any visible leaks i go out for a drive. under boost, stop and go traffic, the gauge is reading perfect. for some odd reason i decide to turn my headlights on, and since there is frost on my rear window i turn on my rear window defroster, and the water temp gauge starts to go up. I pull over into a parking lot and begin testing.........

headlights on by themselves = normal temps
only rear defrost=normal temps
headlights+rear defrost= high temps
headlights+air conditioning=high temps

not sure if any of you have experienced this issue, or have any advice. hopefully this will be a simple fix so i dont have to take the car to mitsu.

2003 evo 8, 44,000 miles, tbe, uicp, intake and tune

 

bump

 

ttt

 

Doesn't sound like a HG. Maybe a bad temp sensor?

 

Does the temperature gauge jump up the instant the accessory is turned on or does the gauge change slowly?

 

its jumps up instantly the accessory is turned on.

 

Well, that tells us the problem is electrical and not a cooling system problem. So, the question then becomes what sort of electrical problem?

The sensor on the engine is a variable resistor that changes resistance with temperature. Current flow is from the gauge cluster to the sensor and then to ground. The wiring diagram shows "control circuit" for whatever is inside of the gauge cluster. I don't know if that is a black box or just a power source. I would be interesting, had Mitsubishi seen fit to include an oil pressure gauge and a voltage gauge, to see if they are similarly affected. Then I would say it is a bad connection near the gauge cluster, maybe a bad ground.

 

i am now leading towards a bad ground. about 2 weeks ago i had to remove the negative battery terminal and broke the wire terminal. went to advanced auto bought a new negative terminal and installed it. after installing it the negative battery wire was to short to replace a bolt that grounds the negative wire back to the chasis. i forgot all about it untill looking today.

i am now trying to think of a easy solution to lengthen the negative battery wire and replace the bolt to see if this is the problem before taking it in to mitsu tomarrow morning.

 

fixed the problem. lengthened the negative battery wire so i could re-attach the bolt that attaches the negative battery wire to the chassis. thanks for the help.

 

your temps are fine now???

 

yes the water temp gauge is normal now when i have accesories on.

if you follow the negative wire from the battery about 4 inches back there is some insulation removed and a bracket for it to be bolted to the body.

 

this is why every car i own, i build my own grounding kit throughout the engine bay to battery neg. it gives slightly improved idle, better gas mileage and some say even slight power gain but if u really really think about it.... 99% of the car runs on electric current. having a solid ground is critical.