ok heres the thing, i have a 99 eclipse rs and during my delivery runs, the temp shoots all the way to 3/4 of the temp scale. but if i have the heater on or im on the freeway it shoots back to normal. i was either thinking its my fan or my radiators clogged, how do i go about looking what my problem would be.

 

you should be able to hear ur fan kick on and off... you could always check ur thermostat

 

If you just drive it around then park it and let it idle pop the hood and wait a little while then just listen or look and you can see it.

 

Ive heard that if you turn the aircondition on then both fans should run. You could try that and see if it works.

 

How many miles? When was your last 60k service? Did you change the water pump as well as the timing belt?

Well it might be your thermostat. The reason it cools down with the heat on is because having the A/C button pushed in turns both fans on.

 

i tried the ac thing, that didnt turn on the fan, i dont hear it turning on and off while i make my deliveries like i do in other cars, i checked the fuse, the fuse is in tact, i was wundering if there was a way for me to connect my battery streight to the fan to check if it works or should i just take it to a shop.
btw. i just bought the car from a crummy dealer and it has 107k miles i dont know if the timing belt and or the water pump has been changed out yet

 

u bought the car from a "crummy dealer' y would u do that?

 

Fan relay or temp sending unit or both. I thinking relay since it will not come on with A/C or defrost on. Switch it with one of the others of the same size and see what happens. Next comes the test light method.

 

I agree, it could be the thermostat. The other reason is that the heater draws the heat from the coolant lines and deposits it into the cabin, in turn the heater cools the fluid.
Agreed, I've found that the temp sending units go bad often enough to call them the culprits over the relay most of the time.

Another thing you can do to check the fans is to take a 9 volt battery and connect two wires you have laying around the house and connect it to the fan plug (disconnect it first of course).

 

i had same problem on my '00 eclipse just fixed it yesterday ...
1st thing you do to diagnose overheating. simplest then hardest
#1 check fan. to do this requires a circit tester (the cheap kind that looks like a screwdriver with a light. and some jumpers ( smll wire with aligator cips at each end. disconnect fan at terminal. connect tester to battery (-) terminal. touch end of each socket of the terminals you just unhooked (female end ). the one that lights up is (+) , now unhook tester. hook one jumper to (-) & one to (+). hook (+) jumper to the fan itself on the (male) end. now touch(-) jumper to one of the male prongs one of them is your (-) and one is a switch . if your fan is alive then it will com on. otherwise replace fan. if you have two fans test both seperatly.

#2 if fans r working next step is to check fuses & fuseable links and relay.testing relays requires an ohm meter.

#3 if fuses and relays r good check temp sensor

#4 if sensors r good check thermostat

#5 if termo is good check waterpump #6 if water pump is good then there is only one thing left it could be THE DREADED HEATER CORE. i pray that not your heater core ... requires full dash board dissassembly and removal . i was fortunate enough to have my heatercore take a crap on me. and stupid enough to take on the job myself. took me 3 days to complete it but i did it. good luck