Neon Over Heating


#1

2005 Dodge Neon SXT 206XXX

Been slowly diagnosing this as my past with troubleshooting cooling systems is none to well. With this car having a different setup on sensors and such (first car I’ve worked on w/o MAF) would like to get some advice and see if I’m on the right track or aiming off into a dark spot.

Long story short on a trip (about a 1 hr. drive) got about a block away from destination and gauge showed it was over heating. Stopped the car started up after five min. just fine. Got home replaced the thermostat and cap (old cap was junk). New cap was junk aftermarket so yesterday I took the same car on a half hour drive to get a Mopar cap ran just fine up again until a block away, pulled off the road turned it off let it set a few min. then didn’t even show it was over heating. Let the pressure off and replaced the cap and added in a bit more coolant ran fine all the way back (even pushed speed in a few spots).

The above is just what seems to be the mechanical side of the issue. After noticing the gauge was going a bit above the normal spot I noticed my cooling fans are not coming on. Checked fuse and tested relays out to be fine. First thought is to check voltage to the fans but also tempted to check coolant temp sensor with bench test. Will be going over to my dads to do voltage testing later today.

Any thoughts on this?


#2

When overheating goes on and on and everything easy has been replaced (t-stat, water pump, sensors) and fans are confirmed to be operable, you’re likely looking at a blown head gasket. A “block test” which detects combustion gases in the cooling system can confirm it. A pressure test which detects coolant in a cylinder is definitely confirmatory.


#3

Do the fans work when the A/C is turned on? Do they run if you jump the circuit?


#4

When the engine is cold, remove the radiator/coolant reservoir cap and replace any lost coolant.

With the cap off, start the engine and let it idle. Watch the coolant, and if bubbles start forming that’s an indication of a blown head gasket.

Tester


#5

On my Corolla if I let the car idle in the driveway the electric fan will turn on within 5 minutes. You could do that in conjunction with @Tester 's idea.

Watch the dash temp gauge during this experiment. After starting the car cold, and idling in the driveway, it should slowly go up, stabilize for a short time at the thermostat temp, then rise again until the electric fan comes on. On the Corolla the thermostat opens when the gauge is 1/3 of the full scale, and the radiator fan turns on when the gauge is 1/2 of the full scale. With the radiator fan on, the temperature immediately decreases and the fan turns off in a minute or two.

If the fan doesn’t come on, it is probably either the fan itself, the fan connector, the fan relay, or the coolant temperature sensor. Some cars use a separate coolant sensor switch, but yours probably uses the same coolant temp sensor that the car’s computer uses, and the computer turns the fan on with a relay.