Where to start, I have a 1997 dodge neon and something is defiantly not right. If i have my car on for about 10 minutes my temp guage will start to rise, and eventually will be at H, but then it will slowly randomly spike back down to mid, and then spike back up again, back down, back to H, and so forth..If i turn my car off with it being all the way at H, and turn my car over to just the guages having power, or even being all the way on, the temp guage goes to about mid. If i leave the car off for awhile, the engine cools like normal. Ive tried replacing the whole cluster unit, and also tried re soldering my old one. Didnt fix it. Since ive noticed that when the car goes to H, my radiator fans dont come on, nor do they ever, thats a problem it self. Also i just replaced the radiator cap and thermostat. When the car goes to H, the therm. doesnt always open. The other day i was letting my car idle and i saw smoke coming from my hood, it was only coming from the side where the overflow tank was and the radiator res. is. And i drove it home quickly to find out all my anti freeze leaked out..weird back pressure perhaps? I told a guy who works solely on neons the symptons and he thinks its a headgasket, anyone else have any ideas?

Thanks

 

Fans not kicking on, very bad. They help pull more cool air across the radiator to reduce the level of heat in your fluid. You really need to diagnose why they are not coming on. If you turn on your AC, the fans should always be on as the AC dumps its heat from the condenser right in front of the radiator and adds to the work load on the radiator.

You can jump the fan relay by running a wire straight from the battery to the fan motor and if they kick on and run at a high speed, then you need to check the fan relay and coolent temp sensor. The fan relay is the same as the horn relay and you can swap them out (if your horn is working) and try to see if that makes a difference. As for the coolent sensor, you can either just replace it (about $11) or try to test it out to see if it is bad. Put the sensor in a cup of boiling hot water and hook it up to a multimeter to see the resistance level change as the water cools. The manual tells you what to look for.

Having said all that. I think your head gasket is shot. If not before, then almost assuredly it is now. If you have run it hot as many times as it sounds like you have done, then I would be replacing the head gasket, have the head redone, put in a new water pump and timing belt kit, etc. and go from there.

Good Luck.

PS: You don't have to open a new thread each time you need to update the status of an existing thread. Whenever you update an old thread, it automatically bumps it to the top, so everyone can see it. Updating an old thread allows everyone to examing the history of the thread to avoid repeating history by offering the same advice over and over. Just a friendly FYI for future postings.

 

Sounds like you have air the coolant lines. Run it with the cap off for a few moment. If you do not see a good amount of fluid, put some in. Straight coolant; not the mix.

 

Replaced the fan relay, and that fixed the fans, they now come on. My temp guage still bounces but not as much. If its at H sometimes my fans arent on. But i feel the hose lines and the top of the radiator and there warm, not cold, not blistering hot, so whats your next suggestions? How do i remove air from the lines? And also, is it possible the transmission fluid is getting to hot, that would warn my guages that something was overheating? Thanks

 

Try replacing the temperature coolent sensor now. It costs about $11. It may be bad.

Finally, if you are not losing coolent and having to replace it, then most likely you are not overheating. Your instrument panel may be going bad (common in Neons). There is a sticky thread that talks about bad panels that has one or more guages going bad and what may (repeat may) fix them.

Don't worry about air. Most likely that is not your problem.

 

Ive replaced the cluster with 2 other clusters, and also have manually repaired mine by the guide, and still does it. What puzzles me and everyone else is that i can drive for 20 miles, and it not bounce once, or i could drive for 5 and it will do it 2 or 3 times, long or short distances doesnt matter. Both do it, never consistently, was able to drive 30 miles the other day without it doing it once, and yesterday drove 20 miles and it did it once in the 1st mile i was in the car, (car being completely cold). Makes no sense to me or anyone else, also if it was the sensor going bad, wouldnt it show up on my CEL dash codes as a problem when i test it? Maybe ill try doing my own compression test with a rent a tool thing from autozone, anyone know how to do it to test for a bad head gasket?

 

i had a similar problem and had to take it to the dealership to get it fixed. what mine ended up being was a temperature sensor (?)(i dont remember the name of it).
mine was not actually overheating even though it said it was. you might take it somewhere and have them check the temp of your engine. mine was normal even though it said it was overheating. just a thought, might help you diagnose the problem. good luck.

 

Just for ****s and giggles, i took it into a shop and had a head gasket test done, passed that, so that was a big sigh of relief, the temp sen. was replaced a month before i bought it, it gives no cel code if i check it, wouldnt it pop up if that temp. was bad, they also said ya my engine was running perfect, fans were doing there job and what not, they said its possible that theres either air in my lines or possibly if theres a ground from the gauge to ?, that it might be grounding out for some reason? They said try driving a lil longer to see if its air, and it could fix itself. any more ideas? thanks guys

 

Yes the sensor would kick an error code if it was bad (or even going bad). You may have air in the system, but I doubt you have that much, and yes, it will eventually work the air bubble out on its own - unless it is so big you have a cavitation or pressure bubble lock somewhere (either one is highly unlikely).

Check the wires all the way from the sensor back to the wire bundle and clean the connector as best you can. Those are your most likely failure points. If that does not help, then you may want to unbundle the wires and check further up the line, but that can be tedious. You may also check continuity of the wires from the PCM to the sensor if you have a multimeter. I found a break in my CAM sensor wire doing that.

 

i had the same problem just did my headgasket and some little motor hop ups wile head was off butt i need to put my timing belt on and cant get this damn hermonic balancer off