Hi,
I have a 2001 Neon with 157,000 miles on it, its a great car and I haven't had a problem with it until now or if it even is a problem. I have had it about 8 months. Its running hotter than normal. When I have the air on going on the highway and through the city the gauge rises to about 3 quarters of the way up not to the H but its not far off. On a hot day it will run normal for a bout 45 minutes before it even starts to rise. It will also come back down and then proceed to go back up again. Sitting in the drive way with the air on doesn't make the gauge go up either. It doesn't go any higher than that and its on hot days when it does this. Is this normal? In the book it says that it will run hotter on hot days or going up steep hills but I am not sure. I replaced the thermostat flushed the coolant several times and even put a new air condenser in it because the old one was pretty bad, and now its getting good air flow. The fan is coming on when it should. The radiator is fine, none of the fins are bent and there is no rust on the inside of it. The water pump is apparently working because when I was flushing it and adding coolant and water you could see the thermostat open and the coolant running through with a good force. I'm not loosing any coolant no oil or anything in the coolant, compression is fine on the car. At night or on rainy days the gauge doesn't move out of the norm. Any Ideas? Anything will be much appreciated. I have never had a little car always Jeeps, but i needed something better on gas and everyone tells me that little cars run hotter in hot weather.

 

It looks like you checked everything. I have a 2000 (175K) and on the return trip home I got a "ding" sound and check gauge light. The temp. gauge was almost to the red. The thermostat was stuck closed so I replaced it, rad. cap, upper and lower hoses. Now it never goes over the gauge 1/4 line mark. Could you tell if the car was really running hot? ie... spilling coolant, smell, engine performance. You might want to look at the coolant temp. sensing switch. Good luck

 

I believe it is running that hot, I have had some boil overs with the gauge up that high when I would shut the vehicle off. I replaced the radiator cap and if I shut it off with the gauge that high, it doesn't boil over. So that problem was fixed. Other than that, I never smell coolant, performance is the same as always. Maybe it is the sensor, when I shut the car off, after I have driven it for awhile and its fully warmed up, if I start it back up within like 3-5 minutes the temperature gauge sky rockets and then the fan kicks on and it comes back down to normal. I know its not over heating just from me shutting it off and turning it back on, but that gauge goes almost up to the H and when the fan kicks on it instantly comes back down to normal, it like falls.

 

Since you replaced everything else I would replace the temp. sensing unit and see what happens. It seems that you checked or replaced everything else and it should be a cheap and easy job. The only thing I would suspect after all that is a blockage in the radiator fins or hoses. Don't you hate it when something that should be an easy fix fights you every step of the way... Keep me posted

 

Okay! Update!

Temp sensor didn't get changed I checked it and its working right. I called my mechanic and he gave me a couple of tips for re flushing the system. Since its supposed to run distilled water and Mopar HOAT antifreeze, I re flushed the system again and chunks of sediments of rust started coming out. It was so much I filled up 2 gallon jugs up with the rust sediments No water with it just the sediments. Hopefully this is the fix! its not been hot enough here to figure it out. There is no more inside of it but I will re flush in a week to make sure it's all out. As soon as all the sediments were out of the system the fan turned off and did not come back on during the rest of the flush! My mechanic thinks that if this does not fix it he wants to change the oil in it to make sure there is no antifreeze in the oil he said there could be just a little bit in it. If that's the case I will have him put a new head on it but I am really thinking its the sediments that came out was clogging the system up. I HOPE!! Crossing my fingers!! The fan hardly comes on now, well like it should at least.

 

Wow, I have seen junk in the cooling system but not that much. I wonder if the prior owner ran it on tap water at one point? If any of the pieces are big you might want to consider pulling the radiator and reverse flushing upside down to clear anything that could be blocking the fins. Or just replace the radiator about $50. Good luck

 

Yeah I just may do that! It was about 90 here today and I drove it about 100 miles, to the big city and back. Air was on the whole time and the gauge did not move! Stayed right on normal the whole time! I am thinking that was it!! Thanks for your help with the matter! I have flushed it so many times and that never happened!