Temperature rising

Maintenance/Repairs
1

I’ve had my car into the shop twice regarding this problem and they just cannot find anything solid wrong. I tend to overanalyse so I thought I’d bring it here and see what people thought.



Basically, my car, a 96 dodge neon, automatic, no air conditioning - the temperature gauge creeps up. It used to hang out around 45-50%, now especially on and after high way driving it stays up around 65-70% max. It doesn’t go above that, and it creeps up there pretty much only when I’m driving on the high way.



The guys at the shop replaced my radiator cap and checked all the fluids and everything but everything is running very smoothly. They kept the car a few days and test drove it multiple times with various errands and could not duplicate my problem.



The car has absolutely no performance issues, just the gauge is higher than i’ve seen it before and while the mechanic says it should be fine as long as it doesn’t get up to the H line, I still am a bit wary to drive it long distances on the highway.



Thank you for any input!

2

Best guesses:

  1. Air in the coolant (although this may just cause erratic needle fluctuations, not constant high temps.)
  2. Radiator or heater core has a plug in it.
  3. Water pump may be failing
  4. Fan may be failing, or not work at all
  5. A plug or blockage somewhere in one of the engine’s coolant passages
  6. Outside of radiator is damaged (bugs or other debris on the rad, or bent a number of fins.
  7. Rad cap isn’t working right
  8. This one’s maybe a long shot, but transmission is overheating - the tranny sends transmission fluid to a small cooler inside the radiator - if the transmission is overheating, maybe the coolant is absorbing all that extra heat.
3

You say they replaced the radiator cap, but you didn’t mention a new thermostat. I’d try that before anything else. It’s 11 years old. Replace it with a new one and see if it helps stabilize the temperature.

The mechanics drove your car on local errands but they didn’t take a highway trip, which is why they couldn’t duplicate the problem.

4

How many miles? If the miles are high, I would add water pump to the thermostat as likely problems.

Good Luck

5

the water pump was replaced two years ago, and they ruled that out at the shop. they did mention that the fins could be bent so that isn’t a surprise answer.

the thermostat being replaced was my thought as well, i’m getting a second opinion on it this week hopefully so we’ll see.

6

oops i should state that the car has around 126k miles.