99 Sebring JX coolant issue?
 

I have a 1999 Sebring JX that I am new to. Last couple times I have driven it in the cold weather, there is no heat until I get on the highway, then it blows hot. Once I exit the highway and drive slower, it blows cold again. The coolant overflow tank is at the full mark when the car is cold, and I do not see any coolant when I take off the radiator cap. A couple times, it started to blow hot while sitting in the driveway, and that was after I heard the cooling fan come on. Manual says to check the level at the overflow tank, and fill there if needed. Should I be seeing fluid when I remove the cap? Could it be very low and causing it to not blow cold when driving slower? Should I fill it at the radiator cap? Thanks for any help and advice.

The coolant should be at the top of the filler tube under the radiator cap. There is bubble in the cooling system that tends to collect in the heater core. At higher engine speeds the coolant is pushed into the heater core and there is heat. As the engine speed drops, the air bubble finds its way back to the heater core.

The coolant is not being pulled from the reservoir back into the engine as the engine cools. Most likely cause is corrosion on the filler tube where the radiator cap sits. The corrosion does not allow for the vacuum needed to pull the coolant back into the engine. This is a common problem with the 2.5l mitsubishi engine. The only sure solution is to replace the filler tube and replace the radiator cap (and replace the metal gasket at the base of the filler tube - may come with the filler tube). Easy enough to replace, 2 bolts at the base of the filler tube. No need to drain any coolant as the level in the engine will be below the filler tube.

Another possibility is the rubber tube from the filler tube to the reservoir has a crack or split in it or is not securely attached at either end. I put a screw clamp on the end at the filler tube.

As noted, this is a mitsubishi engine so the filler tube may be branded as a mitsubishi part.

The cooling system will self-bleed. Top off the filler tube and monitor the reservoir for a week or so and top off the reservoir as needed. To be certain the system is working as it should, remove the radiator cap when the engine is cool. The coolant should be at the top of the filler tube.

Thanks for the reply. Already picked up a radiator cap and some green antifreeze. Just looking the filler neck. Would you recommend a thermostat too?

Filler tube

https://www.rockauto.com/en/catalog/...filler+neck,14

https://www.mitsubishiparts.com/oem-...et-ho-md308982 (should include gasket)

I would not bother to replace the thermostat at this time.

I ran my '97 to 290,000 miles, 3 filler tubes, original thermostat - YMMV

Filled up antifreeze, cleaned top of filler tube and got a new cap. Finally got time and decent weather to fix and drive, and it is blowing hot air now. Just going to keep and eye on it now. Thanks for the help.

Suggest have a new filler tube on hand. I have found that cleaning the top of the filler tube only lasts for maybe 4 months. Having one on hand will allow you to change out when more convenient.