2001 Chrysler 300M overheats after system flush

chrysler
300m

#1

I can’t figure out why my car still overheats even after flushing the system, new thermostat, new water pump, and bled the system. It drives fine through town unless the AC is on for too long. I don’t have any leaks and there is no coolant mixed in with the oil which means I don’t have a cracked head or gasket. Apparently this is a common problem with these cars but I’ve yet to find out how to fix it. I’m thinking about removing and leaving thermostat out, but if it still gets hot, then I’m puzzled.


#2

Stop thinking about that. It won’t help and possibly hurt the problem.

Silly question, maybe, but have you checked to make sure the cooling fans are running?


#3

Yes, lol. I do have good knowledge about cars. I’ve always done my own work, when I have the time or special tools. It’s also had a new radiator put in from the previous owner.


#4

Try a new radiator cap. The symptoms of a bad radiator cap include overheating under heavier load such as high speed, going uphill and/or running AC.


#5

That was one of the first things I got. I always eliminate the cheapest parts first.


#6

Check to see if the radiator fans work for high speed. I have found some of these that seem to operate properly for the first 20 minutes because the fans are running at low speed but after the engine coolant temperature reaches 230 F the PCM switches the fans from low to high, if the fan motors won’t operate on high speed the vehicle overheats.


#7

Yep they work on high, I can hear the difference


#8

The symptoms point to a clogged radiator if the fans are working ok. When it is heating up put an infra red temp gun on the radiator, if there are cooler spots it is plugged. This car is old enough that a neglected cooling system can clog a new radiator.


#9

It was clogged up but I thought that I had got everything out. But I’ll try infrared thing when I get a chance. Should the temp be high or low?


#10

You are looking for cooler spot than the rest of the radiator indicating reduced flow there.


#11

Possibly. You could have a head-gasket breach between the cylinder and the coolant. That will cause overheating. A test for exhaust gasses in the coolant is the best way to determine if that’s the problem. Bubbles in the coolant in the radiator when the engine is warmed up and running is another, esp if the bubbles get visibly worse when the engine rpm is rapidly increased briefly.

That said, given everything you say I’m guessing you aren’t getting the proper flow rate through the engine and/or radiator, due to clogs, or you got air trapped in the cooling system. As mentioned above, removing the thermostat is a bad idea. The thermostat is what decides what % of the flow goes to the engine and which goes to the radiator. Modern cooling systems will almost always overheat if you remove the thermostat.


#12

On some cars, when filling the cooling system you need to have the heater control set on Hot to fully open a valve to the heater core. Otherwise there can be air in the plumbing, and that can cause problems.


#13

Okay well I finally got a thermometer so I will check the radiator the next chance I get. Weird thing is that I can drive the car through town with no problems (without the AC running) however as soon as I hit the highway and with the AC going, Within 5 minutes that’s when the car starts to get hot. After that I pretty much have to baby it home by turning the heater off and on and rev up the gas sometimes. It won’t ever get back to normal until I let the engine completely cool.


#14

But I also never let the temperature get to the red zone.


#15

That symptom sounds like the cooling system isn’t properly holding pressure. If not that, then the radiator is clogged, something is preventing the coolant from freely flowing, or exhaust gasses are getting into the coolant. Did you test the replacement thermostat in a pot of hot water on the stove to make sure it is opening correctly?