2002 Park Ave cooling problem

[bobby49]

The 3.8L engine has 159K miles and runs normally. When started, the coolant temperature starts to climb normally until it hits equilibrium at 183F. This isn't quite right, and it should be about 197F, because that is the thermostat rating. The thermostat was replaced, and that had no effect. The coolant stays around 183F until I get to a long steep uphill. Then the coolant climbs to 216-221F, and this seems abnormally high. The air conditioner is off, naturally. Once past the uphill, the coolant slowly returns to normal around 183F. There are no coolant leaks, steam, or smells.

It was suggested to me to purge any air bubbles from the cooling system, so I removed the radiator cap and let it run up to equilibrium. I cycled the A/C and the heater. No bubbles or smells. This is a normal Dex-Cool mixture in use.

Now what? It doesn't seem like a water pump problem or a thermostat problem.

 

[papa_cadillac]

https://www.youtube.com/watch?v=Qgc6JQ2m_AM

Different vehicle, same engine. Try it and see if it helps.

 

[bobby49]

https://www.youtube.com/watch?v=Qgc6JQ2m_AM

Different vehicle, same engine. Try it and see if it helps.

I tried it, and it had no effect. All that I got out was a dribble of clear orange fluid. No bubbles.

Fundamentally, there are two symptoms here. First, the coolant is staying too cool for normal highway driving. Second, the coolant is getting too warm for steep uphill driving. I can't tell if those two things are part of the same problem.

Now what?

 

[papa_cadillac]

I have had thermostats fail in the recent past, and these days they fail in the open position causing the engine to never really get up to proper operating temperature. That's half of the problem, possibly. As for the rising temp going uphill, not smart enough or haven't had to deal with that before, so I have no good advice other than actually taking it to a trusted mechanic. Sorry, but that's all I got. Maybe someone else has seen this before.

 

[bobby49]

I spent the morning at the repair shop. The system was flushed and a new thermostat was installed, and now the equilibrium temperature is 198F (normal). The theory is that the old thermostat was sticking open, which explained why it was staying too cool for normal driving. Then, it was sticking partially open/closed on the steep uphill run, which explained why it was getting too hot on the uphill. I haven't yet done extensive test-driving, but it seems to operate much differently now. Just to add a little insurance, I dropped in a bottle of RedLine Water Wetter.