Thread: Motor Temp Creeping Up

I am new to the site i just want to give a thumbs up to everyone posting you guys all know your stuff and are a HUGE help to people like me who just bought their GP last week. When i bought the car i knew that the intake manifold gaskets were a common problem with the 3800. This afternoon sitting in traffic in Boston the temp started creeping up but only got to about 210 before i got back on the highway and it was fine. A few other times when i got off the highway i caught it creeping up again but not quite so high. I am suspecting that i need to replace upper plenum and lower gaskets but just wondering for any adivse of possible performance upgrades while im in there or maybe if i am missing the diagnosis here. I plan to pressure test the system in the morning at work but any advise would be much appreciated! Thanks everyone!

I don't think you have a problem yet. If it gets much higher, then yes. When you stop its going to heat up fairly quickly in warm weather. Stock fan turn on is just past 200* so they won't be helping until that point.

You need to do a controlled situation where you let it sit and watch the gauge and see when the fans come on. Both fans should be on by 210 and it shouldn't get any higher than that sitting still idling.

Your thermostat doesn't even open up until 195*, so until then your radiator isn't even being used. The car's normal operating temp is about 195-205* and you were just a little above that, sitting in traffic. To be expected.

Like I said a controlled test, along with your pressure test will shed some light on the situation.

So the system isn't holding pressure? Is that what you mean?

Something that many people overlook is the radiator cap. Just like any other part on a car, it wears out. And if the cap wears out, it won't hold as much pressure, and can let the car heat up more than normal. A new cap could be an good idea.