I have a 2002 Lexus GS430 with 142k miles. It seems to over-heat when I do a lot of stop and go driving, followed by a period of parking for 20 minutes, followed by more stop and go driving. Neither the dealer nor the local mechanic can figure it out. Everything on the car has been checked, from the water pump to compression. There are no leaks and the fans come on when they are supposed to. Any ideas?
It seems to over-heat
Could you be a little more detailed about that? Why exactly do you feel it “seems” to overheat? BTW you did a good job with answering all the other questions most people don’t know to tell us.
Here is the exact sequence: I drive for 20 minutes in Hartford, I park for 20 minutes, I drive for another 20 minutes in Hartford, and the temperature gauge goes to the top and steam comes out from under the hood. The timing belt was replaced recently, so the water pump was examined. The dealer has run the car and driven it in traffic and can’t get it to do the same thing, which, I have done twice. The system was flushed, there are no leaks, compression is great. It is a mystery to everybody.
Ther are two possibilities I can think of. One is a radiator that has built up a coating with age that prevents it from dissipating heat as it should. Some of the tubes may even be plugged.
The second is the often overlooked radiator cap. If it isn’t holding pressure, the boiling point of the coolant will be low. A new one can be bought for about $20 at the parts store.
I replaced the cap and the system was flushed to make sure there was no build up of dirt or tubes plugged. The car still overheated according to the sequence I specified.
So I guess this will remain a mystery for now…