Car runs hot after long highway drive

mricci

Member
Aug 17, 2003
301
0
17
Massachusetts
My car runs cool almost all the time. I only have a stock gauge, but its usually only about 1/4 of the way towards hot. It stays cool while driving, even for long distances. But once i get off the highwayafter driving at least 45 mins, if it sits for more than a few minutes at a light or in traffic it heats up. It hasnt overheated on me yet, but runs up past normal on the stock gauge. Then that causes it to start pinging and running like crap.
 
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yea, at about when the gauge gets halfway they are coming on, i can hear it when im sitting in the car. I can start the car up and let it idle for 30 mins and it wont get that hot, or if i drive a shorter distance then let it idle it wont get hot.
 
Are you saying that you can let the car idle for 30 mins without getting it up to ~210*F (low speed fan comes on there)? How cold is it where you are at (I dont know relative temps back East). I know when it gets real cold out the car runs hottest at idle since it can actually warm up a little - otherwise the cold air rushing over the coil fills the motor with relatively cold coolant as soon as the t-stat opens.

Good luck.
 
It will get up to temp if i let it idle, but if i let it idle after a long drive on the highway it gets much hotter, than if i let it idle after a drive around town. Im going to get an aftermarket gauge so i can know the exact temps. Its not overheating yet, but getting real close. The temp will climb up to the l on the stock gauge in about 1 min after a highway drive.
 
That sounds like a plan - the symptoms dont really make any sense unless your fan is not coming on after being on the highway (like a VSS input hiccup). A real gauge should help narrow it down.

Good luck.
 
Guys,

Our cars are notorious for developing a very slow leak on the passenger side of stock radiators, between the radiator core and the radiator end cap down low on that side.

It’s hard to see, and hard to diagnose, since it it’s a very slow leak and the leak mostly drips down onto the cross-member directly under the radiator, burns off, and never makes it to the garage floor.

Until I fixed that, my car had the same mysterious symptoms of a low coolant light every month or so, and overheating when coming off of a long freeway run and getting back into slow city street traffic!

When you are moving at highway speeds the air flow through the radiator is sufficient to keep the temps down. But, when you then slow to side road speeds and stop & go traffic, the system can't keep up.

Have your coolant system pressure checked to see if it has a slow leak. If it does, it's probably at the location I mentioned above, and may be the cause of the overheating you described.