I have a 91 GMC P/U (350 V8) that showed a temp increase a couple weeks ago.It always ran at 150.All of a sudden it jumped to 190 to 210.I relaced the thermostat & no result.I then flushed the system & replaced both hoses & the thermostat and added a can of water pump lubricant .No change.I thought the antifreeze may be too stronly concentrated so I drained some & deluted .Then I relaced the rad. cap.A small improvement to 190.
I am not leaking antifreeze and it never goes over the halway point,(210).
Is this too hot?
I am going on a 1000 mile trip & I usually drive straight thru.I do not want problems on the road.
I have a new water pump & thought about installing it even though the old one seems (?) OK and replacing the drive belt.
This had done the same thing a year ago & replacing the thermostat did the trick.However no such luck this time.
Any ideas will be greatly appreciated.

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vern

If it heats up in traffic and cools down on the highway, yo might have a bad fan clutch, if your veh has one.

Does it in town,regardless of using not using A/C ,Same on the highway .When Istart up it goes up to 190 and stays there.

Normal operating temp is 190-210.
If you were running at 150 before...THAT would be a problem.
The truck came with a 195 T-stat from the factory.
It must run at 190-210 for proper computer control operation.

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