I have an '84 T/A 5 litre H.O. It runs fine but has this occasional rise in temp. from it's normal 195-200 to 250. As soon as it gets to 250 it begins to decend back to 195. This can happen when riding on the highway at 65 or just idling or in town. I replaced the thermosta ( 195 ) and checked out the fan, all is fine. Water pump doesn't wobble at all. Any suggestions?
Thanks

 

How are you determining that the temp is as high as you say? You really cant trust the gauge in your dash, as they can vary widely.

Even with a new sending unit, my gauge will read 220, but the computer's temp sensor is showing 197. I use an infrared thermo and the temp of the thermostat housing is in the 195 range.... so I tend to believe the computer temp sensor over the dash gauge any day.

 

Very simple and common, but do you still have the black wind deflector?

 

id go with a 180 degree thermo im running a cheapo signature series water pump, replacement radiator from advance and a 180 dgree thermo...my fan doesnt even work and i rarely get past 160 unless i sit for awhile but i have a fan switch so im alright

 

I'd have to agree here, sounds like your temp gauge is inaccurate.

 

It's called an air dam and that shouldn't be the problem since it happens at idle too.

 

Repaced original O.E.M. gauge and sending unit with auto-meter phantom gauge, just to be sure orig. gauge wasn't bad. Still acted the same...Doesn't seem thermostat would make much difference since this happens out of nowhere, just climbs up to 250 and then immediately goes back to 195 !!Someone suggested the water pump might be at fault...any ideas??????

 

Open up your radiator while the engine is cool and when the stat opens you should see the fluid be sucked down, if not this would be signs of a dying water pump. I'd check your radiator cap as well, to make sure it's holding pressure.

 

Sounds like a sticking thermostat to me. Grab the radiator fan with both hands and see if it will move up and down, it should not have any play to it, when the seals start to go you'll notice alot of play in the fan.

 

Replaced thermostat...fan does not moved up or down...?????
Any other ideas??