I have a 1987 GTA with a 350

Yes you will prob. say read the forms and I have but no one is doing the same as mine.

It runs normal for 1/2 an hour or so. (It won't over heat at an idle from the get go). Then as I drive under a load it gets warm. If I go up a hill it gets warm then going down it cools off.

So I flushed the rad. and put in a new thermastat and new coolent. But it did the same. So I was told it's the radiator so I swapped that but still the same.

It has dual fans and they are hot wired to run all the time. Only one works. But it get warm under load while driving when you don't really need the fans. But when it is smooth it calms down.

I really thought the radiator would do it now I am baffled.

 

I'll try.....You say "running hot", how hot? What temp is your t-stat, 192 degrees? Is you air dam intact, not loose,flopping around? And did you put a new water pump in lately? What rotation?
All pre-'88 v8 thirds use standard CW rotation
water pumps.
Just some things to check.

 

yeah check the water pump it might be "lazy" an impeller could be damaged or just clogged up how long have you had the car?

 

When I look into the radiator the water is really moving that is why I don't think it's the water pump. Full solid stream from the heater core return line.

 

Check to make sure fan is sucking not blowing, maybe wired backwards, second fan is supposed to come on when AC is on, is not working at all and wired to be on continuously? Check it to see if functions at all by jumping direct to battery. That will tell you if it is good or not. If it runs start checking your relays and wiring.

I have an 86 Bird with a power bulge hood that I opened up. It vents hot air from under the hood and the car runs really cool.

 

Fix your fans to run as they are intended. Then if it's boiling over, start worrying.

Don't vent through your hood. It works against the air dam.

 

^ How so? Just releases under hood pressure and should actually make air dam work better. Or are you thinking of a forward facing scoop maybe?

http://www.goingfaster.com/1986TA/otherp9.jpg

 

The air dam uses the low pressure air after it to pull air up and over/through the radiator. Putting holes in the top of the engine bay by venting through the hood, power bulge or whatever will wreck how the air flows under the motor.