interstate driving = overheating?

[zz3guy]

I have a gearhead friend with a problem we can't seem to solve. It's overheating when driving down the interstate at 70mph even on cool days.

It's a 40 Ford street rod. He has a Pontiac 400 engine, Quadrajet carb, 350 turbo, "highway" 3.08 gears, aluminum Griffin radiator. This car has been dead nuts reliable since getting it on the road 2 years ago & it doesn't overheat in traffic & runs cool (190-195) on the highway at 55mph. But hit 70 on the interstate & she keeps getting hotter until he has to either pull over & shut her off or hit a highway to keep the speeds down. Any ideas? I heard timing would have an effect on it but I'm sure from driving it that the timing can't be off by much because it runs great & never pings or detonates. It also starts & shuts off just fine too. My pal is at his wit's end on this one & so am I. Anyone on here had a similar problem?:question:

[camcojb]

does he have any pulleys that speed up or slow down his water pump? What water pump is he using?

Jody

[zz3guy]

does he have any pulleys that speed up or slow down his water pump? What water pump is he using?

Jody

He's one of those guys who likes stuff easy to work on & get parts for. He pulled everything - motor, accessories, water pump, pulleys, etc out of a Trans Am he had & put it in the 40. The Trans Am was his car & was a driver but got in some fender benders & was in pretty shoddy shape visually & the interior was shot. I asked him about driving the Trans Am before he removed the motor & he said it ran & performed flawlessly & never got hot - verified by the autometer guage he had in it at the time. Nothing is underdriven so I don't know what it could be. The water pump is a stock unit I'm sure since the motor is still original internally.

[Payton King]

The radiator had gone bad. He may not have enough rad or it may have gotten clogged.

[race-rodz]

make sure the plate behind the waterpump is installed correctly, and the right plate for the waterpump. its a pontiac thing so i have been told.

[andrewmp6]

flush the coolant system replace the thermostat if that dont fix it its something stupid probably.

[clill]

What does he have for a fan ? Is it electric ? It might be a case of the electric fan actually restricting air at that high speed. I had that problem and switched the fan off at high speed and the car ran cooler.

[zz3guy]

flush the coolant system replace the thermostat if that dont fix it its something stupid probably.

I appreciate the help guys. I'm going over there today to do a little "bench racing". I'll tell him about the plate behind the waterpump. As for the fan, he doesn't run it on the interstate, but on or off doesn't help when going 70mph. We are going to the Somerset cruise in this coming weekend (2.5hr drive) so I guess he will have to make do driving his sick 69 Camaro RS/SS convertible. He's got it rough. :lol:

[Pdale]

My dad had this problem with his El Camino when he put the lumina front end on it. It wouldn't get enough air at highway speed. Even with duel high flow fans. The front end deflected the air over and under the radiator. He was able to get a deflector that goes under the car right behind the radiator and it deflects the air up at the radiator. So maybe not enough flow through the radiator?