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?

[MarkM66]

Maybe the pulley on the wp is to small, causing the wp to spin to fast, thus causing cavitation.

[Chris442]

Is there a spring in the lower radiator hose to keep it from collapsing?

Sometimes the high RPM makes the WP pull enough vacuum in that hose to collapse it and stop the flow. Otherwise there is over course tuning issues A/F too lean too much time (it'd have to be a lot).

My car is set up similarly, except with Olds power, 455 Olds, 400 turbo, Edelbrock carb, 3.08 gears, Be Cool radiator, but in a '69 442. Since I live in Phoenix, I went through every possible cooling system fix to make it run cool. I've got the spring in mine, but I don't know if it was ever a problem without. I just figured better safe than sorry,

[astroracer]

What kind of shroud is he running? What type of fan? What is the distance from the fan to the radiator? Is the front of the radiator sealed to the sheet metal so no air can escape around the radiator at high speed?
Just a few things that need to be known to answer this question...
Mark

[Tom Welch]

I had a similar problem wit my 78 T/A. I installed a larger radiator, a new fan clutch and a new thermostat (160). That fixed it for me.

[LS6 Tommy]

What kind of shroud is he running? What type of fan? What is the distance from the fan to the radiator? Is the front of the radiator sealed to the sheet metal so no air can escape around the radiator at high speed?
Just a few things that need to be known to answer this question...
Mark

X2. If it's a flex fan, ditch it for a clutch fan. Flex fans (or siezed clutch fans) actually restrict airflow at highway speeds.

Tommy

[zz3guy]

What kind of shroud is he running? What type of fan? What is the distance from the fan to the radiator? Is the front of the radiator sealed to the sheet metal so no air can escape around the radiator at high speed?
Just a few things that need to be known to answer this question...
Mark

He has the front end sealed off completely to the radiator. He bent up some sheet metal & it is directing all the air from the grille to the radiator. There isn't much room between the radiator & engine. The electric fan is mounted directly to the radiator (it's a 16" spal unit).

[73ta]

Pontiac water pumps come in two styles, one with cast vanes and one with sheetmetal vanes. Cast is reported to be better. There is a devider plate sandwiched between the two gaskets. Because of the differences on rebuilt and new pumps the clearance between the pump vanes and the plate vary wildly. Mine had almot a 1/4" clearance. The plate needs to be massaged down to leave a smaller clearance, set mine at about 0.040". This will increase water flow, reducing temp. There is a huge thread on the PY board about it and Pontiac overheating problems.

[Chad-1stGen]

Well normally,

overheating at highspeeds = coolant flow.
overheating at lowspeeds = airflow.

Looking at the lower rad hose for spring inside and the waterpump pulley size are good ideas. Also, check the condition of the radiator and make sure it is not clogged in anyway. It might also be worth either replacing the waterpump or disasembling it to verify the impellar is in ok shape.

[My427stang]

Listen to Chad, he has it right.

I'd guess lower hose issue, or bad pump.

Only other thing I'd look is if he has something goofy with the timing and its extremely retarded at highway cruise speeds, but it would be a longshot.

[ProdigyCustoms]

Chad is exactly correct. Driving on the highway, the air be pushed through the radiator as the car pushes through the air is far greater then the fan can pull. In fact you can often turn off electric fans at speed. However, the engine is turning more RPMs, and generating more heat then at slower cruise and sitting. I would absolutly be checking timing and air fuel, make sure your not WAY lean or WAY fat. I would also look at moving the water to fast through the radiator. Most people never think about moving TOO MUCH water, but moving the water through the radiator too fast limits the radiator ability to do it's job, which is cool the water.

[zz3guy]

thanks for the ideas. I'm going to print this all out & take it to him tomorrow or Tuesday. He has a 69 RS/SS convertible to hit the interstate with, so he can just hit the backroads in his 40 streetrod until he fixes his cooling problem.

Thanks!
Clint

[Bad94]

We have a customer with a 48 Chevy street rod with a 454 and he is having the same problem, i had it out friday for 2 hours on the highway and city and never over heated on me, then when he drove it home and to a show the next day, he called and said it got hot.


He told me that at goodguys the gauge went to 250, but it never lost anywater , So at the NSRA Nats, im going to cruise the car on the hottest part of the day, and see what it does.


Im thinking its the gauge or sender, cause the gauge will jump around sometimes.

[NOT A TA]

73 TA is correct about the tolerances in orig. type Pontiac pumps. I stopped using them an went to a Flowkooler pump.

If you decide to try a new pump check out the Flowkooler products. I've been running one on my 400 the past few years. No problems around town, on highways, or at drag, road, or top speed tracks with rears ranging from 2.72-3.73 and 26" tires.

http://flowkooler.com/home.php

The flowkooler mounting flange bolt areas are a bit thicker than stock so some minor clearancing for accessory brackets might be necessary.

John

[Dave@RACEWARE]

We had a customer puchase a cooling system from us for a 38 Ford with a 351C. The car would run 220 in traffic and when you got on it the temp gauge looked like the tach. He installed the cooling system including an Edelbrook pump and it did knock out 20 degrees but was still undrivable at highway speeds. I finally convined him to bring us the car. He drove it in the shop and choked everone to death with what seemed like a dead rich condition. We took off the air cleaner and the motor changed pitch. Next step was to pull plugs only to find them to be bone white. To make a long story short we ended up going up 14 jet sizes in the primarys and knocked 60 degrees of temperture out of the motor. Because of a clogged air cleaner to owner kept take jet out of the carb compounding his heating problem.