66 GTO 455 overheating

[thor7726]

Hey Guys,

I put my freshly rebuilt 1970 455 with quadrajet 7040268 in my 66 GTO and at idle or traffic driving it slowly heats up until and will overheat in a few minutes.  Driving down the road it runs great at 180-200.  Here is what I got and have checked:

A.) no 64' 87cc heads
B.) 9.7 compression Ratio
C.) 93 octane
D.) High cylinder deck to piston quench at 0.018"
E.) Bored 0.03" over
F.) Ram air 4 cam
G.) 4 speed


1.) Water pump replaced and with baffle close to impeller.
2.) 66 4 core radiator, tested good for flow and pressure.
3.) 66 declutching fan with half in half out of shroud.
4.) New belts that are not slipping.
5.) Tried both 180F and 160F thermostat new
6.) New hoses with inner springs to keep from collapsing.
7.) 66 'pan cake' air filter.  (Probably restrictive)
8.) 2" duals (Restrictive)

After all of this could it be the carb is out of tune and causing it to run hot?  Sorry for the long post but I wanted to show that I've been through most of the obvious with the cooling system and now wondering if its the carb running lean or rich and what to do about it.  Its my first Quadrajet and I got my parts from Cliff and I have barley touched the carb and it runs great, idles, responsive, etc  Super impressed with the parts! 

Thanks,
Pete

[Jeffs68]

What is your initial timing set at? Vacuum advance hooked up to manifold vacuum, vacuum switch or to the carb somewhere?

Unlikely your carb is the overheating issue.

Even if the fan clutch is new, I've seen out of the box units faulty.

Not sure about the Goats, but are all the filler panels around the shroud in place?

When you say overheating, what is the temperature rising to?

Not uncommon for Pontiacs to run 220-230 in traffic/idling.

[Hillbillyenginering]

I have friend at work who's 70 gto, 400 12/1 comp. Was overheating. Tried everything. New radiator, 160 stat, fan clutch, high flow water pump. Ended up being a bad distributor. Put in an OK aftermarket for China. And no more over heating.
The dyno guy said to run 91 octane pump gas. Open up the jets a little and let the corn help cool it.
Seems to have fixed it

[Spudboy]

   Like what jeffs68 said, what do consider overheating? Sounds like my 70 Judge. Will run 180 going down the road but will run anywhere between 200 to 220 in town, depending on the outside temps. And I've been down the same checklist of
fixes you have. I make it a point to ask other Pontiac owners about the temps their cars run. Rarely, do I find a Pontiac that will run under 200 all the time. 

[qjetsrule]

I read a good article which addressed this exact problem, everything was right with the car but same symptoms. I believe it was a GTO also. The fix was a smaller water pump pulley which circulated more water in traffic. Good luck.

[Jeffs68]

For what it's worth, and i'm not sure about the goat, but the idiot light on my Firebird won't come ON until 242 degrees, that's the spec if I remember correctly.

[thor7726]

I pulled a spark plug and it looked great.  I don't think its running lean or that the carb is causing the overheating issue.  I put my dad' 65 radiator and declutching fan in that his car runs a steady 180 and it didn't fix mine.  The 455 must just need that much more of a cooling system.  I ordered a 4-core Desert Cooler Aluminum radiator to see if that helps.  The flow of the water pump seems to be pretty good when I took the cap off to take a peak before it pressurized.  The engine compartment just gets so hot at 220F...  Thanks for all the help, I'll keep you guys posted.

[Jeffs68]

220 degrees  on a fresh built motor, I don't think you're gonna get much better on that 455.

[77cruiser]

What are your timing specs initial, mechanical & vacuum?

[tayto]

The engine compartment just gets so hot at 220F...  Thanks for all the help, I'll keep you guys posted.

Get something to shut coolant flow off to the heater core then. I've seen guys run a ball valve and shut off flow during warmer weather (extremely low tech). I would opt for a vacuum actuated valve myself, like GM used to shut off coolant flow to the heater core when AC was turned on. I'm sure you could source a 12v solenoid vacuum valve that could be run in parallel with the fan control switch which would allow vacuum to flow to a coolant bypass valve. AC controls of your era are generally a lot different than non-AC controls so it might not be as easy to adapter year correct equipment...

[Jeffs68]

Get something to shut coolant flow off to the heater core then. I've seen guys run a ball valve and shut off flow during warmer weather (extremely low tech). I would opt for a vacuum actuated valve myself, like GM used to shut off coolant flow to the heater core when AC was turned on. I'm sure you could source a 12v solenoid vacuum valve that could be run in parallel with the fan control switch which would allow vacuum to flow to a coolant bypass valve. AC controls of your era are generally a lot different than non-AC controls so it might not be as easy to adapter year correct equipment...

Your fix would only remedy the in car temps, he is talking about underhood temps.

[429bbf]

not a gto guy but i do know a little about cooling and cooling systems . heres a ruff  breakdown . 30plus percent is done by the radiator , 30plus is done by the exhaust and 30plus is thermal . give or take we can argue this all day . heres what I'm getting at . when you stop or drive real slow you just lost about 30 percent of your cooling from thermal you've actually even got worse because the heat from the rad. now has no where to go. so id say on a hot day in slow traffic it might run as hot as 230 with a good cap . you might try putting in straight water , you loose o lot of cooling from a 50-50 mix. fwiw

[tayto]

Your fix would only remedy the in car temps, he is talking about underhood temps.

My bad, I mis-read that the interior gets hot.

[Hillbillyenginering]

429bbf.
I don't want to sound like I am splitting hairs. But  the Brits and euro's diviude out energy created/used by 33.?% exhaust, 33.?% thermal from heat loss, and 33.?% useable energy through drive train.
They way you have it. The engine couldn't run.?
I know. I sound like a loose sphincter muscle. Sorry!

[429bbf]

you must be an engineer . im trying to keep it simple for folks on here like me. example . some folks don't understand that if you put 6 coats of paint on an engine you will loose part of your cooling ability. if you have a heavy antifreeze mix you loose cooling ability.if you move the coolant to fast threw a radiator it will not cool at all . lets keep it simple.