428 Overheating

[MK32713]

I have a 69 428 stroker/455 crank Dport heads, 4 speed m-21....in a 67 firerbird convertible...its a ground up restoration ...just cant get it to run cool...always 220 or higher especially if I step in it...I have a 4 core alum rad...elec fans...checked the water pump..timing etc...any suggestions...im told maybe a block restriction?....giving up hope...lol...may just bite the bullet and drop an LS.....anybody have any ideas....

[Dan 71GP]

Sweet Car!  Off the top of my head i would of mentioned timing but since you have already checked that, gotta ask the basic, have you tried changing your thermostat? Ive seen brand new ones stick and restrict and its a cheap thing to try.  I have also seen restrictions come from intake gaskets with  blocked off ports.  

[TWO LANE BLACK TOP]

Nice car

A lot of reman Pontiac waterpumps...Have too much clearance between the impeller and the walls of the waterpump itself...Also between the impeller and the divider plate ..Or possibly both....Have seen it quite a few times over the years especially on Oldsmobiles and Pontiacs...Can cause the water to cavitate inside of the pump instead of consitantly pushing water thru the cooling system through the whole RPM range....Might look like the water is flowing good at idle...Doesn't  mean that it is pushing enough water volume fast enough to get a real good transfer of heat from the block...Might be something to take a real close hard look at......

One other thing changing the pulley size to try to speed up the pump really won't do any good...As the impeller clearance issues themselves will not allow the pump to have the pressure,volume and speed of water flow in gallons per minute that it is supposed to...No matter how fast you turn it

Edited August 13, 2018 by TWO LANE BLACK TOP

[Frosty]

If a regular (e.g. properly working) water pump doesn't work, have you considered using an electric water pump? Two Lane is spot on that water volume is the key here.  Also I run a wide mouth thermostat from Mr Gasket to help increase the water flow there too.  You mention that you are running electric fans. Are the fans properly shrouded or open (pictures would help here)? If they are open, they should be shrouded similarly to the way the factory fan was. What temp are the fans set to come on? Do you notice any difference when the fans come on?

Does your car have a catch reservoir for the coolant or does it just spray on the ground like it did from the factory, and then you have to add coolant from time to time? I run a medium size catch can that I got from Speedway for around $35. That helps keep the coolant off the ground and in the car.

Another thing that helps insures my 462 (455 .030 over) stays cool is to make sure the engine has the proper level of oil. I noticed my water temps go up when my oil level starts getting low. 

[JoePentium]

You want just enough clearance between the divider plate on the pump and the impellor for it to turn.

mine is less than  1/16" water goes through not around!

[KANE47]

Beautiful car! Did you get this issue resolved?