rongold

I posted this in the C2 forum, but I know that it also affects early 1968 big block cars built before the design change. This might help some of you with hot running 1968 427's. Check the diameter of your water pump pulley--1st design is about 7", second design is smaller--hard to measure--the pulley is on my car right now. Looks to be at least an inch smaller.
=================================
Hi all,


I have a 67 435HP convertible. As all of the 66 425's & 67 435's do, mine runs hot, and if the weather gets up in the 90's, I won't even drive it. Many years ago, in Vette Vues magazine's "Factory Facts" section, there was a story about hot running 68 427 solid lifter engines, and Chevrolet's try at a cure was in there. It was as follows:


Replace the 1968 1st design large water pump pulley (same diameter as 66-67) with the second design 1968 pulley, which was about 1 or 1 1/2 inches smaller. Swap the 5 blade fan with a 7 blade fan--retain the same clutch. Add all of the shroud and radiator support seals that an air conditioned car uses, add the fan shroud extension, and lastly, make sure that you use an OEM Delco thermostat, as they have a small hole for coolant flow.


Their thinking was to speed up the fan for more air flow, make sure that all the air that enters the grille went through the radiator, and slow down the coolant flow (so the coolant stays in the radiator longer) with a small hole in the thermostat. I did all of this to my car back in 1989 or 1990, while that pulley, fan, and fan shroud extension were all still available from GM. Believe it or not, it partially worked. However, if I get stuck in traffic on an 85-90 degree day, the temp still climbs past 210 degrees and I have to shut it down. It used to be, before this mod, if my temp went up to 210, even if I got moving, the temp would not go down. Now with the mod, the temp DOES go down, but it has not fixed the problem of overheating if I get stuck in traffic.


I even changed the vacuum advance to full time---temp still climbs past 210 in traffic. I am thinking of installing a DeWitt aluminum radiator. I hear that an aluminum radiator might cure my problem, and maybe even enable me to reinstall the large water pump pulley (I've gone through 3 pumps since 1989--bearing & seal failure, evidently due to higher pump RPM). Have any of you 425 & 435 HP guys installed the DeWitt aluminum radiator ??? DOES IT WORK ??? Is the car manageable in traffic ???


Only 1 thing bothers me. I own a service station in N.Y. A while back, a friend of mine brought his 454 Chevelle by for me to check out. He had an aluminum radiator in it. I removed the radiator cap to look inside the radiator, and when I did, some aluminum shavings came off along with the cap--same thing when I reinstalled it. Does this always happen ??? How many times can you pull the cap before the neck wears out ??? Right now, that's the only thing that's holding me up. Any ideas ???




P.S. In 1969, GM just about eliminated the hot running problem. They increased the width of the radiator by 5 inches--Something they should have done many years before.

73'454folendore

Here is what worked for my 454. Mine was running 210-230 in Florida traffic on 95 degree day. I flushed my entire rad. system, installed a new thermostate and radiator cap. changed mixture to 60% water and 40% antifreeze. Then changed the fuel mixture to a richer condition. I was running it too lean. Now with the temp in florida hitting the 100% mark I can tear it up at every stop light for a couple of hours and I never go above 195 degrees. Easy fix and easy to do. It may work for you also. Good luck.

ETM

Thats great.Especially for a big block.

Simmo

I live in the tropics and its ALWAYS in the ninties and here's what Ive done to keep my 70 big block cool. Twin electric fans with shroud off late model full sized car. Edelbrock victor water pump (you need a pump with a cast impeller). AMC triple water pump pulley which is smaller than the Chev big block pulley. Milodon high flow theromstat and 19-21psi cap.

Chin spoiler is important and radiator seals. I dont have vacume advance (vertex mag) but would like to run it if I could.

It is a myth that you want to slow down the flow. Tests constantly show the faster you cycle the water through the engine the cooler it runs.

flynhi

check out a plate by FloKooler riveted to the back of the impeller for higher water flow. Or replace water pump with a new design with a more efficient impeller design.

norvalwilhelm

I run a blown bigblock. I run a 3 inch aluminum rad. I run my water pump 30% faster then the motor. I run twin 16 inch electric fans, I run a little spoiler under the front of the car, this makes a difference.
I run NO thermostat and most of the time on the road the fans can be turned off. I did alot of testing with and without the thermostat and it made a difference running without, much cooler.
My motor sits at about 185 most of the time and creeping to 190 in heavy traffic. I also run a very accurate aftermarket gage along with the stock one.
I have a blue warning light set at 210 and unless I forget to turn the fans on it stop and go traffic it never reaches that temp.

GDaina

Well, Ron, I don't know what to tell you, other than to look at the condition of your radiator....I'm running a 533 inch BB, factory radiator that has a new core...the old core had too many loose cooling fins...check the condition of your rad...in you see any loose cooling fins, time for a new one...

Like Norval, I run around 185-190, but I have a 185 degree stat in mine, and am also running twin 11" Spal fans. I can run in traffic all day long and not climb over 200.

sjr1971

My '71BB ran hot after a motor rebuild. The car sat for 12yrs [no insur] I had replaced the rad back then for big bucks so I KNEW it couldn't be the rad. While replacing the H2O pump, I noticed standing H2O in the rad return with the intake disconnected. Turned out 12 cores were plugged. It runs 185-190*. Stop&Go @ >90* touches 200-205*

bigvette1

There are a whole basket of fixes for this but the common thing seems to be electric fans that move the air. The dual Spals are about 2700cfm. What I would really like to use is the new Flex=O=Lite mod 295 that moves I think 5500 cfm. That should suck the paint off the pavement and make the thing run faster with all the air moving to the back of the car.

rongold

All you C-3 guys have to remember that starting in 1969, the radiator width increased from 22.5 to 27.5 inches. That's over a 20% increase in the size of the radiator core. That makes a BIG difference in cooling system capacity. That was the General's fix.

corvettejay

To Fix The Heating Problem On Your 435 Horse
You Need To Make Sure Your Rad. Is In Good Shape, Not Clogged
And Not Damaged. Then Take Off The Small Hose Thats Runs From The Intake To The Water Pump And Get A Brass Soft Plug That Fits Inside The Hose Snugly Then Drill A 1/4" Hole In It Install It In The Hose And Reinstall The Hose. If Your Timing Is Good And Carb Is Tuned Well You Will Not Have Any More Overheating.