Thread: Big Block Chevy Overheating

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Hi to all , I am a new member. I have a 1967 Chevelle SS. I am on year 5 on a full frame off restoration and almost finished.
Engine is a .030 over 454 , with a Comp Thumper , roller cam and roller rockers too , with a 510/510 lift . Using large oval port heads , Edelbrock Performer intake with a 750 Quick Fuel Carb and a Quick Fuel manual fuel pump. Headman Headers , a 700R4 Transmission and the stock 12 bolt rear ( 3:73 ) posi. Also have a Eddie Motorsports Serpentine Belt System that came with the Alt , Water Pump , A/C Compressor and Power Steering Pump. For cooling I have a new Aluminum , Dual Flow Radiator with 2 - 15" Spal Electric Fans.
And yes my problem is , it is overheating ! Only have about 3 hours running time on the engine and about 25 miles on the odometer. I have been working on this overheating problem for about 4 months ! I have tried everything. I trust the engine builder. He has been build performance engines for over 40 years. In fact his father used to build engines for NASCAR !!
Per the engine builder my base timing is set at 15 before TDC. I have been told I can go even higher , as much as 25 but I have not tried that.
I am wondering if it could be running very lean and causing it to overheat. Since the first time I ran it it's been doing the same , no matter what I try. After it starts to warm up the thermostat opens and the temp continues to climb. I have ran it at highway speed for a brief time. And managed to stay around 220 but as soon as I slowed foe a traffic light it starts to climb until it gets to around 230 and I shit it down. I am on the 2rd radiator , the first was a exact replacement , a 2 core with 1 1/4" tubes wit 2 fans pulling 2600 CFM's. Also tried with and without a thermostat , tried a different water pump , I even tried a Steward Electric Water Pump in the lower radiator hose to increase water flow , NOTHING SEAMS TO HELP.
Anyone have an idea ??? IMG_0097.jpg

have you verified that the temperature gauge is accurate?
I find one of those lazer temp guns to be very helpful in these situations, but you can even use a meat thermometer.

Secondly, what do you consider "too hot"? Years ago temps of 180 to 190 were average, now 200 and 210 are pretty much normal.

Lastly, what are you using for a thermostat? Not one of those cheapy poppet styles I hope? If so get yourself a good sleeve type thermostat, it can flow more coolant and is far more stable to keep the engine at an even temperature.

I'm not sure why you chose the electric fans but if you still have the parts, go back to the engine driven fan with a full shroud over the radiator to maximize airflow across the radiator core. The electric fans place the same load on the motor through the alternator so there is no real gain in horsepower. Electric fans work okay when there is no room for an engine driven fan.

I'm not familiar with your cam or the rest of your build so I'll stop here for now. Others will be along and offer more advice. It's nice to see you here too!

Get a mechanical fan and a good fitting shroud.

Verify you have the correct water pump.
Serpentine pumps generally spin opposite of a V - belt
due to the belt route.
There are water pumps that are made to spin in the conventional direction internally when used in a serpentine system.

Verify the fans PULL air through from the rad towards the motor, and they are NOT pushing toward the front of the
car. The hot air will just hang around and not get evacuated.

Take out a few sparkplugs & see if they are fouled in some way.

Basic but a lot of times overlooked --
Verify the cooling system is burped of air bubbles that may be trapped.

I don't know if 2600 cfm is enough for a Big Block.
Or is that 2600 EACH?
Anyone have any thought on cfm for those fans on a Big Block?

Thanks for the reply's. Everything you guys have ask , I have already tried. I been installed a Steward Electric Pump in the lower radiator hose ( $425 ) and it did increase the flow but the engine still overheats. I have now replaced the new radiator with another new one. This one is a dual flow with 2 - 1500 CFM fans with a total of 3000 CFM's. I'm on the 2rd manual temp gauge and I also have a heat gun to check it. And yes the fans pull air thru the radiator.
I have the car at a shop installing the headliner and rear package deck. I should get it back today.
Now it will be complete and after 5 years I still can't drive it. Understand the only original metal is the roof and the doors
It spent 11/2 years on a rotisorie , every nut and bolt is new.

Who assembled the motor? Was it you? If so, are you positive on the headgaskets? All the holes lined up? The possibility of steam holes blocked off? Just thinking out loud here.

Also, have you tried backing down the timing to say, 10 BTDC and then drive it around?

And then have you pulled the plugs and "read" them? What colors were you seeing? Are they all the same?

Few things---------

If it heats up when you slow down you either don't have enough air flow or water flow-----in your case its obvious you probably don't have enough airflow

In your pic---------what kind of radiator cap---lbs pressure? and does it let the radiator refill on cool down????? probably lots of air bubbles circulating thru engine when warm-all new vehicles have closed cooling systems where expansion tank is mounted high in system---------

Head gaskets on correct way? if backwards and/or reversed they ll block/restrict passages and effect coolant flow

If it was in my shop--------I would remove all your serpentine system, and electric fans kit and install a normal rotaion, high flow water pump, etc and see how it ran-------- then reinstall your electric fans to prove them------

Make sure your cap is 16-18 lbs, and is for a closed system with an expansion tank mounted high in the system-------

Unlike some others, I have no problem with properly sized electric fans. Set up properly, they will work fine. Most newer cars have electric fans and work fine. I assume yours are pulling - not pushing?

one basic problem with his setup is that the polished, very shiny alum shroud plate that the fans are mounted to is too close to the rad fins for any air flow thru that area----------

another-it looks to me like he has a temp sensor in the LOWER corner of the bottom tank-------at that point the water IS COOLER so the fans won't even be on until it gets HOT down there-----

3000 CFM isn't enough air flow to cool a big block

In the very first picture, top of the page, I believe you can see the thermo-coupler for a mechanical temperature gauge.

I would think this means it's measuring temp right out of the left side cylinder head.

i have run this same set up on 8 different builds and not one ran hot in july with a/c . i do not run shrouds as they restrict flow at speed.

34 40- yes that's the sender for a mech guage-------not a temp controller for relays to operate electric fans------

Shine--your pic shows a cross flow rad which has a longer travel for the coolant in the fins/tubes--------his rad is a vertical unit with long top/bottom tanks and a very short tube length for cooling-his radiator does have a SHINT top tank tho----

yep at the price i cant beat them. i have used the syclone fan on a vertical flow also. if there is room i run the summit oem 5 blade fan. have that setup on the 56 chevy.
is your a/c condenser right against the rad ?

Are you absolutely sure your timing mark is correct on your balancer? I would verify it so as to eliminate a timing issue.

Well I installed the new radiator on Saturday and drove it to the Interior shop to have the headliner installed. It seamed to get hot on the way over even tho it was onlt about 4 miles. I brought it back home today and found one of the wires for the 2rd fan had pulled out of its connector. So I repaired the wire and went for a ride.
I can't believe it !!!!! It cools !!!! The temp gets to about 190 and the second fan comes on and it goes right down to about 175 !!! I ran it for 45 minutes and it's GREAT !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Finally after playing with it for 4 months , it turned out to be the first radiator I bought was not doing the job !
This one I had custom made for me. It is a DUAL FLOW with 2" tubes , yes 1 Row of 2" tubes and it's a cross flow opposed to a down flow. A little different because the top and bottom hose's come out the pass side , so I had the get a different thermostat housing. It is also about 4" wider than the other radiator. The only thing I don't like is the auto trans cooler lines are both on the drivers side.. A little hard to route the hoses and you can see them when you look at the radiator. I'm ok as long as it cools !!!!!
I'll go out and take a picture and post it.