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I’m looking for an aluminum radiator for my restomod 496 build with a fill cap. I’d like to simplify the system and save space in the engine bay eliminating the expansion tank.
1970 factory A/C big block car. Aluminum heads, higher flowing water pump, large electric fans…should be sufficient to cool the system without the tank.
A couple years ago I purchased a Cold Case unit but purchased the small block unit for the fill cap. The lower hose outlet of this rad contacts the frame horns and sway bar thus cannot be used.
All big block radiators I’ve researched for this year do not have a fill cap on the radiator.
It would have made the bean counters happy not to have one...
There's a reason GM did an overflow tank-
It's to get the air out of the system- as the radiator cap is lower than the engine.
If you are going custom- there are some great looking overflow tanks- this one is a Canton-
Also I noticed that won’t fit. It stops at the 68 and the location of the lower rad hose outlet will interfere with the frame horns. The lower rad hose outlet is in the same location on the radiator tank (all the way at the bottom) as the small block units; which does not fit.
Agreed. But small blocks managed to omit the expansion tank…I was under the impression GM needed extra capacity to cool the larger motor/HP.
Plan was to purge air elsewhere. I know several big block cars have full custom setups and eliminated the expansion tank.
Originally Posted by Richard454
It would have made the bean counters happy not to have one...
There's a reason GM did an overflow tank-
It's to get the air out of the system- as the radiator cap is lower than the engine.
If you are going custom- there are some great looking overflow tanks- this one is a Canton-
I remember being upset near the end of the year, having paid full price, when immediately thereafter deWitts had a pretty good sale. Was a while ago but you might check.
I did find a Dewitt’s unit (part 32-1139073M) which seems to fit the bill and actually clear my frame horns. Admittedly, I was trying to avoid an $800 radiator for a rather run of the mill 600hp 496 build.
Originally Posted by Richard454
Oh- it get it-
then why not do something like this. I try to go with the form and function thingy-
It is doable. The hot expanding fluid needs to go somewhere without splitting the radiator, and return when cold.
The pressure is controlled with the radiator cap.
Systems with radiator caps on the rad, almost always have an air pocket / fill line at the top of the rad, to allow the expanding fluid to rise into. The air pocket compresses very easily without raising the psi dramatically.
The issue with C3s, as I see it, is there are parts of the engine (heads) where the cooling jackets are higher than the rad cap / liquid level. This would allow air pockets to accumulate in the highest point in the system, the heads, and could lead to cracking.
BBs are roughly 1" higher than a SBC, so this issue is exaggerated.
This issue is dodged if the coolant system is run completely full. But the expanding fluid still has to go somewhere, so it will exit the rad cap hose on the rad.
The modern way around this is to have a non-pressurized coolant overflow tank. Technically this does not have to be higher than the rad cap.
The C3 BBCs used a pressurized overflow tank, with a fill line and an air pocket in it. Most modern cars do not do this. But it allows the "water level" in the tank to be the high point. My CTS runs a partially flooded & pressurized fill tank, with rad cap, at the high point in the system, by the windshield wipers. The fill line is at the intake manifold level. You could do it that way also.
You could run a rad cap on the radiator, as long as you run a fully flooded system, and run a non-pressurized overflow tank, and that could be located almost anywhere and be easily hidden. The issue then becomes how to purge all the air out of the system while filling it, if the cap is not the high point? That could prove to be very difficult unless you put a screw cap type fitting at the high point, just to purge this air, just during system fill. A small fitting even, in a hose or in the raised style rad outlet? But only run one rad cap. The last air bubbles re usually trapped in the rad core tubes, so running the engine, after the thermostat opens, at 2000 rpm, flushes these bubbles out and they go right out the open cap. It would be more challenging to get them out of a open fitting in a hose, but it could be done.
These cheap fill funnels make purging the last bit of air out very easy. You can just watch the amount of bubbles. But in your case it would have to be on the hose high point fitting, not the rad.
You would never be able to get the rad cap on fast enough to use it there!
In your case you may also want to investigate a "vacuum fill".
Many ways to skin this cat!
Last edited by leigh1322; Nov 7, 2024 at 02:17 PM.
Early C3 BB had no overflow tank. My 68 BB for example never had and also never had any air purging issues. The water pump will pump all air out of the Heads through the water fitting that sits higher on top of the intake. Never heard that the rad must be higher than the engine .
I remember being upset near the end of the year, having paid full price, when immediately thereafter deWitts had a pretty good sale. Was a while ago but you might check.
Excellent points and ideas. I'm wondering if I'm trying too hard to marry form and function; with the emphasis on form.
What about simply raising the front end of the car when filling to put the radiator and fill cap at the high point?
Originally Posted by leigh1322
It is doable. The hot expanding fluid needs to go somewhere without splitting the radiator, and return when cold.
The pressure is controlled with the radiator cap.
Systems with radiator caps on the rad, almost always have an air pocket / fill line at the top of the rad, to allow the expanding fluid to rise into. The air pocket compresses very easily without raising the psi dramatically.
The issue with C3s, as I see it, is there are parts of the engine (heads) where the cooling jackets are higher than the rad cap / liquid level. This would allow air pockets to accumulate in the highest point in the system, the heads, and could lead to cracking.
BBs are roughly 1" higher than a SBC, so this issue is exaggerated.
This issue is dodged if the coolant system is run completely full. But the expanding fluid still has to go somewhere, so it will exit the rad cap hose on the rad.
The modern way around this is to have a non-pressurized coolant overflow tank. Technically this does not have to be higher than the rad cap.
The C3 BBCs used a pressurized overflow tank, with a fill line and an air pocket in it. Most modern cars do not do this. But it allows the "water level" in the tank to be the high point. My CTS runs a partially flooded & pressurized fill tank, with rad cap, at the high point in the system, by the windshield wipers. The fill line is at the intake manifold level. You could do it that way also.
You could run a rad cap on the radiator, as long as you run a fully flooded system, and run a non-pressurized overflow tank, and that could be located almost anywhere and be easily hidden. The issue then becomes how to purge all the air out of the system while filling it, if the cap is not the high point? That could prove to be very difficult unless you put a screw cap type fitting at the high point, just to purge this air, just during system fill. A small fitting even, in a hose or in the raised style rad outlet? But only run one rad cap. The last air bubbles re usually trapped in the rad core tubes, so running the engine, after the thermostat opens, at 2000 rpm, flushes these bubbles out and they go right out the open cap. It would be more challenging to get them out of a open fitting in a hose, but it could be done.
These cheap fill funnels make purging the last bit of air out very easy. You can just watch the amount of bubbles. But in your case it would have to be on the hose high point fitting, not the rad.
You would never be able to get the rad cap on fast enough to use it there!
In your case you may also want to investigate a "vacuum fill".
Went with Dewitts 32-1139073A - found it on a good sale from Holley. If I can't get the system bled with the radiator fill cap I can always plumb in the expansion tank.
Although I was looking forward to selling my expansion tank since they seem to be pretty rare and go for a good penny.
However you do it to burp out all the air is good!
The higher water level provided by the funnel, or even an upside down & bottomless water bottle, raises the water level and helps you to more quickly burp air out.
My full-radiator method:
Warm it up, til the therm opens, rev it up some to purge bubbles out of where-ever. They will eventually stop.
Then rev it one last time, this drops the water level, pull the funnel and slap the rad cap on. Then let it idle.
You can do it without getting hardly any air back in the rad.
(Revving it makes the hoses swell a touch and hold more water). You kind of rev it just enough to hold the water level right at the neck outlet.
The funnel above just spills less and makes less of a mess.
The real trick is not getting burnt with hot coolant.
The funnel even helps with that.
Love it, thanks. I do have access to the tools needed to perform a vacuum fill so I’ll try that avenue first.
Originally Posted by leigh1322
However you do it to burp out all the air is good!
The higher water level provided by the funnel, or even an upside down & bottomless water bottle, raises the water level and helps you to more quickly burp air out.
My full-radiator method:
Warm it up, til the therm opens, rev it up some to purge bubbles out of where-ever. They will eventually stop.
Then rev it one last time, this drops the water level, pull the funnel and slap the rad cap on. Then let it idle.
You can do it without getting hardly any air back in the rad.
(Revving it makes the hoses swell a touch and hold more water). You kind of rev it just enough to hold the water level right at the neck outlet.
The funnel above just spills less and makes less of a mess.
The real trick is not getting burnt with hot coolant.
The funnel even helps with that.
I too have an early 1968 BB Model Corvette and it has NO expansion tank on it. The mounting pad had never been drilled on the passengers side fender well. I use a standard radiator cap but do have a working overflow container that ensures that the radiator stays full. A good solid Overflow tube and tank ensures that the excess coolant gets removed and replaced as the engine needs it. When I fill it I simply use a funnel on the radiator and don't need to do anything special.
In 33 years of ownership I have never had to Burp anything but my kids. My 427 never has had any trapped coolant in it.
I fill the radiator up and put the cap on it and everything else is automatic. Currently I have a Zero pressure Radiator cap to allow the system to run without any pressure build up which helps the hoses and other cooling system parts last longer.
Agree that a full radiator with some type of expansion tank is better than a rad with a fill line, whether that tank is pressurized or unpressurized.
The engine should burp the air out as it runs. Eventually being the key word here.
It may take a few hot / cold cycles though to push the fluid and air in / out a few times.
Some cars are just difficult to purge all the air out of. The bubbles just seem to keep coming, for a long time.
We did have one car at the shop that cracked a head within a day or so of a new engine build. Another shop had installed the engine, and air bubbles in the head were blamed.
Rightly or wrongly I don't know, it was decades ago.
Afterwards we always made sure to burp them well before they left, and advised customers to do the same.
My buddy and I like erring on the side of caution.
Big block radiator with full cap
