New C3 owner
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Cruising
Joined: Jul 2020
Posts: 10
Likes: 3
From: Renton, WA
New C3 owner
Hello,
I've had my 1970 coupe for about a year now and have been doing a few needed updates. It started out as a 350/350 model, but one of the previous owners installed a custom-built 400 small block. I just recently had the radiator rebuilt and am in the process of completing the reinstall. The car did not originally have an expansion tank and I am wondering if I should add this. The car suffered a boil-over after a high-rev take-off from a traffic light. After inspection of the lower hose, I couldn't find any cracks, but decided to replace it anyway due to age. From what I can tell, coolant spewed out the vent tube on filler neck. I did add coolant on a previous occasion thinking that it was low and never had any overheating issues. I have installed a new thermostat housing along with a lower temperature thermostat, 195 to 185 degree. My question is, with the larger engine, should I install an expansion tank?
I've had my 1970 coupe for about a year now and have been doing a few needed updates. It started out as a 350/350 model, but one of the previous owners installed a custom-built 400 small block. I just recently had the radiator rebuilt and am in the process of completing the reinstall. The car did not originally have an expansion tank and I am wondering if I should add this. The car suffered a boil-over after a high-rev take-off from a traffic light. After inspection of the lower hose, I couldn't find any cracks, but decided to replace it anyway due to age. From what I can tell, coolant spewed out the vent tube on filler neck. I did add coolant on a previous occasion thinking that it was low and never had any overheating issues. I have installed a new thermostat housing along with a lower temperature thermostat, 195 to 185 degree. My question is, with the larger engine, should I install an expansion tank?
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The original factory lower hose had a spring in it to prevent high rpm collapse due to water pump suction.
Did you transfer the spring assuming it was original.
Thermostats have specific numbers not ranges.
They typically are 195, 180, and 160.
You should use a 180 thermostat.
The expansion tank is not needed.
Did you transfer the spring assuming it was original.
Thermostats have specific numbers not ranges.
They typically are 195, 180, and 160.
You should use a 180 thermostat.
The expansion tank is not needed.
Last edited by MelWff; Jul 28, 2020 at 06:56 PM.
Burning Brakes
Joined: Jun 2020
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no expansion tank; don't overfill rad.
look inside rad fill, see where cap's rubber seats? fill to about 1" below that circular seat; no more.
The air in the gap is compressible but full fill is not and will puke when hot coolant expands.
If your rad is OE, it should have a fill line stamped into tank near cap; but 1" below seat works as well.
look inside rad fill, see where cap's rubber seats? fill to about 1" below that circular seat; no more.
The air in the gap is compressible but full fill is not and will puke when hot coolant expands.
If your rad is OE, it should have a fill line stamped into tank near cap; but 1" below seat works as well.
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you could add an overflow bottle to capture that fluid when it gets hot again....it will
Melting Slicks
Joined: Oct 2012
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From: Dunedin NZ.
And if you have antifreeze in the coolant it makes a nice mess all over the engine compartment when the fan blows it around.
Anti freeze is sweet tasting and toxic, because of this spilled antifreeze can be appealing to cats and the like to drink with fatal results.
Running an overflow bottle with syphon return to the radiator allows the radiator to be kept completely full, this helps to minimise aeration of the coolant increasing its effectiveness in both cooling and corrosion protection. JMPO plenty of info available on the web if you want to read on the subject. Sure running the radiator with the level down a bit will work but is it the best way to go is up to you.
Drifting
Joined: Nov 2013
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From: Loud, Raw and Dangerous 1968 327 4S in Southern California
I added a fluid visible overflow bottle since my radiator had an overflow tube already. It is nice to see what the fluid level is and not have any leaking out anywhere. Not technically NCRS correct for the car of course but in my case the car is a 68/73/75 model anyway. 
Last edited by Redvette2; Jul 30, 2020 at 01:21 PM. Reason: Meant overflow bottle not expansion tank.
Thread Starter
Cruising
Joined: Jul 2020
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From: Renton, WA
The overflow bottle isn't the same as an expansion tank then? I understand the advantage of using an enclosed system, my '04 Chevy Silverado uses one, as do most modern vehicles. The radiator in my C3 is original and has a "fill to this line" stamped into the body on the left side. I suppose adding an overflow bottle wouldn't hurt and since the car is not OEM anyway with the replacement engine, it wouldn't devalue the car. I'm wondering why there would be a side nozzle on the filler neck designed to vent any over-expansion of coolant.
Burning Brakes
Joined: Jun 2020
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The overflow bottle isn't the same as an expansion tank then? I understand the advantage of using an enclosed system, my '04 Chevy Silverado uses one, as do most modern vehicles. The radiator in my C3 is original and has a "fill to this line" stamped into the body on the left side. I suppose adding an overflow bottle wouldn't hurt and since the car is not OEM anyway with the replacement engine, it wouldn't devalue the car. I'm wondering why there would be a side nozzle on the filler neck designed to vent any over-expansion of coolant.
Sure you can fit a plastic recovery jug from a later model etc and plumb it to that "nozzle." Many OE recovery jug also have vent hose that'll dump on ground if it overheats badly . IMO it's a nice improvement and you can fill rad up to the seat And fill the jug about halfway or most have a fill mark. If yours not being judged, I'd do it. Yup, take care of our critters but a little AF ain't gonna stop the world
Last edited by 71chimera; Jul 30, 2020 at 11:55 AM.
Drifting
Joined: Nov 2013
Posts: 1,572
Likes: 486
From: Loud, Raw and Dangerous 1968 327 4S in Southern California
The overflow bottle isn't the same as an expansion tank then? I understand the advantage of using an enclosed system, my '04 Chevy Silverado uses one, as do most modern vehicles. The radiator in my C3 is original and has a "fill to this line" stamped into the body on the left side. I suppose adding an overflow bottle wouldn't hurt and since the car is not OEM anyway with the replacement engine, it wouldn't devalue the car. I'm wondering why there would be a side nozzle on the filler neck designed to vent any over-expansion of coolant.
