409/409

I have a 427/390 bored 30 over, 454 crank 10-2 compression, mild comp cam. It has a new correct radiator, new 15# radiator cap, new 180 thermostat and a new fan clutch. The temperature gauge reads from the first hash mark to a hair over 210 degrees. It has about 350 miles on it and whenever I shut it off it spits coolant from the overflow. Does anyone have any ideas how to remedy this?

Thanks

66jack

Dont know if the big block has the overflow tank, but if it does...are you filling to the top or half way...

Powershift

1. How much air gap (free air space) do you have in the top section of the radiator when it is cold?? It should be marked on the radiator, but probably need at least 1-1/2 inches.

2. Have you tested the radiator cap for proper pressure relief?? They are not always correct…….especially the reproduction ones.

3. Suggest using an IR gun to verify the engine coolant temperature.

4 Are you running 50-60 percent glycol in the coolant? Need at least 50%.

Larry

JohnZ

Do you "top off" the radiator after it "spits"? The radiator needs to provide space for coolant expansion, especially during heat-soak after shutdown, which is why the coolant full line stamped into the radiator side tank is several inches below the filler neck. If you stop topping it off, it'll stop spitting once it reaches its "happy level". Have you used an I.R. gun to verify the accuracy (or lack thereof) of the temp gauge so you know what the gauge is telling you?

You might read this so you understand how your Corvette cooling system works and how to diagnose it:

dugsgms74

Dont know exactly how your year is configured but on my 390hp 427 in my 68 there is no overflow. Like others have said, if you fill it to the top it will puke out until it finds its "happy level", only problem with that is it will have "head space" in the radiator after it pukes out what it doesn't want and that head space can lead to corrosion in the system. I added a catch tank and now after a shut down it will puke what it doesn't want into the catch tank and suck it back in when it cools. Its ugly and not NCRS friendly but it works, keeps the sealed part of the system completely filled all the time and the coolant off the floor.

65silververt

Some of the reproduction radiator caps suck. I recently had this problem in a 427 car with a new Dewitt's radiator. It was not overfilled, but would puke coolant regardless and it's max temp was 190. Changed crappy reproduction cap and problem resolved.

409/409

Can the aluminum reservoir from a small block be used as a "catch can" and if so, how would the radiator retrieve coolant if it has a pressure cap???

dugsgms74

I dont know, arent the inlet tubes on those kind of large? Youd need something that has the same size inlet tube as the overflow nipple on the radiator and pulls from the bottom of the tank either with a bottom inlet or a dip tube. I suppose you could modify a SB reservoir and somehow disable the cap on it so it no longer sealed. Also, keep in mind you need a tank thats large enough to hold the full amount puked out w/o overfilling and spilling out, I think mine will puke out nearly a quart on a hot day, will nearly fill the tank when hot and just about sucks it dry when it cools.

65silververt

Sure you can! That is precisely the set up the 1967 L88 427 cars used. Just buy the t-fitting, straps, hoses, etc. and you will be good to go. However, it shouldnt be necessary if you have everything set up properly!

65silververt

Just run the same pressure cap on the radiator and fill tank and you should be fine.

Powershift

The 1967 L-88 cars used an aluminum stacked radiator similar in design to the small block cars. They did not use brass/copper radiators like the other BB cars. Therefore the aluminum expansion tank was an integral part of this L-88 cooling system and is not available for a separate overflow tank.

http://www.dewitts.com/collections/c...ation-radiator

Larry

65silververt

Yes, I realize that, but you can still set up the BB radiator the same way.

409/409

I let it puke out until it reached the "happy level" and I measured about 7" below the top. That seems awful low. The radiator has a "fill cold" on the tank but I can't see where it is because the fan shroud covers it. Does anyone know how low the "fill cold" mark is??? Thanks

PAmotorman

the original BB engine corvette with a side tank rad had it marked on the tank "coolant level" about 3" down from the top