Radiator pressure relief valve vs expansion tank?

[AnthonyG]

Guys, I am deciding whether to go with the pressure relief valve from George " Skip" Haney or the 2 pint Stainless expansion tank available at a # of suppliers.What do you think?

[40cpe]

IF, IF, you have heard from Brassworks and there is no pressure device in the overflow fitting on your tank, consider a Skip pressure valve that dumps into an expansion tank. If Skips valve normally passes water through and pulls air back as the coolant cools down, the water from the tank will be drawn back into the radiator. That is how the modern systems work.

[AnthonyG]

40cpe, Brass Works indicated it was a non pressure radiator. I called today to find out what pressure it could safely withstand if I put a check valve in the system as you indicateand I like the idea of both the valve and an expansion tank. Unfortunately their off for some reason today. Skips relief valve is 3lb, I'd like to go a bit higher than that, 5,6,or 7 lbs and am sure I can but want to know how high as a margin of safety I can go without damaging the radiator. Left a message and EM at The Brass Works and will find out tomorrow probably.
Thx

[40cpe]

How can you pressurize it more than 3 lbs with the overflow where it is? It seems as if the present overflow would have to be sealed off and another installed a fill neck that will accept a pressure cap.

[AnthonyG]

40cpe, first let me say I know I screwed up when ordering the radiator. I told Brass Works I had a 200hp engine I needed to cool along with the rest of the parameters, unfortunately assuming he would build a pressurized setup due to the HP but still looked stock.
Now I do have the cooling system working with a shroud even though I have a small 4 blade fan due to clearance ( another story another thread ) but the weather isn't hot yet and I'd like not to run low on coolant due to the sudden expulsion syndrome and am thinking some pressure would help. I like GM's suggestion on Skips relief valve and yours combining it with expansion tank. To answer your question, "How can you pressurize it more than 3 lbs with the overflow where it is?" I thought I'd research to find a pressure check valve in at a little higher pressure. Also I remember having a '62 Vette which had an expansion tank with a pressure relief cap on the tank and was hard plumbed from the radiator to the expansion tank. Either the expansion tank held it or in an emergency if the water exceeded the pressure it let go at the tank cap.
Probably belt and suspenders but that's me.

[G.M.]

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Pressure is a result of hot water, the hotter it gets the higher the pressure. At 210 degrees you have a little less than 3 lbs. In my opinion if the water temp gets over 210 in a flathead your in trouble. Skips valve won't allow water to come back into the tank it is a one way valve. You can put a hose off the bottom of the 3 lb valve into any plastic bottle and recover any water lost but below 210 there should be no water lose. water recovered by this method would be manually dumped back. If there is water lose below 210 it is from a compression leak pressurizing the system and the valve opens to protect the radiator, etc. You can put your existing over flow hose in a bottle down at the bottom cut on an angle with the bottle vented. Any water going into the bottle will suck back into the radiator as the temperature cools below 155 degrees. But you will not be forcing the water through the radiator tube and will run low on coolant in the top tank. Try the $25.00 valve and go from there. G.M.

[jake197000]

those corvette tanks were basically just an extention of the radiator tank. there was no place to put the rad cap on the radiator as the hood came down on top of the radiator. a lot of ford fe engines had a expansion tank that worked the same way.it just puked it out if it got too hot.

[AnthonyG]

Found out from Brass Works that the tan was tested to 20 lbs, ordered the pressure relief valve but will add pressure relief cap at 7 lbs in case Skips sticks. Again I'm a belt and suspenders type and believe Murphy hides at my house.
Thx guys!

[donald1950]

if you use a 7# cap then teh 3# valve is really irelevent as the cap yoill not release untill 7# pf preasure. if you are going to use the cap, i would recomend going tp NAPA and getting an plastic overflow tank and installing that, then anything that gets past the cap when hot wil be drawn back into the rad when it cools down... if you do the tank make sure the fitting at the bottom of the tank is drilled through. have purchased several that were not drilled.....

[FL&WVMIKE]

If you use Skip's overflow valve, make SURE that you take it off, ever so often, and clean it !
If you have any dirt, rust. etc., at all, in your system, it WILL make it's way into the valve and plug it up. You will then have a totally closed system. I KNOW !
MIKE (mikeburch)

[blucar]

Weather to use a pressure cap, or not use a pressure cap on an old car radiator depends on a lot of factors.. For stators, the majority of the old radiators do not have a neck that will seat a pressure cap, secondly a vast majority of the old water pumps were never designed to hold much pressure..
I have used 7# or higher pressure caps on every 1958 and later vehicle I have owned since the early 1960's. I have also used coolant recovery tanks, in several forms, since the mid '60's.
Generally speaking a pressure cap will raise the boiling point of coolant/water three degrees per pound of pressure.
Air entrainment and coolant expansion can cause a loss of coolant, a recovery tank solves this problem, catching the coolant as it expands, and allowing the coolant to return to the cooling system without sucking air into the system.
From my point of view, if the radiator does not have a provision in the neck of the tank for the pressure cap to seat onto, then there is no need for a pressure cap.
The addition of a valve in the overflow line could be a solution, however, not if the valve is designed to be one way only.
A cap with a good seal to the tank opening will allow the expanded coolant to enter the overflow and the expansion tank. When the engine cools, the coolant will be drawn back into engine, in lieu of being discharged onto the ground..
Like AnthonyG said, "i'm a belt and suspenders type of a guy", however, I married Murphy..

[40cpe]

The problem as I see it in anthony's case: even IF the neck is compatible with a pressure cap, he does not have an overflow tube from the filler neck. As long as the 3# valve functions, a pressure cap will only act as a cap. If the 3# valve clogs or sticks, then pressure released by the pressure cap will have nowhere to go since the cap is sealed at the top surface lip.

GM said the 3# valve is a one-way valve. It seems to me if the valve doesn't breath air as the radiator cools, the radiator will be in a vacuum after it expels coolant and cools down again. If it does breathe air on cool-down, it should allow coolant from a recovery tank to re-enter. GM please explain to me.

Thanks.

[FlatheadTed]

I think 40Cp and Blue car nailed it ! I run a simple unpressurised over flow tank and it surprising how the water now stays in the system .I run a shroud so the temp stays always below 195 .Ted