VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 40 Special Deluxe radiator question

I have noticed that my 40 does not have a pressure releiving rad cap.The cap appears to be original, but does not relieve pressure, rather it is solid inside.The rad does have an overflow
tube, so how does this work?
Any help appreciated. Thanks

1940 Chevrolets did not use a pressure radiator cap.

Your radiator is vented to the atmosphere and the overflow pipe allows for expansion overflow of water if the radiator is overfilled or overheated.

An accessory overflow container will allow the radiator to be filled higher in the top tank. The heated water, which expands, is then captured in the container mounted on the firewall via a hose attached from the overflow pipe/vent. It will enable you to add about a quart of water or so to the system. This will prolong the interval/need for refill owing to evaporation. That's about all it will do.

Of course if the accessory system is not perfect, it may cost you points no matter its rarity or otherwise good condition.

Charlie

The instructions for the overflow tank say to NOT fill the radiator any higher than the level it would be filled to with out the tank.
Any overflow would be held in the tank and sucked back into the radiator when cooled.
The filler neck on a 1940 is not designed to accept a pressure cap although one will fit.

In order for the radiator to suck the coolant from the tank back into the radiator you need a closed system rather than one that is vented to atmosphere. A closed system needs a cap that seals on both sides of the radiator vent tube. Without this type of cap the radiator will just suck air back into the radiator when it cools, and the coolant in the tank will just stay in there. As far as I know the only type cap that seals this way is a pressure cap. These have a spring loaded rubber gasket that seals inside the radiator filler tube under the overflow and another rubber gasket that seals on the top of the filler tube above the overflow. The tangs on a pressure cap are a little too wide to fit a 1940 radiator, but the cap will fit and work fine if you just grind a little bit off the sides of the tangs. The '40 radiators are not designed for very high pressure, so you need a low pressure cap. My '40 has the original Harrison radiator and I use a 7 pound cap. With a closed system you need a full radiator plus a small amount in the tank. That way you will never pull air into the radiator. This is the same type system as used on new cars, just without the really high pressure.

From my experiance the conventional cap used as is can be used with a Chevrolet overflow tank and it will draw the water back into the cooling system.

As per Chevrolet's instructions a gasket must be used with a presure cap and was included in the later tank kits for the year cars that came with a pressure cap. The gasket fits into the cap and seals around the outer edge that contacts the rim of the filler neck.

The 1948 chevrolet was the first year to come from the factory with a pressure cap. According to Chevrolet 1948 Engineering the neck of the radiator was changed sp a pressure cap could be used.

No pressure caps were stock on a 1949-1951 car with a standard transmission but Chevrolet sais one could be used for eextreme conditions.

I can see where a no pressure cap will work, as long as it makes a tight seal above the radiator vent tube and the radiator is vented through the vent tube into the overflow tank, and not to atmosphere.

Scratch what I said about any extra cold coolant in the top radiator tank. I acquiesce to Gene's better documentation and knowledge on the accessory tank on the firewall. Actually I didn't have any documentation.

I just don't understand how the system is of any benefit if the coolant level is not raised above normal half tank or so. Generally, that level will expand but not overflow to go out the overflow tube. It would depend on the water heating well above the normal 189-190 degrees.

Driving the car will cause the amount of coolant in the top tank to seek its own normal expansion level. Then where is the water going to come from to traverse to the accessory tank?

Owing to this logic, then, the accessory tank becomes unnecessary and useless. See what I'm saying? Maybe, when the system is not up to normal condition or at altitude. Not much benefit to us flatlanders.

So, my thinking must be off again. Straighten me out. Somebody. Please. Pretty pleas with sugar on it? (That there is as far as I'll go. Is too! Mercy!)

Charlie

The system is a closed system with a car with no pressure cap. The cap must seal on the filler neck. The hose connects the overflow to the tank. There is a stand pipe in the tank to release water if it exceeds the capacity of the tank.
The pressure cap has a valve in the center to allow coolant to exit if it expands to a high level also to suck the coolant back into the radiator..The pressure cap does not seal to the radiator neck of the outer edge (because it is bare metal) thats why a gasket mut be used at that location.
Also a pressure cap will not work at all on a 1939 and older as the overflow is on the top of the top tank.
I am not sure what a pressure cap will do on a 1940 and up that is not designed for a pressure cap. There I am going by Chevrolets information.
Would be intresting to see if a pressure cap "works" for this application. One test would be to remove the cap when hot and see if it pukes.

Here is a pic of the Stant 7 lb. cap from NAPA that I use on both of my '40 and also on my '48. Notice that it has two gaskets. The upper gasket seals on the mouth of the filler tube, above the vent pipe. The lower is spring loaded and seals on the inside lip of the filer tube below the vent pipe. Notice also the small hole in the center. That is a one way valve. If you use this system and a recovery tank you will have a closed system. It will require a full radiator and about two inches of coolant in the recovery tank at all times to avoid pulling air into the system. When the coolant expands, it opens the spring loaded lower gasket on the cap and the excess coolant will be forced into the recovery tank, rather than just running out of the vent onto the ground. When the radiator cools, and the coolant contracts it will create a vacuum inside the radiator. This will suck the excess coolant in the recovery tank back into the radiator, through the one way valve. If the top gasket on the cap is not a good seal, or if the recovery tank is empty, the vacuum will suck air into the radiator. No big deal except it just reduces the amount of coolant in the system. A closed system is designed to maximize the amount of coolant by giving it a place to go when it expands. The only advantage to a pressure cap is that it also increases the boiling point to a higher temperature. As Gene stated in a previous post, his standard cap will allow the coolant to expand into the recovery tank, and because the cap also has a tight seal on the top of the radiator filler tube it will create a vacuum to suck the coolant out of the tank back into the radiator. That is fine. The only disadvantage is that the boiling point remains at 212 degrees

Looks like the pic did not come through. Another try.
[img]http://images2.snapfish.com/232323232%7Ffp83232%3Euqcshlukaxroqdfv%3A588%3Dot%3E2345%3D56%3C%3D544%3DXROQDF%3E2%3B39%3A7836923%3Bot1lsi[/img]

Well I guess I don't know how to attach pics to this forum. Sorry.

Latigo's picture:

Radiator Cap

The pressure cap is designed to raise the boiling point of the coolant. The boiling point becomes less with altitude. The pressure cap mimics higher atmospheric pressure. Nothing more.


The accessory tank is to collect heat expanded coolant that would otherwise go over the side via the vent. Nothing more.

One does not depend on the other to function.

The pressure cap can be of use when appropriately fitted to a proper radiator. (See Gene's comments)

The coolant tank, like an oil filter on a 216 or 235 which has limited usefulness in that not enough oil will pass through before an oil change is warranted anyway. They are mostly just novelty items. The coolant tank will not store any coolant that has not been raised above the normal engine temperature. If it is of benefit, you have problems that need attention.

Charlie

I wonder why EVERY modern car uses a novelty item that has no useful purpose. I wonder why EVERY gas station in the '40's and 50's had a water hose located right next to the gas pumps, with a curved squeeze nozzle that fit perfectly into a radiator. I wonder why every summer I used to see cars, even new ones, stopped at the top of hills, with the hood up and steam coming out of the radiator. Early cars had an overheating problem that needed attention, and pressure caps and recovery tanks were among the first steps the manufacturers made to address it. I sure don't consider my recovery tanks as novelty items. I drive my cars all the time in all conditions, and really don't want to have some of the problems that were common in early cars.

Thanks leagl, for the help with the pic. I will have to try to figure out what I am doing wrong. Still stuck in the '40's I guess. My electronic skills seem to end with contact points and toasters.

The water hoses at the stations were to replenish the coolant level. The coolant evaporated over time. It will do the same with the gadget on the firewall. Those that were topped off just lost the coolant down the road after a few miles. Any knowing filling station back then knew better than to fill a radiator clean up to where it spilled out the top. They knew that no more than half a tank was enough.

Stopped vehicles at the top of the hill had cooling problems what an accessory coolant collecting gadget would not address or help. How could it?

Pressure caps were effective owing to their ability to raise the boiling point of the coolant. If you fit one on a car that didn't come with one, it will be effective up to the lbs pressure it is rated at. That gadget is effective in upping the boiling point and any benefits derived therefrom.

One does not have to think on the subject very long to realize the effectiveness of coolant tank on the firewall. On modern cars the coolant is filled to the brim and, thus, it needs somewhere to go when heated. If you run a pressure cap and fill the radiator to the top then it may have some positive effect. See?


Charlie

BTW: You missed the water cans at the old service stations. They had a spout with a catch on them so they didn't go too deep into the radiator.

Obviously your experiences are different than mine. I live in the Sierra Nevada foothills where steep grades and summer temperatures over 100 degrees are common. The amount of water that can evaporate through the small radiator vent is minimal but an overheated radiator will blow a lot of water out, over and above the normal level in the radiator. As I said in my previous post, I used to see a lot of cars stopped alongside the road with the hood up and steam coming out. There were places along those steep routes where people could stop and let thier car cool off, as well as getting a cold drink for themselves since there was no air conditioning at that time. All I know is my '40 overheated on me once on a steep grade and 105 degree temp, and blew a bunch of water out. Since adding the recovery system and 7 lb cap I have had no more overheating, so when I built my '48 I just went ahead and put the recovery system on it to be safe. You can call a recovery tank a gadget but if that was all it was the new cars would not bother putting them on as standard equipment. They do exactly the same thing on an old car that they do on a modern one, so as you say in your post, if it allows the radiator to be full to the brim, and gives the expansion a place to go, and the pressure cap raises the boiling point, it may have a positive effect. On my old cars that seems to be true. If you live in a moderate climate with few hills, or you don't drive in hot weather, the standard cooling system will be fine, but where I live those early cooling systems were marginal, even when new. Some people don't drive thier old cars in the rain. I do and upgraded to electric wipers. Some people don't drive thier cars on hot days. I do and upgraded to a better cooling system. Maybe not everyone's cup of tea but works for me.

OK

Charlie