Radiator Cap: vented vs non vented - what is needed?

RJRENTON · Oct 1, 2020

Cranky said:
Pressure only raises the boiling point and has nothing to do with running cooler. Non vented cap? Didn't know you could even get one. What happens if you over pressure the radiator? Something is going to give and you hope a hose does it before you split the radiator. Put a dang douche bag on it and recover your coolant when it expands so it's not always leaving a puddle everywhere you go. Are you running a shroud on the radiator and what type of fan system does it have? Did you know straight water actually cools better than a 50/50 mix of antifreeze? WaterWetter is supposed to do a good job too. I have run straight water before with good results but you had better run a water pump lube and corrosion inhibitor in it. You can buy it as a mix too.

YES...Increasing the cooling system pressure increases the boiling point by 3 degrees F for every pound pressure increase. The specific heat characteristics of the the coolant is another factor. Specific heat is the ability of the coolant to absorb heat in the engine or heat source and subsequently releasing the absorbed heat in the radiator or heat exchanger. A 50% concentration of ethylene glycol and water combined with a 15# pressure cap increases the boiling point of the coolant to 265° F. YES...water is the better alternative and adding a "water wetter", which is an ionic surfactant, which decreases the surface tension of the water, promoting better heat transfer. A modern day water pump does not need a "water pump lubricant", as the pump's bearings are sealed and do not require lubricant. In the old days, the wster pump used a brass bushing and the lubricant was a water "soluble oil", which looked like milk. The modern pump does have a mechanical carbon vs ceramic shaft seal, which is lubricated by the coolant flow. However, if using just water as the coolant, a corrosion inhibitor and an antifoam additive (to refuce or eliminate water pump cavitation) is a definite must. My preference is a full strength coolant (ethylene glycol) with the corrosion inhibitors and I'll dilute it with my water to the 50% concentration rather than the pre-dilluted material, as my water is less expensive.
I believe the non-vented cap allows the use of a coolant recovery system, keeping the radiator 100% full, without any entrained air for better system performance. Just my opinion of course.
BOB RENTON

Cranky · Oct 1, 2020

RJRENTON said:
YES...Increasing the cooling system pressure increases the boiling point by 3 degrees F for every pound pressure increase. The specific heat characteristics of the the coolant is another factor. Specific heat is the ability of the coolant to absorb heat in the engine or heat source and subsequently releasing the absorbed heat in the radiator or heat exchanger. A 50% concentration of ethylene glycol and water combined with a 15# pressure cap increases the boiling point of the coolant to 265° F. YES...water is the better alternative and adding a "water wetter", which is an ionic surfactant, which decreases the surface tension of the water, promoting better heat transfer. A modern day water pump does not need a "water pump lubricant", as the pump's bearings are sealed and do not require lubricant. In the old days, the wster pump used a brass bushing and the lubricant was a water "soluble oil", which looked like milk. The modern pump does have a mechanical carbon vs ceramic shaft seal, which is lubricated by the coolant flow. However, if using just water as the coolant, a corrosion inhibitor and an antifoam additive (to refuce or eliminate water pump cavitation) is a definite must. My preference is a full strength coolant (ethylene glycol) with the corrosion inhibitors and I'll dilute it with my water to the 50% concentration rather than the pre-dilluted material, as my water is less expensive.
I believe the non-vented cap allows the use of a coolant recovery system, keeping the radiator 100% full, without any entrained air for better system performance. Just my opinion of course.
BOB RENTON

Vented caps are for coolant recovery systems like was mentioned in post #20. Makes sense to me..... https://www.coolcatcorp.com/Radiator Caps/Radiatorcaps.html

andyf · Oct 1, 2020

Super-Bee-69 said:
i have a dumb question:

me and my tech had a big discussion about vented vs non vented radiator caps. as we just set in a new 22" us radiator plus fan shroud plus new water pump for my cooling issues of the 69 super bee with no coolant recovery tank, 383 engine and no air condition - this discussion came up!
the car was running on colder days at 205° and on warmer days up to 210° and in stop and go above.

Unless this is a NOS type restoration project you should hook up a coolant recovery tank. The system will work better with a coolant recovery tank and if you use a clear tank then you can quickly see if the system needs water or not. I buy coolant recovery tanks from newer cars and retrofit them on to my project cars. If you do a clean job with the retrofit most people won't even know that it wasn't factory correct.

Wietse · Oct 2, 2020

The trapped pressure in the system does increase the boiling point of the coolant, although it gives a safety factor, i believe that under normal conditions the coolant would never get that hot in the first place.
Besides that the cap should be seen as a pressure relief valve that will relief any excessive pressure prior to bursting a hose or radiator core, but again under normal conditions that should not really happen.
(if your head gasket fails you would blow something up straight away)

I am not filling my radiator to "full", just 1/2 - 3/4" above the core should be enough, the remaining air pocket allows the water to expand and acts as a damper.

With that said, i believe that you will only start to get these issues when your cooling system is just not up to the job.

383man · Oct 4, 2020

TxDon said:
A non-vented cap is used on older cars without coolant recovery systems. If the engine overheats or the coolant level in the radiator is too high the cap will push coolant out the overflow tube onto the ground. When they started equipping cars with coolant recovery systems they added a tank connected to the overflow tube plus a vented cap, and the radiator was filled to the top. The vented cap pushed out coolant if the car ran hot like the non vented cap and it went into the tank. The difference is the vented cap allowed a vacuum to be created when the car was shut off, drawing the overflow coolant out of the tank and back into the radiator. I learned this when I added a coolant recovery tank to my 63 Oldsmobile and I will be doing the same on my 67 GTX.

That is a vented cap. The old caps are vented as they just vent coolant on the ground instead of the overflow bottle. They cant push coolant onto the ground without a relief (vent) valve in the cap and they have to also have the vacum valve in them. Any cap that vents is a vented cap and they all are as they have to vent coolant either on the ground or to an overflow bottle. The older caps still vent and also do have a vacum relief valve as they also have to or they would suck the hoses shut and could do even worse when the cooling system cools down. The only major difference in old cars and newer ones is the newer cars have an overflow bottle so they save the coolant and draw it back into the cooling system. The older cars with no overflow just draw air into the cooling system when it cools down. So they can have to coolant level drop if they run on the hot side and the relief valve goes off and drains coolant on the ground. Ron

383man · Oct 4, 2020

Super-Bee-69 said:
No, no, no - don't mean the lever vented!!

http://www.stant.com/index.php/english/products/consumer-products/caps/radiator-cap-reservoir-caps/

Thats a nice site but the Stanton 10221 is not a factory cap which is what I figured we were talking about. Its good info on their caps. But no matter what they call a cap all the factory caps I have ever seen from the late 50's on up have to vent and relief to work. They make the cap pressurize the cooling system to raise the boiling point of the coolant about 3 degrees for every pound of pressure. But at some point it has to relief (vent) pressure so it cant go to high and blow a hose off. And they have to have a vacum relief for when they cool down so they dont suck hoses shut or do even more damage. Ron

68 Sport Satellite · Dec 24, 2021

Thread resurrection - I was all set to order a Stant 10231 vented 16 psi cap for my Griffin Aluminum 26" rad, but for some reason Summit only carries the non-vented Stant 10230. Speedway Motors does offer the vented 10231.

One question I have is - if my motor cools to 190F in normal driving but when stopped completely at idle after 10 min the temp climbs to 230F, can the radiator cap have anything to do with this? I know other causes are possible, which I've already addressed, but can a sub-par rad cap also cause this? One of my mechanic friends said he's seen some cars at long idle have a partially collapsed upper rad hose which he said is a symptom of a bad rad cap. Once the cap is swapped he said the issue is always solved.

In light of the above, does that point me to the vented or non-vented rad cap? And why doesn't summit sell the vented 10231??

68 Sport Satellite · Dec 27, 2021

383man · Dec 28, 2021

68 Sport Satellite said:
Thread resurrection - I was all set to order a Stant 10231 vented 16 psi cap for my Griffin Aluminum 26" rad, but for some reason Summit only carries the non-vented Stant 10230. Speedway Motors does offer the vented 10231.

One question I have is - if my motor cools to 190F in normal driving but when stopped completely at idle after 10 min the temp climbs to 230F, can the radiator cap have anything to do with this? I know other causes are possible, which I've already addressed, but can a sub-par rad cap also cause this? One of my mechanic friends said he's seen some cars at long idle have a partially collapsed upper rad hose which he said is a symptom of a bad rad cap. Once the cap is swapped he said the issue is always solved.

In light of the above, does that point me to the vented or non-vented rad cap? And why doesn't summit sell the vented 10231??

I would say no the rad cap is not the cause of it creeping up to 230. Remember the cap just pressurizes the cooling system to raise the coolants boiling point of the coolant. It just means if the cap is working and its say a 12 lb cap it would just raise the coolants boiling point 36 degrees from 212 to 248 it does not keep it from running hot. It means if you saw 230 and the coolant is not boiling out the overflow the cap must be working but its not the cause of it rising to 230. Ron

68 Sport Satellite · Dec 28, 2021

So if I was to change the cap (even though it's not a likely cause), just because I'd like a Stant cap on there instead of the generic 2 ear one Griffin sent me, do I go with the non-vented Stant from Summit or the vented Stant from Speedway Motors? Does it matter?

Radiator Cap: vented vs non vented - what is needed?

RJRENTON

FBBO Gold Member

Cranky

Banned Henchman #27

andyf

Well-Known Member

Wietse

Well-Known Member

383man

Well-Known Member

383man

Well-Known Member

68 Sport Satellite

FBBO Gold Member

68 Sport Satellite

FBBO Gold Member

383man

Well-Known Member

68 Sport Satellite

FBBO Gold Member

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