Radiator overflow, anyone added one?

I am thinking of adding one. Would be interested to see how somebody else did it. I have seen some aluminum ones on ebay (tall and skinny) that look like they could mount beside the radiator neatly. Also was thinking a later Cj (80-86?) has a plastic one that mounts on the backside of the driver fender well, might fit?

All else fails I have seen generic square plastic ones that use a mounting bracket that for lack of a better description looks like a wire coat hanger. I have seen these on big panel trucks in the boneyard, but the resevoir is always dry rotted.

 

Yeah, I don't have any cooling problems, but the radiator pukes off enough coolant to run just low enough to piss me off, hence my desire to add an overflow....

I think I am gonna top it off, then put a plastic jug in there to catch the overflow for the next week. Then I can measure it and determine what size can I need.

 

Glenn-
How come they have 2 full lines for hot and cold on the factory installed overflow tanks? I thought that they were functional as well... Or does it depend on the system?
Any who, I have a 16lb cap on mine and it stopped the puking of antifreeze. I have a sbc though and tried a 13lb cap first...not enough. If anyone needs them, I have a 7lb cap and a 13lb cap that I'd give you

 

I had my radiator gone through at a radiator shop a while back. It's working fine but it doesn't have a long life ahead of it though. With its age and condition the shop recomended I go with a 7# cap. They said I could extend it's life a little longer using the low pressure cap. I haven't noticed any loss of fluid. Everything is fine at the moment. Keeping my fingers crossed.

 

Cooling system 101, from my Haynes CJ manual:

"Some models are equipped with a coolant expansion reservoir. As the radiator coolant expands, a pressure relief valve in the cap allows the coolant to flow through the overflow hose into the reservoir. When the system cools and contracts, there is a pressure drop and the coolant is drawn back into the radiator."

Dennis hit it on the head: If the can just catches overflow, why hot and cold check marks? The can could read full while the radiator develops a leak and drains empty. However, the pressure loss draws the fluid from the reservoir, which warns the operator (unless it is a fancy aluminum one you can't see through!)

My custom aluminum radiator runs about 1 1/2" below the filler neck, almost at the level where the core starts. Even if I top it off, that amount of coolant gets puked during a highway run when she gets good and hot.

Back before I stepped on the yellow footprints (Marines will know of what I speak), I earned a degree in automotive technology (fancy way of saying I am a trained grease monkey!).

 

Radiator caps: The primary purpose of a pressurized system is to raise the boiling point of the coolant. There is a relationship between the amount of pressure and how much it raises the boiling point.
http://www.biggreenegg.com/boilingPoint.htm
http://home.mchsi.com/~gweidner/steam-elevation.pdf

Like Tim points out, the radiator has to be able to handle the pressure. If you develop a leak in the rad while wheeling, you can leave the cap off. Some fluid may expand and or slosh out the open rad, and fluid will still escape from the leak, but not as much as would if it was under pressure. A small leak in a hose or hose connection may even stop leaking altogether. Using this trick along with some "bars leaks" "radiator sealer" or even black pepper may be enough to stop a otherwise healthy leak and get you home.

 

http://www.carcarecouncil.org/Cooling_System/reservoir.shtml

The purpose of the expansion tank is to catch overflow. That it provides some level of safety and ease of checking the level is secondary.

Anyone have a Jeep Cherokee XJ? There is no radiator cap (it is on the expansion tank!) and the coolant tank is pressurized along with the system. It does allow you to check the level visually, but you must wait for it to cool before opening it to add more. Those who own one probably know that the tank is prone to failing (mine lasted to the 180,000 mile mark) simply because it has to deal with that pressure.

 

The same thing on my pickup. had to put a pressure relief cap on it so I could check at will. The plastic bottles discolor in no time and you can't see where the level is. That brings me to the point I started out to make. I had a jeep some years ago it had a Plym Valiant radiator cooled well but puked fluid. Put a puke bottle on it to catch it and it filled it up put pressure cap on bottle , never touched one on radiator lived happy ever after or at least as long as I had it.

 

So let me ask...

Would I be better off replacing the 16lb cap with the 13lb cap and adding the overflow tank?
My system can handle the 16lb cap, I checked with the guy that rebuilt the radiator. What do you guys think? (not trying to hyjack, just seems to fit here )

 

Dennis, the higher rated cap will raise the boiling point of the coolant higher than the lower rated one. Do you need that extra protection? I don't know, does your rig run that hot? I doubt it, but you can be the judge. If you are happy with were the coolant level stays at in your rad now I wouldn't go to the bother of adding the expansion tank (don't fix it if it ain't broke?).

I like the idea of my rad being as full as it can be, which it is not with the current setup. When topped off, the first long run I make that gets it fully warmed up, it pukes off about 2 inches of coolant. A expansion reservoir would catch this and allow it to be drawn back in at cool down, keeping the rad topped off.

I'm going to conduct some testing to see how much actually pukes off, I'll post the results here.

 

It runs 180-190* pretty consistantly. The 16lb cap keeps it from puking so I won't worry about it. Keep us posted...

 

Greg: Your observations are absolutely correct. The PO added an expansion tank to mine. Looks like a "generic" one. Works fine. I put a new 13lb Stant cap on it and it functions just like it should. I keep about 2" of coolant in the overflow tank when cold.

BTW, Jags and early Vetts used a "pressure tank" that had the "pressure cap" on the tank instead of on the radiator. Worked fine, except on Jags the tank was soldered brass, which usually leaked and you had to re-solder them. As a replacement on my XJ6, I used an old Vette tank, which was stainless. NO LEAKS.

 

I just checked my cap. It came with my radiator, with a custom made aluminum "cap" that fits over the regular cap, all custom made (I believe they are in Havasu, Jim?!). Anyway, popped the "cover/cap" off so I could read the specs and I am running a 22-24 lb cap!

Jim, where does one get an early Vette overflow? Bet they are kinda scarce!

 

Greg: We talked about this before and the radiator shop is in FixNix (as we call Phoenix). You were kind enough to send me your specs over fax.

22-24 POUNDS! Factory calls for 13 lbs.

I got the Vette tank from a pick-n-pull in San Fernando. Were not really rare at that time. They looked like a small beer barrel with a radiator cap on top. Worked great!

Remember though, they are NOT an overflow. They are a pressure tank. The cap on the radiator just seals it off from leaking--no interior pressure seal. The pressure cap is located on the separate tank and is connected by a 5/15 fuel line to the rad "overflow". This system was used on some cars before what we have now as "overflow" tanks, which are cheaper (no pressure) and serve the purpose fine.

 

I had a plastic one on mine once before and for some reason I decided I wanted a new one. Well I couldn't figure out where to mount the new one as it was made differently than the old one. I took the old one off but never mounted the new one.

Since then, I periodically run a little bit hot. I think the little bit of puke every now and again eventually puts me low of water. As opposed to the little bit of puke being there and able to suck back into the rad to replenish what was lost.

My two cents. I say if it's puking a little bit then put the bottle on it. It'll pull it back in there when it cools off a bit and you won't find yourself stranded with no water.

 

John: Xactlly. That's what they were designed for, and, they do the job great.