Radiator Cap

[Lin]

I have just installed a coolant recovery tank in the bugeye. It is the unit that Cape International sells. Expensive but handsome! I am using it in the Big Healey as well. This unit collects overflow from the radiator at the bottom of the tank and it has a drain line at the top of the tank to the ground.

I assume that I take the original (but nearly new) 7 psi cap and use it on the overflow tank. Do I then use a non-pressurized cap on the radiator? so that coolant can move back and forth with expansion and contraction. If so, where does one get a non-pressurized cap and is it ANY non-pressurized cap or something special? Am I making any sense?

Thanks for the help as always!

Lin
1960 BT7 in restoration
1959 Bugeye

 

[Michael Oritt]

I assume that I take the original (but nearly new) 7 psi cap and use it on the overflow tank. Do I then use a non-pressurized cap on the radiator? so that coolant can move back and forth with expansion and contraction.
----------------------------------

Lin--

I could be wrong but if you put a non-pressurized cap on the radiator and a pressurized cap on the tank then all you have done is added some coolant capacity, but I don't think it will serve as an expansion tank--you want to keep your radiator pressurized.

I added an expansion/recover tank plumbed the way yours is but it has no cap--see the attached photo. The concept is that if coolant expands on shutdown it will go into the tank and as the coolant contracts during cooling the vacuum created will pull the coolant back into the rad through the hole in the radiator cap. Thanks Dave Russell for explaining to me the way that this works and showing me the type of tank I wanted to be using.

 

[Dave Russell]

Hi Lin,
I think Michael is correct. Since the new tank is vented by the hose at the top, a pressure cap on the tank would do nothing. You would end up with a non-pressurized system.

Michael,
Where did you get that neat tank. Mine was too fat to fit between the alternator & vertical shroud support.
D

 

[Keoke]

Well guys, it depends on where the overflow tube is located on the overflow bottle if it is designed to use a pressure cap.I guess I need to ask LIN what kind of cap came with the overflow bottle.Pressurized or not?---Keoke

 

[Michael Oritt]

[ QUOTE ]
Michael,
Where did you get that neat tank. Mine was too fat to fit between the alternator & vertical shroud support.
D

[/ QUOTE ]

Dave--

I got it at a Speed Shop in Clinton, MD--it's about 1 qt. capacity but fills the bill. I also found several others via Google that I think we discussed last year--there are some nice aluminum flat ones that would fit outboard of the distributor. Here's another view--it does make for a nice clean installation.

 

[Hangtown Healey]

If the hose from the radiator to the overflow tank is to the bottom of the overflow tank, the pressure cap is put on the tank and the radiator gets a blanking cap.
If the tank hose is at the top with a tube going down to the bottom, put the pressure cap on the radiator, but you need a cap with the little valve in it so the water can move back and forth and I don't think there is one made for a normal long neck Healey radiator. Although occasionally the water transfer happens anyway with a standard cap despite the theory! figure that out!

 

[Dave Russell]

[ QUOTE ]

If the tank hose is at the top with a tube going down to the bottom, put the pressure cap on the radiator, but you need a cap with the little valve in it so the water can move back and forth and I don't think there is one made for a normal long neck Healey radiator. "Although occasionally the water transfer happens anyway with a standard cap despite the theory! figure that out!"

[/ QUOTE ]
Not hard to figure out. I think most pressure caps have a one way valve in them. It's the little spring loaded disc in the center of the cap bottom part. Otherwise, as the system cools, a vacuum would form in the radiator & collapse the tanks. The NAPA # 703-1411 cap is a 7 psi for long neck that works well. I believe this cap is also available in a higher pound rating.

I really see no functional difference in pressure cap location requirements between a bottom fluid entry/exit tank & one with a top mounted entry/exit with dip tube going to the bottom. The dip tube has the advantage that any junk collecting in the bottom of the tank is not drawn back into the cooling system.

With a blanking cap on the radiator & a pressure cap on the tank, the tank & it's piping are subject to full system pressures & things are harder to keep sealed. I question whether the plastic "Cape" tank would be able to maintain a good pressure cap seal at it's cap flange area.

Some cars use an expansion tank type of system with non pressure cap on the radiator & a pressure cap on the tank. In this case the tank is remotely mounted higher than the radiator to make filling easier. It functions as an extension of the radiator top tank. This is usually done to avoid the extra height of a larger top tank when hood profiles are low.

Many modern cars use a single remote pressure cap, no cap on the radiator, and with a siphon type coolant recovery similar to what we are discussing.
D

 

[Dave Russell]

[ QUOTE ]

I got it at a Speed Shop in Clinton, MD--it's about 1 qt. capacity but fills the bill. I also found several others via Google that I think we discussed last year--there are some nice aluminum flat ones that would fit outboard of the distributor. Here's another view--it does make for a nice clean installation.

[/ QUOTE ]
Just curious. I solved my problem by making a new tank bracket that is located a bit further aft. I do think yours looks better. See pic.
D

 

[Lin]

Michael and Dave,
I like what you did in your cars, but I was after something slightly different. As Dave described in a later post, I was trying to create a system similar to a contemporary auto in which the coolant is added to the expansion reservoir - not into the radiator. I wanted the see-through tank that Cape International offered because I wanted to visually inspect the coolant level in the car without having to open the radiator. The top of the Cape reservoir (tank) is substantial and is clearly designed to handle the pressurized system, and Cape's instructions do indicate that the pressurized cap should be used on the reservoir.

I asked my question because I have heard both answers on which cap goes where and sure enough we have both responses on this thread. Isn't this fairly simple physics (meaning beyond me)? I have the greatest respect for you guys and almost always defer to your advice, but on this one I think I will ask a physics professor tomorrow. I will report back on my findings.

Lin
1960 BT7 in restoration
1959 Bugeye

 

[Dave Russell]

Hi Lin,
As you can see, there are two slightly different systems that are widely used. One is an expansion tank, the other is a recovery tank. Both systems work pretty much in the same way. There are advantages & disadvantages to each & they both work. It wasn't apparent from the pics which type your tank is. From your info, It is designed as an expansion tank. No great cause for concern about the differences. The objective is to keep the radiator full at all times & not dump excess coolant on the ground. Both types will do this.

You can see a variety of both type tanks here:
https://www.cantonracingproducts.com/tanks/expansion_tanks.html
D

 

[Keoke]

/ubbthreads/images/graemlins/savewave.gif
LIN, that PHISIC is unrequired all you need to tell us is; did the unit come with a pressurised cap or not!---Keoke /ubbthreads/images/graemlins/yesnod.gif

 

[Dave Russell]

[ QUOTE ]
did the unit come with a pressurised cap or not!---Keoke /ubbthreads/images/graemlins/yesnod.gif

[/ QUOTE ]
To quote Lin's earlier post:
"Cape's instructions do indicate that the pressurized cap should be used on the reservoir."
D

 

[Keoke]

I must have missed that Dave, However, if the over flow bottle is designed for a pressurized cap,then you have the option of using a pressurized cap on the radiator and the bottle, or you can use an unpressurized cap on the radiator and a pressurized one on the bottle. I usually use a slightly higher rated pressure cap on the bottle when I use on at both locations.---Keoke

 

[ron wilson]

All of the cars I have ever seen since they started putting recovery tanks on them when they are built have a presurized cap on the radiator and a non presurized cap on the recovery tank.

Also I have reecovery tanks on both a 66 Healey and a 59 Tr3 A neithe of which have any type of special cap anywhere because of the recovery feature but for some reason they both work. They both have standard pressurized caps on the radiators and non presurized on the recovery tank.

 

[Dave Russell]

Hi Ron,
I pointed out earlier that there are "expansion tanks" & "recovery tanks". Expansion tanks have a pressure cap. Recovery tanks don't need a pressure cap.

For both types, a one way valve is needed to prevent vacuum from forming on the system when it cools. This valve is a standard part of nearly all caps. The recovery tank radiator cap needs a good seal at the top in order to work. Most caps have this top seal, a few maybe don't. Older recovery kits were supplied with a top seal in case the existing cap did not have one. See attached pic of a NAPA #703-1411 cap which fits the long neck radiator fillers & has good top & bottom seals.
D

 

[Keoke]

/ubbthreads/images/graemlins/savewave.gif

[ QUOTE ]
All of the cars I have ever seen since they started

putting recovery tanks on them when they are built have a presurized cap on the radiator and a non presurized cap on the recovery tank.



[/ QUOTE ]

Volvos as built back in the 60s did not do it that way RON. /ubbthreads/images/graemlins/nonono.gif However, later on someone figured out how to save a buck. /ubbthreads/images/graemlins/yesnod.gif---Keoke /ubbthreads/images/graemlins/grin.gif

 

[tahoe healey]

I don't get it. If the cap is pressurized at the radiator, how can the coolant get back in? Iseems to me that it would have to be pressurized at the resivoir making a sealed system.

 

[Dave Russell]

See my previous message to Ron & the attached pic of the one way valve in the cap. The valve is how the coolant gets back in.
D

 

[Keoke]

[ QUOTE ]
I don't get it. If the cap is pressurized at the radiator, how can the coolant get back in? Iseems to me that it would have to be pressurized at the resivoir making a sealed system.

[/ QUOTE ]

HI TH, it Sucks.---Keoke-- /ubbthreads/images/graemlins/grin.gif

 

[ron wilson]

Hi Keoke
Thanks for the clarification.
Some might be interested to know the reason I put the recovery tank on the Healey in the first place was that every time I filed the radiator and then when the water expanded and then I stopped somewhere it would spit some fluid on the ground and some kind soul would point out to me that I probably had a leak when all it was was the system creating it's own level as a result of the expanion.
So I put a recovery tank on not expecting it to work properly. I just wanted to collect the fluid somewhere to save people the trouble of pointing out the apparent leak to me. I thot that would be ok even if I had to pour the fluid back in the radiator at the end of the trip. But for some reason it actually works as it is supposed to.