radiator overflow

[nevets]

a minor but vexing issue...

sometimes after a long drive in the hot weather, the water temp will go up to near boil once I cut the engine. this I believe is normal because with the engine off, the coolant is not circulating and so it gets hotter for a while. my question is this... usually on these occasions I will get some coolant oozing from the overflow tube. lately however, I'm also getting some coolant leaking around the radiator cap. this coolant, being hot is damaging the paint on the radiator and fan shroud. why is there leakage around the cap? the cap is screwed down tight and the overflow tube is not clogged... could it be that I need to replace the radiator cap or is there something more sinister amiss? oh and the coolant level in the radiator is approx 2" below cap level.

 

[Dave Russell]

Radiator caps have two seals. The lower spring loaded pressure seal, & an upper seal where the cap seats. On some caps this upper seal is a piece of springy brass. Other caps have a rubber upper seal which works much better.

If your upper seal is good, it may be that the filler neck seating flange is distorted, dirty, or other wise impaired.

You do know that the original Healey fillers require a longer than normal cap?

The NAPA #703-1411 cap works well.
D

 

[nevets]

Dave - the NAPA one sounds like an easy fix. What do you mean by "longer than normal neck" and what is a "Healey filler"? Thanks

 

[Dave Russell]

The Healey radiator filler neck is longer from the upper cap seating surface to lower cap pressure sealing surface.

Healey caps have a distance of about one inch from top seal to bottom seal.

More modern caps have a distance of about 3/4" from top seal to bottom seal.

If a short reach cap is put on a Healey, the pressure ring will never seat on the bottom of the radiator neck & you will in essence have a non-pressurized system.

This happens frequently to unwary owners, assuming all caps of a given pressure rating are the same, & they loose the benefit of a pressurized system.

The previously mentioned NAPA cap has the correct length, pressure rating, & a good upper seal.

To carry it a stem further, as on more modern cars, a coolant recovery tank (about one quart) could be added which would allow the radiator tank to be completely filled when cold. As the hot coolant expands it will be pushed out the overflow tube into the recovery tank & then be sucked back into the radiator as it cools. There is a small one way valve on the bottom center of the cap which allows coolant to flow back into the radiator as needed.

Radiator always full, no mess running out on the ground. No air in the system means no oxidation of the coolant & better coolant flow within the radiator. Any topping up of coolant is done via the recovery tank when the engine is cold.
D

 

[nevets]

Thanks for the detailed information Dave. Sounds like a recovery take would be a good addition. Am I correct in assuming that the recovery tank would need to be vented?

 

[Randy Forbes]

Based on Dave's recommendation of the NAPA cap the last time this subject was brought up, I finalized the recovery tank installation for my car.

My problem with spitting out the coolant (small amount after spirited driving) was corrected by putting the engine-driven fan back on. The electric fan just couldn't do it by itself.

I used a recovery tank from a later model Spridget. Sprigetech supplied a NOS tank for approximately 1/4th the going price of a reproduction. Only thing I'm not overly pleased about, is the routing of the hoses, so they may get developed further as better ideas crop up.

This tank is vented to the atmosphere, as a result of using a "gutted" regular radiator cap. It's not shown in theses pictures because the fresh black paint was still curing.

 

[nevets]

Randy, your engine bay is an impressive sight. Thanks for sending the pic. One question, is it necessary to have 2 tubes? wouldn't a single tube work? and where does the 2nd tube connect on the radiator?

 

[Randy Forbes]

Randy, your engine bay is an impressive sight. Thanks for sending the pic. One question, is it necessary to have 2 tubes? wouldn't a single tube work? and where does the 2nd tube connect on the radiator?

One (1) leads from the radiator to the surge tank (then a copper tube extends to near the bottom of tank).

Second tube is surge tank overflow and dangles to the street. Actually, I ran it back to the radiator and used the original clips to point it to the road.

Thanks for the compliment, but as most of what you see was last painted over twenty (>20) years ago, it's seen better days. While the engine doesn't require any mechanical work, I've considered pulling it out just for a respray (engine only__not the compartment).

 

[andrea]

looking at your very good motor comp. I see that probably you don't needs heat on the car i see two
grommets inside the pipes holes, is right?
Compliments

 

[glemon]

I am unclear on this idea of venting the overflow tank, I thought the idea was that it be a closed system to that when the radiator cools down suction pulls the overflow back into the radiator. That is how I have done it and it seems to work well, the Midget overflow tanks look good, if you can't source one most of the chain parts houses sell a plastic one for few bucks, I hid mine inside the left front fenderwell and it worked fine there.

 

[Dave Russell]

Thanks for the detailed information Dave. Sounds like a recovery take would be a good addition. Am I correct in assuming that the recovery tank would need to be vented?

Yes, the recovery tank is vented. Attached is a pic of a different variation of Randy's method. It uses an aftermarket recovery tank.

The hose from the radiator overflow leads to the top center of the tank. This fitting has an internal dip tube that goes nearly to the bottom of the tank.

Not shown in the pic is a small hex head filler cap on the top behind the inlet tube. On the side of the tank near the top is a tube for overflow & venting. Also on the side of the tank is a sight glass which permits quick inspection of tank level.

I have run for several years without the need for topping up the tank.
D

 

[Dave Russell]

I am unclear on this idea of venting the overflow tank, I thought the idea was that it be a closed system to that when the radiator cools down suction pulls the overflow back into the radiator.

With this type of recovery system, as the radiator/engine cools, the coolant is drawn back in via the small one way valve in the bottom of the radiator pressure cap. See pic. If the recovery tank were not vented it would pull a vacuum on the recovery tank & the coolant would not return. Also if the tank were not vented it would build up pressure & prevent entry of the overflow.
D

 

[Jerry]

I too have one of the Brass MG recovery tanks but it does not look as good as the one above. I think mine was made on Friday by the apprentice. There is enough solder used on the brass that I cannot leave it without paint. A nice shape tank that will fit almost anywhere.

Jerry

 

[Ed_K]

Here is the one I use;
https://www.macsradiator.com/polishedoverflowtank.aspx
It mounts at the same place as Dave's and Randy's.
One of the metal tubes ends in the bottom of the tank. That is the one that the hose to the radiator overflow is connected to. The other metal tube runs up inside the tank to within an inch of the top. It establishes the maximum level of coolant in the tank and is also the vent for the tank. The lid screws on the top and seals the top ( but the tank is vented through one of the tubes going out the bottom ). It works great and I have never lost or had to add any coolant since I finished the car, even when I was still using the original radiator which allowed the car to run much hotter than it does now with an upgraded radiator core.
Ed

 

[tahoe healey]

I haven't lost any coolant since I put in water wetter or what ever it is called. I have seen the brass tanks at LBC swap markets from time to time for about $10 to $20 bucks.

 

[Louie]

The overflow tank can overflow too, if it is too full when cold, plus I under stand the venting is needed to allow water to enter and leave the overflow tank.
On my system, I used the same metal overflow tank and got a NAPA cap which has no
spring & seal, just a cap to seal the neck of the overflow tank.
The suction and pressure are controlled by the radiator cap on the radiator.

If you look at the aftermarket units at Kragen, you will see that the overflow tank has a flimsy plastic cap on it--no sealing at the overflow tank.

I have seen the caps in the reverse, not sure if it makes a difference.
On the Jag XJ6, the overflow tank has the one and only pressure cap on the system.

Anyway, I drove the BN1 up and down California twice to meets, without having to worry about the water level (just the water temp!)

 

[glemon]

That makes sense about the venting, perhaps the aftermarket piece I bought had some sort of venting mechanism built into the design, maybe as simple as the cap allowing air to escape when coolant flows out and the suction sealing it is the coolant is sucked back in, I always marveled that it worked as well as it did.

Greg