Expansion Tank Explained

[SourceLee]

Can someone explain the benefits of an expansion tank as opposed to a recovery tank. Some photos of the original Cobras show the engine compartment with an expansion tank. Why one and not the other? I can’t seem to find a definitive advantage of having an expansion tank. To avoid any mixing of terms and for the sake of this post here’s a quick description of the two.

Expansion tank: Is a tank that allows the expansion of coolant in the cooling system. It’s located on the pressure side and the highest point in the cooling system. It serves the same purpose as a residential hot water heater’s expansion tank (cold water heater?!?!). More or less. Hot engine therefore hot coolant. Hot coolant expands and expands into the expansion tank. In the process it pressurizes air inside the tank. Engine stops and cools off. Coolant contracts back to it’s original volume as if nothing ever happened.

Recovery tank: Is a tank which also allows for the expansion of coolant in the cooling system. However it’s located on the non-pressurized side. It’s directly exposed to atmospheric air pressure. Usually via a vented tank cap. A good portion of “daily driver” vehicles have recovery tanks. The coolant expands as the engine warms up. The expanded coolant passes by the spring seal on the radiator cap. Then into the bottom of the recovery tank. After the engine has stopped and cooled off the coolant contracts. The contracting coolant creates a vacuum in the system. This vacuum pulls the expanded coolant back out of the recovery tank. It recovers the coolant hence the name.

Here’s the only advantage I can come up with. The expansion tank automatically purges the system. To a large extent any air in the system eventually ends up in the expansion tank. Any help on this subject would be appreciated.

[NAZ]

The expanded coolant in the recovery tank adds no cooling capacity while in the catch can. If more coolant is transferred to the recovery tank that it has capacity to hold, some will be expelled overboard and not recovered when the coolant system cools which results in sucking air into the radiator and a system that is now less than full. And a recovery tank provides no degas function.

In contrast, an expansion (degas) tank is a part of the closed circulating system and is always the highest point in the system. There is an air space above the liquid level that allows the coolant to expand without expelling it so the same amount of coolant is always being circulated. And since the expansion tank is the highest point, it is always allowing gas bubbles to make their way to the air space above the liquid level. This degassing function eliminates almost all gas bubbles throughout the system and improves heat transfer as entrained air in the system reduces the heat transfer.

[nucjd19]

Great questions and discussion SourceLee. And awesome answer and reason NAZ. Thank you! I learn something new everyday :)

[CraigS]

I would prefer to use an expansion tank but the required height is the problem. Obviously in an FFR, several builders have incorporated an expansion tank so it is doable in our cars. But, from what I have read, it takes some fab work to make up a mount etc. A recovery tank can be mounted much lower in the car. I am not sure how low it can go, but I think this is the reason recovery tanks are so common in daily drivers.

[rich grsc]

The height isn't really a problem, just like the radiator fill cap, just needs to be the highest point in the system. But fab work is involved!:) I find that all part of the fun, built not bought:D.

150840
Every time, turns the picture sideways :mad:

[Hoooper]

Lots of people mounting expansion tanks to the upper radiator support it seems, using a coyote style surge tank. Not sure that I would call it fab work but securing the bottom tab does require a little bracket to be made.

The extra coolant capacity is nice if you are overheating on brief runs, doesnt really do anything if youre overheating on track or any constant load though. The big benefit to a surge tank style system is that it gets air out of the water/coolant.

[SourceLee]

Thanks all. Now I have a better understanding on what and how it works. Naz, the term you used, "degassing" was the tipping point of my understanding what it's function is. I honestly thought DeGas was the last name of a French aristocrat! Peugot, Renault. It's the little things.
Inspired by this discussion I started some research on expansion (degas) tanks. This is when I discovered Cobra Earl's water neck. Wow, what a fine piece of engine jewelry! If I died and came back as an engine part, it would be that water neck. Or maybe an alternator.

[CraigS]

This is the type I was thinking of. I think there are now some sold that will work w/ a 302/351 but used to be guys would find a tank where the tank portion was correct but all the mounting pieces would only fit a big block. So fabbing was needed and not everyone has the skill to solder brass.

[rich grsc]

Craig, the ones made to fit SB's are very nice $$$$$$. :rolleyes::eek:

[CraigS]

Sorry, this is the link I should have put in post #8.
https://www.shellvalley.com/index.cfm/page/ptype=product/product_id=134/category_id=34/mode=prod/prd134.htm

[Jim1855]

Superformance included the engine mounted style with their install kits, no welding required and should still be available. I had a really pretty polished stainless piece in 2004 for my 351/427. They also had them painted black. I always thought that the tank was in the way and some of the plumbing was a bit difficult. The tank did work well as a tool holder.

Kirkham has or had a stunning machined billet unit. I friend had one, I have photos somewhere. That one was expensive.

If I can figure out how to insert photos (I'm challenged) I'll dig 'em up.

Jim

[BEAR-AvHistory]

Lots of people mounting expansion tanks to the upper radiator support it seems, using a coyote style surge tank. Not sure that I would call it fab work but securing the bottom tab does require a little bracket to be made.

The extra coolant capacity is nice if you are overheating on brief runs, doesnt really do anything if youre overheating on track or any constant load though. The big benefit to a surge tank style system is that it gets air out of the water/coolant.

https://cimg0.ibsrv.net/gimg/acurazine.com-vbulletin/850x637/80-80_5l_bfd891ba41532988fd9cfd5582dc837185bc2183_512 8ef8935857b7d6c745b04d8bdd088a7562d78.jpg

3 pieces of aluminum flat stock bent by hand (one end in a vise) Two short tabs one longer piece for tanks lower mount point. Spray them black & they sort of disappear. You can see the driver side tab at the very end of the tank. Large unpainted rivet. Functions 100%. Drive all year round in NC & have never added coolant between by-annual replacement. Car is abut 6 years old now

[johnnybgoode]

Will include a plug for Mike Fortes Degas tank. https://fortesparts.com/product/aluminum-degas-tank/

I just upgraded a couple of years ago to Mike's latest tank which works great. It bolts to the F-panel. I've also got mine plumbed into a recovery tank and have my fan switch plumbed into the 3/8" port on the bottom of the tank. Nice piece all-in-all. Scott

[Jaguar Engineer]

Surge style expansion tanks have a surge line that connects to the lower radiator hose. In addition to the expansion benefits, it also helps prevent water pump cavitation by putting positive head on the pump inlet.