One thing I have not seen mentioned here (which I only recently discovered) is the ability for a rad cap to allow air/ water BACK into the rad during cooliing/contraction.

 Imagine you have a mini radiator with a 15lb rad cap, if you block off the pipe to the waterpump and blow into the hole where the top hose connects you will have to blow 15psi of air in for the rad cap to release air through the little overflow pipe..... Now, if you suck, you will find that you can suck air in through the overflow pipe no problems just using your mouth.

 So this means water that is blown out into a non presurised  overflow tank is likly to be sucked back into the rad when the engine cools.

 

 

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=119064&lastpost=1

Thought I would show you guys what I did this afternoon. Installed an MGB expansion tank, opposite side of the engine bay, but working nicely. Now all I have to do is remove the old steel fan and install the new plastic one.......GOD I hate working on the radiator....... I just bleed so much.

Terry 

If you're not on the edge............ you're taking up to much space.

"So you can take a system with a pressurize overflow tank, and turn it into a non-pressurized tank system simply by replacing the radiator cap."

It takes a while ....but eventually the truth will out ..... and you don't need to start with a pressurised overflow tank.

Basically either system allows excess water to escape, be captured and returned to the rad when things cool down, thereby keeping the rad full.

My Honda had a pressurised system .. while my Subie system is not. Even the professionals can't agree......

Cheers, Ian

Not sure if you can see it, this picture is kind of far away.  Tucked in behind the rad filler cap.

Never put off till tomorrow what you can avoid all together.

the Howstuffworks article addresses the late-model systems. Here http://www.custompistols.com/cars/articles/overflow.htm the one with the blanking cap is discussed.

So you can take a system with a pressurize overflow tank, and turn it into a non-pressurized tank system simply by replacing the radiator cap.

www.itsamini.com

-Wes

The Elf Preservation Society www.itsamini.com

oh, cool!

thanks, minifly, that makes good sense. Finally, the overflow tank, explained.

In fact, how much do you wanna bet that all radiator caps have this feature, but when you've got an expansion tank it just never gets used!

Norm

I think I found the answer to the coolant return question.

http://auto.howstuffworks.com/cooling-system7.htm

I think for it to work in our cars we would need a cap that has a coolant return valve.

Henry

One more pic for you.  The pressure cap is on the expansion tank and then a blanking cap on the radiator, this means the tank is at the same pressure as the radiator and fluid can flow to and from the tank to the radiator as it heats/cools. 

 Seems to me having a pressure cap on the radiator only serves to let coolant out and not back in, all your doing is collecting what pukes out and at the same time defeating the purpose of an expansion tank

Si

Good question Norm. I was wondering this myself. If the radiator cap does only open to release the pressure when it is hot and therefore forces overflow water out into the overflow tank, how does the water get back from the overflow tank into the radiator against the pressure?

smithj86, the older models didn't have any tanks, just the overflow tube like you describe.

One easy thing to do with a car like that is to add an overflow tank. It just collects the fluid that is expelled by the radiator when it is heated up.

Maybe someone else can answer this: how does the fluid get back IN to the radiator from an overflow (non-pressurized) tank? I have always wondered about that, though I have never had to find out as none of my cars have ever overheated (two have overflow tanks, and one has an expansion tank).

The reason why I ask is because the radiator cap is sealed, and only lets fluid go one way (out), so maybe an overflow tank is only useful to protect the environment by collecting the excess coolant?

If you car is overheating, and you are not driving in, say, 90F or above while towing a trailer, then most likely you've got a worn out/rusted out radiator that needs recoring / replacing. Other possible culprits are: weak radiator cap (the spring is weak and is not holding the proper pressure), slipping fan belt, clogged radiator fins, partially blocked thermostat.

When you replace a radiator, ALWAYS flush out the engine real well until the water runs clear.

hope this helps,

Norm

 Mazda 343 late -80s,non pressure.Radiator cap is 1990-95 Cooper.

My 1962 Cooper doesn't have an expansion tank--it just has a tube that exits under the engine. The engine runs a little warm, although a radiator flush helps. I ordered a lower temp thermostat as well. Did the older models come qith expansion tanks?

"There's more to life than books you know, but not much more."  The Smiths, Handsome Devil, 1983.

"Swedishtreasures".  Damn!  I had my hopes up and everything. Not normally one for the blonde women folk, but I was ready to take a peak. 

----------------------------------------------
My Higher Authority is the German Purity Law of 1516 . 

Americas, Spridgets and Marinas all came with expansion tanks, which might lead one to think there was a reason that these 1300 engine'd cars had this.  One reason is suggested in print as long ago as Vizard's How to Modify Your Mini.  In any case, a pressurised expansion chamber really helps a cooling system dealing with a tuned 1300 based engine.  Old people with essentially powerless 1380s can probably get by with a placebo such as an oil cooler.

These tanks are most useful when they add volume to the system, this means using a blanking cap in place of the regular rad cap, and then having the pressure cap fitted to the expansion tank.

I recommend the Volvo 140/120 series expansion tank.  It mounts on a tidy bracket and is more space efficient than the BMC equivalent.

This might be a link:

http://www.swedishtreasures.com/686833.jpg

 

I used the same tank on my 1380,I think it came from a Austin America. I now have a S Racer S/S tank.

****** I know this is a different animal but I like the way this is mounted in the Moke. It's in our shop for some brake work, the brass overflow tank is from another Brit car if I'm not mistaken, TR3 maybe.

Cheers

Don

 " sometimes it's tougher to look than to leap "

Internet hodrod stuff.. 2 1/2"x10". $25.

N J

"Remember...pillage first, then burn!"

over the years there have been two different systems installed on minis:

- one is a pressurized expansion tank. The radiator has a solid cap, and the expansion tank has the pressure relief cap. The tank is made of metal to survive the 7 ~ 15psi pressure. The tube that connects them is also pressurized.

- the other is an overflow tank. The radiator has the pressure relief cap and the tube to the overflow tank is "outside" of that pressure cap. As a result, the overflow tank never sees any pressure other than atmospheric.

Depending on what kind you have will depend on what kind of tank you need.

In either case, you can locate it anywhere you want to because the water that goes out will be "pushed" there, and the water that gets siphoned back in will be pulled in regardless of the tank height.

Norm

In preperation of the summer heat coming up I hooked up a 10" electric puller fan in the inner fender well and an overflow tank in my Mini this weekend. I got the little tank from a Kubota Diesel engine. It's aluminum and it's wrapped in insulation and as you can see not much bigger than my ignition coil.

 

Mad Dog

www.miniownersoftexas.org

You can buy caps which allow fluid to escape when hot and then be sucked back into the rad as it cools - mine's a Nippon Denso.

Add a suitable container (a used 500 ml brake fluid bottle works really well) - and make sure that the overflow tube reaches down to the bottom of the container and away you go.

Tuck it in the corner in front of the wiper motor.

I suppose you could paint it to make it looks fancy.......

Cheers, Ian