How to connect an expansion tank

Plumb the line that leaves the rad via the filler neck to a tank from the wreckers? The coolent is forced out the rad under pressure and then gets sucked back in when everything gets cooled down. You can use the little overflow line that is at the radiator cap neck, but you HAVE to change the radiator cap to the correct style. This style will have a rubber gasket that acts as a one way valve to allow fluid to be "sucked" back in as the radiator cools and the volume decreases. On Blue, I used a Mazda RX-7 reservior and mounting bracket which I tucked up under the wing with just enough space to slip the tank off the bracket and check the fluid level. The tank really snaps in solidly to the bracket and is very robust. I still have the part numbers for these somewhere in my records....

From: David McCartney
[unmodified]

Somebody'll probasbly second-guess me with a better answer, but here's what I've done in the past.

On the radiator you put a solid rubber-sealed cap to close it off at the upper lip of the aperture. Spring-loaded pressure caps seal against the inner lip - no good for this new setup.

Now expanding coolant can flow right out via the tubing into your catch tank, which will have a pressure relief cap like you formerly used on the radiator itself.

You know, of course, any pressure leak that surrenders at a lower pressure than your spring-loaded cap effectively resets the pressure limit and causes overheating. You need 13 or more pounds. The more pressure, the higher the point before boiling occurs. Always suspect a leak when the car boils over too soon.

This much info I think is correct. See what others write about highfalootin thermodynamicles and siphon etcetera.

Rocky Frisco adds:

Nothing to add except to make sure the tube from the rad to the expansion tank goes into the very *bottom* of the tank. If this is like telling the list to make sure the headlights point forwards, I apologize, but I still get calls from people who are indignant because they can't send e-mail during a power failure. "Well the *telephone* works, doesn't it? I'm *talking* to you right now!" ;)

From: Peter S.
["first"/"second"/"later" terms might be in wrong order]

The first being one where the expansion tank (metal) has the standard rad cap and the rad has a blanking cap. The second where a lesser pressure cap is installed on the rad and a simple plastic bottle is used to collect the released coolant. In fact, the later method is used far more than the first in todays car. The extra tank is really called a 'recovery tank' in that style because it doens't hold pressure. Its only a place to hold it. This one is easier to supply since you don't have to source a metal tank and it can be very narrow and fit anywhere.

From: John Lieberman

[Quote from Patrick who asked the question in the first place] I would like to fit an expansion tank to keep the coolent in the car, instead of having it run on to the street after topping up. Can I plumb the line that leaves the rad via the filler neck to a tank I get at the wreckers? I assume that the coolent is forced out the rad under pressure and then gets sucked back in when everything gets cooled down.

You've got it, Patrick! That's exactly the way to do it. I got a plastic expansion tank and mounting bracket from a junkyard Mitsubishi pickup truck and mounted it to the firewall behind the radiator. Works great in my race car. Of course, I don't have any windshield wipers or anything else of that nature that might get in the way of mounting it in a street car. Just decide where you want to put it, measure how much room you've got, then start roaming the junkyards with tape measure in hand until you find one that will fit. Be sure you get the mounting bracket, too. And make sure you mount the intake point of the expansion tank even with or a little lower than the overflow nipple on the filler neck.