Header tank below top of radiator

A garage in England decided to add a header tank to my 140. But the overflow hose of the radiator is higher than the tube’s attachment to the expansion/header tank…so the coolant can’t flow back into the radiator once cooled down. Or does the pressure in the tank make it ”climb” back into the rad? Don’t think so!
Today, in the city of Stockholm, on hot day, I saw the temp rise to 90 at a red light. When I opened the lid to rad and header tank, at home and after a few hrs, I saw that the coolant level was very low in the tank and a bit low in the rad. So I added in both and will check tomorrow.

The connection tube inside that tank should go to the bottom, so it will suck liquid back into the radiator on cool down when the coolant volume contracts. The other tube should be at or near the top to let air in and out without letting out liquid.
Here’s mine. I think it came from Summit Racing; they have a wide assortment. Both hose connection tubes are on the bottom, one is just a short one that does not extend up at all and the other extends up inside to near the top. I have a normal rad cap that permits flow either way depending on the pressure differential when hot or cold.

The overflow tube should be mounted at the bottom of the header tank.
Also the should be no air trapped at the top of the radiator.
And just a sealing cap on top of the radiator, but it looks like you have that allready.
Only in that case it will work, and will the cooling water flow back.

Exactly. Thisus what BMW used in the late 60s

Here is what my XJ12 has.
XJ12 header tank


The only way that tank will be of real benefit is if the connection from the radiator goes into a tube internal to that tank which gies to the bottom of the tank. Take the cap off and see if there is a tube inside.

If there is a tube as thw water cools it will be sucked back into the radiator.


Thanks Matthew. Yes, there is what feels like a tube going from the hose attachment, and down inside, to near the bottom😊

The overflow tank in Peder’s car looks like the aftermarket model sold by several of the major vendors. Just out of curiosity, has anyone installed a tank from another Jaguar such as an E-Type in an XK and if so does how has it functioned?

I have a 150 with alu rad and overflow tank from anE-type S2. Works well. Picture in 24 hrs.

This is my version of an overflow tank on my 150 and it work pricelessly.
Got it on E bay and believe it came from a Mini, but have also seen them on Jags.
Radiator cap MUST have a two way valve in cap, to let water out and then suck it back in, there must be a pipe in the small tank going to the bottom and it must be covered with fluid or else it will syphon back air, bottom of pipe must be covered when vehicle and water is cold with about an inch of fluid.
There is just a basic sealed cap on the reservoir with an overflow.
After a run and cool down my radiator is now always full.
Constantly check the small tank to make sure the bottom of the pipe is covered with water.

I like that set up. Not original, but still looks more period correct and less obtrusive within the engine bay than the larger, welded aluminum units.