Expansion tank coolant level
 

When I purchased my XJS - V12 the expansion tank was full up to half or higher of the fuller tube.
Since I have cleaned out the atmospheric tank and made sure the hose is clear, unblocked the self bleed pipes and added the upgraded longer banjo with larger bleed hole the expansion tank is only full to the bottom of the fuller neck. I have added more coolant and when I check again it is back to the bottom of the expansion filler neck.

Is this normal?

I have not checked to see how much coolant is in the atmospheric tank... do I need to?

Thanks

Nope.

The metal tank will ONLY stay full if the pressure cap on that tank is a double seal style, and those 2 seals, and the small valve on the disc seal, are all working correctly.

If the outer seal, up under the metal section that is gripped to remove said cap, is faulty, the system will suck air instead of coolant out of the atmospheric tank.

ALSO

It the plastic atmospheric tank is NOT prefilled with approx 2ltrs of coolant, the suck back will drain it, and then the system will suck air.

ALSO #2

Every time you lift that pressure cap to "check" the level, you let air in, kind of a rock and a hard place situation. I twigged to this a very long time age, and used a CLEAR braided (air compressor) hose, to go the the atmospheric tank, so I could look, and if there was Green liquid in that hose, the system is FULL, leave the bloody caps alone and drink beer.

Some very careful systematic checking is needed.

Thanks Grant, no coolant in the atmospheric tank, so i will fill this with 2L. When I took of the metal tank cap level was low, below the filler neck, I then removed the radiator cap and there was a hiss of air as the coolant flowed in to the metal tank and the level was 2inch from the top of the fuller neck.

Also the radiator cap is new, looks new, nice and shinny where the metal tank cap is original Jag and looks old, both the same rating.
The metal tank needs the best seal correct?

MMMMM,

That HISS is air entering the system via the filler pipe, and thus allowing the system to level out.

You now have air is the system, so a "basic" bleed is needed.

By that, both caps OFF, bleed plug OUT, vac hose on heater tap OFF, and fill it SLOWLY, 1ltr of coolant (car), 1 beer (you),, 1ltr of coolant, 1 beer, and when both are FULL, you are done. Fill that system too fast, and air will get trapped.

BOTH caps need to have 100% top seals. The filler cap uses the "top" seal ONLY, and the header tank cap uses both seals to what it does.

I run 13lb header, and whatever on the filler, a CPS 2001 IF I can find one is best, as it only uses the top seal to close the system to atmosphere.

Thanks - I did a search on CPS 2001 radiator cap and not much joy... any other info for this?I read I should run the car and idle it around 2000rpm?"I run 13lb header, and whatever on the filler, a CPS 2001 IF I can find one is best, as it only uses the top seal to close the system to atmosphere."

Probably obsolete. We used them on Mini;s, the real Mini, S2 Jags, and anything else that only needed a blank sealed cap.

Modern plastic screw on caps have probably made manufacturing of these a no no.

ANY cap on the filler, as long as it has a decent upper seal is all that is needed. If it has the spring etc hanging below, does not matter, as the TOP seal is the one that counts here.

Grant,

What do you mean by this?

vac hose on heater tap OFF - Do you mean pull the vac hose off the heater thing by the firewall?
Or just turn on the heater to defrost?

TA

Hose pulled off, just in case you have a very special Jag that actually holds vac in the system for more than a few seconds after shut down. The only one of mine that did so was the HE, it held overnight, all the rest dumped vac within 30 seconds.

That heater tap is default to ON whenever there is NO vac, so you could look at the tap, and if the lever/arm is in the DOWN position, that tap is ON, so coolant/Air will flow through the heater and out of the system.

Added 2L to the atmospheric tank, did not take much to fill the metal tank overflowed first after squeezing the hoses I put on the cap, filled the radiator to the top and when coolant came out the bleeder hole closed that and filled the radiator to the top and put on the cap.

Went for a 20k drive, heater of full for 10k and the temp stayed under N when it would normally be in the middle, heavy traffic, stop / go and open road back home, hotest it got was bottom of the N...
So far so good.

I REALLY want to check the levels when its cool but i will NOT!
Winter job will be clear hose for the overflow... good to see what is happening.

Thanks Grant heaps.

Goodo.

"Stop go traffic" in NZ, come on mate, there aint that many cars, ARE THERE ?????, HAHA.

Have a beer, drive the damn thing, it will LUV ya.

Come on Grant I am sure it took 10min to get through that roundabout, there were 20 cars in front of me!
Beer yes, in true NZ style from a big 750ml bottle, in hand, no glass, sitting on an empty crate.
Just like my mate Jake the Muss.... (training video for NZ youth).