XJ12 Series III coolant overflow tank hoses

Hi- 1987 XJ12 Series III coolant overflow tank has two opening on top, but there is only one obvious hose/pipe that goes in there… which hole is which, and what’s the “other one” for?

I took this all apart far too long ago to remember.

I removed that tank in my 1990 V12 Vanden Plas (a Canadian market DD6) several years ago and flushed the tank out, replaced the hoses, and checked the pipes to make sure the coolant ran through without problems. The supply line from the coolant tank goes into one of the holes and there is a hose in the other hole that spills coolant on the ground if the overflow tank gets over filled. I will check tomorrow to see if I have any pictures of those hoses, or look to see on my car if I can tell which hose goes to which hole. With the carbon canister in the way it might be hard to see those hoses on the car.


This photo of my 1990 V12 VdP from 2018 should help.


Great, thank you, I appreciate the help.

Would it be logical that the expansion tank hose go to the bottom of the overflow tank, and that the overflow-tank-overflow hose would end (or start) just an inch or two down from the top?

Digression… It didn’t cross my mind that it would just dump the excess-excess on the ground. I’d say I figured that was over by the 1980’s, but in 1984 they were still running the “Lackawanna Electrics” in my hometown… the train restrooms literally were seats over holes that went right on the tracks. They had a sign to not use the restroom when in the train station, but other than that… right on the tracks.

To amplify, John; as coolant expands it is forced into the expansion tank - and the coolant pressure is controlled by pressure relief valve in the filler cap.

If/when coolant pressure exceeds the relief pressure, the relief valve opens to the overflow/atmospheric recovery tank - venting fluid or air into that tank from the filler neck hose. Principally, this overflow hose should be below the fluid level in the recovery tank - and if/when the recovery tank overflows - it is vented to ground…

The other hoses on the expansion tank are basically vent hoses - taking eventual trapped air from high points in the cooling system…

xj6 85 Sov Europe 9UK/NZ)