Help! I have an XJS which has a leaking coolant hose which is a complete mystery

Hello Folks,
I noticed coolant on the ground and traced it to the left side down low above where the shift linkage enters the side of the transmission. Towards the rear, it is a zinc colored tube that goes into a black runner hose. It is a roughly 1/4 inch tube. The tube looks to enter the cabin. I have no idea what it comes from or goes to? Any ideas? I will eventually figure it out but was hoping this has happened to someone else and that there is a way to run a new line or replace the existing one. It is very hard to get at the hose clamp but was finally able to tighten it up and it still leaks. I have a feeling that the rubber hose has a cut or slit in it beyond the clamp. Does anyone have any clues? It is much appreciated.

Wes Keyes
York, Maine

Heater related? If it goes through the bulkhead it’s probably to the heater matrix.

It would help if you provided your car’s Model Year and engine.


There are no coolant hoses that far back. It must be leaking elsewhere and running back towards the tranny. There are plenty of options where it could be leaking. The best way to find the leak is go to your local auto parts store (AutoZone, OReilleys, etc.) and rent a coolant pressure test unit. Usually it is “free”. They will ask you to pay a deposit but you should get it all back when you return the unit.

Remove the radiator cap, connect the pressure tester in its place and pump it up to 14psi or so. Then start looking for the leak.

Gotta be heater hose related. Those are the only hoses on the back of the engine I know of, if this is a V12.

I have stopped guessing. :wink:

When the posts don’t even include the most basic info like year and model info I either ignore the posts or ask for it.


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It sounds to me it may be one of the air con drains. About the only “wet” thing that far back and suits the tube size you mention.


Hello Folks,
Sorry 1988 V-12 XJS. I found the hose. It comes from the heater control valve above it out the drivers side of it. A larger line comes in on the passenger side. Down under neath the car is has a clamp where the rubber hiose changes to tubing. I had a loose clamp which I tightened and have stopped the leak. I have pressurized the system with a hand pump and can hear a "wet leak sound from that area. I am trying to determine whether or not it is the head gasket. As you know access is a problem. I may replace the hose any way as it may be leaking under the foam insulation which is around it.

Many thanks for the replies.

Can you do a pic of what you speak.
Parts of your description are not matching the heater system l have. No heater related stuff underneath the car and only foam insulation is on transmission in tunnel.

This picture shows the underside of the transmission tunnel, minus the transmission. You can see the heavy positive battery cable, and the two A/C drains. The metal tubing carries the vacuum signal back to the ECU, and just out of sight is the rubber hose, clamped to the metal tubing, making the connection to the crossover tube between the two intake manifolds. My first thought was a coolant leak from the heater hose/valve, running back to about where the shifter linkage would be. A long shot, maybe.