My 1999 XK8 coolant recovery tank continues to increase in fluid level (I can view thru open passenger door), but never seems to return to the header tank.
I have to continually add a small amount of coolant after each vehicle use. I don’t see any fluid on the floor, but recovery tank is getting pretty full and will overflow soon if I don’t drain the tank. Any advice?

 

Sounds like the coolant reservoir cap is faulty.
The cap is what regulates the IN/OUT of coolant to atmospheric catchment tank.

 

Agreed. Replace your cap with a decent new one....

 

Thank You….will replace this week

 

OK….I replaced the cap with no change. The recovery bottle in the right front wheel well seems to be full and pushing fluid out, nothing being drawn back into the system.

 

If the fluid is not being sucked back into the header tank when it cools down then there must either be a vacuum present in the tank, which seems highly unlikely, or the vacuum must be being relieved by air coming in from elsewhere rather than coolant being sucked up from the atmospheric tank. Are you sure that there is not a split in the header tank or in any of the hoses going to the header tank?

First check whether there is an inrush of air when you release the cap once the engine is cold. If there is no inrush you need to find out where the air is being sucked in. You could probably do this with a coolant system pressure test kit or perhaps using a compressor airline and pressurising the header tank through one of its hoses. I recall the design of the tank being changed at some point and one of the spigots being blocked off. Perhaps have a look at this video


to check that your tank is connected correctly.

Richard

 

Update on my coolant not sucking back into the header tank.
Seems that previous owner (or mechanic) broke off the plastic attachment portion of the unit and just stuck the hose in creating an air gap. From what I’ve been able to find online the tank should have a rubber hose that secures the line from the header tank.

Does the tube from the header tank extend into the fluid and clamp or just enough to make an air tight seal?
I plan on ordering a replacement similar to the picture

 

The tube which enters from the header tank must go to the bottom of the atmospheric tank or it obviously cannot suck up liquid back into the header tank when the system cools down. The other tube is a vent which simply needs to maintain the space above the liquid in the atmospheric tank at atmospheric pressure.

Richard

 

While shopping for a new coolant recovery bottle and thinking mine was defective I’m even more confused.
photo 1: mine…I thought it had the hose connection point broken off
photo 2: looks like mine and I see many of these for sale
photo 3: thought this was correct, but now not sure if there was a change from 1996 and my 1999.
Mine doesn’t suck the fluid back into expansion tank and was thinking it was because the line going into the recovery tank wasn’t sealed and allowed air into recovery tank.

 

Can I just ask whether you are actually reading my posts as I keep explaining what you need to look for but you seem intent on ploughing your own furrow? 🤔

Richard

 

I did read your reply….did you read and understand mine.
There seem to be two different tanks for sale online for 1999 XK8….one like mine and one with a secure connection for the incoming line. Which one is correct for my car?
My current one has the line unsecured and extended to the bottom of the tank and doesn’t return fluid.
I’ve changed the expansion tank cap and the line seems to have no holes or cracks.

 

As I have explained, the only requirement is that the line from the header tank must reach to the bottom of the coolant in the atmospheric tank whilst the top of the tank above the coolant level must be open to the atmosphere. If both the tanks meet this requirement in whatever way chosen by their designers, then either tank would be suitable.

Did you check out the Modurol video above to perhaps confirm that your header tank is plumbed in correctly? Did you check the header tank for a vacuum once the engine cools down?

There must be a simple solution to the problem, such as a small split in a hose which is not letting water out but letting air in, but more tests are required,

Richard

 

I did watch the video…had seen before.
Header tank is updated with one outlet plugged.
When removing the header cap I do hear the pressure release.
The only fluid I’ve seen is a small amount behind the front wheel, appears to come out where the header line goes in not the overflow tube.
My next step seems to be a pressure test on the header line.

On a different subject, I see that you own an X150. What are your thoughts on the aluminum body.
I’m retired from Ford, but worked at Jaguar engineering center in Whitley for 6 months in 1997/98. I was a Weight Engineer and put together the manufacturing/Business plan to convert the XJ and all future jaguars to aluminum. I did get one of the first aluminum XJ’s for a 2,000 mile drive evaluation, but have never driven a x150.

 

That is interesting. If the engine is completely cold and has been left overnight then there should not be pressure or vacuum in the header tank. I believe that this is directly related to the problem.

Unfortunately, the two (pressure and vacuum) can be difficult to tell apart as both sound like a whooshing noise when you unscrew the cap at normal speed. To be 100% sure you might be able to release the car slowly with the fingers around the bottom of the car and actually feel the outrush or inrush of air. You could also spray water or water/detergent mixture around the cap and it should be obvious whether the water/bubbles are being blown away from the cap or sucked towards the cap when you release it.

I can't say that I notice any particular difference with the aluminium body. It does not rust, but it does corrode, particularly where is is in contact with steel fastenings, I believe that it almost promotes surface rusting in steel sections such as sub-frames, suspension and steering components etc.

Richard