Hi everybody! Hoping you can yet again bail me out of my own stupidity...

Over the last few weeks my 97 XK8 had been mysteriously losing all of it's coolant after a drive. It would be full at departure, drive with no issues and park up fine. After returning to the car the next day, the low coolant light was on and the bottle was empty. I refilled it three times before deciding that there must be a small leak somewhere that was cooking off before hitting the ground as there was no obvious puddles or coolant under the hood. As I had no gauge as to when any of the valley or rear hoses had been done and the heater pump has been dead since I brought the car home, I bought everything needed for a tear down from the thermostat tower all the way back to the heater pump. Thankful that I had already done the radiator hoses, water pump and crossover I dug in.

I removed everything and was unable to find anything obviously leaking but again assuming a pinhole, didn't concern myself with really examining each piece. I put everything back together and fired it up thinking 'job well done' 'aren't you special' etc. That was until it hit 180F on my torque app, the thermostat opened and the temp immediately jumped to 230 almost peaking at 250F before I shut it down. This temp spike was within 5 mins of start up at idle in the driveway... And in a fun twist, now there is zero heat coming from the hvac in the cabin where before I at least had some heat at half throttle.

After trying to bleed the air from the system again and another 240F temp spike, I came to find out that there is another coolant bottle in the passenger fender?!? I discovered it when I released the under hood bottle before it completely cooled and it overflowed from the fender liner.

So everyone, what have I done wrong? There is nothing leaking from the valley, the octopus or the front of the motor. Everything I installed was new and nothing was obviously damaged. Some guesses are below and your thoughts are massively appreciated:

I have misrouted one of the octopus connections to the heater valve and the system isn't flowing correctly?
The system still isn't bled correctly (the under hood bottle is continuing to settle to 3/4 full after several attempts to fill it) and a massive air bubble is blocking the flow?
The heater core is trashed after sitting forever with no real flow through it (the new / remand heater pump is definitely making buzzy noises now) and causing issues?
The heater valve now has an issue?
One of the octopus connections has some sort of shipping plug in it that I missed on install and the system isn't flowing to the back?
Something to do with the mystery bottle in the fender?

What really stinks is that I didn't do enough research before ripping everything apart and the original issue could have been the system balancing the fender bottle. That would defs explain where the coolant was going and I couldn't find it. It would have also saved tearing the car completely apart for no reason (the heater pump could have waited till late October).



cooling system routing as I understand it

 

It could be something as simple as a failed cap on your coolant expansion reservoir. When the cap goes bad internally, coolant can move from the expansion reservoir to the tank in the fender well, but often it cannot return to the expansion reservoir as needed. If you are certain that you have no leaks, I would replace that cap as a first step....

We have owned my wife's 2006 XK8 since early February 2012. I have replaced the coolant expansion reservoir once, but I have replaced the cap twice....

 

Well considering all the work you've put in, you shouldn't be getting the problem of engine overheating 5 min on idle. That's definitely a 9 out of 10 Bugger score .... especially as you think it's all buttoned up !

In reference to your pencil sketch, here's the Jaguar diagram for the cooling system for the NA system. (BTW The stickies thread above has the full Engine Guide, which is superhelpful.) The supercharged engine cooling system is far more complex.


I would separate your cooling problem into two separate issues as looking at the cabin heater blower system, it shouldn't be affecting the engine cooling circulation.

For engine overheating, non-functional thermostat ( air bleed nipple is installed up? not back to front?) or the coolant pump seem the ideal candidate. If you're sure that they are working, then there's a blockage/air trapped somewhere. Radiator is always a prime candidate and not on the list of items you've changed. From a full drain of this pressurized system, it's not unusual to have to come back 2 or 3 times, to top up the expansion tank. Burping pipes with the system open often leads to bubbles coming through.

More knowledgeable people here on the Forum, will chip in on the heater blower issue. Here in Bahrain it's 122degF in summer and I've never had to turn the heater on, even in winter.

 

Double check the overflow tank in the engine compartment. The '97 has an extra bleed hose to the radiator that is no longer used in later cars, so new tanks come with that "nipple" plugged. There is a lengthy TSB on this:

303-15.pdf

 

Make sure the thermostat is installed in the right direction. It will fit in either direction, but only works in the correct direction (which has slipped my mind...but I know this to be true.)

 

Thanks y'all for your rapid replies. I appreciate the help with this as somebody who won't be mentioned (it was me) may have spilled a gallon of soda in the computer running JTIS21 which then let the magic smoke out. leaving me somewhat blind on this.

David, I think that one is probably a 10 out of 10 on the bugger scale...

Thanks all for the other suggestions:

• I have the 97 specific coolant bottle since Fmertz caught it back when I was doing the water pump saving another purchase and return then.
• Jon, the o ring on the cap wasn't seated correctly which is probably why the fender bottle filled so quickly. fixed now.

I did do some digging around the web this and found the diagram attached below. It very much looks like I incorrectly routed the octopus to the heater valve by flipping top to bottom (at least according to my memory drawing). Once I get everything torn back down (sigh), i will let everyone know.

Hopefully I haven't done any permanent damage by letting the car get as hot as it was during the bleeding phase.