V12 HE Coolant Problem

[Brakebuster]

or

maybe my flat level ground wasn't as flat and level as it needs to be , lmfao

BB

[steve_m]

I've read to park it nose up so that the rad bleed nut is at the highest point.

[b.l.hayward]

If you look at the HE parts list, the cap on the cross tube has the part number EAC4192 with the legend 20lbs which, to me, suggests it is a pressure relief cap. My EAC4192 also has the draw-back poppet valve in its middle like the cap on the expansion tank. In addition, on my HE, the cross tube filler neck has the same configuration as the neck on the Expansion Tank. There is an outlet pipe above the cap seal which goes, via the pipework sitting on the radiator slam panel, to the expansion tank - the parts list shows a 'jiggle-pin' at this point as well (just like the thermostats). Will look for the plug/bleed cap tomorrow.....

[b.l.hayward]

Time for an update....The new, genuine Jaguar Pressure caps arrived from SNGB but I have had to wait for it to stop raining long enough to footle about - my garage is big enough for the XJ-S but not both of us! So....located the radiator bleed screw (tks for the pointer BB) which turned out to be only marginally tighter than finger tight! Removed it and no coolant was visible below the threads. Topped-up using BB's modus operandi and EVENTUALLY coolant started to dribble out of the bleed hole. At this point, it is interesting to note that despite having run the engine/topped-up etc several times there was still air IN the radiator top ie above the level of the two top rad hoses (when you think about it, this is entirely logical - unless you take out the bleed screw - which is not mentioned in the ROM!). Time to put the pressure caps on and run the engine for 30 mins (BB's MO).

As the cap for the Expansion Tank has a lower blow-off pressure and is in-line with the CT I thought I would have a look at the old one's flexible seal to see if this held any clues - it had a deep circular groove from the tank neck and was also pitted so, it seems to me, that it may well leak under pressure - and FILL THE CT! Discarded this and used one of my brand new sparkly ones which was quite difficult to turn onto the neck of Expansion Tank - the old one was easy, OR the old cap spring/seal was weaker (and therefore might lift at lower pressure anyway).
Started up and ran the engine on tick-over for 30 mins; no leaks or steam from anywhere , the hose to the CT warmed up but did not stay hot-to-touch for very long after start-up, unlike previously (hopefully this means that the initial expansion had occurred and then stopped - the system having stabilised internal heat/pressure) and the temp gauge showed between N and C as it always has done.

Now, a question for BB, please. I am fighting the desire to check the coolant level at the cross-tube filler cap (as the Owners Handbook says you should periodically in any case). Do you feel it is best not to (ref your previous contributions to the thread) and rely solely on the temp gauge? I can sort-of appreciate that once the system has been thru a heat cycle then it is a stabilised, closed system (assuming it's working ok). If you take the cross-tube filler cap off (which is actually connected at its neck, via hose and pipe connections, with the Expansion tank), then that effectively 'opens' the closed system. Or am I missing something?

[Brakebuster]

excellent news, and glad you feel you have at least seem happy with the results

the big issue with removing the caps, is that the engine needs to have fully sucked back any expanded fluid from the CT , you can only be sure of this once the engine is completely cold ( like the next morning ) , this means the system is effectively balanced at that time, and you can take off the cap at that point, you should see coolant in the engine fill tube ( crossover pipe ) at the desired level ,

In addition to what you have done, I always cycle the in car heater matrix to allow fully heated coolant around it, and to expel any air that might be in there, this should be included when doing the ' full heat cycle ' after filling ,

and of course, none of this means anything is the system is not fully functional as designed ( rad caps, one way valves in bleed lines operating, heater valve operating correctly (default is open and closes on vacuum ) , good pump , unblocked radiator etc etc

BB ( must...... resist....... removing rad caps )

btw, an in-depth investigation and component check was carried out on my own 1989 V12 by several peeps at the breakfast meet last Saturday , with relation to this topic, rad bleed screws and venting systems were fully traced, lol

[b.l.hayward]

Thanks for the clarification, BB. Just took off the cross-tube filler cap on a stone cold engine.....and the coolant was at the correct level - deep joyl!! .

I suspect that both using the right coolant refill MO and replacing the duff pressure cap on the Expansion Tank worked in combination. I realise that I had subconsciously assumed that as the Pressure Cap did not leak visibly externally it must be ok (just like the old pressure caps without a CT). What I had failed to take into account is that when the first seal leaks coolant past it, it leaks into the space between the seal and the external cap and is then pushed into the CT...which eventually fills and overflows if the cap seal doesn't close/seal as it should after initial coolant expansion.

Many thanks to all contributors - it really helped exploring the issues.

Now for an MoT......