Of course when the tank is too full it will push it out once, and that it the purpose of the little drain hose on the expansion tanks neck. Later XJs had a catch tank in front of the left wheel, open to atmosphere, to deal with that excess coolant. So you can fill up the expansion tank as much as you want and it will be alright, but expect the level to stabilize, that is drop a little at first.
That is when the system is functional, but I think it is. I wonder- is the vented cap at the highest point of the system?
David
Hi David,
Iām sorry Iām not sure about your question regarding the vented cap?
The vented cap as I understand the term is on the expansion tank attached to the inner wing which is a lot lower than the thermostat housing of course.
Regards,
Bob
I think the vented cap should be the highest point so trapped air can be bled out first. Hence the long neck on the original expansion tank and the routing of the feed lines. I know that the XJS is unusual and sometimes problematic with its cap below the highest point of the cooling system, and BMWs need to be bled while running for that reason. If you have the tank mounted below the highest point you would have to remove all air via the thermostat cap, which would probably work, but it does mean that air can accumulate up there if Iām not on the wrong track which of course is not unlikely either. Maybe the POās reasoning got to that point when they switched the caps. Maybe.
Iād say continue, but have a look every now and then, and good luck of course!
Best regards
David
I just looked at the drawing Jochen provided and it is not obvious from that one. Early Series I and the plastic S3 tanks have all hoses entering at the top. The principle should still apply though, no air bubbles in the head, they should be pushed out first, and vented out the expansion tank first.
Thanks David, I do wonder why the PO changed the expansion tank, could rust have been an issue, although there is no rust anywhere else in the car, but who knows?
I was also wondering about the capacity of the the new expansion tank, my rough guess would be that it would hold around 3 litres. Does anyone have any idea how much coolant is expelled to the expansion tank? If the coolant system needs an expansion tank of, say 3.5 or 4 litres then once the expansion tank is full anything else will end up on the road.
Regards,
Bob
Bob, I think that is absolutely fine.
The tanks do rust badly, I removed a rust heap from one that was too much to carry in my hands and it was rusted through. This and the exhaust were the only parts gone.
If just right my guess is that somewhere between 1-2 litres of expansion capacity will do well. More is better just in case, but the standard expansion canāt be much more. Regarding capacity your tank seems good!
Besides, I have refilled a few litres of coolant before, on highway gas stations no less, and it has not exploded so you will not lose the engine during your shake down runs.
David
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All coolant level testing is done at the expansion tank, Bob - after the initial fill, the blank header/thermostat housing cap is left in peace. Opening the header tank just lets air into the engine circulation - which is counterproductive.
On the later cooling versions, the header tank cap was omitted - and the housing was changed accordingly and just named the āthermostat housingā.
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Indeed, filling up the expansion tank at each check is a common source of āa leakāā¦
However, this still leaves the question, in your case; where did the excess go. You say there is no venting at the expansion tank - which begs the question. Ie; there must be a venting as indeed on the original expansion tank filler neckā¦
Venting is absolutely crucial; coolant is incompressible. With a completely closed system the expanding coolant may exert a force, not measured in pounds per square inch, but in tons per square inch. Which cannot be contained - coolant will force its way out through the weakest link. Normally bursting a hose, or out through hose connections - or worse.
An equally important feature of the expansion tank cap function; as coolant is fully expanded hot, some pint and a half, the cooling coolant contracts. The venting now allows air to be drawn into the expansion tank - preventing a vacuum build-up.
On subsequent heating cycles; this air is compressed, air is easily compressible, allowing the coolant to freely expand - and coolant system is pressurized. No further coolant is expelled - unless coolant temps increase beyond the initial temp. Ie; the level in the the expansion tank reflects maximum temp reached - which may also seem like leak to the unwaryā¦
I see no other flaws in your plan - but do check temps with an infrared thermometer. Which may indicate that a replacement thermostat is called forā¦
Frank
xj6 85 Sov Europe (UK/NZ)
And the plastic expansion tank has a large hose to the bottom of the radiator so the thermostat cap is not needed to fill the engine. Then it has two small hoses connected, one from the highest point on the engine and one from the highest point on the radiator.
Frank - what do you say regarding the air bubble at the highest point? It could work as it is (some air would be accumulating) but I donāt think it would work well. The coolant rail would collect the rest and shouldnāt. I think the expansion tank should be mounted with the neck as high as the little step above the shock mount, or at least as high as the thermostat cap.
David
Hi Frank,
Thank you for this information, I didnāt know that on later models the cap was omitted. The expansion tank does have a vent in the neck so I think that thatās where the coolant has been going due to too much coolant in the tank when cold, then more coolant enters the tank due to expansion and then it is expelled making me think that I have a leak - thatās my theory for now anyway.
I was going to check the coolant level in the thermostat housing just to make sure that there was sufficient coolant in there - perhaps Iām getting paranoid!
Regards,
Bob
Youāre right on all accounts, Bob - all goodā¦
On the original expansion tank there was a spigot to attach a hose - either venting to the ground or to an atmospheric tank.
Air in the system naturally rises, collecting at high points. Care was taken to avoid air being trapped inside the block - ādriftingā into the header tank. To be forced into the expansion tank as coolant expands.
The air venting on the later versions was improved, with vent hoses both from the thermostat housing and the top of the radiator. Both systems are sort of self-venting by water pump action, but more care was required at initial fill with the older set-up - filling both at the header and expansion tanks. The latter system was just filled up from the expansion tank filler neck. But in both cases; the heating was set to āhotā at initial fill to avoid air trapped in the heater core.
However, as said before; a couple of heat cycles is usually required for the level to stabilizeā¦
Frank
xj6 85 Sov Europe (UK/NZ)
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I agree, David - the mounting height of the expansion tank is certainly not immaterial.
In principle, without interference the fluid in a connected system will be at the same level in all places - so the filler neck of the expansion tank should indeed be level, or higher, than the header/thermostat housing.
However, after the initial heat cycles; when hot, a cushion of compressed air forms in the expansion tank. So the level in the engine, when cold, is higher than in the expansion tankā¦
Frank
xj6 85 Sov Europe (UK/NZ)
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A bit off topic, but a relevant question nonetheless. On the series 3 1986 XJ6, is it ok to use the 82 degrees C thermostat instead of the 88 degrees thermostat? My mechanic installed the 82 degree one several years ago after replacing the previous thermostat, which, not surprisingly, was a pita to remove. I live in a warm weather climate, and he suggested the 82. The only potential problem Iāve seen, ( hope it isnāt a problem), is on cold days the temp gauge usually sits a notch below 90 degrees C. On very warm days gauge goes up close to 90, but fortunately, not beyond 90. Is there anything to be concerned about, or is the 82 degree thermostat acceptable? Thanks
Mel R.
Mine is a tad below 90 all the time (well mostly) and I distinctly remember that this is just right. I donāt know if 82 would in theory mean that the fuel injection runs a little richer, and maybe you just cured a high reading temperature senderā¦ but you should be doing well if it does read just below 90.
So yes, you are good and the only thing I would look at would be the fuel consumption/richness and those seem to be in order.
David
Hi, just an update on my 74 series 2. Iāve now replaced the temperature sender and I have taken the car for a āspiritedā one hours drive. I have the blank cap on the thermostat housing and the pressure cap on the expansion tank (as per spec). I filled up the thermostat housing with coolant and left the expansion tank with about an inch of coolant in it. The temperature gauge worked just fine and stayed on the 11 oāclock position for the entire drive. Came back home and left the engine to cool down completely. The expansion tank was a little lower than when I started but the main thing from my point of view was that the level in the thermostat housing was still where it was when I filled it up.
Feeling proud that all seems well (I will keep checking) but the kudos goes to you guys who helped me out, Iām more than a bit humbled by your knowledge and also your willingness to help out an amateur on a limited budget.
I love this car more than any other that I have ever owned in my 50 years on the road, itās the sort of car where youāre sorry to get home after a drive because you want to keep on driving it! Iāve had some pretty desirable modern cars in my time but none of them competes with my 46 year old XJ6, Iāve looked hard and I cannot find an angle to view it from that isnāt perfect (perhaps beauty is in the eye of the beholder!) and that XK engine! Thanks all.
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All good, Bob - but stop checking level at the header tankā¦
And it does not come amiss to check actual engine temp - with an infrared thermometer eitherā¦
Frank
xj6 85 Sov Europe (UK/NZ)
Frank - will do and thanks
Well, itās been a while since this discussion on my āmysteryā coolant loss and Iām just keeping you guys updated here. I found out late last year that the coolant was getting into 2 cylinders (numbers 1 and 2). It became obvious when I started the engine one day and the car almost disappeared in white smoke, I mean huge amounts of it.
So I got a mechanic to carry out the coolant test where it changes colour which confirmed exhaust gas in the coolant and he removed the head (with some interference from me!) and it was obvious that a PO had replaced the head gasket relatively recently and had done a poor job, bolts were not tightened to spec etc.
Also all was not well with the head itself and this was despatched to a specialist firm (read expensive!). 2 exhaust valve sleeves were just beginning to come adrift and had made very slight contact with the cam, no damage at all to the cam itself fortunately. The cam bearings would have just been reusable but I decided to replace them, 9 valves were unusable and the valve guides were starting to become loose. So, new valves, valve springs, cam bearings, cam followers, valve sleeves, hold down kit - pretty much a full rebuild and machining of the head. Iām pleased to report that they carried out a vacuum test and the head is probably now better than new.
All this occurred just before our summer/Christmas break and so I have been without the car since the end of November and I am hoping to have it back on the road next week (all being well).
I think that, in some respects I was lucky that the issues were found before something came adrift and caused catastrophic failure.
Anyway, just an update for you all and a note of caution for those with āmysteryā coolant leaks.
Thanks Robert!
With the analysis you did it didnāt come as a big surprise, I guess, but still ā¦ ouch!
Good job though! A lot better than the first one and hopefully good to last for the next 30 years.
Best
Jochen
75 XJ6L 4.2 auto (UK spec)
I really have splashed the cash to make this head the best it can be. Canāt wait to try it
We canāt wait hearing about it!
Good luck
Jochen
75 XJ6L 4.2 auto (US spec.)
Robert I sent a PM to you did you receive it?