Expansion tank SII - Take 2

XJ
21

Eric,

Jaguar chose to call our two tanks “header tank” (right in front of the engine), instructing to check and, if necessary, top up to the base of the filler neck, and the “expansion tank”, situated at the left fender, instructing that the expansion tank should be approx. half full. The caps have different pressure ratings - so don’t get them mixed up. All info as per OM p.23.

As for your question: the OM specifies 18.5 litres of coolant. That should include a correctly, i.e. half full, expansion tank, probably measured at approx 20°C. The expansion coefficient of water (antifreeze would be different, but I don’t find figures for glycol) is 0.00018/K. If the pressure in the coolant cycle permits a boiling temp of approx. 100°C, you get a temp delta of 80. Now 18.5l x 0.00018 x1/K x 80K = 0.26 litres.

This calculation does not correctly mirror expansion to the true boiling point that may be affected by the coolant itself, nor the change of expansion of the coolant given that you should use coolant. A chart relating to coolants suggests that upon heating from 20 to 105°C volume will expand by 0.84 litres without coolant added and by 0.83 litres with 50% coolant. Not a hill of beans though …

From the seat of my pants I’d guess though that 2 litres in the expansion tank should be okay. The expansion bottle in my Spitfire is approx 1 litre and caters to a coolant circle of 4.5 litres. The OM advises to keep it half full on a cold engine. I tend to fill it like one quarter and have plenty of reserve.

Friendly, but inexperienced service staff tend to “fill her up” at the expansion tank causing green (yellow, red, blue) puddles behind the left front wheel at the next stop when the heat soak leads to expansion …

Good luck

Jochen

75 XJ6L 4.2 auto (UK spec)

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22

I finally did what I should have done to start with. Measured the volume of the original expansion tank: 1.7l like the SI. So this cute 2l aluminum tank will be fine :slight_smile:
Now need to figure out how to fit it, with top of the neck level with the top of the engine side filler.
Wish me luck :slight_smile:

23

**
Doug expanded on the terminology, Frankie - and why it is confusing…:slight_smile:

With Jaguar; the early versions, small xk engine, had the (pressurized) header tank in/on the radiator - used to both fill and check/replenish coolant. Fitted with a pressure cap to maintain system pressure…

The large xk engine had the header tank on the water rail, used only for initial fill of the system - a sealed cap was used for the initial fill, then left in peace. A separate expansion tank was fitted to accept expanding coolant - and a pressure cap fitted to maintain system pressure. The expansion tank used for check/replenisment of coolant…

On the later xk versions; the header tank was omitted, and the expansion tank, with a pressure cap, accepted expanding coolant. Expansion tank used both for initial fill and check/replenishment.

At some stage; an atmospheric recovery tank was added - to accept excess coolant ejected from the expansion tank.
Basically used to avoid wasting coolant after the initial fill.

In all cases; the initial fill, topping up, includes excessive amounts of coolant - and the excess, due to hot expanding coolant, must(!) be vented out of the system via a hose at the pressure cap. If not, water being incompressible, extremely high pressure is generated at molecular levels - breaking the weakest links…

With the atmospheric tank fitted; as the coolant cools and contracts, coolant may be drawn from that tank back into the expansion tank. If not fitted, or the recovery tank is empty, air is drawn, through the pressure cap, into the expansion tank. This air cushion is then compressed as the coolant heats and expands - to fill the system…

On the V12 the expansion tank is replaced by a remote header tank - with an atmospheric recovery tank added for the HE versions. But the header tanks otherwise functions like the expansion tanks on the xk, but the fill/replenishment is a bit more involved - a doug rightfully points out…

These are xk ‘official’ Jaguar terms used in ‘our’ Jaguar manuals - but there was no industrial standard. Causing confusion for anyone with experience from other makes. Though all cooling systems follow the same principles; room and venting must be accommodating expanding and contracting coolant…somehow…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
**

2 Likes
24

One of the things that surprises me greatly is the severity of the corrosion in Eric’s tank (see earlier photo he posted). He says the tank is 15 years old but we don’t know what coolant changing regime has been employed.

With coolant changes every 3 years and a 50/50 concentration of the correct “antifreeze” I would have thought that the corrosion inhibitors would have prevented anything this severe.

One of the things I have noticed in my own system is that the “expansion” tank needs to be independently flushed and replenished - it is pretty much a “dead leg” in the system that otherwise doesn’t get proper attention.

Coolant is high on my list at the moment and I have seen an interesting way of checking corrosion protection by measuring voltage between the header tank coolant and earth - apparently above 0.25 volts indicates less than optimum protection. Is this a reliable check?

Frankie

25

I cannot say that I have been very disciplined with coolant maintenance…

The condition of the tank might be strongly driven by my lack of discipline.
Yet, the day I bought the car on a hot day of 2003, on my way back from South London, the tank failed in a traffic jam on the motorway. The PO had repaired it with fiberglass… (when I took that engine apart, for fun… the block was cracked between every single cylinder!).

The replacement tank I got at an extertionate price back then, from one of the usual suppliers now has its guts open for all to see.

So my personal experience with these items has not been a good one. I deserve to offer myself a different way of doing things (and be more disciplined with maintenance…). :slight_smile:

Hopefully this aluminum tank will be “Eric-proof” :slight_smile:

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26

I admire your perseverance Eric, and am sure it is being rewarded!!!

F

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27

Uh oh… you should be! Not sure if aluminium will fare better than steel - the S3 is plastic and doesn’t care. But it isn’t as pretty. Capacity wise, you’ll be fine. Isn’t the spigot on the filler neck intended for a recovery tank? You‘d need a double-seal cap.

Wouldn’t gas-tank sealer (por-15 and the like) work? Is the tank isolated like the radiator?

David

28

It is curious indeed…
I don’t know if my original tank was ever changed before my ownership, but I own the car for 20 years and my tank is still fine even with a very relaxed coolant change regime.

29

That’s great.
My tank was “fine” until I decided to flush it with vinegar like I do with all my other possibly rusty bits. Then the pinholes appeared and I opened it to see…

30

So I think I will fit the aluminum tank in place of the screen washer bottle. Obviously it will need an adhoc bracket and that gonna be a fun project to apply my growing fabrication and welding skills. :slight_smile:

IMG_20200523_084135
IMG_20200523_0841352016×1512 1.19 MB

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31

A little video why not.

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