Coolant pressure

[MyQuest]

On checking my ’99 XK8 (54K miles) when the engine is cold, I’ve notice that the large coolant hoses are ‘sucked in’ / partially collapsed. Presumably caused by the water/air contracting as it cools. Undoing the expansion chamber/reservoir allows air to enter, equalising the pressure and returns the hoses to normal. If left for a couple of days it slowly sorts itself out.
Question: Is this normal and is there - or should there be - a vacuum relief valve in the reservoir/cap/system?

Michael

[mike020150]

Modern systems are sealed to eliminate water loss and the need to top up regularly. So, some pressure or vacuum can exist in the system quite naturally. The abnormal thing is the way your hoses are distorting. If they are the originals, it sounds as if they have gone soggy with age and would be best changed before risking failure on the road. I'm old fashioned and regard hoses as routine service items to be changed after 4/5 years. As a quick check on their age, there's a good chance that any in service replacements will have been secured with jubilee clips whereas the factory used crimped clips. Mike.

[MyQuest]

Thanks for that Mike.
Will have a looksee tomorrow but suspect they are the originals - even though the engine was replaced under warranty at 30K.
At last year's 6 year service (very expensive...), I had the coolant replaced - wonder if they bothered to check the hoses?
If I change them I'll fit 'eelibuj pilcs' - (old aviation engineer's joke - run it backwards....).

At the same time I'll suss out the complexities of checking the camchain tensioners - vide this month's magazine article. No doubt more expense..

Michael

[Nik]

I had this problem and it was cured by the jaguar centre replacing the water pump with one that had a impeller attached to the shaft !!!!
they also replaced the thermostat and said the hoses were in good order and were soft intentionally!!

[ainslin1]

Hi, I have a 98 XK8 and the expansion tank exploded on Saturday at high speed! Has anyone experienced this? I'm thinking the pressure too high but where is it regulated? The engine runs fine and got me home temp at normal!

[M100TWO]

The expansion tank screw cap has a pressure valve built in, has the tank split?

[Astromorg]

As M100TWO says, there's a pressure relief valve built into the expansion tank cap, but importantly, yet missed in earlier posts, there is also a vacuum release valve. Collapsing hoses are an indicator of a faulty suction valve in the coolant cap. An exploding expansion tank suggests the pressure relief valve has a problem. A new tank deserves a new cap!

Excess pressure and/or coolant is released through the small bore pipe from the expansion tank that points towards the bulkhead and on to the overflow tank in the righthand front wheel arch.(That's for 4.2. The 4.0 arrangement may be positioned differently)

If the level in that overflow tank is above the end of the pipe from the expansion tank, when the coolant system cools down it will suck the coolant back. If the level in that overflow tank is below the inlet pipe, then a small amount of air will be drawn back to the system to be pushed out again when the engine heats up.

I prefer to keep a level of coolant in the overflow tank so the system never sucks air even though such air would be expelled on heating up, but it's not important.

The tank can be viewed by opening the driver's door and shining a torch through the openings above and below the door hinge.

[ainslin1]

Many thanks for the input. Astromorg, M100TWO.

[ainslin1]

Hi, XK8 46K miles, expansion tank exploded, well new tank fitted and now believe is the thermostat seized, so more here soon.

[paul463]

Hi Have you found the reason for the exploding expansion tank?
My 2013 XKR, had sudden temperature rise then it dropped as quick, then fine but I took to garage and had thermostat changed and checked that fans were working. Half a dozen trips later the temp shot up, I pulled over and the expansion tank bottom blew out.
Recovered back to garage, new tank fitted all was good or so we thought but when they had it back two week later for MOT the tank exploded again during emissions test.
Garage has been told the material the tanks are made from age and this could be the fault, then people switch to alloy tanks. But I am concerned there is another issue with the cooling system.
Any ideas?

[mike020150]

Hi Paul,
You do sound as if you have been unlucky. Coolant header tanks are a weak spot on many makes including Jaguars but to have two go so quickly is unlucky. Can you be certain the thermostat was changed and for the correct one? If there's a deeper problem, I would have anticipated older hoses blowing rather than a new tank. Hence, assuming the tank was new and not second hand, my initial suspicions would centre on a close examination of the tank and a request for a refund. Mike.