Heater feed hose exploding

[taylor6632]

Jaguar xk8 - 1998

Evening all,

The heater hose that runs from the thermostat area, under the inlet manifold and then to the octopus pipes? at the rear split the other day just where it joins the plastic pipe at the front of the engine next to the thermostat.

To save hassle and to get me home i cut off 2" of the pipe and then re-attached the pipe back up, basically cutting out the split section. However, once the car got up to temperature i was watching under the bonnet and the hose literally let go, burst and split again, showering the engine and front wings and beyond with coolant as it was a fair pressure. The car heater was off.

Should it be under that much pressure? If so, then maybe to whole hose is a weak link and needs to be replaced but i wouldn't have thought that pipe would be under much pressure. Not had any overheating issues in last month i've owned it and starts cold and drives lovely.

Any help is appreciated

[J44EAG]

If it is the same hose as fitted on the 4 litre and 4.2 litre S-type R, X350R, XKR and XFR, then that would appear to be a similar issue to that of the supercharged variants.

Certainly on an R, that hose gets cooked to extinction at the front where it joins the rear of there thermostat tower area. It literally fries to death under the supercharger.

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I`d be most interested to hear if the hose that has gone is 2W93-9F814-BC.

Around six months ago, I high lighted this issue on R models in the X350 pages in the magazine. Then and indeed now, I`ve been unable to confirm if this hose is also fitted to naturally aspirated models. It would be useful to know.

Mike K

[taylor6632]

Cheers for the reply, I'm on about the other hose. Runs along next to that one in the picture but snakes up to front of the engine and to the water splitting bit in front of the thermostat.

[J44EAG]

We could really do with seeing a picture if you could upload one.

I`ll see what I can find on the parts listings, hopefully with an illustration.

Mike

[oldtimer]

Mike,
Hose failure has been discussed by you and others across a number of Jaguar variants for what seems years. It makes me wonder if some of these complicated shaped hoses are up to the job. Having said that, the vehicle in question is now eighteen years old with an unknown total mileage. Is this another case of unscheduled maintenance that needs attending too at say fifteen years. As you recently described hose failure in the "valley" can have catastrophic results. If I found myself in the same predicament as Taylor I would have to consider changing every hose in the cooling system to avoid the catastrophe you previously described.

Taylor made reference to the system pressure, unless things have changed , the system shares a common pressure throughout and is regulated by the relief valve built into the Radiator or header tank cap. The system pressure will be that marked on the cap.

You talk about hoses being fried but I suspect that the under bonnet temperatures are no more than those of a V12 but cannot recall hose failure being a particular problem .

I'll be interested to hear your comments

P

[J44EAG]

Points about replacement after a number of years are very valid, Phil.

I only have to site the issues I had with a small 1/8" ID pressure hose which worked the pressure side of the S/C by-pass actuator to know that at thirteen years, that pipe was also cooked dry to extinction. It just crumbled in my fingers. Whether silicon hoses stand the heat any better, I can`t pass personal comment on that other than to say that Viper Performance offer some quite seriously up-specd quality coolant hoses. It is work looking at their site.

Similarly a friends X300R blew a hose on me on the M27. I was encouraged to give it some wellie, so I did. The un-maintainable, one foot long water pump to the side of the block ripped open like a ripe banana. I say unmaintainable because it is so well buried below the inter-cooler matrix that you can`t get to it without seven hours of demolition! Something eventually has to give, and when it does, just like the 300R which blew on me, the amount of gutting out before you can get to the offending part can be quite daunting. These buried hoses can`t be inspected at service time and I`m afraid they get forgotten about when the car gets to banger status. Only when it goes to classic, do those hoses ever get changed.

Hot is hot what ever engine it is on. Heat, pressure and age conspire to catch up all at the same time. Whoosh!

Mike

[J44EAG]

I wonder if this diagram helps?

Mike K

[taylor6632]

[taylor6632]

[taylor6632]

those are photos of just after it split on my drive. Had driven it 5/6 miles after the first split had been temporarily repaired and then as i popped the bonnet on drive at home she let go.

Its the one with the cable tie tied to it in case you can't see the split.

[J44EAG]

Looks like the inlet manifold will have to come off.

Worth the effort in my opinion. At least the bolts are accessible. It will give you a chance to look at every other buried pipe and replace as needed.

Nice to see that the thermostat tower has at some time been replaced with a metal version. The original unit was plastic and the threaded inserts would spin when you tried to get the thermostat nozzle off. The plastic could also become extremely brittle. The pipe across the front of the engine also has a tenancy to fall apart where the hoses join on to it. Replace if at all suspect!

If you have this section in bits, my own experience suggests it would be no bad idea to check you have a metal impeller in the water pump. Early water pumps have a plastic impeller which can disintegrate. Fit the later 4.2 pump which has two extra bolt heads forward of the bolt holes around the periphery of the pump mounting. Berkshire Jag Components have some OE quality pumps available for about £40.

Also replace the thermostat which with age and mileage can become sluggish. The cylinder head temp sensor can also fail from around 80k miles. That gives a full hot, in the red, temp gauge reading and diabolical cold starts if the sensor has gone duff. Buy only the genuine OE sensors NOT after-market units! I`ve seen stat, sensor and thermostat issues on my V8 S-type and X350R when both were just coming up to the 80K mileage. All this from personal experience.

Mike K

[taylor6632]

I have a new water pump, thermostat and hose in the post but i don't want to take all the manifold off for the pipe to burst again. I'd rather try repair or replace the pipe without much hassle as if it blows again then i know it won't be the water pump nor thermostat. Should it be fine after replacing all those bits, then i can put the work in and do both hoses under the manifold and all gaskets etc

[taylor6632]

So i've stripped it down this evening. Got brand new looking water pump with metal impeller, brand new looking thermostat (probably replaced when last owner did stat tower, few months ago). Coolant once drained looked clear and healthy.

I've no idea why i've got so much pressure in the system and hoses are bulging and bursting. I'll order up a new bypass hose as that one is well and truly had it!

[J44EAG]

Check to see how much of the old plastic impeller is left, or if it slips around the drive shaft.

Your thermostat should open at 87C and be fully open at 95c. I`d ditch the current stat and fit new OE only. That gets you back to a base start point. Old sluggish stats can cause issues with burping air out and that will cause pressure. I`ve seen this type of issue on my V8 and it was all stat related.

When you get system pressure, do the cooling fans switch on? Has the heater been working OK?

Mike K

[taylor6632]

There is no plastic impeller as the water pumps been upgraded along with the stat tower i reckon.


Fans used to kick in fine and heater has worked without fault. Previous owner replaced the heater pump and octopus pipes, just not the ones under the manifold unfortunately, haha.