i have got an XJS V12 sports coverable 1986. I am getting trouble with the water pumping out of the side not centre radiator. The temp does go to normal it is not overheating but throwing the water out i have removed the air con radiator and replaced the two thermostats and two radiator caps centre and side, and flushed out the engine but she is still throwing the water out of the side radiator before the temperature leaves normal. Can anybody give me any help or suggestions on what this could be and how to fix it.
Thanks Paul Trike

 

Have you filled it and blead it correctly?

Is the athmospheric bottle (sits in the left side wheel well) "working"? The hose from the "water bottle" to the wheel arch can easily clog up and can result in the water bottle spouting water out, which would normally drain to the athmospheric recovery bottle.

The "side radiator" as you call is is just a water reservoir... You fill in there and in the bypass between the cylinder heads.

How much do you fill in? Do you open the "bleed valve" on the radiator when filling water? How full do you fill the bottle and bypass pipe?

 

Paul,

Firstly welcome to the forum.

Your location is unknown to me, so I will do a quicky list for now. Some different markets have market specific issues.

Please go to the "new member" area and intro yourself. It is the proper thing to do, and keeps everyone warm and fuzzy.

The V12 doing that purge after new stats and caps is not common.

Obviously I always have doubts about the replaced items. By that I mean "just because its new does not mean its OK", as dud items do happen, and again RARE.

1) The main radiator sounds like it is clogged internally, thus preventing flow, and since pressure builds quickly in a V12 it has to go somewhere, and the header tank cap is the obvious passage.

2) The small hose from the header tank travelling towards the rear of the engine bay, goes to the atmospheric bottle inside that wing panel, and it is PRONE to blockage, and again, when pressure builds, it "should" vent down that hose TO that bottle, but since that hose is blocked, it cannot do so.

3) The system has air in it, MAINLY behind the stats, and the V12 can be a fair MONGREL to bleed, and if it is NOT bled 100%, it will purge coolant forever. A member called Doug has an excellent write up on bleeding these beasts, and a quick search should find it, OR, he will slide by and give you a link, as I am not that clever.
The fact it is purging coolant prior to leaving the C, I am sure the stats are NOT opening, and that will be FACT with air in the system, as mostly the air sits right behind the stats, and they refuse to operate if not immersed in liquid.

4) Blown head gasket/s. NOT common on the V12 at all, so it is LAST on my quicky list.

 

Further to Grant's post, did you use the OEM type stat with the little hole in the top of the round plate that is clamped by the gasket? This allows air to purge when the stats are closed.

Greg

 

The center radiator cap must either be a high pressure one, or not pressure relief. The only pressure relief should be the side one. If the center is pressure relief, then you will almost certainly have leaks all over.

 

My " center" and side caps are both 16 lbs after market pressure relief caps and I drive in NE Florida year round with NO problems and NO leaks ever for well over 6 years. I was out yesterday in 99 degree heat for 4 hours in the car with no problems what so ever.

 

When you replaced the thermostats did you use the style of thermostat with the "jiggle pin"?
This bleed hole with pin are absolutely necessary to permit the V12 cooling system to properly bleed/purge the air out of the system.


"Regular" thermostats, (those w/out the bleed hole and pin), are called out in many parts manuals but they just don't work.

 

HI JT, You can be lucky and have a center cap that seals the top or is a higher pressure than the side. I only mention it as if the center is a pressure relief, and it 'vents' before the side, then the full pressure is on the top seal and that is not a great seal and it has no where to go but all over the engine and make a mess.

The original center cap was non-venting.

 

Actually, I believe that none of the points are 100% true, though there is some truth in them. It does not matter much what the centre cap rating is. This is because, on an HE V12 at least, the spout does not vent to the engine bay. It vents to the radiator top banjo bleed system. This take-off point is below the cap lower seal. If the lower pressure seal on the centre cap lifts up, the pressure so relieved should not vent out of the top of the spout because it should be prevented by the top seal of the cap on the top flange of the spout.
Having said that, it is true that the top seal of the cap might leak a bit while this is happening, as it is not normally such a brilliant seal on many makes of cap.

If the centre cap is replaced with a solid cap that just seals the spout top, and does not have an inner lower pressure lift relief part, it will have no effect on the cooling system at all. In fact, I have done this on my car and it stopped the very slight water loss I experienced - so some coolant was getting past the top seal on my previous cap, even though it was a top quality cap.

Finally, there should be a one-way non-return valve in the rubber tube from the spout to the purge system to ensure water only leaves the spout and cannot get back into it from the rad. If this valve is blocked (quite likely) or the rad top purge system is, so there is no way out of the spout to the rad, it would certainly put more strain on the top level cap seal, given a low-rated lower cap seal due to an incorrect one being fitted, which might make it leak. The main point to understand is that the centre spout should vent into the rad system, NOT into the engine bay, if the system is set up and the cap top seal working as OEM designed. If you cannot find a solid cap, fitting (say) a 22 llb cap in the centre spout and the OEm specified 16 llb cap on the header tank, should mean no possibility of leaks from the spout, as the 22llb pressure should never be reached to let water get to the cap top seal.

Greg

 

16 lbs radiator caps were approved by Jaguar years ago for our XJS's...