Xj12 cooling issues
 

I inherited an XJ12 from my son after it blew the rad, I had tried to tell him there must be a problem after several coolant hose failures, but what does a Father know? I am guessing a head gasket problem or cavitation erosion or liner crack.... None of which I like the sound of! Does anyone have any advise? What's the best method to pressuring the cooling system and or to check for leak back? Would appreciate any help before I start pulling the heads off..... Thanks!:icon_doh:

You can buy a radiator pressure tester kit that will allow you to pressurize the system and identify leaks in the hoses and in the head gasket.

I suspect that you can buy it locally but if not, search ebay for "radiator pressure tester"

This is what I have and it cost me around $100. It has fittings for pretty much any model car.

I suspect the above shown pressure tester will be most useful in seeing just how high the pressure is getting :-).

If the engine isn't running hot (you didn't specifically mention) the pressure (to blow the radiator and hoses) is almost certainly the result of compression being pumped into the cooling system. I would've thought the pressure cap would've limited this to 16psi or so <shrug>

Alternatives would be a "block test" kit....which uses a dye to detect hydrocarbons in the coolant. Or visit a repair shop with an exhaust analyzer...which can be used to "sniff" the coolant for hydrocarbons

Or.....

If coolant is churning in the header tank with the engine running is a sure bet that compression is entering the cooling system

Cheers
DD

Nice inheritance.

You are NEW, so WELCOME. You will enjoy your time here, trust us, fun will be had, and the best part is your car will be FIXED.

You have not stated which year this beast is. There are many variations to the cooling system over the life of a V12 in the XJ series.

Head gasket issues are rare, NOT unknown, but rare in the true sense of that word.

Thermostats STUCK is common.
Radiator tanks seperating due to old age is common enough.
Water pump issues from age are now creeping in.

I agree with what has already been said, and it will all fit as you delve in the deep end.
I would start the engine with the cap/s OFF, and if you get a fountain of water/coolant, then compression pressure is getting into the cooling system, and deeper work will be required.

However if the coolant just sort of flows out as the temp rises then that is NOT compression pressure. Bear in mind that compression pressure is at least 140psi, and even higher on the HE engine, so a good spray will occur if that is getting in.

A blocked radiator core (internally) will give wierd spurtings also, so dont rule that out too early. If the radiator maintenence is unknown, I would be looking in that direction, due to over pressure from lack of flow can blow hoses, but, as Doug said the cap/s should take of that blow off I would expect.

If it is a HE, the small hose from the header tank to the atmopheric tank may be blocked, so blow off from the cap CANNOT happen, it has nowhere to go, common on the XJ-S models.

The cap may be a dud, it happens, and is not blowing off until a much higher pressure. I test ALL caps when I buy new ones (they hate me), and the variance in blow off pressure of the same spec cap is just plain scary.

Thanks to all for the good advice, now I'm inspired to pull the old girl out of the garage and make a start of the tests you advised. To answer some of the questions, I think the car is a '93 model from memory (don't have the papers to hand) and I'm not aware of overheating issues but all you mention makes perfect sense! I'll certainly let you know how I get on. I'm in the middle of rebuilding my old XL 500 Honda right now but suck for parts so the Jag will kep me busy for a bit! Thanks again.

One more quick question... What should be the correct rad cap pressure and the correct thermostat opening temperature?

16psi on the pressure cap and 88ºC on the thermostats

Cheers
DD

Many thanks! I'll check it out.

Well folks, it doesn't look good, to me at least! I dug may way to the back of a rented garage and uncovered my '93 XJ12 with about 100k miles on her, popped a good battery on, checked oil and water, turned the key and she burst into life! I drove the few hundred yards home and gently removed the rad cap with the engine still running (I was surprised how warm/hot the coolant was already?). Water flowed up and out of the header tank followed by a steady rythem of water raising, follows by bubbles, water rising again and more bubbles that come every 5 seconds or so. To me this looks very much like the systems being pressurized. Now I'm losing confidence, I still think it's head gasket(s).... Is this a job you can do yourself, cams, chains, timing and so on may need special tools and or training /knowledge? Is there more I could do before pullings bit off?

Mmmm, a 1993 MAY BE an XJ40 body shape, and MAY BE a 6ltr engine. I know you are new, but have a look around here and see if you can identify your car for us, is it a Series 3 body shape, OR, the squarer XJ40 body shape?????. This will be VERY helpful with advice, coz the 2 models are SOOOOO different.

OK, stuck thermostats will give that heat in that distance. My HE is too hot to touch the stat housings after 1/2 a km (500metres) of driving, so no real surprises with that finding.

Since it has now got heat in it, it also has pressure, so removing that cap with the engine running will give the overflow you discussed. Much like removing the cap from a soda bottle after you shook it, and releasing that pressure quickly gives that same basic affect.

The way I read your description of events, sounds like stuck stats, and an internally clogged radiator. That would cause the coolant out of the header tank cause it cannot get through the blocked radiator, it has to go somewhere. The bubbles are maybe just air in the system from this blockage.

As you said it burst into life etc etc, and that would NOT happen with head gasket issues, as some cylinders would have water/coolant in them, and a distinct mis-fire would be present until it cleared, mmmm.

Head gaskets are a PAIN, and labour intensive at best. Actually getting the heads off insitu is not easy, do-able, but not easy.

I take the engine out, it just makes sense to me, but then again I am down here, and we do things strangely by some peoples standards.

Thanks Grant. If you have an Internet address I could send you some pics or I'll try and put them in 'My Garage!' I would say it's kinda squareish and according to the log book it's a 5990 cc engine. Exact reg date is 01.06 1993 and SN is SAJ JHA LS4 AP68 3505 if this helps? Now it's all cleaned up it looks fabulous and it would break my heart to effectively scap it so I'm committed to sorting it out somehow.

I hear what you say and I would love to think this would be the solution. I dont have access to car lifts, hosts etc so engine out is prohibitive, i can't pressure test becuase the rads leaking! Certainly I will change the stats and of course I would need to whip the rad out anyway cos it's leaking, so the exchange will solve any issues of blockage there, I have to see where I can find a rad somewhere... I'll scan the net ASAP.

Just to add that it did run a bit lumpy in the beginning but hasn't run for 2 years... With a 12 cal it's hard to say it it was missing significantly, I don't know this car well enough for now.

Pics are up now: Can you tell me what it is exactly?

OK, sounds like a 6ltr, in an XJ40 body shape. Garage is still empty, so maybe waiting for "verification" from the mod/s.

The XJ40 onward have only ONE wiper arm/blade, as compared with the S3, which has 2.

My email is gyfrancis@adam.com.au.

The leaking radiator will be reeking havoc with the system, so that is a MUST, as you say. It MAY BE a plastic tank unit, not sure when they arrived in the production scheme. Either way a decent/reputable radiator repairer should be able to sort it for you.

I would look at some of the suppliers sponsoring on here, and then the ones in the UK, which should be able to sort a new one if that is the only option.

I agree with your comment re the missing, especially after 2 years of sitting idle, a rough running is "normal", but water etc in there will be very noticeable.

Yes! Single wiper arm and 6liter so that makes it a XJ40, what does the 40 stand for? I've ordered the stats and cap but the rad in uk looked pretty esxpensive at £560 so i' look around a bit in this forum. Thanks a million for sticking with me on this one, I really appreciate it. I have the pics in my albums but didn't work out the my garage bit yet! Cheers for now and thanks again. Tim

I've just been doing some more research and I now believe this car to be an XJ81 because it has the in dash glove box and the BBS lattice style wheels, built between 93 and 94 and of course the 6 cyl engine, do you concur? Wold this make any difference to my problems and or remedies? Cheers.

NAH.

The '40, '300, '308 are all Jag production jargon, and I did once work it out (when i was at Jaguar), but it really means little in the "real world".

Your XJ81 sounds about right, but down here its an XJ40 6ltr V12, build date "??", and parts sourcing etc is as simple as it gets.

The V12 only arrived "back" in the XJ40 body with the introduction of the 6ltr engine. The 5.3ltr engine never got fitted to the XJ40, that is why the S3 body shape stayed until late '92.

Check your radiator, see if the side tanks are metal or plastic. If metal, any radiator specialist can clean it to "as new" fairly cheaply. If its a plastic tank radiator, then cleaning is more involved, sourcing the tank seals is difficult at best, so a new unit is usually more efficient all round.