Good morning, guys maybe this forum will help. Already 3rd mechanic shop and no good news..
1994 Jag XJS V12 6.0L

1. Car for most of the time is running fine, temperature is not stable but not far away from N;
2. In Idle (standing position) it goes more than N - around 3/4 up to Max;
3. Changed - new Radiator, new Thermostat (82 Degrees), New Pump, new belts, new AAV, most of new hoses, new temp senders;
4. Did Head Gasket test - no leaks;

After riding some time, no pre-conditions it starts overheating and splitting coolant via Wheel Arch (Left - close to firewall); - See video;
Spills a lot - around 5-10 Liters and then stops;
Then again - refill and for 1-2 days - no issues; afterwards - same story;

Any suggestions, help - would be appreciated;

 

That coolant flow indicates that the atmospheric catch tank in the wing behind the stone baffle is being pressurised from the inner wing header tank as the car overheats and coolant is expelled. Filling the V12 with coolant needs care, did you bleed the radiator carefully and run the car with the defrost setting on, preferably pointing uphill, while you bled the radiator and filled it through the bleed screw hole?

Before doing anything else I suggest that the first thing is to renew the mechanical fan viscous unit and check the fan belt. Second thing is to verify that the auxiliary fan is working properly and that the temperature switch on the water pump inlet is accurate and working.
Thirdly: what temperature thermostats did you install (there are two, one each side) and are you 100% sure they were of the correct type that
1) blocks off the coolant cross pipe when hot? and
2) has the 1/8 inch bleed hole in the rim so that when the thermostat is fitted the hole is uppermost?
See this thread:
https://www.jaguarforums.com/forum/x...ywhere-213647/

 

Greg, thank you for your reply.
Forgot to mention - Bleeding was done many many times according to the manuals (Kirby + Web one) - Car was raised and bleeded via Bleeding screws on top Left side with RPM's raised;
Fan Clutch - new.
Thermostats - please see attached picture - seems to be 82 degrees and correct ones;

Really seems strange, because you can drive for 1-2 days - no issues and them suddenly temp. starts raising and overflowing begins followed with a huuuge leak..

 

In that case i would change the thermostats, I think you have one or both faulty. I recommend the Stant ones as in the link I posted earlier. You just need to drill a small hole in the rim. Do you understand about fitting the thermostat with the bleed hole at the top?

 

Greg, do you have a part number for the thermostats?
Best regards
Alfredo

 

Greg, just followed your link above... Sorry about that.

 

I agree with Greg 100%.

That atmospheric tank in the wing needs to be removed, washed out of all the settled mud, and reinstalled with it being 1/2 filled with coolant.

The hose FROM the engine bay tank TO that atmospheric tank must be checked for blockage, very common.

The stats are a high suspect.

This attachment I wrote years ago might help with that fiasco.

 

Dear Greg, yes, bleed hole is at the top.
I will try to replace them, but i believe that they are not the main problem. If it would be defective or incorrect i would have overheeting problems/issues all the time. And here i have them occasionally once per 2-3 days.

 

Dear Grant,

Thank you for your reply;
I assume that if hose FROM engine bay tank to atmospheric tank would be blocked i wouldn't get such a flud next to the wheel (As seen in the video) - so here i believe problem is solved;
I will clean this tank obviously but i really don't think that i will solve the issue with overheating and unstable engine temperature..

 

Agreed.

These systems are involved, but simple, if that makes sense.

All my investigation, was a LONG time before computers and Forums. A good shade tree, with a chair, and LOTS of beer.

Starting at the simple stuff is the only way, throwing parts rarely sorts any car. All mine had mud in that tank, and 3 of them had the "drop hose" cut square on, and not at 45dgrees, so sucking coolant back as the system cooled was a hit and miss at best.

The pressure cap on the engine bay tank is critical. The seal under the top section MUST seal to atmosphere 100%.
Also, I had floating temps on the Red car, dribbling the same as yours. Eventually, the NEW pressure cap was blowing off at 4psi, not the 13psi as specified. I went through all the caps at work and found 2 that actually were inside spec, 1 for the car, 1 for the shed, and the rest were returned to the supplier.
A simple $5 cap caused me grief for weeks, but simply sorted with the proper cap pressure.

 

I've double checked the listing from where i bought Thermostats - shorturl.at/xLPVW
I see that Ben from Simply Performance is writing that these would fit up to 1992; My car is 1994 - is there any difference between these 2? I doubt..

 

Nope.

The fully open length is the key here, and many years ago Jaguar had the wrong stats, too short by 4mm or more.

I worked for Jaguar at the time, and trying to get them to understand the blunder was a nightmare.

I have heard they finally sorted it, but I rarely use Genuine for anything, unless push comes to shove, so I may be out of date.. Simple enough to heat them up and measure the open length, 43mm is the aim length, disc to disc.

 

I suggest changing the 'stats for Stant ones because a 'stat can jam intermittently; either this or the caps, as Grant mentioned, are about the only things that can fail intermittently in the system. My post above gives the thermostat reference, this is the cap type I suggest:

 

Ok, sooo, i've ordered bunch of new different type of Thermostats - stating they fit XJS V12.
As soon as they will arrive i will double check length of opened position.
After opening i've found out that Heater matrix (Inside the Heater Box) was really filthy and kindish blocked. - Maybe this is one of the overheating reasons as well?

 

For sure.

 

Agreed, sort of.

The matrix restricted will make bleeding near impossible.
The matrix blocked is a general indication the cooling system, as a whole, is in sad condition.

I would do the stats first, providing they are long enough when open, and flush that matrix.

If you still have floating temps after that, the water pump will need to come off, and the block washed out of al lthe settled mud over many years. This is NOT unique to your car, all mine have needed that task, and the muck that washes out is just plain scary.
Radiator out and professionally cleaned inside and outside.

Repeat in 25 years.

 

Dear Grant,
Everything would be fine, but the problem is that i'm here not the first time.. Last year i did a major service (Excluding and not touching matrix) - changing everything "in the front" of the car - including - Cooling clutch, new rad, new hoses, new pump, flushed the whole system with garden hose (Though a very ideal tool ). This winter i bought a new Bleeding nut and refurbished AAV - happy here because world famous supplier for these also lives in Lithuania; 2021-June, July,August, Sept- all was pprox fine - temp. not stable, but not jumping to the max as well.
Only in the beginning of 2022 Season - all those problems started. Mileage on the car is approx 80.000KM - so quite a strong horse till now;
Also, i've found out that both of my caps are 16PSI; which is not according to the manuals since it states that the main one should be 20PSI - ordered, waiting for them to arrive.
To sum up this issue - will be waiting for new Thermostats and Heater Matrix followed with couple new hoses.

Simultaneously while waiting for parts i'm undergoing the process of AC Box refurbished (Inside the car) - thus i have checked Heater Matrix and it seemed to be in a poor condition, but NOT leaking; - this process started due to lack of heat in the car followed with debris caused by disintegrated foam inside heater box.

Kindish not a NOOB but far away from expert

 

I know you said it was tested for a head gasket leak, but I'm still wondering about it. You dump a lot of coolant, that is either due to pressure from a head gasket leak, or boiling inside the engine. Do you have any cold start misfires, or excess steam from either exhaust pipe? Or does the oil have any milky look? Either of those would suggest a head gasket leak. If you still think the gaskets are OK, I would be wondering about something restricting coolant flow. Yes, it could be thermostats, but as you said, that probably would be a more consistent problem. Have you tried an infra red thermometer to see if you can determine if just part of the engine is overheating? It appears this issue started AFTER you replaced the rad, stats and pump? Does the new radiator have air bleeds on the top like the original? Trapped air might cause your issue. It's possible there is debris inside the new radiator that intermittently covers the outlet, causing overheating. Also possible that your new pump has a loose impeller.

 

Thanks for your reply.
I've tested head gasket 3 times with the same chemical test - "Smelling" exhaust fumes in the coolant. - all times same - answer - negative.
Currently i'm waiting for the new Heater Matrix, Heater Valve, different types of thermostats and couple new coolant hoses. - Should be with me within couple weeks. Hopefully (Although when having Jaguars you don't believe in miracles anymore..) i will see positive result in engine temperature. Taking into consideration that Rad, Clutch, pump is new .. fingers crossed.

If not... Head gasket change - here i come. Here the biggest issue is finding new Head Studs (Bolts); - i've seen new ones going for around 500USD - for nuts - sounds crazy...

 

I do not believe that the head gasket has failed! If it had, then the coolant would fail the sniff tester, and/or the oil would have water in it.