It had become more & more clear that I had a serious cooling problem with the XJR.

I'd been to the local 1/4 mile drag stip a couple of weeks back, & could not better my time from Santa Pod, and worse, the car was getting really hot, in fact one one run I watched the coolant temperature in the test mode & it hit 103°C as I was crossing the line. It was heat soaking badly at idle too.

Fast forward to our trackday last weekend https://www.jaguarforums.com/forum/x...ck-day-105254/ and the overheating became very apparent. I could only get three or for quick laps in before the gauge started rising. It even went into the red & brought the light on. Monitoring the temps via Torque on my phone, I saw well over 110°C several times.

So it was time (probably even too late) to look at the thermostat.

James (34by151) managed to find a locally manufactured thermostat that would fit our engines, I lot of hunting around in Sydney I eventually located a parts store that had some in stock.

So yesterday it was time to change the thermostat, this is where things started to go wrong...it should be a 30 minute job, but it ended up a day & a half of stress and drama.

It's not that hard, drain a couple of litres of coolant out the drain in the bottom of the radiator, open the three bolts in the thermostat housing, put in the new thermostat, bolt it all together, refill with coolant, away we go.

Not for me.....

Someone must have done the thermostat on this car previously, as the three bolts on the housing were rock solid & would not budge, later we would find some sort of thread sealer or Loctite on the bits of bolts that we managed to extract.

One came out without issue. The second twisted the head clean off. The third stripped the Torx key in the bolt head....bugger....

Luckily i'd been able to get a few turns out of the last bolt before the head stripped, so I was able to hacksaw the head off without any damage to the housing.

With the thermostat out, it was time to check the operation. Dropped it in a glass of boiling water straight out of the kettle. And nothing, it did not open at all. Well that was clear enough, but now we have to deal with two bolts jammed in the housing with no heads.

The first one came out easy enough with some vice-grips. The second one did a couple of turns then sheared off leaving nothing on the outside, jammed solid in the thermostat housing. "oh dear" i said in a soft, calm voice...

Quick run down to the hardware store before it closed for a dremel, some bits & a bolt extractor. 2 hours later, 4 destroyed drill bits, we had drilled out no more than 3mm from about 15mm of bolt left in the housing.



We called it a night & I tried again this morning, bought some cobalt drill bits, which lasted about 30 seconds each (these Jaguar bolts are the most amazing material, hard as a coffin nail, but the heads will twist straight off)

This is what it looked like at that stage



We didn't want to try removing the thermostat housing from the block, if there was loctite here then it was likely on the rest as well, and if those bolts sheared or stripped it would be closing time...

A guy on a local Aussie peformance forum suggested I call in a proffessional thread repair guy. I never heard of such things, but sure enough there was one local to me, so I sent him some pictures & he said "not possible, you will have to get the housing off the engine" so I started removing hoses, and got onto the four bolts.

Of course, the first three came out easy enough, but the last one, the hardest to get to, was tighter that a <insert racist joke here> and it started to strip the head off the bolt....

Lined up the Thread Repair guy to come over ASAP, and then started pulling the rest out for him to extract the last bolt, and then to get the broken one out of the housing.

So after pulling all the hoses, the reservoir, airbox and the fan, it looked like this;



Thread Repair guy arrived, I went to the bank up the road to get him some cash, & when I got back he had the housing off the engine & was working on the snapped bolt. Not 30 minutes after he started it was finished. Best $170 I ever spent on a car.

It's all back together now, with high-tensile bolts, washers and everything coated with anti-seize paste.

And the car is running nice & cool again. Thanks James for your help & thanks Tim for suggesting the Thread Repair guy.

Let this be a warning for anyone attempting to change a thermostat! LOL

 

That's awesome glad to hear all is well. If you don't mind me asking, what are the temp readings now? On my BMW 7 series the temps used to be from 100c to 105c..on really hot days other members would claim to be as high as 110c.
I lately installed a lower tstat at 90c and it gets to about 100c at idle. The heat really kills the seals on these cars. In your opinion, would you say JAGs have the same issue with heat? I hope not I'm about to get one..

 

Sounds like a right royal PITA but well worth doing obviously.

Nice post Cambo, thanks for sharing

 

I have used the thread guys up here Cam a dam lifesaver especially when you don't have a huge tool chest

Maybe put studs in it next time they would clamp harder and be easier to remove and repair not a fan of bolts in engines
I replaced all the bolts in the essex V6 I am building for my Xpack I brought over from the UK 2 years ago big job but if I ever have to pull it apart again its going to be a lot easier LOL

 

Temps are much lower now, driving around town i'm seeing 93°C and sitting stopped in traffic with the a/c on it gets up to 96/97°C, but drops down very quickly once i'm moving again.

The factory thermostat is an 84°C, i.e. it starts to open at 84°C. We couldn't find one locally so had to put in a 77°C unit. So it takes a little while for the engine to warm up, but so far it seems the temps on the road are basically the same as 34by151's XJR. So long as the overheating is gone i'm happy.

Doc I was going to put in studs but the bottom bolt (the one that had to be drilled out) is really hard to get to, it would be hard to get a socket or spanner onto it.

The other thing is that the housing is sealed with o-rings (to the block and where the thermostat is), so it's not necessary to torque the bolts up so tight. Once the mating surfaces are together that's it, the o-ring does the job. I went for high-tensile in the hope that the heads will be a bit stronger & resist stripping. But I can't see it that being an issue again now the bolts have antisieze on them.

EDIT

One other thing to mention, when refilling the coolant you are meant to open the vent at the top of the supercharger to fill, as well as to bleed the air out, as that's the highest point in the cooling system. It's a 19mm hex. I bought a bolt & two nuts with 19mm hex' & made a tool to open the plug just using a 19mm spanner. The bolt & nuts cost $3, an M19 Hex drive was $37 from the same shop.

But if you can get the car on a slope with the nose up (like my driveway) and the reservoir cap get's higher than the vent port then you don't need to bleed it out. I checked it just to be sure and there was no more air in there. Another little trick from 34by151

 

2 Tips

First if you have the front wheels on on ramps the SC fill port is lower than the reservoir.
There is no need to remove the SC fill plug, just refill the reservoir as normal

Second Tip
A backend of a spark plug socket is a 19mm Hex, Just drill a hole on the socket and use a big screwdriver though the holes.

Ill post a pic tomorrow when im filling the system

Cheers
34by151

 

That's awesome. I like the idea of having a lower tstats, when I see cars climb to 110/115c at idle it makes me cringe.

 

Panthera13, a lower thermostat will not lower your peak temps
All it will do it will do is open sooner

Cambo replaced a broken thermostat, this is why his peak temps were too high
IE is thermostat was not opening

The xjr will operate around 95C
The stock thermostat opens at 84C, so it is fully open at 95C
Changing to a lower thermostat will only cause it to open sooner, it will still operate at 95C but will take longer to get there

Where it will help is on the track
As iy open sooner it will take longer to get up to 95C, so if you start cold you may get an extra lap before it heats up

Ill go back to Cambos's thermostat was faulty and this is why it over heated
On the track he was getting 110C after 4 laps where my peak was 98C
Both of these were with the fan running flat out the whole time on the track
As a comparison when I ran with the fan controlled by the eCU i peaked at 101C

Cheers
34by151

 

Understood thanks.

 

A lower temp t stat will also kick off a p0128, and i dont know about thread locker on them. Never seen from the factory. But you do know what happens when steel is inside aluminum....it electrolically(?) corrodes and locks. Another good reason to run a sacrifical electrode inside the cooling system

 

So far it hasn't put the Check Engine light on so i think we are OK. And i've definitely done the two consecutive "trips" as per the JTIS description.

There appeared to be a dark coloured thread sealant on the bolts that we extracted, so if it's not from the factory we can only assume someone did the thermostat before & put it on then.

The 4th bolt holding the housing to the block was likely due to electrolitic corrosion. In any case, a good dose of silver anti-seize means we won't be seeing this issue again. I hope...

 

I have read with great interest this thread and discovered how electrolytic corrosion between parts of different metals could trigger failures in mechanical components.
I was naively assuming that engine designers took all provisions to avoid such effects, especially within components that are vital for engine life, such as in mechanical parts of pumps.
Are there other known failures (or risks of) of mechanical components due to electrolytic corrosion in Jag engines ?

 

My experience is a bit different.

My current Vette came w a 187* F stat and I replaced it w a 160* F stat. Highway and around-town temps (traffic jams not included) are about 20* F lower with the 160* but after several laps on track day the high temps are the same w either stat.

YMMV.