I know that I've seen it somewhere in my Jaguar documentation, but for the life of me I can't find it at the moment

So does anyone know the table of resistance values vs temp, for the water gauge temp sensor on a 1980 pre-HE V12 XJS?

I'm convinced my gauge is not reading correctly, never reaching the halfway mark. But the engine seems to be heating up ok, based on the feel of the hoses, heat through the heater and the inevitable heat in the engine bay after a run.

So, gauge, wiring or sensor. I want to start by checking the resistance reading on the sensor and see if its roughly right from cold and as it warms up.

Any help gratefully received.

Tks

PAul

 

The ohm readings should be something like this:

0 degrees C (32F) 5.9 kohms
10 degrees C (50F) 3.7 kohms
30 degrees C (86F) 1.7 kohms
50 degrees C (122F) 840 ohms
70 degrees C (158F) 435 ohms
90 degrees C (194F) 250 ohms

 

andegra,

That's great, thanks!

Do you know where those readings might equate to on the gauge?

Tks again

Paul

 

Each car is different, I KNOW, they should NOT be, but fact is fact.

I had a master gauge in mine, A Bank rear housing., and 185F on that was ABOUT a full needle width below the N, with just a hint of gauge background visible above the needle.

Same master gauge in the now Clarke Goose, and the gauge was about 2mm lower.

Same gauge in a 1978 PreHE, and the gauge was middle of the N.

The same master gauge in the 5 Series 2 cars ( 6 & 12) in my fleet at the time, all gave different gauge needle placements at that same master temp.

Then it was Beer O'clock, too hard.

The additional earth wire to the instrument cluster did help most of them, but mainly the Volts, and Fuel benefited the most.

This is why I have stated for longer than the brain will recall, YOU MUST ESTABLISH WHAT YOUR CAR READS, AND FORGET THE REST, and ONLY then can you continue the "running too hot:saga.

 

Paul
I feel there is a more reliable way to go about this. If you want reliable gauges, not just a reliable temp gauge, I would suggest:

• remove instrument cluster
• dismantle it by removing the white part from the black part (just a few screws). Winter is coming on, a nice clean white sheet on the table (very important) and a day or so's work tops.
• very carefully clean every contact point on the blue flexible circuit thing. This involves undoing tiny screws or nuts and with very fine paper cleaning up the surfaces. They may look OK, but they will not be. The earth bar along the top and all tiny fragile copper connections to it is particularly important.
• Go over the oblong holes that accept the multiplugs and clean all the tabs similarly. They will probably have come away from the flexible. If so, a drop of superglue will hold them perfectly, but re-clean afterwards.
• change all the warning lights push-fits, renew the feeble 2 watt push-fits for the instrument illumination with 5 watts of the same size. Then remove the green "bowler hat" filters over the illumination bulbs; they will have gone black, and without them you can see the instruments perfectly.
• Now we get to the barrel gauges. The Great Palm is very good on these. The electricity path to them is astonishingly gimcrack, and needs to be carefully cleaned and fixed as Palm describes. I have done this and the gauges immediately worked as they should - for example my fuel gauge consistently under-read and now when 1/4 full it shows 1/4.

Then to the temp reading itself. I would buy a 10 quid twin channel remote temp reader (all over ebay etc) such as:

and tape the wires to each thermostat exit. Then use the car (you run the wires past the door seals and have the meter in the car) and, as it comes up to temp, as Grant said, you will know the water temp as it exits the engine. Then look at your gauge and you will know what a given reading means.
Addtionally, once you see how easy it is to use the temp meter, you will have hours of fun reading oil temps, under bonnet temps etc etc, and all sorts of myths will be exploded: eg the bypass oil cooler system is not efficient and other shibboleths!
One thing i must mention: if you have a decent rad, thermostats etc etc, I would be amazed if the exit water is any hotter than 95C or so. What makes people panic about engine temps on the V12 is not a higher temp per se, but a higher temp caused by blocked rads etc etc, because this means no proper cooling going on. And all the "high temp is death" stuff is really "a blocked rad is death" which is a far more sensible statement. On my car, when the gauge is halfway between the N and the H, water entering the engine from the rad is only 5 degrees higher than when it is below the N; ie no cause to worry at all providing the fans and rad are as they should be. It is at this point that my main electric fan comes on automatically, and when it does I can see the gauge dropping.
Finally, if you would like any pics of the cluster in bits, just ask.

 

Grant & Greg,

Thank you both for your very helpful suggestions. I'm fast starting to realise that even once I've improved the integrity of the instrument cluster, my low temp readings may not necessarily be caused by a weak sensor.

As a result of my deliberations and all your input (both now and previously on V12 cooling issues), I've now decided to do the following:


1. First remove my instrument gauge and effect any repairs and modifications to improve its performance

2. Monitor temps of heads, 'stat housings, lower hose etc using my 4-channel temp reader leads. Establish a benchmark of temps vs gauge position and sensor ohm readings.

3. Drain coolant and flush engine and rad as well as I can whilst in situ. Don't really think I need to replace rad. Any thoughts on best approach for flushing this engine and rad without removing rad? I'm guessing that it's not worth playing around with the small drain tap but easier just to remove the lower hose to initially drain?

4. Clean up cooling fins and any obstructions in front of rad. I know my rad isn't too bad externally in respect of cooling fins, so again, trying to avoid having to remove / replace it.

5. Remove 'stats and all hoses. What is the smallest amount of dismantling work that I need to do to get to all hoses? I'm thinking of doing cam cover gaskets at the same time, so would like to optimise the dismantling work and do it in one hit.

6. Change 'stats. Is there still an issue with the Jaguar 'stats as regards the fully open length? If so, best UK source of known good 88 'stats? Gaskets or sealant?

7. Change hoses. Some have definitely been changed in last 5 years, but seems easier to do the lot in one go. Whilst in there, which pipes should I also change with more modern options? Should I also change crossover pipe, and if so, what better options are available?

8. "Re-assembly is the reverse of the above", as a Haynes manual might say! Any difficulties I might encounter?


Any input so gratefully received.

Tks

Paul

 

Paul:

1) Good idea.
2) Not a bad idea, but I have never gone that far.
3 & 4) Good again, but radiator internal integrity is critical if you are wanting trouble free years of use. If your radiators age in an unknown, out it should come and be dealt with properly. To best flush a V12 without dismantling the engine, there is NO fool proof way, sorry, fact is fact. Water pump off, stats out, AAV off, RH rear water rail housing off, the garden hose pressure from the back forcing water out the front, with an opened coathanger being prodded from the front. This will achieve about a 60% mud extraction, and about as best you will get. This road I have traveled too many times.
5) Inlet manifolds, Injector rails off, then the cam covers are accessable, as will be the RH rear water housing for the 3/4 above. NO idea on Jag stats, I have not been that road for 25 years, as the aftermarket I established are just too good. OE stat gaskets, NO sealant for the Gortex gaskets. ALL the hoses, oh dear, water pump is off, so the 2 there are easy, the crosspipe end hoses just a plain mongrel no matter in or out of the car. The heater, suck it up and swear a LOT and do them. The small ones under the metal header tank, 2 hours maybe. Might as well replace the 4 belts,as they are off for the water pump.
6) See the scribe in #5.
7) The water rail "top hat" seals, 4 per car, and the pipes associated should be changed whilst the Inlet manifold is off. These are the pipes and seals that run between the front and rear water housing on top of the cyl head. Cross pipe, nope, unless its rotted from the inside out.
8) HAHAHAHA, we all wish. Honestly, YES, but always LOOK carefully at any hose clamp you fit (you will be using NEW clamps, trust us all on that one), and ensure that you can get AT that clamp in a weeks time to tighten it about 1 full turn without ripping the engine apart again.

NOW

To do what you propose without removing the radiator is pretty much a wasted exercise, sorry again. The V12 of that age WILL have a huge build up of gunk around the rear 3 cylinders on each side, mainly from dissolved head gasket material, and NORMAL. To flush from the rear, with the rodding from the front is about as best you will get. My HE was clean in my opinion, having done the above, but when I dismantled the engine for oil leaks, HA again, I remove about 1KG of gunk stuff from around the rear liners. This does not appear to do any harm, but since you want to flush the engine, best you understand how this beast operates. To attempt to do this block flush with the water pump blocking both sides is fruitless.
Rodding down thru the AAV hole, and the 2 holes on the A bank, will loosen a lot, but not all.

 

Gotta agree with Grant. Deal with the radiator now. It's the heart of the system. Take it to a radiator shop. They'll take it apart and tell you if you need a new one. If not, they'll clean it and 'rod out' the tubes. It'll come back clean as a whistle.

This is no place to be uncertain ! If the radiator isn't 100% then nothing else you do will mean a thing.

"Just do it"

Cheers
DD

 

Grant / Doug

You're both right; I knew it anyway but was just trying to convince myself that it wasn't necessary so that I could leave the car inside whilst I did this. I had this deluded naïve view that I could leave the rad in place, plug the bottom of the rad, fill with a warm caustic soda solution leave for a day and drain. Then use a watering can to put some water in the block and carefully catch it as a small amount of sludge gently drains in a single stream out the front. Of course, I'm completely deluded and it isn't going to work. Grant bursts my bubble and then to cap it all, Doug joins in as well and brings me back to reality!

So, I've now got to find a way of maybe draining the rad and block inside the storage unit without causing too much mess, then strip all the parts off. Is that feasible or am I going to end up with coolant running off subframe, cross member and creating a huge mess everywhere? I'll then have to roll the car (with help) outside and then do the flush. Then get some help to push it back in once dry and gradually reassemble.

I've taken a rad out of my 4 litre and did it without splitting the aircon receiver or removing the bonnet. Now I've read somewhere that you can ignore the Jaguar instructions to split the aircon but you still need to remove the bonnet on a V12. Is that true. Can I pull a pre-HE rad without removing the bonnet?

I suppose the one small consolation is that it might be easier to change the original yellow fan whilst it's all apart and put in a black one? And I guess I might as well change all the belts whilst the water pump is now off......

It's going to be one of those "expanding" jobs, isn't it?

Tks

Paul

 

Paul
I am so glad you realise the rad has to come out and be (almost certainly) recored! The rad comes out OK without needing to undo the aircon tube that goes over A bank and forward.
The thing about the V12 is that the more you do, and the more you remove, the easier and quicker all the individual jobs are. I would do it all , do it once, etc etc! A rough list (bonnet can stay attached, you might need a mate to help pull the rad out, but that is all. A long-handled broom - a la orangeblossom - is a good plan with the struts undone at the car end):

• radtop panel off (detach aircon dryer brackets and bleed tube - if the pre HE has one)
• undo any loom attachments, undo the shroud nuts (7/16ths) top and bottom, undo top hoses and bottom hoses. Cut the bottom if you are going to renew, and you ARE aren't you.
• Pull out rad, inspect crossbeam under rad, blow out the condenser and oil rad with compressed air
• Remove all the drive belts (renew and keep old ones in boot) do NOT refit yet.
• If you are going to flush the block - I am a bit sceptical it will be needed but it cannot hurt - then remove the cross pipe and water pump and follow Grant's instructions.
• Then refit the water pump
• Now the cross pipe can be replaced pretty easily, with new hoses and clips. The best way to do it is to slide a bit of grease onto the pipe ends and push the end hoses right onto the pipe, not forgetting the new jubilee clips also! Then fit the middle hoses in place and position the pipe, then slide the end hoses off the pipe onto the water manifold castings.
• Now refit the belts
• It is pretty daunting removing the induction stuff, but it all comes off as a unit once the 24 7/16ths manifold securing nuts are undone and the fuel lines and injection loom are disconnected. It all comes off easily with two doing the removal, fuel rail, the lot, amazingly easy! see pic. In your case, if the aircon is not to be disturbed, just undo the fuel connections to the B bank mounted cooler and unbolt it from the intake stuff.
• After that the cam cover gaskets are dead easy, and renewing the oil senders a must. I cannot recommend the metal half moons too much either. Doing some sealing round the tappet block/head line is important, if you see oil leak evidence in that area - usually shows up as oil marks on the head above the exhaust manifolds. Roughing up the join and using high temp silicone has held up perfectly for me for years. second pic
• To renew the top hat seals on the water manifolds to water tube joins, undoing just the front ones is all that is needed, as the tube can the be pulled out of the rear one; BUT be very careful undoing the fixings indeed as the fixing bolts sheer.
• As to thermostats, apart from testing them in hot water which is a wise precaution, the normal UK suppliers are fine. In my car I fitted some Stant superstats which are very well made and hardly any more costly. if you want the part number, just ask.

All this sounds a lot, but, believe it or not, I would be amazed if it took more than a few days. But once the intakes are off, immediately stuff balled-up rags into the intakes in the heads! The worst part of the job is cleaning off the old gasket material from the heads, and rethreading all the 24 manifold nuts onto their studs - I used a magnet stuck onto the side of a steel (not chrome vanadium) 7/16ths nut spinner, with the nut jammed into the spinner with a bit of tissue paper. Once started they can be finished off easily with a normal 1/4 drive socket and extension.

 

Do it all. Do it right. Do it once.

I know this mantra gets beaten to death but, if at all possible, it really IS the best way to go.

I've been on Jag discussion groups for 20 years and can't tell you how often people have prolonged their own misery by taking the alá carte approach to V12 cooling system repairs (and a few other things).

Just reducing the number of times you have to bleed the system is a big plus, as it's a messy task.

I DO understand that logistics, time, and budget sometimes get in the way.

Cheers
DD

 

Just had my radiator cleaned up - didn't look that bad. It has had no air con for a long time - so nothing in front of the radiator to catch garbage

Still over 50% clogged

So well worth the experience

Cheers
Steve

 

Greg,

That picture of the intake system all intact makes me feel quite positive that the stripdown is less intimidating than it initially appears!

I've drawn up an initial list of all the parts that I'm expecting to change, but I need to check the car carefully as there are quite a few changes that happened over the years of the pre-HE and I need to ensure the exact current spec of my car. I'll start another thread once I'm ready to verify the parts list and start the work.

I just need to decide do I really have to change all those fuel pipes when the inlet is off? I'm worried that I might know the answer....

Cheers

Paul

 

You do Paul, you do! (know the answer and have to change them).