Heat always on ?

[Bingo]

The temp slide is set to the far right, to cool.
But after 15 minutes the accessory tray, foot wells above our feet are radiating heat.

Is this common with your cars ?

Outside temp is 90 degrees.
Seems seems like the bypass valve is not working properly ?
But the entire engine and engine compartment becomes really hot. It take an hour or more with the hood up to cool the heads to touch.

Jim

[Glyn Ruck]

What is your engine temperature gauge showing? Might need a new sender unit.

Sounds as if your vacuum operated water tap is jammed open/corroded.

It is likely that all your heater box flap seals are shot & might be stuck as well.

Good luck.

[cass3958]

On the S Type there are two means of heating or distributing the heat.

The first is the way the heated water gets to the matrix in the heater box. There is a vacuum valve which is notorious for going wrong. The valve is on the water pipes going in to the heater box situated just below the heater box on the bulkhead. It looks like a little UFO. This heater valve is a sealed unit with a diaphragm inside which is operated by a vacuum. The vacuum pulls the diaphragm down and opens the valve. They go wrong because of two things. If the incorrect coolant has been used over the years the centre of the diaphragm which is steel corrodes and the valve starts to leak water out of the small hole. Secondly the diaphragm which is made of rubber can split allowing water to leak again out of the small hole on the diaphragm side. Both of these faults will cause the heater to heat up as they will allow hot water into the matrix and hot air into the cab. This vacuum valve is no longer available so you can either look for a new old stock one and decent secondhand replacement or SNG Barrett now supply an alternative which is an adapted XJ6 vacuum valve which fits.

Vacuum valve that looks like a UFO.

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Inside the vacuum valve when corroded.

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Replacement vacuum valve.

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The second way the hot air can get into the cab is hot air going from a hot engine bay into the heater box and then pushed into the cab via the fan. The slider flap you are talking about operates a cable that in turn operates a lever on the side of the heater box that operates a flap in the heater box. The flap controls if you are letting hot air which has passed through the heater matrix in to the cab or if it has blocked this passage of hot air off allowing cool air from the scuttle flap to pass into the cab. The flap is sealed with foam but over the years the foam deteriorates and there is no seal anymore and air will pass the flap and go into the cab. As the engine compartment heats up, any air drawn through the heater will be hot air unless you open the scuttle flap allowing cold fresh air to flow to the cab but with a defective seal even this air will be mixed hot and cold. The only way to replace the foam seals is by stripping the heater box. I replaced mine a couple of years ago and I thought I had photos but cannot find them. I used 3mm sticky backed closed cell foam and replaced all the seals including those from the heater box to the bulkhead.

So there are several problems here. First the slider which operates the flap via a push pull cable can get stiff or disconnected meaning the flap is not closing. The seal on the flap has gone allowing hot air to flow past the flap. The vacuum valve is defective allowing the heater matrix to be constantly hot and lastly your scuttle flap is not working. If the scuttle flap is not working it has its own problems. These are that the piano hing can get rusty and seize up. The hinge is difficult to get to to oil but several of us have had this problem and with patience you will eventually get it freed up. There is another vacuum valve that operates this flap and this tends not to fail but if you are not creating a vacuum and storing it in the vacuum reservoir situated under the front left wing the scuttle flap nor the heater valve will work anyway. The reservoir is known to corrode where the fixing bracket is welded to the side so air is allowed to pass into and fill the vacuum.

Vacuum tank showing where corrosion can be found.

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Once you establish which part of your system is defective we can then give you more information to how you can repair it.

[cass3958]

Further to my reply the other problem you were concerned with was the engine bay getting too hot. In the UK we do not have an awful lot of really hot weather so cooling the engine and engine bay is not too much of a problem.

Remember the engine is cooled by three elements. Air, Water and Oil.

For the engine to remain cool you need a good flow of all three. To increase air flow make sure the fan shroud is in place as this directs air through the radiator not around it. Clean the radiator with an air hose to remove dead bugs and dirt to allow better air flow. You can buy a radiator with larger cooling fins and a double bank of cooling tubes. You can increase the number of blades on your engine fan to get more air flowing. You can fit an auxiliary fan, a Kenlow fan behind the front grill to push more air through the radiator. Have your exhaust manifolds heat treated or wrapped to stop heat going into the engine bay.

Water. There are some waterless products which reduce the temperature of the coolant in the engine but most over heating is caused by silted up water ways. Make sure that at your next service you flush the radiator and engine block with a high powered flow of clean water. You will be amazed at the amount of rust, sand and dirt that comes out of the system. If the coolant can't flow it can't cool the engine. The XK engine does have a tendency to drop expanded water out of the over flow meaning after a couple of weeks your water levels can become low. Check you water levels and we have just had a long conversation about fitting expansion tanks to the engine to stop fluid loss. Details of that topic can be found here. viewtopic.php?f=22&t=1294

Contrary to believe the majority of engine cooling is done by the oil. Friction causes heat and oil controls the friction. Having good clean oil and clean unobstructed oil ways will keep the engine cooler. So again at your next service get the engine oil flushed out not just drained or vacuumed out. Empty the oil and then flush the system out. there are products out there for this but I fill the engine with a fifty fifty mix of clean cheap engine oil and paraffin. Then I allow the engine to tick over for a couple of minutes so this mixture flushes out all the silt and debris before draining it again and filling with the correct oil. You can also fit an oil cooler to the engine.

Good clean air, water and oil ways will keep your engine running cooler.

[Glyn Ruck]

Outstanding response Rob. I was awaiting a response however you have covered all in excellent detail. Better than I could with my impatient ways.

All I have to add as you have alluded to anyway. Sometimes one should bite the bullet and replace the radiator with a superior unit. Saves extra fans etc. Cut out the middle men & go direct. Forget Chinese Aluminium horrors. You can use citric acid for a very safe cooling system flush.

Northhampton Radiators makes an excellent uprated "Tropical" unit for the Jaguar S Type. It is what I have fitted to my car & she runs as cool as a cucumber in the African heat. Nigel & others here have done the same. As Cass says, however ~ oil plays a large part in the cooling.

The unit looks authentic but has far greater cooling capacity.

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[Bingo]

Good grief !

All of you are just so nice and forthcoming, just fantastic.

I will dive into you suggestions.

Thank you,
Jim

[Bingo]

1st issue I found was the vacuum lines to the vacuum control box were incorrect.

I connected the line that runs to the valve that actuated the cold air door to the air button.

I disconnected the vacuum line at the vacuum valve and sent pressurized air through the line to identify it and attached it to the heat button.

I attached the last line to the off selection.

Test drive tomorrow.

[cass3958]

That's good and I did not even get to describing what each of those buttons do but they are fairly self explanatory as long as you have found, they have been plugged into the correct tubes.
Basically HEAT opens or should open the heater vacuum valve to allow hot water to the heater matrix. AIR opens the scuttle flap and I can't remember what OFF does. lol.
If you open the AIR scuttle flap you will know if you have a good vacuum or not because once you switch the engine off the scuttle flap will close almost immediately so you have a poor vacuum store and possible a leak or it stays open for five mins or possibly longer showing a good vacuum store.

If you come across any problems please come back and ask. There are loads of us on here who have stripped and rebuilt their cars all willing to give answers.

[Glyn Ruck]

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[John Quilter]

I think OFF on the three button control closes the scuttle vent and presumably closes off the water valve. My scuttle vent sinks down to closed after a minute of two. I can live with it. Not sure if it is the vacuum capsule, the rubbber lines or the three button device that has some minor leaks after 56 years of use.