Oops - this is exactly how I by-passed the vacuum. The heater tap may be a problem - the tap seems very stiff and can only be levered up with the aid of a flat screwdriver. If I wedge it open would this do for bleeding? I can replace the vaccuum later. I located the Dayco in the US - just need to check if they will ship to Europe. Busy day tomorrow but I am leaning more and more towards a bleeding issue.

Brendan

 

OK, the heater tap is toast, so common.

If the lever is in the down position, that is open. Trouble is, there is NO way of telling if the internals have reacted to the external lever, mostly they do not. This now indicates to me why you have NO heat. That tap is jammed shut, or rust plugged, on the inside.

Remove the tap, use a 5/8" hose joiner to connect the 2 hoses. That way the coolant flows through the heater core, and does what it does, and then returns to the lower radiator hose spigot. This "flow" will bleed the system, and provide max heat inside the car.

The actual temp sender unit is still a bit suspect to me.

 

Success!. Sometimes it's the simple things. This morning I drained the coolant, manually opened the heater vacuum switch (it was very stiff), removed the vacuum pipe and refilled very slowly. After idling for 15 minutes the gauge was at mid normal and on the open road it dropped slightly and remained on the "r". Still no thermostat fitted but I'll wait till I get a 34mm. Still no heat but it's not a road (or hose) I'm prepared to go down just yet. Many thanks for all the advice and best regards to the forum. Now there's a little matter of a Porsche 924 Turbo in my drive!

 

Good to hear, ENJOY.

The Porsche, you are a brave warrior young man.

 

Best to check out the thermostat issue. These engines need the thermostat fitted. I have to say that I also suspect the radiator if its the original core, you can get a lot of lime scale that doesn't get flushed unless a chemical cleaner has been used to dissolve it. The block cracking was much more prevalent in the later 70s and early 80s until slotted blocks were introduced, so you may be lucky on this one. I rebuilt a 4.2 around an uncracked block and that was an early 70s block, whereas mine was a 1979 one and cracked.

You also need to replace the vac-operated heater valve too.

 

I second the thought of heat verification. An IR gun is ideal for measuring temps at various locations. OTH, an engine that is really hot and still has coolant will gurgle something awful. My 85 Ford pickup did that once. I fixed it with a new thermostat. I devined it was stuck in the closed position!!

I don't know if the heater matrix is a built in cooling requirement on your 4.2. Many engines have run just fine with the matrixes not connected or way back, never had them. But, in a pinch, running the heater in hot weather will give the cooling system a boost. Tough on the occupants, but better than walking.

Now, my car is a lump. But it retains the Jaguar cabin heater and vacuum control. I installed a valve on the other hose. Thusly, in summer, no coolant flows in the matrix.

No ill effects on engine cooling. And, I can power vent w/o need of AC.

I would clarify the mechanism that the shop used to "strip" the radiator. One is to remove both tanks and run wicked little strip of steel into each tube scraping out goop and calcium. Tis a rugged process and a weak core will spring a bunch of leaks. Done completely and if the core survives, it should cool. A competent shop will then test the flow. The other is a mere chemical boil out. Sometimes OK. Again, a flow check to verify.

A recore removes any doubt! Best short of a new radiator. But, caveat, all cores are not equal

You can do a rough flow check in situ. Not as easy on side tanked radiators as on top and bottom tankers, but doable. Use a garden hose with a rag to make it fit the top hose spigot as tightly as possible. Turn the hose on and see if water comes out the bottom spigot freely. It oughta pour out. Anything less means occluded tubes. Not scientific but indicative.

But, back to temperature verification before taking on the tougher work.

 

Maybe I'm not using the forum correctly - I posted some replies which I don't see on the thread. The latest is that the overheating is resolved. I drained the coolant, manually opened the heater vacuum, removed the vacuum hose and refilled very slowly. The gauge is now sitting at mid normal during idling and open road. Heater still not working but that's for another day. No thermostat is fitted but I have ordered a 34mm model. Thanks again for all the help.

 

I'm pleased to know you are getting the car sorted out. Older XJ saloons can be a bit of a pain to get sorted but they are a very satisfying car to drive once you have done so.