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1988 Jaguar XJSC 5.3 V-12 automatic (USA). Been having a constant battle with losing coolant and fluctuating engine temps. Replaced the thermostats with new ones with the jiggle pins. No change. Replaced the radiator with a used one that was tested and cleaned. No change. Decided to change spark plugs, wires and fuel injector hoses as they were nasty. All spark plugs looked good except cylinder 5 which had a broken fuel injection plug & clip which I have fixed. I have no steam out the exhaust, no valve chatter and no mixing of coolant and oil. I have bled, re bled and bled the system again and again. I even got an aftermarket temp gauge so I could see a number instead of the C to H gauge in the cluster. I even went as far as to bypass the heater core because i know it leaked a little. So far I've bought 3 different sets of radiator caps, replaced all of the lines including the metal ones to the purge tank in the fender well. Still, my problem persists. on a 10 mile trip to work I have to add anywhere from 1 qt. to 3 gallons. Not consistent at all. Sometimes purges, sometime not. I am completely baffled and every improvement seems to make it worse.
A few ideas, as you have not said where the coolant is leaking from, here is what I would do. First drain the coolant then:
1) remove the header tank on the inner wing (USA driver's side) and chack all the tubes and exit points are unblocked. THEN, run a small tube from the overflow spigot (the one just below the cap that is normally connected to the tank in the rear of the front wing) down to wards the ground by the engine front. This way you can easily see if pressure is building and overdflowing;
3) your water pump could be the ultimate problem, if it is failing to circulate the coolant properly (this failure to circulate is why your problem is occurring, the question is why!). In your position, assuming I wanted to keep the car, I would replace the water pump anyway, but that is just me. At the very least, ensure the belt driving it is tight.
4) The hotter area on A bank front. Your temp gun is pointing at the front water manifold. That pipe that runs rearwards from it is carrying hot water exiting the head from the rear of the engine to the thermostat and to the rad. The hot water exiting the front of the engine joins in there. carefully unbolt this front water manifold and look to see if it is blocked at all. If so, unblock it.
5) the cross pipe that has the rad cap on top and links the two banks. Ensure this is not blocked.
Whether your second hand rad is any good or not, I do not know, but in your position, I would not trust it, but fit a new one. Finally, it is quite possible that you have a head gasket failing and, while that is not putting coolant inot the oil yet, it IS pressurising the coolant. you can get a test kit for combustion products in the coolant, so before spending any more effort, you might do that test first.
Greg
Last edited by Greg in France; 07-09-2015 at 01:15 AM.
That header tank on the LH inner guard is a trap for all the gunk in the cooling system to gather, as there is no spigot out the bottom to drain it, as the early cars did have.
The hose that runs FROM the metal header tank mentioned above, TO the atmospheric tank in the LH inner guard (wheel and panel off for access) is a known problem, in that it blocks up with gunk, and that prevents the cooling system from "breathing", and when that happens it will purge coolant randomly.
The banjo bolt fiasco on the RH top of the radiator is also a PITA, and also blocks up, and if it is, the system will NOT bleed, no matter how many times you do it.
The small metal pipe arrangement running across the top of the radiator panel is also a blockage area.
The thermostats, OK, I know they are new, but are they the correct length??.
Have a read of the attachments. I chased this on one of mine for a very long time, and I kept notes.
1988 Jaguar XJSC 5.3 V-12 automatic (USA). Been having a constant battle with losing coolant and fluctuating engine temps. Replaced the thermostats with new ones with the jiggle pins. No change. Replaced the radiator with a used one that was tested and cleaned. No change. Decided to change spark plugs, wires and fuel injector hoses as they were nasty. All spark plugs looked good except cylinder 5 which had a broken fuel injection plug & clip which I have fixed. I have no steam out the exhaust, no valve chatter and no mixing of coolant and oil. I have bled, re bled and bled the system again and again. I even got an aftermarket temp gauge so I could see a number instead of the C to H gauge in the cluster. I even went as far as to bypass the heater core because i know it leaked a little. So far I've bought 3 different sets of radiator caps, replaced all of the lines including the metal ones to the purge tank in the fender well. Still, my problem persists. on a 10 mile trip to work I have to add anywhere from 1 qt. to 3 gallons. Not consistent at all. Sometimes purges, sometime not. I am completely baffled and every improvement seems to make it worse.
If you are adding three gallons of coolant are you leaving a slick stream behind you or does it vanish??
A quart could easily be superheated by a failing hg and vacate through the exhaust without you knowing (while cruising down the road), but three gallons would be full blown James Bond ;-)..
Sorry, what a pita!!
I agree that a leak down should be in your future before going any further into bit replacement, but your loss variation is huge / doesn't make sense.
I had blocked small steel section of pipe which joins the rubber hose which runs from the header tank to the overflow inside the LH guard (fender to you) I then borrowed a pressure tester and pumped up the system to operating pressure and voila! leaks appeared around 6-7 hose ends that were NOT evident beforehand. I crawled under and tightened all clamps probably no more than 1/2 turn each, problem solved. every Jag owner should have a mate with a cooling system pressure tester. temps sits just below N even at 40C traffic.
Thank you all for the advice, I've tried a couple more things mentioned here but have this Thursday off and will nearly complete the list and i'm in the process of making a video of my experience which i'll post Thursday night with more details.
Got the water pump off yesterday and rebuilding it this weekend. I'm in no hurry, I bought a second car off ebay til "Sybil" is fixed. J had gone over all cooling hoses and accessible passages and found no blockages. The car has only sat for 5 days and the water pump had this white residue in it. What is it? It's not hard and crusty either. TIP: I did get the water pump off without having to remove the Harmonic balancer/ Crank pulleys. All we had to do is remove all the bolts and the two studs form the A side and it came right out :-)
Seems to me that that something in the cooling system can't "breathe" or vent correctly. Was hoping to find a blocked passage in the A side but no luck. Power spraying the channels this weekend, maybe I'll find something new.
07-08-2015, 08:13 PM
5.3 v-12 cooling issue - baffled
