You don't have to remove the DCCV to test it. Details here, post #2:

https://www.jaguarforums.com/forum/s...2/#post1714570

 

Wow, that's a strange one. I'm not doubting you, just curious how it all went down. What prompted you to try the aux pump?

I have to wonder if the failed aux pump was the root of the overheating. There may still be another fault present, and is being partially masked with the new pump. If you look at the document linked in post #16, and scroll down to page 3.3.2, it shows the aux pump is only in the heater circuit.

Consider this scenario: On any car, if the cooling system is not up to snuff for whatever reason (clogged radiator, for example) and the engine starts to overheat, you can turn on the heater to drop the coolant temperature. The heater core is basically a small radiator, and that extra cooling action can be just enough to prevent overheating.

On the V8 S-type, in an overheat situation, the aux coolant pump is automatically commanded to run. If (a big if) the AC system is in good condition, it could automatically put out enough cold air that you may not realize the heater is also cranking out heat to keep the coolant temperature down.

Just a thought, not meaning to hijack the thread from the original poster.

 

Its all overheating related so its all good stuff

 

First sign of overheating was cooling fans running on after parking. Checked fluid level, bled system, changed thermostat all to no avail. Discovered aux coolant pump in manual and tested with multimeter. No circuit. Changed it out and problem solved. This was 5 yrs ago and still running strong.

 

Karl are you sure about the AUX pump?
When I worked on mine it seemed to run 100% of the time just like the inter-cooler pump?
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Am I sure? Heck no! I'm just blindly repeating what I saw in a factory training manual, with an excerpt in post #16 above:

https://www.jaguarforums.com/forum/s...7&postcount=16


Note the reference to the selected temperature on the HVAC panel. Perhaps your temp selection was high enough for the aux pump to be commanded on. What if you checked again, but with the HVAC selected off?

 

I think your right. I live in hot country and the AC is always on so the AUX pump would also be always on then too.
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Well I did some more things this weekend. (finally found some time) I completely flushed the cooling system out and put in all new fluids. Also replaced the thermostat. Took it out for a drive and everything was great for the first 10 mins. Then like always BANG, overheat. I have my temp running on my Torque app and could see that the temp was moving up and down around 185-195. Normal operation I think. Long story short I now have 3 thermostats and none of them make a lick of difference. Next step??

Also used a pressure checking system to check the coolant system. Holds pressure past 25 psi. Ran the engine with the tester on and didn't see any pressure movement on the dial so I hope that can rule out the head gasket I fear. Tested this at all different pressures to make sure it didn't have to much pressure to read correctly.

I tried to bleed the coolant system by the book and I still can't get any heat from the vents. I think I am going to try to test the DCCV nest. I just need a thermo gun and whatever else it takes.

Maybe I will try to replace the coolant tank cap as well even though I don't think that is it.

 

I just read through all the posts.

Sounds like a failing water pump to me. If your haven't changed it you might want to get that sorted, quickly. I saw your comment about feeling the top hose and presuming your water pump is working. Another pointer for me to the water pump is you cannot properly "burp" the cooling system.

These coolant systems are not basic like the old days. They're pretty complicated then add the SC cooling circuit to boot.

Take a second look at the water pump.

Use an OEM Jaguar water pump. You'll thank me later.

You might find one of the plastic fins is compromised. If you changed the water pump then I'm at a loss.

DCCV failing with the solenoids in the closed position (it happens) would be next although would not be a high contributor to an over heat condition as you described as with a proper working water pump, fan, thermostat and radiator the only sign you would have is no heat at vents.

Aux Cooling Pump even if not working would not cause an over heat condition.

Finally, have you checked your cooling fan for proper operation? Should kick on low speed when needle approaches middle and should constantly run then as your overheat condition shows its ugly face that fan should be going full speed.

Just my $0.02 but my money is on your water pump.

PS - if (and when) you change your water pump change out your serp and SC belts and check your idler pulleys for play/noise since you will have the belts off to access your Water Pump.

Bolt torque spec on Water Pump: 8Nm + 90 deg (about 6.8 ft lbs)

Very important, don't over tighten those bolts and use a 6 point - 8mm socket when attempting to remove those bolts. Last thing you want to do is round off the bolt head. (I did on my 04 XJR - what a PITA to rectify)

 

I will say that if I floor it and let off and cost my temps will go down a little. Seems like temp rise much faster when I'm just driving normal.

I guess I should just do more full throttle fun!

 

You could have a collapsed house causing a restriction.

Gus
www.jagrepair.com

 

Excuse me while I get up on my soapbox again, but did you test them? I'm talking about suspending each from a piece of wire in a big pot of water on the stove. Record the water temperature at the point where each thermostat fully opens. Please re-read my earlier tale of woe, dealing with bad thermostats.

Did the second and third replacements come from the same source? Years ago, I had a car that ran worse after a tune-up. As I had done a bunch of work at once, I had to reverse multiple steps to reach my best guess of a defective distributor cap. Without thinking, I went back to the same store and got another defective cap from the same bad batch. I fell prey to "The part must be good because it's new" line of reasoning, reinforced by no improvement with another replacement. It was at least a week before I tried a different brand part and then all was groovy. It was a tough lesson to get through my thick, concrete-filled skull.

Is it likely you've purchased multiple bad thermostats in a row? No, not really. But is it super easy to rule out by spending ten minutes in the kitchen, coffee in hand? It certainly is, and then you can safely rule that out. There's no need to remove the installed thermostat for testing, but definitely check the previous one at least.

 

+1 on that!

This is easy enough to check. Warm up the engine so the hoses are soft and pliable. Squeeze the lower radiator hose. Usually there's a spiral wire inside (or other means) to prevent the hose from collapsing under suction from the water pump.

 

Ooh, don't overpressurize the cooling system. Is 16psi the rated pressure? That's all you need for pressure testing.

Did you pressure test the cap? If venting pressure early, the cooling system will not behave properly. I can't stress this strongly enough. With the cap at the high point, you may not even get any coolant escaping, just air.

Also, make sure the expansion tank neck is clean and smooth where the cap seals. If not, even a perfectly good cap will vent too soon if it can't seal properly. I went through some similar grief on my old pickup. Although the design is different than the S-type, it kept venting coolant from the overflow line at the cap. A pressure test of the cooling system was fine. The cap itself tested fine. Eventually I figured out the cap wasn't sealing properly at the primary mating surface down inside the neck, even though it looked fine.

So at the minimum, pressure test the cap. Or gamble $10 on a name brand replacement. But if that doesn't fix it, don't rule out a problem with the new one or the tank's mating surface.

Also, will the car overheat while stationary? If so, you could connect the pressure tester while cold, and run the engine without pumping up the tester. You'd just be using the gauge, not the pump. As the engine warms to normal temperature, the pressure should increase and you'll see it on the gauge. You will have to monitor the gauge VERY carefully, as you don't have the cap to automatically relieve pressure above the max rating. You will have to manually burp the tester to keep pressure within specs, so pay close attention. If the engine would have previously overheated but now is good with a correctly pressurized system, then you know the problem is pressure-related, such as a bad cap or lack of a good seal.

 

Sometimes it will overheat stationary sometimes it wont. I am going to test the pressure of the system from cold with the tester just to see what I get. The cap is not out of the question in my book.

 

Please post what you found to be the problem.

Gus
www.jagrepair.cim

 

once I do I will send an update for sure

 

Can someone confirm the correct way to bleed the air out of the system? I have read a few different things now.

 

I guess my advice regarding the water pump is falling upon deaf ears.. oh well