Dear Forum,
I have discovered that Forum Member Jagnew lives three kilometers away from me here in Dubai. He has a 2004 XJ6 3.0 V6 with around 100,000 miles on the clock.
I am trying to be of help to him.
He has brown gunk in his expansion tank (see photo), but he topped up with green coolant about 18 months ago so I think this is the resulting reaction? Perhaps Jaguar should have put the notice on the tank saying 'only use orange coolant' in neon lights?
I do not think he has oil in his coolant and his oil filler and dipstick are free of water contamination? Obviously his cooling system is going to need flushing and refilling with the correct coolant, but right now, could gunk blocking his radiator cause overheating within 15 minutes of startup?

His car is overheating and pushing coolant out past his filler cap. In a past life (when cars were much simpler) I would look at a Thermostat failed shut?

The top hose gets hot and hard (I say, steady there), so I am assuming the water pump is working but there is incomplete circulation. There are codes, but none for the cooling system. However, my code reader stays on open loop, even though it shows coolant temp @ 98 degrees etc, so the coolant temp sensor must be working?
The bleed screw is weeping and I will fix that by renewing the o ring, but I cannot imagine that this tiny loss of pressure would cause a boil-over?

My instantaneous reaction is 'get that cooling system flushed', but I am still pondering whether its a gunk-blocked radiator or the thermostat as the likely cause, but I also lack understanding as to why no closed loop? Am I missing something obvious, please?

 

Good to hear that it was mixed coolant rather than transmission fluid. As long as the engine didn't warp this should be a huge sigh of relief.
The mixture does lead to congealing and blockage and can quickly cause the engine to overheat. I once had lost a water pump belt on a 3.0 Ford Escape which would cause it to over heat within 5 minutes. I would remove the thermostat for now and try to flush the system with water or a radiator flushing solvent.
If it's bad you have to remove radiator and heater core to give them a good back flush.

Here's a good read with a similar experience on a ford truck and some suggestions such as using laundry detergent or vinegar.
https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/4282894/all/Mixing_antifreeze_=__brown_slu

 

I am not totally convinced that this would have been caused right now when 18 months ago the wrong coolant was added.

The mess coming out just looks like coolant plus transmission oil.

I hope I am wrong.

 

It does look like an emulsion of oil and water

 

If it is oil you may try and catch some in a clear container. The oil will settle on top of the water. I do not know what will happen with different. I have yet to find oil that will blend with coolant for long, although maybe the Jag orange type might act differently and be more "lubricating) . Perhaps the sludge has blocked passages completely so the coolant is not circulating completely through the system (or it is foamy) The sensors will not be able to read the foam due to the air. Many times I have seen vehicles lose so much coolant the light never came on because there was only steam in the system. I would not expect it to stay in open loop though since I believe there a lot of different sensors feed the information that is looked at for that function.

 

Thanks Jackra_1. There are no trans fault codes related to trans fluid? Shouldn't there at least be a Trans Fault light? How about I get a sample of the trans fluid from the drain plug?
I think what I am trying to say is that if there is trans fluid in the coolant, shouldn't there also be coolant in the trans fluid?

Incidentally, this car has been subjected to UAE mechanics, so trans fluid could well be red? Maybe?

 

I'll do that and post.

 

In this situation you may well not get a trans fault code.

Yes you would expect coolant in the trans fluid in this situation. So yes try and get a sample of the trans fluid. I would go thru the top up plug as if you loosen the drain plug you might get a whole lot more than you want.

I have seen a post in this forum before where the trans cooler blew inside the radiator causing a lot of damage to the transmission.

I had it happen on a Dakota truck where the pressure blew the top off the overflow reservoir. The transmission was toast in that truck immediately because of the clutch plates being ruined. Not sure about the ZF transmission tho whether it would be toast immediately.

 

Thanks and understood.

Jackra, does the permanent open loop give us any further clues, please? For example, could a failed thermostat cause that?

 

+1 on getting that sample.
Just REMEMBER the engine has to be running, with the trans level.

 

Meanwhile, anyone got any ideas as to why open loop, please?

 

Not sure what you mean by "open loop".

With the engine running the internal transmission pump will be running and IF there is a leak from the transmission into the radiator this situation will cause excessive pressure within the coolant system.

With the engine COLD try taking cap of coolant reservoir and start the engine to see whether anything comes out of the reservoir.

 

[QUOTE=jackra_1;2088577]Not sure what you mean by "open loop"./QUOTE]

Jackra, I mean that when I plug in my OBD2 it does not go from open loop to closed loop, irrespective of what it says is the coolant temp? Temp goes over 100 C and still 'open loop' which states something like: 'engine coolant temp insufficient to close loop'?

Nothing comes up with coolant cap off and engine started but cold.

So, I imagine temp sensor working, so why (given that the ECU is being told that the temp is 100 C) is it staying open loop?

Perhaps try removing thermostat and testing with a thermometer in a saucepan?

Do you see my confusion, please? Failed thermostat closed?

Jackra, if possible, I want to try to get a better idea of what this is before doing anything major. My problem is that his car is in a basement car park and is literally sat on its tyres. We can try driving it back and forward until (maybe) we wake the Air Suspension Module from its slumbers, but if this is trans cooler failure, do I really want to even engage drive?
I cannot even get the crappy Jag scissor jack under it to lift it enough to get a trolley jack under! Air suspension is a wonderful thing, but boy doesn't it cause a few headaches!
We are even considering reversing it over a couple of bricks, just to get enough height to get a jack under there!!
We cannot even drag it out of there with a tow to take it anywhere, it is too low to go up the ramp to the street....Unless we can drag it there on its belly....

Kind of makes me realise just how little my own Jag has tested me so far!

 

Ok Esray understand what you are saying. I have no idea why it is doing that.

With nothing coming out of the coolant reservoir with engine running that hopefully is a good sign however if there is not much "coolant" left in the system it might not mean much.

If you can get at the fill plug in the transmission to definitively discount coolant in it that would be the best thing to do I think.

But jacking it up in your current situation will be a bit hard I know.

Any chance of getting as much coolant flushed out and topping up with water to see what happens?

 

Thanks jackra_1, that's exactly what I am going to try first. The easiest step. If it still overheats quickly, it reduces the likelihood that it is being caused by mixed coolant reaction and increases the possibility of either a failed shut thermostat or oil contamination.

 

Good luck!

 

You probably will not be able to get a sample of transmission fluid from the fill plug that will separate if it has coolant in it. Unless it is really overfull (which would also indicate coolant in the transmission). The water will sink to the bottom of the pan and the oil will float on top. Any sample would need to be from the bottom of the pan. (I have checked, and found coolant, in my motorcycle by loosening the oil drain plug. Water will drip out before oil does. The sludge that is in pictures should almost be enough to test. I also agree that 18 months is a long time to wait before a bad reaction from a different coolant would appear. Could this be the result of foul play? How does it taste? (I know it is not good so don't swallow ) If so maybe it is just in the engine.
Can you remove the sensor in the thermostat housing to see if there is coolant there. If the coolant is not circulating it may not be sending a signal to the ECU. I had a bad MAF/IAT on a Ford Vulcan 3.0 that kept the ECU in open loop.
I would be afraid that just starting the engine while the transmission is contaminated will probably be really bad. Even without putting it in any gear I would guess bad fluid is everywhere from the TC to the tail shaft. The clutches may not be burnt but they won't be very happy .
On a side note perhaps a auto body tool I know as a "Port-a-Power" with some blocks could help raise it enough to get a jack under it.

 

Update;
Well we eventually got her up on axle stands. We flushed her 10 times and the coolant is running clear. Haven't managed to test to destruction (or boil-over) yet, because the expansion tank filler cap has suddenly decided to start letting by and leaking? The clicks you get when it is fully home have become much quieter? There is no o-ring on the cap, so not sure how exactly it achieves a pressure-proof seal?

Anyway, I'm off back to 'Blighty' on Tuesday for three weeks, so I will update you (my excellent helpers) again when I return to battle!

 

Esray,

Is it possible upon your return to at least pull the thermostat if you haven't already? Another thing that happens is the ridiculous plastic thermostat housing (or riser it is sometimes called will crumble around the thermostat and allow bypass of the thermostat. In any event it would require replacement. Runs about 150 here in the States. I have 2 for 2 on this happening, so I wanted to call your attention to it. Glad it isnt oil/trans fluid from what you have seen to date.

 

Happy journey;