Has anyone experienced this before? Our 2006 XK 4.2 has had a slow coolant leak for the last year or so. I had the car on the lift this morning to replace the rear drop links and tie bars so whilst I was underneath I decided to have a look for the leak which I soon found with the red coolant residue all around the the two rubber bungs in the bottom of the torque converter housing. Removing the bungs revealed the presence of a significant amount of coolant actually inside the bellhousing.

I've checked the workshop manual and I cannot see any coolant pipes or similar inside the housing which presumably means that a core plug/freeze plug on the end of one of the coolant galleries inside the bellhousing has started leaking? An alternative would presumably be a cracked block but that seems very unlikely.

Has anyone heard of this happening with the 4.2 engine before? I'm obviously going to have to drop the gearbox to see what is really going on which is a complete pain but I can't see any alternatives.

Any thoughts anyone?

Richard

 

Hmm transmission cooler?

 

Indeed. It was one of my first thoughts and there are certainly metal pipes that run from the gearbox through to the transmission cooler mounted at the front of the car but these don't pass through the bellhousing, as far as I can see, and are carrying transmission fluid rather than coolant. Once I thought about it, I realised that I cannot visualise why any components carrying coolant would be situated in, or passing through, the bellhousing.

Richard

 

Is it possible the leak is in the valley/valley hoses and running down and into the bell housing?

 

Unfortunately not. That is what I was hoping for but the outside upper bellhousing has no coolant residue but the inside of the housing has a lot of coolant in it. A leak at the top would not be able to enter the bellhousing as there is no vent or gap in the top.

Richard

 

does the 4.2 xk transmission cooler have a heat exchanger with both transmission lines and coolant lines?
the 5.0 does.

 

It does have a transmission cooler which is cooled by the engine coolant but it is built into the radiator at the front of the car. It is only pipes carrying transmission fluid which travel from the gearbox to the radiator assembly and even these do not pass through the bellhousing.
I would guess that the 5.0 uses something similar at the front of the car? I can't see any reason why any of the transmission cooling components would ever be situated inside the bellhousing. With the torque converter and flex plate in there, there's not a lot of room anyway.

Richard

 

The solution that is too quick and too simple is to put a hole in the bung for self draining, and then add coolant sealer to the system.
Now back to finding the cause...
Cee Jay speaks of this problem on 09-13-2022. Possibly the oil cooler!

 

I thought about adding sealer but decided that it would be preferable to address the actual problem. I have a suspicion that adding sealer can cause coolant circulation problems further down the line.
I can't recall Cee Jay's post but the oil cooler is presumably the engine oil cooler rather than the transmission oil cooler so the pipework/valves etc would be at the front/side of the engine block/radiator rather in the bellhousing which is rearwards of the engine block? There is presumably no engine oil circulation rearwards of the engine block?

Richard

 

RichardS I am referring to the post by Cee Jay that can be easily seen, by simply scrolling down to the second line of "Related Topics".
There is a lot of info there!

 

Ah, I see it now. CeeJay's car is a 2010 XKR which I believe is the 5 litre engine. Thanks for the pointer.

CeeJay does not say that the coolant residue was actually inside the bellhousing so I suspect that it was on the outside and had run down from the top of the bellhousing. That is probably why he thought that it would be a valley cooling pipes leak. I believe that the oil cooler on the 5.0 engines is installed in the cylinder valley and is water cooled so a leaking oil cooler would manifest itself in similar way to a leak in the valley hoses.

Richard

 

Also there was reference to a different type of coolant by Evans, that doesn't leak! I am not sure what is involved, there.

 

I suspect that waterless coolant is being referred to. It runs at a much lower pressure than water when hot but any actual leaks would need to be sealed before the switch was made as it will still leak from gaps and, when it does, it is a lot more expensive to replace.

Richard

 

I'm suggesting that your transmission cooler is drawing in coolant from your radiator into your transmission and then leaking into the bell housing.

 

Hi Richard,

You have a mystery on your hands. The only three possibilities I can think of are:

1. trkyam is correct if the fluid in the bellhousing is a mixture of coolant and transmission fluid;

2. One of the freeze plugs above the crankshaft and below the oil galley plug has cracked, rusted through or pushed out; see the two plugs in this photo of a 4.0L courtesy of nunger1330:



3. Your block is cracked in a highly unusual place on the rear of the engine.

I'll be following your diagnosis with great interest.

Cheers,

Don

 

It's an interesting suggestion but I can't see how that would work in practice.
Firstly, I believe that an automatic gearbox is typically running at a higher pressure in the lines than the engine coolant system so any transfer of fluids would be in the opposite direction.
Secondly, if coolant was getting into the auto fluid at the radiator, it would find its way into the gearbox sump before being pumped through the torque converter. However, the oil and water would not remain separate but would quickly form an oil in water emulsion. To get into the bellhousing, a seal on the mainshaft on either the gearbox or the torque converter would have to fail but, either way, it would be an oily emulsion which would accumulate in the bellhousing rather than pure coolant.

I suppose that the bottom line is that even if your suggestion were correct, I would still have to drop the gearbox to change the seals as well as changing the radiator/cooler. ☹

Richard

 

Many thanks Don. My reply to Trykam crossed with your post.

I cannot find a single documented case on the internet of this ever happening before. However, my Son is an engineer who used to work on Range Rover Classic restorations some years ago and he apparently saw leaking bellhousing core plugs on one or two cars. Of course, these were much older car and they usually put it down to owners not using sufficient (or any!) antifreeze/anticorrosion additive but that is certainly not the case with our XK.
I suspect that this is some kind of freak manufacturing fault which has taken many years to manifest itself but I will take some photos in due course just in case this happens to anyone else.

Richard

 

If it has the zf6hp26 there is a trans vent tube the discharges into top of bellhousing. As you stated even if coolant is getting into the trans fluid somehow it should mix into an emulsion only separating after sitting. Oil floats on water so even if it were that happening oil should be coming out. The only other scenario i can think of is if the vent tube broke off flush or came out at the top of the bellhousing coolant leaking from above could enter the tube fitting. But again you should see coolant down the side which you do not. Truly a mystery

 

A benefit to switching to the Evans coolant is that it operates at about half the PSI, and thus less leakage per hour of running time. If the viscosity is greater than the regular stuff, then that should be a plus as well.

 

Richard,

I forgot to chime in on the topic of cooling system sealers. I do not recommend them in modern vehicles due to the very small coolant passages in the heater core, which could potentially be clogged by the particulates in the sealer. Jaguars that use OAT coolant are known for clogged heater cores as it is. Better to mechanically repair the leak than to create yet another expensive and time-consuming problem.

Cheers,

Don