I finally got a photo of the leak I thought I saw under my expansion tank. Tis time it actually made a tiny bubble as I looked at it. Odd that I don't see any dried residue on the pipe. Could it actually evaporate before it can drip? That's the location I'm getting the strong smell from.
I've ordered a new expansion tank and plan to use a new clamp as well. Doesn't look as if the hose is bad.

 

Here's a close up of the leak. It's actually right at the hose where it meets the plastic pipe.

 

Looks like you found it. I had a similar problem but it turned out to be the clamp. I replaced it and all is good.

 

That's my point. Is this tiny dribble capable of such an offensive smell?!?!?!?!

 

Probably is. I switched out my expansion tank and while it cured the Low Coolant light issue, I still had the smell. After a few days I realized it wasn't going away. Some detective work turned up a loose clamp with a drizzle very much like yours. New clamp and the problem (and smell) went away.

 

Ok. New tank, new cap and new clamps. I hope this does it but I have a feeling it won't. Tried to clean any spilled coolant so hopefully when it burns off it won't smell.
After this, if it still smells, I guess a pressure test is the last option.

 

Yes. This has been an issue on both my XK8 and XKR. On my XK8, it was the hose clamp, on my XKR the plastic right by the connector cracked. A little, tiny, almost unnoticeable leak here causes a bad smell.

 

So once you fixed these issues, the smell eventually went away? I know there will be burn off from slight coolant spill while changing.

 

Yes, it fixed the smell. If that's your only leak, then fixing it should get rid of the smell.

 

Leaks from the Expansion Tank or it's bottom hose put coolant onto the hot exhaust manifold. This is often the reason such leaks are so difficult to trace - the evidence has gone up in steam!

It also accounts for the dreadful smell. OAT coolant has a very pungent odour when boiled.

Graham

 

My reservoir and sensor were replaced months ago, then I started getting low coolant warnings briefly. Coolant level looked ok at first look, then noticed leakage onto the adjacent throttle body, aha, that's were it was going...

 

Well, it's back. Smell strong as ever. New tank cap and clamps. Running out of ideas.

 

Head Gasket failure? That would account for the smell and the disappearance of the coolant.

 

The classic method of testing for a coolant leak is to do a "pressure test." Sometimes, it helps to put a tracing dye into the coolant. Then, if the leak is not apparent in the engine compartment the logical conclusion is that it is elsewhere, possibly the heater core.

 

I finally found actual coolant leaking from the area under the throttle body and it turned out to be the one way valve on the damn octopus hose!! And you can't purchase just the plastic piece of crap valve. You've got to order the whole hose.
While replacing, we replaced the clamps too with regular worm clamps.
I really hope this is it. We got some coolant in places that we couldn't get to to clean so until that burns off, I won't know for absolute sure it's finally fixed!!

 

I had the same continuing leak in my 1998 and eventually it got big enough to show up. Mine was the hoses that run under the top of the engine. Got that fixed and no more leaks or smell.

 

I had my 2005 S Type dash light up every now and then with low Coolant, took it to the dealership thinking all the time of the head gasket and was pleasantly informed that it was a hose leak. The compression test gave good results of the head with all the cylinders giving a 180-190 psi range.