Guys please accept my apologies if I'm becoming paranoid here. This is intended more as psychotherapy session than anything else...

When I open the expansion cap to check the coolant in the morning, there's a smell of petrol coming out of the tank.

There is no oil or sludge or any other visible contamination in the coolant and there are no bubbles either. Bleeding through the screw on the tank produces a solid stream of coolant. I am quite familiar with the headgasket woes but I could be getting unduly concerned with this one.

The car does consume a modest amount of coolant, like 0,5-0,7 ltrs over the course of 4 to 5 weeks of daily driving in various conditions. But this could be justified by small leaks on the top radiator hose, coolant return hose joint etc. which I am not planning on fixing unless they become a real problem or along with some othe major work. Having owned Landies for years, I've somehow learnt to live with these minor issues , manage and tackle them in time.

I' ve had small quantities of coolant expelled through the cap in the past but it turned out to have been all my fault as I used to overfill during the time I had a leaking water pump seal until I got that replaced.

There are no other symptoms such as hissing through the cap while hot, no coolant spewing out, no overheating, no funny smells or smoke from the exhaust and no loss of performance. The car has never overheated in my hands.

The smell is not present if I bring the car near operating temperature and carefully unscrew the cap. It's only felt right after opening the cap having sat to cool overnight.

The engine bay does smell very similarly, I guess they all do. So is it possible that during cool down, smelly air from the engine bay is drawn into the tank through the cap and that's what I'm actually picking up first thing when opening??

This whole thinking process is driving me nuts Because if I am to do the head gaskets, I'll certainly have to do the timing chains as well plus the Vanos and valves for good measure. I already have a quote of 12K all inclusive so that's the worst case scenario. I could source most of the parts myself and reduce that sum by 30% but still anything well above 5k puts the fat girl's @ss on the decisions' line...The car is in a very good condition over all and I would have no regrets paying 15k and make her new again as long as the jobs quality could be guaranteed...

I am totally with you... "If it ain't broke, don't fix it"

It's an old engine now and trying to get to the bottom of the smell will just drive you mad....

If there are no other symptoms then LEAVE IT ALONE....

I know I keep barking on about it but the best thing you can do for your fatty and your blood pressure is

CHANGE THAT THERMOSTATE FOR A LOWER TEMP ONE....

JLR did not make it run soo hot for any reason other than passing part throttle emissions at the time, reducing the temp has a host of benefits and no downsides, you would be returning the engine to the spec that BMW used, the correct one for the engine....

You can get a test kit to tell if the cylinder head gasket has gone, personally I wouldn't believe them too much on an old engine...

Here endeth the lesson (well it is Sunday and I am preaching...)

 Pete
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2014 L405 Autobiography SDV8 4.4 Loire Blue Ebony interior
2011 L322 Vogue SE 4.4 TDV8 Baltic Blue. Parchment over Navy Interior. Sold
2012 L322 Autobiography 5.0 Supercharged Ipanema Sand, Jet Interior. Sold
2002 L322 Vogue 4.4 V8 Epson Green, Ivory over Aspen Interior (Fatty Offroader) Sold
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Thanks Pete. I was about to pull the trigger on the thermostat mod if I couldn't get the electrical circuit code sorted after all. Now I'll take my time to read, study, locate parts, educate my indy on it and just schedule it all for the next service in February unless something else comes up in the meantime that could be done in combination. Winter is easier on the cooling system anyway...

Amen! 🙏

You'll prob find that this job is either the Valley pan gasket or the coolant cross over pipe at the back. Mine done the same, kept loosing water so I replaced the radiator, hose pipes, pump, thermostat, alternator, expansion bottle, cap and it was still leaking. Once I done this, run it around for 2 months and it still lost coolant so thought well it's gotta be something further back then looking on the bmw forums a lot of them say the coolant cross over pipe seals are known to go. Two O rings cost me £3.50 from jlr but took me 8 hours to replace. As good measure I thought inmight as well do the Valley pan gasket, rocker cover gaskets as well.

Hardest part of the job mate is getting the gaskets on the waterpipe cross over at the rear of the engine to stay on

Thanks for the advice. I've already been there shortly after purchased. Valley pan itself is new as well as cross over piping and associated seals etc. A pig of a job... My mechanic and I just made sure we'd never have to get back in there, not a healthy environment. Radiator, expansion tank, oil cooler + manifold + stat thereof, several hoses and main thermostat + water pump are also new or newish...
My comcer isn't the coolant loss, I pretty much know where it comes from (or I can at least justify it) but the smell of petrol upon popping the expansion tank open in the morning which is driving me ...

And it's official...

Spark plug on the left:

Click image to enlarge