The fattie has (again) deveoped a leak from the water pump's base, where the body mates with the block, just under the bottom left bolt. Coolant seeps slowly forming a drop and finds its way down onto the PAS pump, then onto the undertray and eventually on the driveway overnight. Running the engine for a couple mnutes is enough to make the leak stop, as the metals expand. So the leak only happens with a stone-cold engine.

I had the exact same problem (only difference the leak was on the right side bottom) just a year ago and opted to replace the entire pump and thermostat so that I wouldn' t have to deal with those again, in the foreseeable future. Yet here we are again just a year and 30K km later.

I used a HEPU pump with a MAHLE thermostat but since the previous pump was also a relatively new HEPU I'm beginning to think they may be facing quality control issues. I also had a brand new MAHLE thermostat fail in its electrical heating circuitry! As far as I understand the aforesaid brands are OEM that's why I insisted going with them but now I'm considering other makes.

Since the leak is from the particular point and not the shaft, I could perhaps get away with just a gasket but the amount of work is all the same if not more, cleaning the surfaces to fit a used pump back... I've had that done before with the previous pump that ended up leakng and blamed it on the refitting.

I've used/fitted FEBI Bilstein PCV, washer pumps, Inlet manifold gaskets and even coolant with zero complaints. As I see FEBI Bilstein water pumps sit somewhere above average price-wise, at around 70 Eur with HEPU being the priciest at around 100 Eur.

On a related note, how does the 85 C thermostat mod affect the engine performance? since there would no longer be on-demand thermostat opening. I understand the lower temp arguably prolongs service life of the cooling system components but on the other hand, I'm reluctant to change the default configuration as it should be reliable if maintained properly.

Any suggestions and recommendations are welcome

Thank you

Last year I replaced the water pump as mine failed (seized and took the belts out with it), and while I was changing it thought I'd change to the lower temperature thermostat, as I wanted to lower the temperature (my OEM pump had a problem with the electric sensor too).

I'd probably look at taking yours off, cleaning everything up, replacing the gasket and seeing how you go, but if you do look at replacing I replaced my pump with this one:

https://www.island-4x4.co.uk/water-pump-02...37675.html

and the thermostat with this one:

https://www.buycarparts.co.uk/mahle-original/7815123

The running is great, engine warms up nice and quickly getting heat, and it doesn't smell hot after a drive in hot weather or sitting in traffic, so I assume it's keeping everything cooler than before, which is going o be good for the gearbox cooler too.

Cheers

Thanks

Been too busy lately and the car didn't leak all these days, until this morning. I hadn't moved it since Friday and temperatures drop as low as 1-2C overnight. So I wasn't too surprised to find a small puddle of coolant underneath.
This time I took the undertray off and was able to reach the bottom left bolt and the leftmost one from the underneath with a wrench. The former took about 1/8 of a turn and the latter 1/4 of a turn with minimal force. Was unable to reach any other bolt so I guess I'll see how that works. I would prefer not to touch the cooling system at all if I don't absolutely have to (was perfect before this).

So after the entire week with my daily work commute and temperatures dropping as low as 2-3C overnight, I'm glad to observe no more leaks. Coolant level has also been stable. I really hope that was all...