So I needed a new thermostat for my MY2011 SD4 because the original was sticking. I fitted the replacement yesterday and it all went well apart from the connection between the thermostat housing and the pipe that goes to the expansion tank. It's the pipe that has the two "claws" that you release. On the original it's a tight fit into the housing but on my replacement its a looser fit and it leaks. At first I thought an o-ring was missing but this is not the case. The new thermostat is not a LR part but neither was it one of the very cheap ones. It seems like a quality item but maybe there's a manufacturing error with this particular one. Has anyone come across this problem before? am I missing something (before I remove it and lose a load more expensive coolant)?

If you have to drain the system again , you could catch the clean coolant and filter it before you put it back. I'd have thought a coffee filter paper or gauze in a funnel would do. Jules

Thanks, I'll do that. I'm going to drain it down again today and measure the internal diameter of the pipe spigot and see if it's different to the old one. It's puzzling because all the diesel 2.2 thermostats have the same part number and should be identical.

Improvise...
If it's really loose, use a heat shrinking tubing on the pipe's end and increase in this way it's diameter. Then insert it tight, this time...
Or use a thicker o-ring on the thermostat housing.

Problem is the pipe end is not a straightforward design. Even the socket for it has a cut-out so it only locates one way. Even the O-ring is not an "O" in section! I tried a second O-ring but it still leaks slightly. The pipe looks like this: https://landstore.pl/przewod-tekalonowy-od...2-2-diesel

Sorry, didn't have to remove up until now so I've thought that it's a straightforward pipe...

It seems that the internal diameter of the spigot on the new thermostat housing is about 0.5mm oversize. Looks like i should have paid the extra for the Land Rover original