Rover V8 Engine Blocks Cracking
The large bore (3.7") versions of the Rover V8 are all prone to the block cracking. This covers the 3.9, 4.0, 4.2 and 4.6litre engines.
The failure isn't catastrophic, but what does happen is that the crack allows coolant to get between the block and the liner. It then finds its way up and around the top of the liner into the combustion chamer.
So you end up losing coolant, but with no apparent leaks. Eventually you start to get a misfire, at which point it's time for a rebuild!
If you take an engine with this symptom to your non specialist mechanic, he will make utterances like 'headgaskets mate', or similar, which will NOT fix the problem.
The fix is to have new liners fitted which seal against the block. So although the crack is still there, and water is still getting to the liner, it can go no further.
The question of course is why?
This issue never arose on the 3.5 litre engine (with its 3.5" bore), simply because there was more metal around the liner.
The problem with these larger bore engines is that the metal became thinner, so the position of the water jacket in relation to the cylinder location became critical. Ideally the water jacket is centrally located, but in the photos below you can see that it's not, presumably due to vagaries in the casting process.
The following pictures show the cross section of the engine in this area (with the waterways conveniently pink where some doofus of a previous owner tried this magical crack sealant from eBay).
Crack in block clearly visible, and asymmetry of the water jacket on the right hand side.
General view of cut up block.
A bit more cut away so you can compare on the cracked cylinder, and the next cylinder down. You can see on the cracked cylinder that the wall is pretty thin on the left hand side, when compared with the right hand side of the other cylinder.
Closeup of cross section right next to crack. Pretty obvious which side the crack will occur on.
A view of the area, again see how thin the casting is where the crack occurs.
Land Rover knew about this issue, but rather than fix it, they ultrasonically scanned the blocks to identify the best ones, and put those in the higher powered vehicles. It would have been better to fix the casting process!