I have bought 12 - 03/04 definitely are prone to more serious engine problems. There are lots of threads about what to look for. Most people do not mention checking the oil pressure, but I do it when I buy. Super easy on the 03/04, not much more difficult on the earlier models. I bring a mechanical gauge with me and pop a plug out of the front cover from the top, screw in my gauge, and check it. The factory light won't come on if it is over 6 psi idling, but that is far too low. If the engine ticks while idling, then it could be any number of issues, but oil pressure gives you a clue if it is just parts or a slipping liner.

The other big thing is the frame rust.

 

no boring from 4.0 -> 4.6 the block is identical. It was only stroked. The casting issues however may hold some water in the later 4.6 blocks.

 

@NewToTheTwo There are definitely bad castings out there, but the block/head gasket issues have existed for years. And while the RPI videos are great explanation you will notice they do not speak to how many iffy vs ok castings they see nor how well maintained the vehicle and engine were at the time of failure.

In fact the 4.0 and 4.6 have exactly the same bore 94 only the stroke changed, which is why we can use a 4.0 block to rebuild a 4.6.

Block cracking in aluminum engines is generally a combination of heat, corrosion from bad AF as well as other causes, and vibration. A bad casting will make it more likely but not in magnitudes of difference from and "ok" casting. Even the 3.9 liters could crack a block.

 

Just as note I read a ton on these engines before buying,they are used in a lot of vehicles other than Disco's and Range Rovers, and the major issues Liner, cracking and oil pump gears. All of which are greatly worsened by either poor or bad maint, you have accept we have 16+ year old vehicles of uncertain history and stuff will go bad.
It is frustrating to me how much poor information is out there on the causes of those issues beyond age.
For example some of the 3.9 blocks had the exact same casting issues as RPI shows for the 4.6's with the same results, at that time the implication was the 4.6 engines got the better blocks and 3.9 the lesser blocks, but that was just when the 4.6 was new.

 

On the engine issue, I bought a 03 with a bad HG. After I fixed it the engine went out after about 10K more miles. I got my engine fully rebuilt last year and have had no issues with it. I knew what I was getting into when I got the truck. Just saying, be prepared to re-build if you want to keep it. So far after the engine rebuild, the suspension lift, bumpers, rock sliders etc... I spent so much money on it that I'll just keep it. I'm finally down to the cosmetics. lol

 

Check out this attachment for Disco 2 pre-purchase inspection areas. This list was made for UK personnel specifically for Td5 diesel engines but it still can be used for other areas of the Disco.

 

Sunroofs are worth checking. Many leak or are sealed up. They can ruin the headliner and in the worst case, cause corrosion of the floors as all that sound deadening material on the floor acts like a sponge and insures it remains wet for a long time.

 

ALL Leak - no such thing as a non leaking sunroof without a HELL of a lot of work. The only non-leaking ones are in Arizona and Nevada.

 

The base S model doesn't have sunroof leaks.