I have put this together from a couple of replies I put on another forum earlier this week, it may sound a little disjointed where I stuck the two posts together and was aimed towards someone specifically looking at buying an ex-MOD 90 but all the info is relevant.
The 2.5NA D is a fine engine in when in good condition but mileage is very misleading as an FFR could have spent hundreds of hours idling away while putting no mileage on the speedo.
When I bought my ex-MOD 90 in 1999 I bought it direct and although it looked tatty on the outside it had undergone a very thorough mechanical rebuild prior to being cast including a reconditioned engine which was a real peach.
When solo it would pull top gear most situations however put a fully loaded Sankey behind it and it did slow down on the hills etc. I checked the (very accurate) speedo against a GPS and I found that it would rev out at a genuine 73MPH, the beauty of my engine was that it would pull this most of the time while still returning between 26-28MPG.
I drove it hard for over 5-years because I knew one day I would be changing the engine but I just couldn't bring myself to get rid of what turned out to be a very effective power-plant. In the end it was only the fact that production was soon to stop of the licence built 300TDi that I decided to go for a LR Genuine Parts re-power kit.
There is no getting away from the fact that a TDi is a much more powerful & economical engine but don't disregrad the NA D out of hand as depending on what use you are to put it to, they can be a nice engine to live with.
When the TD & 200TDi were introduced to other markets the MOD stuck with the NA D and it was not until the introduction of the Defender XD that a military version of the 300TDi was used. There are plenty of ex-MOD 90/110's out there which although manufactured and brought into service in the 1990's are fitted with the NA D.
I believe that early versions of the NA D in the MOD fleet initially obtained a poor reputation for reliabilty but after some investment by LR the problems were ironed out and it proved to be an ultra-reliable unit which is more important than outright performance in most situations.
