Disco is Range rover Classic in Working cloths; hauled along by 300TDi from the defender... did later ones get TD5?
2.5 in P38 is a different engine, as far as I'm aware.
300Tdi is better than a RR 2.5.... but still not got the grunt of a V8.
3.9V8 has nearly 200bhp, 4.6 has I think 280!
300Tdi & RR2.5TD are quoted at 130PS.... a PS being a little german pit ponie, to a good old british Shire Horse Power!
Now lets run this again;
NONE of the oil burners make as much power as ANY of the V8's.
Therfore, they will not put as much motive force to the road as any of the V8's, which means that none of them will pull as much load or the same load as easily as the V8's.
And a 4.6 is chucking out over DOUBLE what a TD does!
That means that a 4.6, will be able to put as much shear force to the road in high box, as a deseasil will in low!
Given identical vehicles, with identical tyres and identical loads, in a Tug of War, v8 should be able to drag a screaming struiggling Turbo diesil backwards like a TD would drag the V8 back...... if the engine was turned off and the hand brake on!
TD's would 'Do the job', yes; and probably quite adequetly; but thats different to 'well'..... or 'comfortably'.
TD might do the job, but clattering away like a London taxi that needs a service, belching black smoke, and screaming its nuts off to get at the power.
V8 would haul the same load at half the revs in a higher gear, nice and quietly and with bags of grunt in 'reserve'.
Comparison to caravans is a bit fatiouse I'm afraid; caravans are big, but they tend not to be that heavy; thier weight is usually fairly low and they dont have a moving load inside them.
Pulling a horse box or stock trailer......
Well, it's not nice; P38 has a kerb weight of I think 2.5tonne? ish. All up weight of a couple of horses and stock-box easily equal that.
The centre of gravity of a horse is around about its belly; somewhat higher then a Range Rover's CofG, before you get the horse to go stand over the tralier axle lifting it another foot.
Then horses have a habbit of shuffling in the stall, EVEN if they are calm and a snug fit, in the ----- sorry there's a word for the tack used to leash them in place, and I cant remember it - holster?
It's been twenty years since I've ridden; But, I remember watching a nervouse colt lead into a stock-box, hitched to a big Merc S-Class; at the time they were one of the few non commercial vehicles with the 'weight' to do the job, having kerb weight over 2 tonnes; the colt was not happy about going in, and I watched aghast, as the colts antics jumping about trying to resist going in, had the back of the merc actually lifted in the air a good six inches by the box hitch!
Dynamically, it comes down to concervation of momentum, and the more mass you have in the towing vehicle compared to the mass in the traler, more advantage the tow car has to resist any 'changes' in attitude or instability from the box.
More power te tow car has, the more capability it has to pull the heavier load, and be something like responsive to any sudden change of loading or instability.
I have towed all sorts of things over the years; but after hauling a stock box full of pigs just accross our farm..... sorry, but I WONT haul a stock box n the road!
It's worse than having unruly children in the back of the car!
I would want as much weight as I could get, and as much power, to give myself as much chance as I could get.........
4.6 p38 balasted with paving slabs on the floor!
Disco II 300Tdi would 'probably' be adequete........
But its half a don down on kerb weight and got half the power.
V8i disco? still down on kerb weight.
I'd be FAR happier in P38, or new Rangie Rover.
I'd be happier still in a Defender 130 V8!
It is, I guess down a lot to personal choice and what you are happiest with, or prepared to compromise on.
Reliability wise, Disco II would be better bet; towing 'security' wise, definitely 4.6 P38.
Diesils in the middle would do the job adequetly, if not nicely; V8 Classic would do it reasonably well, just a bit down on mass, 4.0 or 4.2, P38's, same weight just a bit less power, but still more than a diesil.
It's a case of balencing priorities.
End of the day; once upon a time, we used to tow caravans with Moris Minor 1000's, and I can remember the farm stock tralier hitched to the back of my grandad's hilman hunter; what was that a 1600, about the weight of an Astra?
Eight years ago, I bought a Meastro for the wife; and the bloke selling it was an old chap, near retirement, and he ulagised to me at length that 'being a 1600, its great for towing the caravan', pointing to a 20ft four wheel van, MOST people would presume they need a 4x4 or big 3+l saloon to haul these days.
And that meastro, WOULD pull traliers like that; Iused it to drag a 2tom builders box about, overloaded with pre-fabricated concrete panels!
But there's 'adequete' and there's 'good', and when towing, bigger. heavier and more powerful is befinitely better; and when you have a load with a mind of its own to worry about, I'd rather have plenty in reserve.