One of the best ways to wreck an otherwise sound engine is to overheat it. Ok, coolant is pumped through the radiator but what about oil? Any modern (and old) engine relies on the cooling action of oil too. And oil has only the sump to cool down.
Normally though this is not much of a problem. In standard conditions modern oils have plenty of reserves built in. But many of our cars aren't used in "standard" conditions. Modern high performance oils can go up to 200°C until they get destroyed. However this margin is not what the manufacturers wants us to believe. The standard stuff Landrover prescripts ages 4 times as fast when it reaches 150°C as 120° oil. And this rate continues. So driving with real hot oil may ruin the oil in less than 1000 miles and leads to engine failure.
Pretty scary, isn't it?
That's what oil coolers are designed for. Look at those older Landrovers. Did they have an oil cooler? No. They had a large radiator. Todays engines, especially TDI's need the cool oil much more than Series. So they built an oil cooler into the radiator. Good idea? I don't think so. It's way cheaper than separate coolers and it heats the oil quicker to operation temperatures but it also means that the water coolant will get hotter once the oil temperature goes up. And the space for the water radiator is smaller.
I think of a better solution. Get rid of that old radiator once it starts to leak or overheat. Put in a new radiator without oil cooler built in. And mount an additional oil cooler somewhere else.
We offer oil coolers made by Racimex. They re both small and performant. The biggest model with 19 cooling ribs sells for 4.000.- FLux. Add to this the mounting kit for another 4.250 FLux. This kit contains all the fittings, lines and adapters you need. And it has an built-in thermostat. This means the oil will only flow through the cooler once it gets hotter than standard. This is good for engine wear as it will stay under all conditions at the same temperature.
An idea for mounting an oil cooler is naturally behind the water cooler. Most people do this as it's easy. Better is to mount it under the radiator so it sits in an fresh air stream. However you'll have to protect it if you go into the rough.
Another position on Defenders is under the plain plate on top of the wing. One side has the inlet for the heating, the other side is a plain plate. Replace this plate with an open one (available at any dealer) and you'll have an wonderful place for an radiator.
Air flow should be helped though. There are 2 ways of doing this:
You can either fit an intake on top of the wing. There were some advertised through LRO but I haven't seen any yet. You can also make your own intake yourself out of some spare aluminium sheet. It's enough when it has a height of 2" over the top of the wing. Or better, make 2 of them and fit the heating inlet also with one. This improves heating greatly. You can also cut a small rubber ball up and rivet it in place. Not pretty but very effective.
Or you can fit a small ventilator under the radiator. Cheap small ones are available from Computer shops (but don't ask for an ventilator for an 300 TDI, they might call those nice guys with the white jackets). i don't know however how long those will live in the dirty conditions. Or you can source another small unit from an heater and adapt it. Couple it to an thermostatic sensor and you'll have an high-tech setup.