Interesting...
I've always thought my truck ran hotter oil than anyone else, and worse fuel consumption... but sort of come to the conclusion that I have to believe what I see, and measure myself... even if that's always 10C more temp or 10% less mpg.
But it is Syncro Doka usually with knobblies on... here's a mix of long distance and days of off-road driving, mTdis and eTDis seem to get a fair bit better.
Pink is the mpg-to-date, obviously becoming fairly unvarying as it progresses. Blue is actual raw fillup data, black is always a good trend to plot
Simon will no doubt be using high spec reinforced hose in those kits, 1/2" BSP as well.
As soon as I did a few sums with 3/4" and 7 litres total capacity popped up on the calculator, that was pretty well it.
Unreinforced 3/4" hoses at £50 in my hand, terminated, was a gamble. Need a big radius to prevent kinking. The engine Bay is the worst bit, but the Doka has more height to play with - length is pretty critical and struck lucky first time, you definitely don't want too much, 3" would be a lot to lose with a big bore hose. Then there's those cut and clamp solutions... we are only talking about 100~200 psi in extremis, most auto cooler pipes seem to be made up to take 1,000's of psi!!!
I should have gone for a 25 row cooler, in retrospect... it would also reduce an pressure loss, but there';s very little I should think at 3/4". Nor 5/8 or 1/2"; 3/8" front to back is not uncommon
High pressure loss is not an issue it seems, from 1/2" upwards with a 19 or 25 row full width(235mm) cooler.
Whilst changing oil with the filter off, I motor the engine a bit with the fuel off, which seems to pump some out of the cooler circuit, or it self-siphons out of the filter housing at some angles. Not too bothered, as long as I'm changing a filter and get most of it out... can be blown through if necessary I suppose.
Another thing, am running fully synthetic turbo diesel oil, 10W-40, which can be got here now around the £20 / 5 litres price.
So it's all down to the pipework as you say, buy a complete kit or seek out a tame hydraulics shop.