Hi everyone,

My 300tdi has a lot of black smoke when under load (I mean a lot!). The engine has done this since I owned it, but since I recently took it out of my discovery, and put it in my 110, including disco gearbox and transfer box, the longer ratios, plus slightly larger tyres are causing the engine to be under load more often and therefore more black smoke.

Here’s my state of play:
I’ve done all the filters. The fuel pump still has its security band thing on, so I don’t think anyone has mucked about with the pump. The smoke issue was present with both the disco and defender air routing. EGR valve has been blanked off.

Here’s some suspect things:
my temp gauge climbs to about 1/3 up from cold and stays there. Same on disco and defender (stuck open thermostat maybe?) - would this cause the smoke?
Oily hoses coming off the bottom of the intercooler - blocked/restricted cyclone breather? One of the turbo intake hoses (the elbow that goes into the turbo) burst a few months ago and I had to limp the car home. Could my intercooler be full of soot due to that?

The engine runs beautifully. Did in the discovery, and does in the 110 (it replaced a knacked 2.5na so feels like a rocket regardless!). Puff of smoke on start. No smoke on idle, or when revving the engine in neutral.

Obviously I could start replacing bits, and I already ordered a replacement thermostat ready to check if the old one is stuck. But would love some other directions to explore.

Thanks!

How about the boost pin, is that original and running in the correct place?

It's fuel, or to be more pecise, too much fuel.
The thermostst won't effect it although diesels are more efficient when warm than cold.

Intercoolers can gum up as there is always a little oil from the turbo bearings getting through.
Too much fuel can also be too little air, but your description sounds like too much fuel.

I'd start by unscrewing the fuel pin by 1 full turn (you said the security band was still on but that nominally stops it screwing in).

Well yes it's too much fuel for the amount of air it is getting, so turbo could be the issue , or a hole in the intercooler or pipes. I put a bicycle valve in my top boost hose linked to the manual gauge inside the cab in my D1 300 tdi - cheap and is a needed for diagnosing issue's

That's where i would start before injector replacement and pump refurb etc.

Oily pipes on the whole air circuit is "normal". If it's dripping oil then that's an issue .