Quick Fix: Replacing 300Tdi leak-off pipes

This is one of the quickest and cheapest fixes you can do on a 300Tdi. The leak off pipes link the injectors to a spill rail (diagram label 7), which takes excess fuel back to the injection pump and then back to the tank. They are small braided hoses that can wear over time and can introduce air into the system.

The fuel that runs through them is of a low pressure and it is not common for them to leak diesel when running, but to introduce air when the engine is off. This can cause long cranking times when starting, attributed to the diesel draining back to the tank. On a cold start the fuel then has to be drawn up the pipes again to the engine. It's not always the cause, but is such a cheap and quick fix that it's worth doing anyway. My leak off pipes were in a less than ideal state and were starting to perish.

What you''ll need

  • 3-4mm ID nylon braided fuel hose
  • A knife

This is the injector leak off (or spill rail) pipe

And the condition of some of mine

Measure up the replacement pipe and put a rag underneath to protect against spillage. There shouldn't be much, if at all.

Remove the pipe (it pulls off easily). You can see the difference between the old and new pipes.

Fit the new pipe and repeat for the other 3

Some of the pipes on my 300Tdi engine were really starting to wear. I had been having a long cranking time when starting in cold weather. I tried this and it didn't make a difference, but it was worth a shot for a couple of quid and 15 minutes!

It's always a good idea to check the easiest and cheapest things first.

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