Temporary knocking from a diesel?
 

Just turned into a junction and there's a terrible low frequency knocking from the engine. Turn off, no obvious lose metal work or anything in the engine bay so fire up again and the knocking has gone!

Drive off for 100 yards and then at low revs is starts again, but only at idling speed. Turn off, start again and it's gone again. I've now driven three miles whilst looking for a garage and no repeat of the knocking.

So rather than go to a garage and ask about a fault that's not currently there, anyone got any ideas? I'm currently on holiday in Weston Super Mare to make things even worse.

Crank pulley ?
Pete

Thanks. Doesn't sound like something I can fix by the road! I've called the AA, hopefully they can diagnose it, even though I can no longer hear it.

I second crank pulley.

Common failure on the Diesels.

Whilst it's making a noise, pour some water over the pulley.

If the noise disappears, there's your answer.

Trouble is, the noise isn't there now!

The AA man has been, very promptly, but can't find an issue. He did wonder if it's the dual mass flywheel, but thought it unlikely. Going to have to drive with it and hope.

Another option:- engine mount?
...

Apologies to resurrect an old thread, but I have exactly the same symptoms. Bob, did you resolve the problem and get to the bottom of the knocking sound?

I've just replaced the crank pulley, and am certain it's not the issue (knocking was there before it was replaced)

Did you check all the other pulleys for play and roughness when you replaced the crank pulley?

A worn water pump will give you a similar noise to a shot crank pulley.

not a bit of heat shield hanging down on the exhaust downpipe???

I know this sounds odd but I have found Forte Injector cleaner can fix diesel knock. I can only presume it is over or under fuelling that causes it on some vehicles.

I have had a couple of instances recently where a vehicle sounding as rough as sounded sweet after a dose of the above product on a 1/4 of a tank of fuel and leaving it to sit for 24 hours after a short run once dosed. After 24 hours or even longer if possible take it for a decent run and then fill up with premium diesel and a 300ml shot of two stroke oil.