Assuming the engine is cold how long should it take for oil to fully circulate a diesel multijet engine including bearings, cylinders and turbo after starting?

a few seconds

It's almost instant.
The pump/filter are designed not to drain back so should be always primed.
(that's why they always quote two oil capacity amounts, one with and one without a filter change as the oil in the filter won't drain back to the sump and out the drain hole).

The oil galleries from the filter/pump to the mains, big ends, turbo etc only hold small amounts of oil and the pump can fill these really quickly.
The pump will usually fill these galleries before you've let go of the ignition key at start up.

I once accidentally loosened the turbo oil feed union of my old X type and started it up. (who puts this next to the bloody alternator bolt up the blind side of the engine??)

It chucked 6 litres of Castrols finest out in around 4 seconds!

Another, and perhaps more useful, question to ask is how long it takes before the oil has reached a temperature at which it is capable of offering full protection to the engine.

You might find this an interesting read.

Goudrons said:

I once accidentally loosened the turbo oil feed union of my old X type and started it up. (who puts this next to the bloody alternator bolt up the blind side of the engine??)

It chucked 6 litres of Castrol's finest out in around 4 seconds!

Click to expand...

Oil pumps need to deliver an almost instant high flow so put a significant power demand on the engine. The latest innovation is variable rate oil pumps, that reduce engine load when there is enough oil flowing.

The issue with over-reving any engine is the mass of moving parts. But in diesels the pistons and valves are heavier than petrol engines and the head to piston top clearance is closer. At high revs, it's possible for con-rods to stretch enough for pistons to hit the cylinder head. Valves have similar inertial issues which will be a big part of why Fiat went to 16 valves.

Saying all that we have no doubt all seen rednecks on You Tube running engines to destruction. It's really amazing how long they can last (not with zero damage of course) before they explode or stop dead.

how long does it take for the oil pressure light to go out.

jrkitching said:

Another, and perhaps more useful, question to ask is how long it takes before the oil has reached a temperature at which it is capable of offering full protection to the engine.

You might find this an interesting read.

Click to expand...

This is the question, & a more important one at that. The demise of some vehicles are determined on the way they are driven & looked after (obviously) Ragging any vehicle from start up (every forum has these drivers) can/will shorten the life of your chosen mode of conveyance. Especially so with turbo cars.

In the Panda Multijet, the oil filter is a paper element within an outer housing. If you leave the engine switched off for a short while it is possible to unscrew the housing without loss of oil, because the oil in the housing has drained back into the sump.

So although oil circulation is almost instant (hence oil pressure light going off within a couple of seconds), it is not correct to say that the oil in the filter housing remains there after the engine has switched off.