Best guides are your oil consumption and your fuel consumption - if both are reasonable and no different to previously then all is well.

Agreed - if the engine suddenly starts needing topping up with oil regularly, that's when to be concerned.

Maybe not VERY concerned, since oil is cheap.

OTOH, with a diesel you could eventually get into an engine runaway situation, where it starts running on its lubrication oil and self destructs.

If that looks to be a possibility it might be an idea to drill stopping the engine by blocking off its air supply, and have something available to do that.

I've never tried this, and wonder if its actually possible with a racing engine without damage.

It might collapse the air intake plumbing, creating an air leak and not stopping.

I suppose a CO2 fire extinguisher would do the job though.

Agreed - if the engine suddenly starts needing topping up with oil regularly, that's when to be concerned.

Maybe not VERY concerned, since oil is cheap.

Yes, if it's a pint every 1,000 miles or so I'd be quite happy to carry on with that.

I remember Car Magazine had a 6-cylinder petrol Merc on long-term test in the early 90s, and they reported that it was using a pint every 300 miles during their ownership, which is rather extreme.

Oil consumption of a litre per 1,000 miles seems to be the dividing line between acceptability and not.

I do not see anything that would cause me to be concerned.

A diesel running on its own sump oil is usually down to the turbo oil seals being worn, so the sump oil gets sucked back into the engine. Renault 1.9dCi engines built up to June 2003 were quite bad for this.

I would not want to be anywhere near the engine bay of a diesel that is 'running away'. Try and stall it (if a manual obviously...) otherwise let nature do its thing.

I understand it was especially a "nature thing" when running on waste vegetable oil, which stuck the piston rings, allowing sufficient blowby to run the engine.

(Turbo's would be especially contraindicated for WVO running, since carbon chunks could break turbine blades.)

Like I said, CO2 should stop it, but using a conventional extinguisher you''d have to stop and get out of the vehicle, with the engine in neutral.

Not likely to be a relaxing minute or two.

It would probably be possible to rig an extinguisher in the engine bay you could operate from the cab, but probably too much trouble on a just-in-case basis.

I have experience of worn petrol engines which would throw out oil drops (not mist) when you removed the oil cap !

The camshaft or tappets will do that. Remember when Vauxhalls required tappet adjustment on a hot engine with it running? Oil everywhere and ruined feeler gauges, although you could buy gauges by the foot.