A few months ago I gave Olivia an oil change. By mistake I put oil meant for diesel engines in her, instead of the petrol engine oil. Total and utter blonde day! But, as it was a rather large financial investment's worth of oil, we thought we'd go with it and see what happened.
Meantime, a thread on the Land Rover UK Forums mentioned diesel oil and petrol engines, so of course my virtual ears pricked up and I kept an eye on it. All sorts of fascinating info came out.
For one thing, diesel oil has scrubbers and cleaners in. You'd think this would be a very good thing - but perhaps not in an old Series engine. You see, sometimes a build-up of stuff helps protect the engine components (not a HUGE build-up, mind) - and scrubbing it off changes the entire way the engine functions. You start with a low compression engine, add a cleaning oil - and the compression may plummet further! You might also risk exposing problems that had been happily non-problematic under the gunge, or loosen up stuff that could damage the engine when it starts to circulate.
I've noticed the oil has gotten blacker quicker - so there is some cleaning going on in there. Also seems to need topping up regularly, but that's par for the course on a Landy. If it's not dripping oil, you don't have any.
I know these old engines are built to run on just about anything. They're made tough to deal with tough conditions, but they do still need love and attention, a careful eye to make sure they're functioning optimally. Choosing the right oil for the job is part of that.
Olivia has been going OK, as Olivia generally does. I haven't picked up any really big issues with a different oil going through her system. But I won't be diesel-oiling her petrol engine again, just in case. I'd much rather give her optimal ingredients to handle the roads she travels than take a chance.