tow starting a diesel is a bit different to tow starting a petrol and often involves "barreling" down the road at considerable speed!
I worked in a little 'village garage' at 14-17 yrs old (weekends, school holidays). The breakdown truck was an early Land Rover, series 1, 86" wheelbase, 1600cc petrol. Complete with crane on the rear deck.
We had a customer who was a one-man business, driving an 8-wheeler tipper truck, mostly working from the quarries on Portland. With a temporary cashflow issue, and needing new batteries for his truck, he resorted to two starting it each morning. After this cold start, it would start ok for the rest of the day.
The process:
Collect Land Rover, and take next door to his yard.
Attach Land Rover by solid bar to the front of the truck.
Use truck batteries to heat the glow plugs once.
Release truck brakes. (Luckily air pressure held overnight sufficient for this, and later stopping)
Back to the Land Rover, select low ratio 1st gear, move away gently, pulling the truck. Speed at tickover was much clower than normal walking pace.
With whole 'train' moving, hop out and leap into the truck.
Engage 2nd gear, turn on ign to heat glow plugs again, as soon as light went out, up with the clutch.
Truck started first time, then use truck brakes to stall teh Land Rover, before meeting the traffic on the road outside.
Leave truck ticking over, return Land Rover.
He did this every working day for about three weeks, until he had the cash for new batteries.
Mildly frightening if you put too much thought into this, but for me, a memory that will never fade.
... this homogeneous mix of air and fuel EXPLODES! long before the piston reaches the top of it's stroke.
I've seen the remains of a spark plug, blown apart by this process, with a small outwards dent in the bonnet.
... I'm wondering if, ... the oil could have been so thick that it was suffering from hydraulic tappet pump up.
I'm not sure the oil pressure will jack up the tappets. As I understand it, the tappet is held snug between cam and valve stem by a spring inside. The oil fills the tappet, and as the cam turns, the internal valve closes, so the oil, being uncompressible, keeps the tappet extended to open the valve. As wear occurs, more oil will fill the tappet.
The tappets should not drain overnight, so thick oil not refilling them should not be a problem. I wonder if valves (inlet or exhaust) were stuck open due to the cold? That would only occur if clearances were tight, or insufficient oil was there, the opposite of the jacking up theory.
I wonder how much oil is in there now.
How long ago it was last serviced, and if the invoic eshows the grade or viscosity of the oil used.
Depending on access, I'm thinking a timing check would be a good idea, and a compression test, as well as the oil check.
Don't we all just love intermittent problems.