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Yup using veg from a friend who was brewing it from waste oils from a large base near here, also using a mix from a retail operator in the other end of the city (has duty built in so was barely aby cheaper thwn regular diesel). And yeah gumming issues started happening within a few thousand miles of first use.
Pump etc is dead happy just the rings! Oil gets changed regularly (quantum synta 10w40 which is vw trades own brand oil for vp and pd engines, its like £9 for 5 litres) every 6k.
Having worked on a few they rarely go mechanically bad, it's more their ageing control systems and mechanics that aren't familiar with them that is the common cause for them to end up in the bin.
Was at least 2 years of not 3 since last using anything other than pump diesel, but still the damage has been done. Tried leaving cylinders to soak in that carbon melting stuff (some kind of stinking organic compound) just before an oil change but made no real difference.
Has all new rings in it now, gaps and wear seem ok, had to buy a bore gauge as my friendly engine builder is shut, often borrow his sexy spec tools.
Lesson learned cheap fuels or improper use kills engines
BrickMan-
Thought I had replied.
Didn't know about the ring gumming problem, thought if there would be issues were with the pumps. The VW engines were supposed to be fine on I used SVO as I was lazy and could get 20l for £15 so ran the 2.2 laguna (called chippy as it smelt like a chipshop) on that but used to go through halfords glowplugs in about 6 months a set. But then they were being replaced for free.
Bore gauge, that is posh isn't and old piston ring and feeler gauge enough for you ;) Had access to a scanner that I found fascinating as the accuracy was interesting as you could 'see' different manufactures tolerances. Lancia v4 tolerances were better than the ford/lotus pre crossflow blocks compered to the ford pre crossflow and crossflow block from around the late 60s, then manufacturing gets better at ford for the crossflow blocks used in formula ford.
lynx
The T4 5 pot diesel is an amazing engine due to it tolerance for abuse and lack of maintenance. As I have mentioned before.
Were you using svo or mixing it? How long before the engine suffered sticky rings?