Ring gumming is a serious ting!
When exposed to heat and oxygen Veggy-Oil will start to break down. It starts to thicken and polymerise and as time goes on, it turns from a sticky brown \'goo\' into a hard black Coke/Carbon material. Just take a look at the frying-pan in your favorite Greasy-Spoon!
Any unburned veggy or partially burned veggy hitting the cylinder-walls will find its way to the Piston-Ring grooves on the next upward stroke of the piston. This veggy will collect in the gap behind the rings and the small clearances either side of the ring and piston. As time heat and plenty of oxygen are available, it breaks down and sets solid, sticking the ring in its groove, so it can no longer follow the irregularities of the cylinder-wall and seal the piston, as it was intended.
This ring gumming is slow and progressive, The speed at which it happens is dependent on Many factors The main ones being the temperature of the combustion-chamber and the condition of the injector atomisation, but as it progresses, gets faster and faster, at a weirdly logarithmic rate...
This causes loss of compression pressure gradually over weeks/months of use. which contributes to the secondary effect....Often the slow and progressive slight power loss may not even be noticed, or blamed on other issues, such as blocking filters or the choice of veggy oil or even the weather (No one wants to admit even to themselves there\'s something nasty growing in the Crank-Case!)....
(A Diesel Engine relies on the fact that when air is compressed, it gets hot, just like the effect noticed when pumping up a bicycle tyre. It depends on this heat for the ignition of the fuel. If for some reason there is a loss of air, say, from leaky rings, the peak temperature attained by the air at the point where the piston is at Top Dead-Centre, A.K.A. Top of the cylinder, the point of maximum compression pressure, the air will be cooler than intended, thus there is a very real danger of incomplete combustion, or even a complete Misfire, where the veggy wont burn at all, Pale bluish or White-Smoke in exhaust and maybe an unsteady engine when idling)
Not all the veggy is burned Particularly when cold, so this just adds to the supply of \'Ring-Glue\'
As it progresses, the amounts of unburned veggy in the combustion chamber/cylinder, increase where it will pass to the lubrication oil by the operation of the oil control rings scraping it off the bores. The Oil Scraper/Control rings, being the lowest on the piston are last to be affected, The Top ring, which is the main sealing ring and subject to the full force of combustion pressure is first to go...
(Just as well the Oil-Control ring is last to go, or the engine could have otherwise end up in a runaway condition where it burns all its lube-oil in a minute or two and hits revs the makers would never have dreamed possible...The danger to life when driving a vehicle when this happens is better not even imagined, You CANT SHUT IT DOWN!....although I dont need to imagine it...Its happened many years ago to me....)
This ring gumming is Progressive and Accelerating Process, Thats why its so Insidious!
The Veggy builds up in the engine lube-oil....
There comes a \'Critical Mass\' point, (although before this, it can thicken to some extent but without careful testing the amount of contamination cannot really be assessed),- where the Mineral Lube-oil and the Veggy oil are in the right proportions with the normal engine heat and other forces to react to form a polymer, and on that fateful day the engine cools after the \'Critical-Mass\' has been reached where the lube-oil will set solid, just like jelly!
-Seen it happen, Very strange stuff is evolved...Same consistancy as Dessert Jelly, with the wobble and shake to b00t, but greenish black opaque and covered in a clear yellow thin oily fluid. It has a slight but weird almost linseed/white spirit type smell too....
Next engine start, you\'ll not have any oil pressure, and if not noticed, engine destruction will occur within minutes.....
IF the Lube-Oil is changed, then the risk of Polymerisation is removed....For Now...
The Ring-Gumming continues its destructive course, untill the point that there is insufficient compression to attain combustion at all. The outcome is the engine just will not start, Maybe a tow-start will get it going but it will soon die perminently!
OK, So you keep an eye on the Lube-Oil level....Great, Spiffin, Marvelous!
This will only tell you that incomplete combustion and ring problems have already started, if you see an increase in level....
You could have an engine, maybe not in its first flush of youth or just because of its design, that normally uses a small amount of Lube-Oil anyway, so the slow dilution with veggy will keep pace with its normal oil use....The lube dilution will then not be noticed, or maybe mistaken that the engine is no longer using up its lube-oil....The outcome is inevitable....