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Motor Run On

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At least in the US, the retail octane boosters are all priced so it's cheaper to buy premium gas. Most of them do almost nothing anyway, so you need multiple cans per tankful to see any difference.

However, when I was running a really high compression head, I found that additives containing MMT worked well for me. Apparently, the coating that MMT builds up in the combustion chamber helped keep the hot spots cool, or something. Didn't work as well for my friend with the supercharged Miata though, so YMMV.

Talked to my Dad (a retired PhD chemist) about making my own TEL; but he convinced me it was too dangerous. Apparently, pure TEL can be absorbed through the skin; he claimed a spot the size of a half-dollar would give you lead poisoning in a matter of minutes.

Stopping the engine with the clutch probably does involve some slight extra wear on clutch, bearings, etc. But it's less than the wear of a single takeoff from a stop sign, so insignificant, IMO.
 
I never had any problems with run-on until we stopped leaded petrol here. Since changing to unleaded it is a constant problem when the engine is hot. I am reluctant to muck about with the timing as the car runs fine as it is and there was no run-on valve fitted to a TR3.
I tend to just stall the engine after switching off. I have noticed though that it is much less of a problem now that I have reduced the idling speed.
Also noticed that the engine runs backwards when running-on and if I slip the clutch when stalling it the car moves backwards!
 
NickMorgan said:
Also noticed that the engine runs backwards when running-on and if I slip the clutch when stalling it the car moves backwards!
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FWIW and IMO, it's better to kill it before it starts turning backwards.
 
Yes, I can't imagine it does it any good at all. I try to make sure that I kill it straight away now.
 
vettedog72 said:
Common sense should tell you that repeated events of “bog down shut off” results in premature bearing wear. Oil pressure is at its lowest and the rod bearings, main bearings and piston pins are getting additional stress from engine run on. Clutch wear? Yea, that too.
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The way you use the clutch to stall the engine on switching off is preemptive and not done only when the dieseling has started. When you know you have the potential for dieseling you stall the engine every time. You're engaging the clutch as you turn the key off so the engine stalls before it can start dieseling. The common analogy would be lawnmowers whose dead-man circuit simultaneously engages an electrical kill switch and applies a brake to the turning engine flywheel.

In a car this creates no more wear and tear than driving away from a stoplight... actually less because you're not allowing the engine to spin the clutch as long as you do when you're pulling away and accelerating. Stalling the engine is a tried and true fix for dieseling when/if you don't want to decoke the engine, change its tuning, and switch to premium fuel. Just remember, when you know that there is the potential for your car to diesel you stall the engine every time and never let it diesel.
 
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