I agree. First, Popular Mechanics does a pretty good job vetting urban legends from fact. Second, there have been plenty of other stories done, with interviews of guys who own repair shops, that have reported similar findings.
Does it mean that every small engine will have problems or behave the same? No. Personally, I've had mixed results. My lawn mower, leaf blower, edger, and chain saw have been fine. However, my Tecumseh snowblower carb, for some reason, gets fouled up within a couple months max. I've had it be fine at the start of the winter when tested, then fail to start because of the carb a month and a half later. And that is with gas stabilizer added. Yet that same gas can be used in the other engines, left in them for 3X as long, with no problems.
So, I'd say it depends. And I'd tend to believe repair shops, who have far more experience with this than we do.
Gee 25 years using ethanol and I have no complaints, I just dont keep it more than 4-6 months in humid temps. Alcohol is a solvent that reduces varnishing, I dont buy your oxidation theory- urban legand crap. You are not going to get seperation if you use the gas instead of letting it sit a few years, more urban legend crap. Water got absorbed in regular gas to, or did you forget "water on the bottom of the tank' it happens from condensation forming from changes in the weather, google it. Alcohol does alow it to be burnt off instead of sitting in the tank, a true benefit. So you posted 3 versions for excuses of "its bad gas" vs " I was an idiot to keep it for several years and why isnt it good anymore, it must be the alcohol. Bottom line, use your gas in a few months, gas by itself goes stale, even without alcohol, or the effects weather can have to increase moisture content. And your alternative to ethanol, you dont have one unless you waste your time.
You are wrong about the temp , you are guessing it was too hot, the plugs read correctly and did not burn hot. Knocking was present and that is proven fact to blow pistons. 2, I got 110000 and when I blew it I was beating the crap out of it in the country with that 4 barrel wide open, that day I would have ruined any motor. Yes it ignites at a higher temp- increases octane rating. And bottom line it ran 100% better with alcohol and kept the carb clean as it is a high solvent, and never any gas issues at even -25f. Alcohol, if you cant drink anymore, your car can finish the bottle.
You don't have to buy my theory, and 4 to 6 months CAN be too long to keep fuel. Water is not "absorbed" in straight gas. Yes, you got water in the tank, but it was separated from the gasoline. It DOES cause problems, whether you have experienced it or believe it, or not. As a mechanic I see it happen.
If it ran lean, it would be running too hot. If it ran lean the plug temperature would have shown it burning white. Only once did I add 5% alcohol by volume, the day it didnt go up a grade, its was always normaly 1.25% or so, a Liter per 20 gallons, and that liter made a dramatic difference in Europes crap gas. Knocking beat it up, and when I blew it the plugs-cilinders were running way under normal temp from lower compression, and probably in need of timing, it was an old car using oil. The amount of alcohol I added and the type of city driving it was getting I cant see 1.25% of alcohol affecting it negatively, but in performance it was great. .
MAybe I'm confused here, but AFAIK, the compression ratio is determine by the engine parameters and is fixed. It doesn't vary by fuel used. Compression ratio is the volume of the cylinder with the piston fully down divided by the volume with it all the way up, no? What kind of fuel the engine can safely run on then depends on the compression ratio as well as fuel/air ratio, timing, etc.
And 1.25% alky did NOTHING for the octane rating. Absolutely NO noticeable change in octane - and virtually no MEASURABLE change.. The R+M/2 octane of anhydrous ethanol (200 proof) is 100.5.
What goes in fuel is NOT anhydrous, and is denatured to boot - so MABEE 99 octane. Added to 87 octane regular at 50% would give you less than 10 points improvement, so at 5% perhaps 1 point. Being real optimistic, 1.25% MIGHT get you 0.2 points octain improvement.
What it DOES do is lean the mixture, AND make it run COOLER. Most people do not understand the relationship between mixture, combustion temp, and engine temp.
Engines RUN hot when too lean only under load - due to detonation disturbing the boundary layer that keeps the metal from absorbing all the heat of the "dragon's breath".
A LEAN mixture (leaner than optimum, or stoich) actually produces LESS heat - and since Ethanol has only half the heat value of gasoline, it LEANS the mixture, and REDUCES the combustion temperature in the cyl.. I'm not saying the ethanol did not make it run better - but it wasn't the OCTANE change that did it. And if that 390 was as tired as you say, it likely didn't have enough compression to require high octane fuel anymore anyway. Also, with it burning oil it is IMPOSSIBLE to get an accurate "reading" of the plug as far as mixture OR temperature are concerned.
You don't have to believe me. And I'm 90% sure you won't, but it is absolutely true. I've been servicing and tuning engines of all kinds for over 40 years, and running them on fuel a lot worse than Euro fuel for several of those years (you want CRAP gas, you want to try burning the stuff they sell in central Africa - Zambia was bad enough - the swill they sold in Zaire was even worse - and at $2.65 per liter back in the seventies!!! There's a reason Deisels are more common there (and in Europe)
You've got it pretty close. "mechanical" or calculated compression ratio is the ratio of the volume of the cyl with the piston at bottom dead center to the volume of the cyl with the piston at top dead center (or swept volume plus clearance volume devided by clearance volume) ACTUAL or EFFECTIVE compression ratio is generally reduced somewhat by
2 factors. On old engines, cyl leakage reduces the effective ratio - and more at low RPM than at high RPM. Cam timing also reduces the effective compression ratio at low speeds
- the hotter the cam (the more overlap) the lower the effective compression ratio, and the lower the compression pressure.
Since detonation is always more of a problem under high cyl pressures, you usually experience it under load at lower RPM - where thankfully the effective CR is lower, - so you can have an engine with a hot cam and 15:1 CR that will run on 92 octane without a problem in a light car, and an engine otherwise the same, but with a mild cam and 12:1 compression in a pickup truck, that pings on 97 octane.
Octane requirements also change with combustion chamber design. High turbulence chambers, with lots of "squish" and "quench" (which generally translates to higher CR as well, due to design restrictions) can require lower octane at higher compression ratios than open chambers.
Oil consumption can RAISE the octane requirement of an engine - partly because the oil has a much lower octane, and partly because it SLOWS DOWN combustion. SLOWER combustion, NOT faster combustion, is most likely to cause detonation. The theory that faster burning fuels lower octane, and slower burning fuels have higher octane is a total missunderstanding of the detonatipon phenomenon, and octane equivalency of fuels.
The longer the "end gasses" stay in the cyl, the more likely they are to detonate, because they absorb more heat and are subjected to the high pressures longer. If the fuel is fully burned, there are no "end gasses" to disassociate and detonate .
The other reason older, worn out engines can require higher octane fuel is engine deposits. If lead, carbon, etc have built up in the engine combustion chamber, 2 things (can) happen. Compression ratio can increase because the clearance volume is reduced by the accumulation. This can cause, or at least contribute to, detonation. The carbon can glow hot, causing "pre-ignition" which is similar to, different than, often mistaken for, and can contribute to - DETONATION.
Badly worn engines can also have narrow "valve margins", with almost knife edges on the valves - which can also overheat, causing pre-ignition.
Just remember - preignition is NOT detonation, but preignition can contribute to detonation - and detonation can contribute to pre-ignition. Pre-ignition is independent of ignition timing, and happens BEFORE the spark. Detonation happens AFTER the spark.
Pre-ignition is caused by (among other things) overheating, while detonation CAUSES overheating.
If you have an engine instrumented with exhaust temperature guages and cyl head temp guages, exhaust temperature will DROP when either too rich or too lean, and the interesting thing is, when you have detonation, the Cyl head temperature will climb, while the exhaust temperature drops. This is a common way to determine if an aircraft engine has reached the point of "incipient detonation" - which means "get the throttle back NOW!!!!!"
With all this yapping about alcohol in fuel, I had a thought, what the heck are they doing in Brazil where many internal combustion engines are run on straight alcohol? What problems have they overcome over the years when their flex-fuel vehicles run E100 and E20 to E25 blends? o_O
They had their fun too, but their vehicles are ENGINEERED to use ethanol as a fuel - and the high ethanol blends (basically just heavily "denatured" ethanol) behaves much differently than, say E10 or E15. With 80% ethanol, and particularly in a warm climate, phase separation is not much of a problem.
Their injectors are stainless steel, all fuel system components are designed to be highly corrosion resistant and ethanol resistant. They use different "O" rings and seal materials, and different fuel lines to withstand the chemical environment (teflon lined hoses come to mind)
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