Today’s Fuels, Yesterday’s Engines
By Bob Donalds
     The idea that gas is the same today as it was in the ‘60s and ‘70s except for the lack of lead is an easy notion to follow.  It’s also not something that is given much thought, but I'm here to tell you that there is a world of difference between the two! Let’s start with the price. Back in the good old leaded fuel days I can remember pumping fuel at 28 cents a gallon. Today it’s as much as $1.49 (or more) for high test.  The next thing that comes to mind is the alcohol that’s blended in today’s fuel. At the end of ‘94 many of us in the U.S. have had to switch to "reformulated" fuel containing oxygenated additives to reduce ground level ozone. The most common of these is ethanol which is alcohol and MTBE which is an ether. This makes the fuel more expensive to produce and also produces 15-17% less pollution than non-reformulated gas. Unfortunately this alcohol or ether makes the fuel more likely to boil in the injectors and fuel pump of my air-cooled VW engine. Older engines can suffer valve and ring damage that can occur under full load conditions when pre-ignition and overheating is most likely to happen. 

         Finally, there is the formula for determining octane which is displayed on the pump. It has changed to the (R+M)/2 method from the old MON (Motor Octane Number) method. While in Europe the RON method is the standard.  The "R"  in the (R+M)/2 equation stands for Research Octane Number (RON).  The "M" in the equation stands for MON.  RON  serves as the essential index of acceleration knock. The Motor Octane Number (MON)  provides an indication of the tendency to knock at speed under loads. The MON figures are lower than the RON numbers. For instance,  93(R+M)/2 method octane  "high-test " is not even sufficient for the upright VW engine with a posted minimum RON octane number of 91. I see the results of this inadequate octane in the number of early failures I’ve torn down and seen evidence of over-heating and pre-ignition. What do these changes in gasoline mean to the guy or gal pulling up to the pump?,  not too much unless you’re driving a classic machine from the sixties or earlier under full load conditions (on the highway, or with a trailer in tow), or you have an modified air-cooled engine with its normally hotter head temps.  These were designed to run on yesterday’s higher octane leaded fuel. Obviously  there are some vehicles out there, albeit a declining number, that are at risk. The manufacturers of our "reformulated" gas were well aware that it would not meet the needs of some vehicles at the time, but it compromised so little of their market and the environmental needs were more paramount, that they had to proceed with new fuels. This began in the 70’s with unleaded fuel and has continued right up through today with continually evolving fuel formulations.  Avoiding the "reformulated" fuel was an option at first, but is no longer one. In addition, most older engines had carburetors, not fuel management systems which do a much better job of fuel delivery.  Today’s cars also have knock sensors that retard the timing when they detect pre-ignition. Pre-ignition is a very destructive force that increases peak combustion chamber pressure and temps. The pinging noise of pre-ignition is not always heard but must be prevented to ensure maximum overall performance and ensure long engine life.  The VW air-cooled engines that I build for ice machines and for street have a lowered compression ratio to help keep the head temps where they belong.  This change by itself has made the aircooled engines last two to three times longer in the ice re-surfacer machines that we are frequently supplying engines for.  The other things to prevent the air-cooled engine from thermal overload include making sure the tin work is in place, including thermostat and linkage.   Also, the fan should draw in fresh air that has not been through the engine’s cooling system, or that has passed by or through the exhaust system.  In other words, the coolest air possible. Scoops and duct work can help a great deal in getting the coolest air to the fan. Timing is also a large factor in engine temps. As little as 10 degrees off in timing can melt pistons and decrease performance.  Also frequent oil changes can keep the internal friction to a minimum. I have seen engine compartment temps influence  fuel and intake manifold temps and the dramatic drop in the horse power readings on the dynamometer as these temps go up. 

        So how do we prevent overheating? Never put the gas pedal to the metal on the hills,  especially on those hot summer days. Lowering the compression ratio is essential!  Without doing this the engine will easily be pushed to the point of pre-ignition.  Always running the best octane fuel is necessary as well.  Also, the tune up should be regularly checked the oil changed every 1500 miles ("yes, I do it to mine") or at least twice a year if you don't do enough mileage to justify the change. The weight of the oil is determined by the average air temps for you’re particular part of the world. For me 10W-30 works most of the time, except for the heat of the summer (somewhat limited here in New England) when I use a quart or two of 20W-50 with a couple of 10W-40.

        Starting the engine and just going a couple of miles a day does the oil in faster than anything else. The engine never has a chance to fully warm up and burn off all the fuel left over from the cold start cycle. The carb choke (on older engines) makes the engine run rich, resulting in unburned fuel that eventually ends up in the crankcase. Built up fuel in the crankcase can make the engine run with as much as 1% more CO than with freshly changed oil. The car can literally be "running on fumes" and even throw off the tune-up so far that it could prevent passing emission tests.  The fuel thins out the oil, destroying its ability to lubricate properly. Not to mention the fact that in extreme cases the engine gaskets can’t hold back fuel-oil mix. The engine ends up seeping all over the place. 

        Just because oil are better lubricants than used to be (including synthetics) doesn’t change the fact that there is still a fair amount of fuel contamination in the air-cooled crankcase. As I said before 1500 mile oil changes (30-50 hours of running on the ice re-surfacers) is my recommendation to maintain proper lubrication and prevent the contamination from building up. This is especially true for winter use where the oil is more likely to become contaminated due to the engine not reaching full operating temperature on most local trips. You can’t count on the usual pinging of pre-ignition to always be loud enough to hear it. It may only happen occasionally, like on the highway under severe duty use. Especially cruising along with the noise of the windows open, the radio on and all the extra noise of speeding along in a tin box. At that point how do you know the spark plugs are not just along for the ride? 

        Unfortunately we can’t do much about today’s fuels. Environmental controls may continue to make the fuel less user friendly to older engines. However, by taking some simple steps and knowing what the needs of the engine are you can keep it going with today’s fuels.

~Boston Bob

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