Apparently VW had over inflated tires, 3.5 bar (45-50 psi) and diluted the engine oil with diesel to reduce viscosity: Report: VW engineer told bosses about CO2 manipulation | News | DW.COM | 08.11.2015 According to the weekly paper's report, tampering with CO2 emissions began in 2013 and continued until early 2015. The technicians had allegedly manipulated emissions values by increasing tire pressure to over 3.5 bar, and by mixing diesel into the engine oil to make the car consume less fuel. Personally I am OK with over inflated tires if it leads to a modified suspension to deal with it. A lighter grade of engine oil is also OK if the engine is designed for it. Bob Wilson
If that was what they were recommending to their customers, I am OK with that. If the owners manual gives other recommendations, they are cheating their prospective customers.
Our prius: replacement tires Sumitomo/Yokohama - 51 psi, right-sized on 2010 for accurate speed, distance, and MPG. The 2003 is running over-drive sized tires. Using 2010 oil, 0W-20, in 2003, 0W-30, synthetic. But I won't be diluting engine oil with diesel. Bob Wilson
Is this just to reduce oil viscosity, or is it also a way to get a little extra fuel into the combustion chamber without being metered?
Source: Diesel engine runaway - Wikipedia, the free encyclopedia In many vehicles, a crankcase breather pipe feeds into the air intake to vent the crankcase without releasing raw hydrocarbon vapors into the atmosphere. In a highly worn engine, gases can blow past the sides of the pistons and into the crankcase, creating excess oil mist, which is then drawn from the crankcase into the air intake via the breather. A diesel engine will readily burn this oil mist as fuel, since engine oil has similar energy content and combustion properties as diesel fuel. The extra fuel causes the engine revolutions to increase, causing still more oil mist to be forced out of the crankcase and into the engine, and a positive feedback loop is created. The engine quickly reaches a point where it is generating so much fuel from its own crankcase oil that it can sustain operation even with the normal fuel supply shut off, and it will run faster and faster until it is destroyed.[2] Bob Wilson
I was aware of the gasoline engine run-on problem known as 'dieseling', but haven't been around diesels enough to know anything about the above issue. U.S. EPA testing of gasoline engines measures MPG by monitoring the tailpipe emissions, not by metering fuel input. Thus, intentional crankcase outgassing or misting cannot monkeywrench or artificially boost their fuel economy ratings. I'm not sufficiently familiar with diesel or Euro regulations to know whether or not it might work on them. But past discussions have revealed that less specific test procedure specs over there have allowed much greater 'optimization' than is possible in the U.S.
