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Why 5W-20 is Specified.

Old 09-22-2013
GMG is offline
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Why 5W-20 is Specified.

The main reason 5W-20 or 0W-20 oil was specified for your engine is to increase the CAFE (Corporate Average Fuel Economy) reported to the Federal Government.

CAFE is the combined average fuel economy of all of a vehicle manufacturers product line. Minimum CAFE levels are specified by the Federal Government.

In order for a vehicle manufacturer to continue selling profitable large trucks and SUV's, which typically have poor fuel mileage ratings, as compared to smaller cars, and still meet mandated CAFE requirements, they must also sell enough of the smaller cars which have much better fuel economy ratings to offset the poor fuel economy ratings of the larger vehicles.

For model year 2001, the change to a 5W-20 oil will allow Honda and Ford's overall CAFE to increase by a very small amount, typically in the tenths of a mile per gallon range

Old 09-22-2013
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That may be a factor but it also has to do with many of the newer vehicles relying on oil pressure and specific viscosity to do certain things, like the timing chain tensioners in the 4.0 SOHC V6's or the VCT solenoids and variable cam timing phasers in some of the V8's. Also the tighter tolerances used in the manufacturing of todays engines require the use of such oil weights.
Old 07-20-2017
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However, for an engine designed in the mid/late 80's, 3.0l V6, even with the marginal update tweaks, it's really not going to be that happy with water when it's hot.

Sorry for necro, but i figured this was a good place to make the point.
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