A1B@PSUVM.BITNET (12/12/84)
<If you see this the oil may be two thin>
Note: I tried to mail this reply separately, but I had problems in
sending it out.
In (slight) reference to your question one on having 10W40 oil thin...
I have had problems with 10W40 oil thinning too much during the summer (90
degrees, with AC on). The oil pressure normally reads 65 PSI, but during
hot days, the pressure would drop to 30 PSI at stop signs. I changed to
20W50 oil, and the problem went away. Note that the higher the viscosity
number, the thicker the oil is. In theory, 10W30 is thinner than 10WW40.
As for GM's recommendation for using 5W30 oil, and not using 10W40
oil, I don't know their reasoning for sure, but it may have something to do
with the fact that thinner oils have less friction than thicker oils.
Gas mileage can be increased by using a thinner oil. Of course oil pressure
in hot weather or high speed driving is lower, and engine tolerances
must be tighter, but those are the things one must pay for higher mileage.
* * *
Wayne Toy
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