in the days before multigrade oils, we would always drain the 30 or 40 weight
oil from tractors and farm equipment during the winter and replace with 5W or
10W(W stands for Winter) oil. the 30 weight would get thick like syrup and
keep the engine from turning over with the old six volt battery, or ruin your
arm if you were using a crank to start. winter oil would still flow easily.
of course in summer you want the thick oil because winter oil would be like
water. oil pressure is directly related to viscosity and temperature. i have
had to shut down aircraft engines when oil coolers would fail and the temp
would go up and the pressure reduce to almost nothing. my healey has a
rebuilt engine, but oil pressure goes way down when idling at a stop light on
a 115 degree day here in vegas. i use 20W-50 oil which is a 20weight winter
oil which has additives that make it like a 50 weight when the engine is warm.
on hot days i watch the oil pressure more closely, but do not worry about it
as long as i have some presssure at idle. i could be wrong, but has worked so
far. healeymanjim
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