At 03:03 PM 3/3/2001 -0800, Steve Tritle wrote:
>My TD runs with lighter weight oil in the winter here in PA. I changed to
20/50 wt. yesterday and my pressure guage is doing some "crazy" things. My
pressure usually shows about 45# with both 10/30 and 20/50. Now at start up
it shows 25# and slowly creeps up to 35#. ....
I have also noticed this same "anomoly" with my MGA with cold start in cold
weather when using 20W50 oil. The reason for this nearly escapes logic,
because we're used to thicker oil giving slightly higher pressure in warm
weather, but I have a theory. The cold oil is very viscus (lots of
resistance to flow), so there is substantial pressure drop all along the
flow path. The pressure will be high coming out of the oil pump and lower
as you go farther along. It may well be 100 psi at the pump, 60 PSI at the
pressure relief valve, and only 25 psi by the time it gets to the gauge
point. Farther along the flow path it would be even lower pressure,
perhaps only 10 psi at the crankshaft bearings (yikes).
Two things to think about here. It is not a good idea to use high
viscosity oil in very cold weather, 'cause it don't flow well when cold.
And if you do use 20W50 in sub-freezing temperatures, then you may want to
allow the engine to warm up some before you put a load on it and drive off.
$.02,
Barney Gatlord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
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