Understanding oil viscosity numbers
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 793
Likes: 1
From: Houston Texas
Understanding oil viscosity numbers
OK, hope I don't get killed for sticking my little head up. Just looking to understand from one of you educated types, by what magnitude is a 20W-50 more difficult for an oil pump to move than a 10W-30 at start-up?
Pro
Joined: May 2006
Posts: 583
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From: Pittsburgh PA
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Your question is more complicated than it sounds. Viscosity is just a measure of oil "thickness" or resistance to flow. While a higher viscosity oil will take more effort to force through a specific sized opening, the size of that opening makes a lot of difference to the pump. Also, the colder the oil, the greater increase in work required to accomplish the task of maintaining a fixed pressure. Assuming that the two oils you selected are running in a stock SB Chevy engine with a stock pump on a nice summer day, not much difference at all....maybe 10-20% more load at 'cold' start; less than 5% when warmed up. Now, if you are trying to start that car in -10F weather, you might need an oil pan heater if you have the higher weight oil in your engine.
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 793
Likes: 1
From: Houston Texas
Your question is more complicated than it sounds. Viscosity is just a measure of oil "thickness" or resistance to flow. While a higher viscosity oil will take more effort to force through a specific sized opening, the size of that opening makes a lot of difference to the pump. Also, the colder the oil, the greater increase in work required to accomplish the task of maintaining a fixed pressure. Assuming that the two oils you selected are running in a stock SB Chevy engine with a stock pump on a nice summer day, not much difference at all....maybe 10-20% more load at 'cold' start; less than 5% when warmed up. Now, if you are trying to start that car in -10F weather, you might need an oil pan heater if you have the higher weight oil in your engine.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
I would think that the higher viscosity oil (assuming dino type) would be a better protectant than the thinner oil in TX summers. Probably not the case in winters, as start-up [cold] condition would provide the worst wear during winter. If it were me, I would choose a 30W synthetic for your situation...not too thick in winter; not too thin in summer; good lubricity all year around.
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 793
Likes: 1
From: Houston Texas
Based on what I remember reading on all the "what's the best oil for not rounding lobes on hard lifter cams" threads, the best alternative for this engine (GM spec except for the higher lift Comp Cam [not my choice] original block L71) is a 20-50 mineral oil with some additive such as ZDDP. Trust me, I don't want this to get theoretical and I don't want to start wars over my seeking info. I just wanted to try and better understand the ramifications of a 20-50 oil on my precious metal in my climate with this engine. Thanks for your kind input so far!
Pro
Joined: Dec 2008
Posts: 531
Likes: 0
From: Frisco TX
It also has to do with how the engine is set up and how tight the clearances are - my wife's '09 Honda uses 5w20 OEM.
Any GM Gen 1 V-8 driven in Tx should be fine on 20w50 - although I would run a 10w40 during Fall/Winter if I lived up North.
BTW, what kind of jet do you jockey
Any GM Gen 1 V-8 driven in Tx should be fine on 20w50 - although I would run a 10w40 during Fall/Winter if I lived up North.
BTW, what kind of jet do you jockey
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