This is a generic question - but the subject vehicle is a 2005 GMC 4.3 engine.
Sleeve-type bearings are lubricated because a hydraulic oil ‘wedge' is formed as the shaft rotates relative to the bearing. This is also true of roller type bearings, now that I'm thinking about it, as each roller acts as a rotating shaft - just on a smaller scale.
But I am really asking about bearing design / performance in terms of a ‘bushing type' of bearing - such as an auto engine or a large hermetic or open-drive compressor.
And in that context:
What benefit does oil pressure provide? More / higher oil pressure is not what actually supports the rotating shaft inside the bearing - it is the hydraulic-wedge which is created by the rotation. So: so long as sufficient oil is provided to ensure a full layer of oil on the bearing - isn't any higher oil pressure just a wasted effort?
I ask because I recently installed a good-used engine in a 2006 GMC truck. The old engine (essentially a small block chevy ) always ran the 5W30 oil that GM specified. And it always showed about 18-20 lbs oil pressure at hot idle. Maybe 40 lbs. cold at speed - with about 30 lbs. hot at speed.
New (er) engine initially idled hot at about 10-12 lbs and ran at about 20-25 lbs. on the road. That troubled me so I asked the shop what oil they had used. They claimed not to know, saying only: "whatever was the right oil for that engine."
I use Mobil 1 in everything, and I doubt they used that, so at about 1000 miles or so I changed the oil. Truck calls for 5W30 but it lives in south Florida so I thought: oh I'll just use 10W40 instead - I don't need any 5 weight oil characteristics.
Now the cold idle/speed pressures are about 35 & 65 - with the hot idle/speed pressures about 25 & 60 lbs. Which was sort of ‘comforting' to me.
All of which has made me ponder the actual benefits of higher oil pressure. I now theorize that the engine shop used 0W20 as that is what many modern Asian vehicles use - and that was why my initial oil pressure was so ‘low'. OK; so now I have oil pressure which seems 'normal' to my virtually antique mechanical mind - but . . . is it actually better for the engine? Thinking about how oil actually acts inside a bearing, and also about how all the newer engines use physically thin oil, am I making a mistake in judgment? Maybe I am just wasting horsepower creating a higher oil pressure while it is actually no actual benefit to the engine?
Yes; it does make me Feel better - but is it Actually better?
What do you all think?
Sleeve-type bearings are lubricated because a hydraulic oil ‘wedge' is formed as the shaft rotates relative to the bearing. This is also true of roller type bearings, now that I'm thinking about it, as each roller acts as a rotating shaft - just on a smaller scale.
But I am really asking about bearing design / performance in terms of a ‘bushing type' of bearing - such as an auto engine or a large hermetic or open-drive compressor.
And in that context:
What benefit does oil pressure provide? More / higher oil pressure is not what actually supports the rotating shaft inside the bearing - it is the hydraulic-wedge which is created by the rotation. So: so long as sufficient oil is provided to ensure a full layer of oil on the bearing - isn't any higher oil pressure just a wasted effort?
I ask because I recently installed a good-used engine in a 2006 GMC truck. The old engine (essentially a small block chevy ) always ran the 5W30 oil that GM specified. And it always showed about 18-20 lbs oil pressure at hot idle. Maybe 40 lbs. cold at speed - with about 30 lbs. hot at speed.
New (er) engine initially idled hot at about 10-12 lbs and ran at about 20-25 lbs. on the road. That troubled me so I asked the shop what oil they had used. They claimed not to know, saying only: "whatever was the right oil for that engine."
I use Mobil 1 in everything, and I doubt they used that, so at about 1000 miles or so I changed the oil. Truck calls for 5W30 but it lives in south Florida so I thought: oh I'll just use 10W40 instead - I don't need any 5 weight oil characteristics.
Now the cold idle/speed pressures are about 35 & 65 - with the hot idle/speed pressures about 25 & 60 lbs. Which was sort of ‘comforting' to me.
All of which has made me ponder the actual benefits of higher oil pressure. I now theorize that the engine shop used 0W20 as that is what many modern Asian vehicles use - and that was why my initial oil pressure was so ‘low'. OK; so now I have oil pressure which seems 'normal' to my virtually antique mechanical mind - but . . . is it actually better for the engine? Thinking about how oil actually acts inside a bearing, and also about how all the newer engines use physically thin oil, am I making a mistake in judgment? Maybe I am just wasting horsepower creating a higher oil pressure while it is actually no actual benefit to the engine?
Yes; it does make me Feel better - but is it Actually better?
What do you all think?