Oil Viscosity vs Bearing Clearance

Joined
May 28, 2011
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SW Missouri
This is another interesting article on oil viscosity and bearing clearance. https://blog.k1technologies.com/bearing-clearance-and-oil-viscosity-explained

There are several interesting take-aways:
1) The typical rule that most engine builders follow is that bearing clearance establishes the viscosity of the oil to use within a given oil temperature range.
2) Generally, the tighter the bearing clearance, the lower the viscosity the engine can use while wider clearances require thicker oil.
3) A bearing’s load carrying capacity is directly affected by clearance. As the clearance is tightened, load carrying capacity increases.
4) Common sense dictates that bearing clearance directly affects oil flow with predicable results. Reducing the clearance will increase the restriction to flow and reduce the volume of oil past the bearing. Because of this reduced flow, the localized bearing temperature will increase. If this temperature exceeds the oil’s thermal stability limit, the oil will begin to oxidize and break down, reducing its ability to lubricate.

So maybe, just maybe the manufacturer knows what they're talking about when they recommend a 5W-20 oil.
 
Joined
Oct 6, 2020
Messages
1,653
This is another interesting article on oil viscosity and bearing clearance. https://blog.k1technologies.com/bearing-clearance-and-oil-viscosity-explained

There are several interesting take-aways:
1) The typical rule that most engine builders follow is that bearing clearance establishes the viscosity of the oil to use within a given oil temperature range.
2) Generally, the tighter the bearing clearance, the lower the viscosity the engine can use while wider clearances require thicker oil.
3) A bearing’s load carrying capacity is directly affected by clearance. As the clearance is tightened, load carrying capacity increases.
4) Common sense dictates that bearing clearance directly affects oil flow with predicable results. Reducing the clearance will increase the restriction to flow and reduce the volume of oil past the bearing. Because of this reduced flow, the localized bearing temperature will increase. If this temperature exceeds the oil’s thermal stability limit, the oil will begin to oxidize and break down, reducing its ability to lubricate.

So maybe, just maybe the manufacturer knows what they're talking about when they recommend a 5W-20 oil.
Oh gosh. I can’t
 
Joined
Nov 27, 2020
Messages
147
Location
Phoenix, AZ
The Toyota 2020 1GR-FE engine sold in Europe has an oil viscosity specification ranging from 5W-30 to 20W-50, which is a difference of 15 points in the first value and 20 points in the second. In the USA, Toyota recommends 0W-20 for my 1GR-FE engine. I think it will run just fine with 5W-30.
 
Joined
Jul 12, 2012
Messages
5,963
Location
Caldwell Idaho
This is another interesting article on oil viscosity and bearing clearance. https://blog.k1technologies.com/bearing-clearance-and-oil-viscosity-explained

There are several interesting take-aways:
1) The typical rule that most engine builders follow is that bearing clearance establishes the viscosity of the oil to use within a given oil temperature range.
2) Generally, the tighter the bearing clearance, the lower the viscosity the engine can use while wider clearances require thicker oil.
3) A bearing’s load carrying capacity is directly affected by clearance. As the clearance is tightened, load carrying capacity increases.
4) Common sense dictates that bearing clearance directly affects oil flow with predicable results. Reducing the clearance will increase the restriction to flow and reduce the volume of oil past the bearing. Because of this reduced flow, the localized bearing temperature will increase. If this temperature exceeds the oil’s thermal stability limit, the oil will begin to oxidize and break down, reducing its ability to lubricate.

So maybe, just maybe the manufacturer knows what they're talking about when they recommend a 5W-20 oil.
Yes, no or maybe. lets just say no for now. Engine clearances choices are quite complex. The size of the engine Vibration ,flex of the crank and block, the size of the bearings and their speed and more . I don't know if we have machinists that do engines on board.
 
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Joined
Jul 12, 2012
Messages
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Location
Caldwell Idaho
The Toyota 2020 1GR-FE engine sold in Europe has an oil viscosity specification ranging from 5W-30 to 20W-50, which is a difference of 15 points in the first value and 20 points in the second. In the USA, Toyota recommends 0W-20 for my 1GR-FE engine. I think it will run just fine with 5W-30.
USA has CAFE credits based on the how the it is tested. Tested with 0W-20 means the recommended oil is 0W-20
 
Joined
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Messages
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Phoenix, AZ
USA has CAFE credits based on the how the it is tested. Tested with 0W-20 means the recommended oil is 0W-20
I'm very much aware of this. It should be noted that this topic is about bearing clearance vs oil viscosity. I'm not about to hijack a thread by diverting it into a discussion of CAFE.

The recommended viscosity range in Europe indicates a wide range of viscosity is acceptable depending on ambient temperature, operating conditions and bearing clearance. Shall we assume Toyota tested the European 1GR-FE engine over the recommended viscosity range? Perhaps 1GR-FE bearing clearance in the US is about 0.0005 inch less than in Europe? Do you have access to bearing clearance data for the 1GR-FE?
 
Joined
Feb 6, 2010
Messages
906
Location
KY, USA
I have a suggestion you run your 5w20, I'll run my 10w40 and we'll both be happy. I've been running 10w40 in engines spec'd for 5w20 and 5w30 for over 30 years with a combined mileage of approximately 1 million miles and all the engines have been happy. Even the one I retired at 518K miles because there were other problems with the car I didn't feel like messing with. I suspect if I'd have taken care of the things the car needed the engine would probably still be running and would be at approximately 650,000 by now. Sometimes a car gets so old as does it's owner that it's not worth paying a mechanic to do the work and the owner has enough aches and pains he doesn't feel like being bothered with it any longer. The owners manual for my '16 Nissan lists you can use a variety of weights based on ambient temperature not bearing clearance.
 
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Joined
Dec 26, 2005
Messages
21,999
Location
Upper Midwest
Or maybe, just maybe, the manufacturer is high on CAFE... and likes that stay clear of the EPA...
Anybody that wishes to learn from the EPA letters that have been posted here numerous times knows for a fact that this is the reason.

The one drives the mechanical changes, not the other way around.
 
Joined
Sep 4, 2015
Messages
712
Location
Munich, Germany
Because we discussed it before, i just came up with the idea of checking all my workshop manuals for oil reccomendation and bearing clerances. Printed in the manuals are the follwing Crank and Rod bearing clearances, measurments in Millimeter:

1. Crank: 0.013-0.040 Rod: 0.028-0.052
2. Crank: 0.020-0.044 Rod: 0.032-0.056
3. Crank: 0.017-0.042 Rod: 0.030-0.054
4. Crank: 0.020-0.044 Rod: 0.042-0.070

Three of them are motorcycles where 10w-40 is recomended, one is a car where 10w-30 is recomended.

Could you tell wich ones are the bikes and wich one is the car? :)
While i was higly sceptical about oil viscosity and was thinking that thicker is not better, i start to re-think. :unsure:
 
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