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Unread 05-23-2013, 12:24 PM   #16
tp72chev
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1997 WJ 
 
Join Date: Apr 2013
Location: Holland, MI
Posts: 10
Quote:
Originally Posted by cruiser54

Yep. When you see something like this, follow the money or the government.

Especially if you're told it's good for you.
You right that this change was brought on by government regulation but in order to make it work engineers had to set bearing clearances closer for a thinner weight oil to limit oil seer. If anyone on here was an engine builder instead of an opinionest they would know that. 15w40 will operate the same as a 5w30 (which is what your vehicle calls for) ONCE your engine reaches operating temperature but on cold start-up depending on your climate you live in is when it is too thick and CAN cause premature bearing wear over time. I think people have over looked the fact that you said 2005 not 1998.

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Unread 05-23-2013, 12:33 PM   #17
blackjeep05
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2008 JK Wrangler 
 
Join Date: Sep 2012
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Posts: 1,398
Run 10w-30 and call it good. No need in 15w-40 or anything thicker than 10w-30 for that matter. There's a reason why Jeep calls for 10w-30 and has preferred on the viscosity chart and it’s on the 2000 and newer 4.0L oil caps. It won't burn it up but, will cause more bearing wear and bore wear especially when temps do get cooler out. The one thing Jeep has left that is sound is the 4.0L along with the 10w-30 recommendation.


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Unread 05-23-2013, 01:32 PM   #18
BIGBADWOLF
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2004 WJ 
 
Join Date: Aug 2012
Location: Charlotte, North Carolina
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Quote:
Originally Posted by tp72chev View Post
You right that this change was brought on by government regulation but in order to make it work engineers had to set bearing clearances closer for a thinner weight oil to limit oil seer. If anyone on here was an engine builder instead of an opinionest they would know that. 15w40 will operate the same as a 5w30 (which is what your vehicle calls for) ONCE your engine reaches operating temperature but on cold start-up depending on your climate you live in is when it is too thick and CAN cause premature bearing wear over time. I think people have over looked the fact that you said 2005 not 1998.
Bearing clearances have not changed in the history of the 4.0. There is a limit for minimum clearance. Clearance is required for 2 purposes;
1. to allow oil to flow out of crank journal
2. To provide an elliptical motion in order to form a wedge of oil and then compress it...in theory,act like an oil pump to create over a thousand PSI.
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Unread 05-23-2013, 01:41 PM   #19
tp72chev
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1997 WJ 
 
Join Date: Apr 2013
Location: Holland, MI
Posts: 10
Bearing clearance changes in 2000. So did the piston to wall clearance. But it looks like we could all have a spitting contest all day long on this.
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Unread 05-23-2013, 01:54 PM   #20
tp72chev
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Quote:
Originally Posted by tp72chev
Bearing clearance changes in 2000. So did the piston to wall clearance. But it looks like we could all have a spitting contest all day long on this.
From the factory the grind on the crank is tighter to the bearing while still using the same bearing that they have for years. In a rebuild situation the crank is polished or ground to a standards size that would match the standard size from 99 and older.
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Unread 05-23-2013, 02:34 PM   #21
BIGBADWOLF
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Quote:
Originally Posted by tp72chev View Post
From the factory the grind on the crank is tighter to the bearing while still using the same bearing that they have for years. In a rebuild situation the crank is polished or ground to a standards size that would match the standard size from 99 and older.
1970 spec .001 to .002
2004 spec .0005 to .0022

Max allowable is .003 for all years

CNC machining and better technology and quality control practices have tightened tolerance range but the target centerline remains the same.
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Unread 05-23-2013, 05:59 PM   #22
Newtons3
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2006 TJ Wrangler 
 
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Quote:
Originally Posted by tp72chev View Post
You right that this change was brought on by government regulation but in order to make it work engineers had to set bearing clearances closer for a thinner weight oil to limit oil seer. If anyone on here was an engine builder instead of an opinionest they would know that. 15w40 will operate the same as a 5w30 (which is what your vehicle calls for) ONCE your engine reaches operating temperature but on cold start-up depending on your climate you live in is when it is too thick and CAN cause premature bearing wear over time. I think people have over looked the fact that you said 2005 not 1998.
I'm not sure what credentials you need to be called an engine builder, but by any standards at all, I am that. I've also been privileged to spend time with some of the best to learn and debate. I've built more than my share of many types. I've also participated in R&D work with several oil companies and independent labs. There are no tolerances in my 06 4.0 which, when subjected to the pressures and conditions we can see, would cause the damage you predict. The only time ,again, that we've seen this type of damage has been with a combination of much tighter tolerances and much higher oil pressures. Further, your claim that the two oil weights act the same is a bit off. A 30 weight oil is rated between 9.3 and 12.4 centistokes and a 40w between 12.4 and 16.8 (at 100 degrees C). So, by definition, the 40w is somewhat thicker. Exactly how much? Depends on the two oils. A 30w that comes in on the top of the scale and a 40w that comes in on the bottom will be extremely close; almost identical.

Run 15w-40 if you choose and don't sweat it.
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