Yet another viscosity question

[47HO]

I have a 2002 Jeep Grand Cherokee with the 4.7 liter, high output engine. In my owner's manual it recommends 5W-30 oil for the standard 4.7, but insists that I use 10W-30 in the 4.7 H.O. Why the difference?

 

[MolaKule]

The engine is most likely running hotter and producing slightly more power, due to a number of factors such as different spark and fuel delivery curves, etc.

They want a thicker oil film for the HO version because of the tendency for oils to thin out at higher temps and higher loads.

 

[Patman]

MoleKule is onto something there! The HO version requires premium fuel I believe, as it has a more agressive spark curve. So thus the manufacturer felt more comfortable calling for the more durable 10w30.

 

[dragboat]

Nope on the ignition curve only,,the HO has a hotter cam,heavier valve springs is why they want the 10/30.

They also have shorter intake runners and a different combustion chamber design,,guess I will continue with heavy duty rod and main bearings ,connecting rods and higher compression which would require altered ignition timing to a degree.Probably because it has better heads,they gave the motor more ignition lead even though it does have more compression the HO cam also has more overlap to bleed off down low as well. A number of factors here,the cam and valve springs being number 1 and 2 for the 10/30 IMHO

 

[47HO]

Then what ya'll are saying is that the 10W-30 is prefered because its less likely to shear as much as a 5W-30 (I'm thinking of the cam/valve train)?

 

[MolaKule]

"The engine is most likely running hotter and producing slightly more power, due to a number of factors such as different spark and fuel delivery curves, etc."

The "etc" included higher lift cam and other factors. You can bet your bippy that if they have a more aggressive cam profile the computer will contain different command curves.

My daughter-in-laws jeep is running synthetic 10W30 in her HO version.

 

[Patman]

quote:

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Originally posted by 47HO:
Then what ya'll are saying is that the 10W-30 is prefered because its less likely to shear as much as a 5W-30 (I'm thinking of the cam/valve train)?

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Exactly, the 10w30 won't shear back as easily as 5w30 will. In some cars 10w30 burns less oil than 5w30 also (such as in the LS1 engines)