Fuel dilution the reason for 10w30 being spec'd?

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G-MAN

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I've brought this up before, but it's always puzzled me why Chrysler specified 10w30 for the 3.5 HO engine in my 300M. This engine was designed concurrently with the 2.7 (a totally different design), which was spec'd for 5w30. RI_RS4's posts about his Audi and its high fuel dilution issues got me to thinking so I went back and looked at all my UOAs. They all show relatively high fuel dilution levels (though nowhere near as high as his Audi's).

So now I'm wondering if Chrysler recognized early on that this engine was going to run slightly elevated fuel levels in the oil so they spec'd 10w30 rather than 5w30.

Any thoughts?
 
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Maybe Chrysler just saw little difference in5w-30 and 10w-30, I dunno?

Have you seen any other UOAs with fuel dilution issues with this engine?

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I think I'm the only one who's ever posted a UOA from a 3.5 HO.
 
Quote:

You give Dodge/Chrysler a lot of credit.

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I do give them credit for having a valid reason to spec 10w30 over 5w30. I'm just trying to figure out what that reason was.
 
Will 10W30 really help that much vice a properly formulated 5W30. Oh wait, they use API ratings not properly formulated list of oils for their applications don't they. Of course, in the case of the RS4, a list of oils means squat.
 
It is possible the 3.5 engine runs harder on the oil.. did your OUA(s) have any signs of shearing?
I'm thinking that the high fuel levels have nothing to do with the oil grade they chose
 
probably so, the toyota prius specs 5w-30 while the rest of the lineup has gone to 5w-20. Fuel dilution and the UOA's prove it.
 
Could be. I think the Mitsu EVO calls for M1 10w-30, which is a rarity these days. One thing I think we've all seen a lot of over the years are many engines have fuel dilution issues and apparenlty oil selection is very important in these particular engines.
 
I guess it's possible that Chrysler thought about oil viscosity when they designed their engine for fuel dilution. It doesn't seem to ring true for Honda though. The UOA's of Honda engines showing fuel dilution seem to have 5W20 recommendations, while the engines that have 10W30 recommendations seem to never have fuel in the oil. Maybe 10W30 is preventative?
 
I belive that all of DC's engines that have H.O. in their designation recomend 10W30. Look at the 4.7V8 in regular trim they called for 5W30 from their release date. When they introduced the H.O. version it called for 10W30. They use the same block and rods but the pistons,cams,intake and bearings were different. I can not rember if the oil pump was different part number or not it has been too long since I played with them. So I would imagine that with your car and CAFE credits being king they had a good reason for sticking to 10W30.It is not unheard of for higher output engines to run slightly looser clearances while haveing slightly tighter tolerances. So the extra clearance alone could make a difference in prefered/recomended viscosity. I do not think that anyone with half a brain would tell you that was the only option for the engine though! It is after all simply their recomendation for overall best comprimise in terms of durability and ecconomy.
 
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