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2022 Rubicon 4xe 2016 BMW M6 GC
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Discussion Starter · #1 ·
Hey All -

I'm a soon-to-be first time Jeep owner come mid-July as I have a sting grey Rubicon 4xe on the way and I'm excited to join the Jeep community!

Doing some preliminary research as I do before I buy cars, the topic of oil selection is one of the first things I generally try to address from a maintenance perspective, even before mods and other things. For context, my current daily driver is a 2016 BMW M6 Gran Coupe and I have always had really good experience using Liqui Moly fluids in all of my German cars, however this will be my first FCA vehicle and am unsure if I should be applying what I've learned on my previous vehicles to this one.

With the BMW, the factory calls for 5W-30 full synthetic, but the general consensus among owners circles is to use a 5W-40 oil to better protect the engine in higher temp ranges as it typically shears down to a 30 weight at full operating temp (the twin turbo V8 generates a lot of heat, particularly in the two cylinders closest to the firewall so having an oil that doesn't break down under the additional heat in order to prolong rod bearing life is important for longevity)

My question is this: should I apply my previous experience using a 5W-40 oil with the anticipation that it will shear down to a 30 weight at temp so the internals remain protected, or do these engines typically not generate enough heat at operating temp for it to be a factor and I should just stick to 5W-30? Consistent summertime oil temps in my M6 are usually in the 195-205F range for reference.

Thanks in advance for your help!
 

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Discussion Starter · #3 ·
If I was picking an oil, I'd be more concerned about picking an oil that was as resistant to viscosity break down with fuel dilution than anything else.
This is a fair point and one that I've never had to consider before as this is also my first PHEV - although is there any oil that specifically is designed to withstand the fuel-ingress and burn-off cycle that's seen with them? There may be, I just don't know
 

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Discussion Starter · #5 ·
There's some back on forth on that topic

Thanks for this - I'll spend some more time reading but it looks like at first glance, the idea of going to a heavier weight oil (up to 5W-40 from 5W-30) will be beneficial although for a different reason than I'm used to. It looks like the heavier weight will provide some degree of a 'safety net' from the reduced viscocity resulting from fuel dilution.

Additionally, it looks like the additive package could also play a factor, which I know from experience to be one of the strengths of the Liqui Moly Molygen oil that I have been seeing good results with over the Blackstone reports done since buying the M6 and using that oil since then.

I typically also change fluids at a 2:1 ratio from factory intervals, so that should also help curb some of the negative side effects from fuel dilution long-term.

Nonetheless, it will be interesting to observe the ongoing trends with the Blackstone reports using this oil on this engine
 

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It might also be interesting to have an analysis performed by one of the other labs that measures fuel dilution differently. I have seen lots of discussion as to the validity of extrapolating the fuel dilution from the viscosity.
 

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Discussion Starter · #7 ·
It might also be interesting to have an analysis performed by one of the other labs that measures fuel dilution differently. I have seen lots of discussion as to the validity of extrapolating the fuel dilution from the viscosity.
Yeah true, I noticed a few mentions of the questionable validity of Blackstone's method of calculation for fuel dilution versus others. While I feel like I've had reasonable accuracy with Blackstone over the last 2 years worth of analysis on my M6, what I may do is send out two or maybe even three samples out to different labs to see how well they corroborate one another so I can have a clearer picture of what the real story looks like inside the engine
 

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If you care about warranty stick with 5W-30. Powertrain engineers designed the oil passages, bearing clearances and cooling systems assuming a 5W-30 for use in a habitable climate environment. Contrary to conventional wisdom, "thicker" oil does not directly mean better lubrication. The typical engine cycles through its entire oil reservoir several times per minute; that's engineered lube and heat transfer. A thicker oil might affect the flow rate...enough to matter or not long term is the question. On my Hemi, a thicker oil would cause temporary ops failure of it's cylinder deactivation.

I use the Penzoil Platinum synthetic with its Chrysler Spec rating and run the 5W-20 on my Hemi and 5W-30 on the 4xe. At 10,000 miles on the 4xe there's still no soot buildup on the intake valves (scoped them). On the WK2 Hemi Grand Cherokee pushing 100,000 miles the valvetrain looks like brand new. If warranty wasn't a concern, I'd probably run Motul synthetic (ran that in Audis and custom 800hp+ big blocks).
 

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I would use the highest-quality oil in the recommended weight, and change more often, if driving style or habits are severe.
The above poster touched on a few of the criteria for a given oil weight. There are many, many more.
 

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Discussion Starter · #10 ·
If you care about warranty stick with 5W-30. Powertrain engineers designed the oil passages, bearing clearances and cooling systems assuming a 5W-30 for use in a habitable climate environment. Contrary to conventional wisdom, "thicker" oil does not directly mean better lubrication. The typical engine cycles through its entire oil reservoir several times per minute; that's engineered lube and heat transfer. A thicker oil might affect the flow rate...enough to matter or not long term is the question. On my Hemi, a thicker oil would cause temporary ops failure of it's cylinder deactivation.

I use the Penzoil Platinum synthetic with its Chrysler Spec rating and run the 5W-20 on my Hemi and 5W-30 on the 4xe. At 10,000 miles on the 4xe there's still no soot buildup on the intake valves (scoped them). On the WK2 Hemi Grand Cherokee pushing 100,000 miles the valvetrain looks like brand new. If warranty wasn't a concern, I'd probably run Motul synthetic (ran that in Audis and custom 800hp+ big blocks).
Thank you for your insight and perspective. Wouldn't soot/residue on intake valves be more of a fuel quality and burn versus oil weight? You do bring up a good point regarding warranty though, and I have heard great things about Motul's products.

I would use the highest-quality oil in the recommended weight, and change more often, if driving style or habits are severe.
The above poster touched on a few of the criteria for a given oil weight. There are many, many more.
I wouldn't classify my driving style / habits to be severe, I simply want to be selecting the best possible oil to preserve the internals as well as possible. In my M6, that means running a slightly heavier oil to preserve rod bearing life, and it sounds like the ICE in these PHEV are fairly tricky although for different reasons due to fuel dilution. As I mentioned, I would by default be aiming for a more frequent oil change interval at every 5,000mi
 

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The analysis will help inform for the need to change more or less frequently, based on the remaining additive package and the physical properties of the oil itself.

In a previously-owned turbocharged SUV, Blackstone suggested I extend my oil change interval by ~30%, and I did so with no apparent added wear. This blunted the pain of the $220 synthetic changes slightly.
 

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Discussion Starter · #12 ·
The analysis will help inform for the need to change more or less frequently, based on the remaining additive package and the physical properties of the oil itself.

In a previously-owned turbocharged SUV, Blackstone suggested I extend my oil change interval by ~30%, and I did so with no apparent added wear. This blunted the pain of the $220 synthetic changes slightly.
Thanks, yes with the Liqui Moly Molygen 5W-40 I use in my M6, I always get a TBN as well to understand how much of the additive package is remaining and at 5,000mi intervals in that car, a healthy level of the additives is always still present. My hope is that with half the cylinders and less than half the torque/power under the same interval with the 4xe that it will be a similar story, even with some fuel dilution. But this will be a learning process for me and comparing the two is not an apples to apples thing
 

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Thank you for your insight and perspective. Wouldn't soot/residue on intake valves be more of a fuel quality and burn versus oil weight?...
No problem. The soot/residue is prevalent on direct injection engines and can be a real problem if people use bad gas and/or the wrong oil type and/or extend oil change intervals too far apart. On port injection engines (the Hemi, the 3.6, for example), the fuel mix flows over the intake valves and helps keep them clean. Knowing this is a problem long term on direct injection systems, some direct injection engines now have supplemental port injection to keep the valves clean (the new Bronco, I believe, is one of them). People have used catch cans to mitigate the EGR oil soot buildup on intake valves by culling the oil from the EGR return with good results but the Jeep 2.0T doesn't seem to benefit.

In the case of the Wrangler 2.0T, for some reason this engine has not shown a tendency to develop much intake valve buildup; I've read about some people adding catch cans and caught almost no oil; I have only peripheral knowledge of this tidbit and cannot verify the validity to say it applies to ALL the 2.0T engines. In my engine-building-head, I think if you run the 2.0T at full operating temps for a while (20min?) and avoid idling as much as possible after that each time you drive it, that should reduce the chance of soot buildup on the intakes. An "Italian tune up" on a regular basis when entering highway ramps (after fully warmed up) is good, too.
 

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Discussion Starter · #14 ·
No problem. The soot/residue is prevalent on direct injection engines and can be a real problem if people use bad gas and/or the wrong oil type and/or extend oil change intervals too far apart. On port injection engines (the Hemi, the 3.6, for example), the fuel mix flows over the intake valves and helps keep them clean. Knowing this is a problem long term on direct injection systems, some direct injection engines now have supplemental port injection to keep the valves clean (the new Bronco, I believe, is one of them). People have used catch cans to mitigate the EGR oil soot buildup on intake valves by culling the oil from the EGR return with good results but the Jeep 2.0T doesn't seem to benefit.

In the case of the Wrangler 2.0T, for some reason this engine has not shown a tendency to develop much intake valve buildup; I've read about some people adding catch cans and caught almost no oil; I have only peripheral knowledge of this tidbit and cannot verify the validity to say it applies to ALL the 2.0T engines. In my engine-building-head, I think if you run the 2.0T at full operating temps for a while (20min?) and avoid idling as much as possible after that each time you drive it, that should reduce the chance of soot buildup on the intakes. An "Italian tune up" on a regular basis when entering highway ramps (after fully warmed up) is good, too.
Thanks again for your insight here -- I'm hoping my religious use of 93 octane (yes I know I don't need to, but I do it anyways) will aid even further in mitigating soot buildup on the intake valves or gunking up injectors due to the added detergents and fuller/cleaner burn
 
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