Running thinner oil, is my reasoning skewed?

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This is a follow up to another thread i made a while back asking people about their experience running 0/5W20 in old engines.

I've been leaning towards thick oil since i know what oil is and only cared about xW40 ones. Probably because i'm european and have been told about the inevitable disasters that will happen if 5W30 is used in an engine because it's like water. I am more and more interested in experimenting with thinner oils in my application as i am learning about the possible benefits they can offer as well as how bearing clearances and oil pressure work. I've established that running a synthetic ressource conserving 5W30 is in my engine is in fact more than safe.

Here are the values found in the service manual for my engine:

Main bearing clearance: between .025 and .045mm = between .00098 and .00177 in inch.
Rod bearing clearance: between .030 and .050mm = between .00118 and .00197 in inch.

Mininum oil pressure at hot idle: .3 bar = 4.35 psi.
Minimum oil pressure at 3,000 rpm : 3 bar = 43.51 psi.

I've heard about the 10 psi per 1,000 rpm rule and from experience these engines run much higher pressure than that even if MB says 4.35 is acceptable at hot idle (that seems extremely low). The typical pressure is more like 1.5 bar (14.5 psi) at hot idle and the gauge usually pegs at 3 bar (43.5 psi) between 1,500 and 2,000 rpm when hot on all the M1xx gas and OM6xx diesel engines.

I've never been able to get my oil temp higher than 95c (203f) after an italian tune up but that was in winter and it seems to follow coolant temps most of the time, around 80c. It is safe to say that i will rarely encounter extreme oil temps. Most of my driving is very relaxed, mostly 2,500 rpm highway cruising and hypermiling.

I just came accross this chart on the Driven Oil catalog, i've circled what corresponds to my engine's bearing clearances and oil temps.

Capture d’écran 2022-02-27 160232.jpg

Capture d’écran 2022-02-27 160322.jpg


Driven XP10 = 0W10
Driven XP2 = 0W20

Here's the chart on my (somewhat outdated?) owner's manual: The requirement was MB229.1 or API SH if not available.

IMG_20220224_140425.jpg


Conclusion: It seems evident than running a low HTHS 5W30 (A5/B5 or ILSAC) should be harmless year round in my application, theoretically even a 20 but that raises others questions and a few concerns about other things likes piston rings etc. Is my logic skewed? please chime in!
 
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Why would any one want to run a thinner oil and what does the psi, per 1000 rpm have to do with oil viscosity choice? The oil wedge is what is important.
 
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M119

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Why would any one want to run a thinner oil and what does the psi, per 1000 rpm have to do with oil viscosity choice? The oil wedge is what is important. We hear and read lots, of stuff but we must learn to discern fact from fiction.
I notice better throttle response and less drag until the oil is hot and isn't a minimum oil pressure required to maintain that wedge?
 

M119

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Buckle up here we go with another thick vs. thin battle. ;)
I thought about that after starting the thread... :( Usually not my cup of tea but this is a genuine question and i hope it doesn't end up in another war but maybe i am gullible. I just want to make sure that running thin oils is safe for my application. By thin i mean a 5W30 that isn't a A3/B4.
 
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Why would any one want to run a thinner oil and what does the psi, per 1000 rpm have to do with oil viscosity choice? The oil wedge is what is important. We hear and read lots, of stuff but we must learn to discern fact from fiction. For example I rebuilt a 455 Pontiac engine for a friend about 10 years ago, just a simple stock rebuild nothing that was over the skill level i have. Upon the initial firing of the engine and running it a 2,000 RPM one of them people there told me I had too thick oil in the engine because after 2 minutes of running the oil pressure was 80 psi. I asked what makes the oil too thick. Guess where the guy got the information and what did he know?
Thinner=slightly more power, better flow on cold starts, better MPG. Up to the point of damage. 5W20 might be fine for the OP’s engine, but I think I would go a little thicker if I was headed out on the Autobahn (or whatever extended high speed road is in France). A 455 Pontiac would get 15W40 HDEO, and whatever zinc additive I could find.
 
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Probably not as thin oil typically does protect less since it has a lower hths but if you've got a much more resilient and closer to "true synthetic" base stock with a great anti wear package m1 ep 0w-20 would probably protect more than some ultra cheap cf sae 40 off highway diesel i can find in Mexico for a $2 a quart that is molecularly inferior. And on top of that you dont seem to drive hard so thicker than 3.1-3.3 hths isn't all that necessary. 5w-30 isn't that thin. Also the psi rule is kind of gone. Toyotas dynamic oil pump would like a word.

I'm not a typically a thin oil guy but I'm also not a short bus rider. Thinner than spec can actually be okay in some specific engines if it meets the criteria like engine type, usage type, and oil quality and intervals. I'd use M1 0w-16 instead of 5w-20 in the hybrid fords like the maverick with my driving style if they have no oil consumption and 'id expect it to still last 150k since i do a lot of cruising and not much stop and go but it being a hybrid it wont suffer as much in spiking engine loads.
 

M119

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Thinner=slightly more power, better flow on cold starts, better MPG. Up to the point of damage. 5W20 might be fine for the OP’s engine, but I think I would go a little thicker if I was headed out on the Autobahn (or whatever extended high speed road is in France). A 455 Pontiac would get 15W40 HDEO, and whatever zinc additive I could find.
Speed limits in France = 110 or 130 km/h on the highways. 68 mph or 80 mph. I never drive 80 mph to get better fuel mileage. 60 to 68 max. 2,500 rpm.
 
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I notice better throttle response and less drag until the oil is hot and isn't a minimum oil pressure required to maintain that wedge?
No the wedge thickness is viscosity and clearance dependent. Thinner oil leaks out of the bearings faster than thicker oil. Remember it is a compromise.
All things equal and in theory If you started an engine and never turned it off it would last longer with a straight 40 than running a 5W-20 . Most of us do not start and engine and never turn it off so we have starting and warmup considerations, Too thin not is good too thick not good. A multi viscosity oil is a wonderful compromise.
 

M119

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No the wedge thickness is viscosity and clearance dependent. Thinner oil leaks out of the bearings faster than thicker oil. Remember it is a compromise.
Thanks for the clarification. I keep hearing about the 10 psi/thousand rpm rule of thumb. Is there truth in it? Alos, does the Driven chart above have any value?
 

FZ1

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Buckle up here we go with another thick vs. thin battle. ;)
I'll play. Let's discuss how thin is too thin? I Understand too thin depends on the Ride, the Drive ,and the Driver, etc. but what is the vis # others feel too thin? My dealer filled my 17 Camry with, I presume 0w-16 in error, and it was noisey so I extracted it and installed 0w-20 AFE at 8.8 vis.
Noise goes away and car is smooth. Mpg increase. So now I understand MOFT, first hand. So what is the thinnest MOFT others feel is optimal for their rides? As of now I'm going with 8.8 vis. AFE or Ultra and extract it at 3 months. Figgure my exit vis will be about 8.0 after 3,000. what do you guys like MOFT wise in your Rides?
 

M119

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It's only been a few days but throttle response seems better with 5W30 compared to a 5/10W40, more so with a cold engine. Other than that i don't really notice anything. I'll see if gas mileage improves a bit or not and if it burns more oil.
 

FZ1

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This is a follow up to another thread i made a while back asking people about their experience running 0/5W20 in old engines.

I've been leaning towards thick oil since i know what oil is and only cared about xW40 ones. Probably because i'm european and have been told about the inevitable disasters that will happen if 5W30 is used in an engine because it's like water. I am more and more interested in experimenting with thinner oils in my application as i am learning about the possible benefits they can offer as well as how bearing clearances and oil pressure work. I've established that running a synthetic ressource conserving 5W30 is in my engine is in fact more than safe.

Here are the values found in the service manual for my engine:

Main bearing clearance: between .025 and .045mm = between .00098 and .00177 in inch.
Rod bearing clearance: between .030 and .050mm = between .00118 and .00197 in inch.

Mininum oil pressure at hot idle: .3 bar = 4.35 psi.
Minimum oil pressure at 3,000 rpm : 3 bar = 43.51 psi.

I've heard about the 10 psi per 1,000 rpm rule and from experience these engines run much higher pressure than that even if MB says 4.35 is acceptable at hot idle (that seems extremely low). The typical pressure is more like 1.5 bar (14.5 psi) at hot idle and the gauge usually pegs at 3 bar (43.5 psi) between 1,500 and 2,000 rpm when hot on all the M1xx gas and OM6xx diesel engines.

I've never been able to get my oil temp higher than 95c (203f) after an italian tune up but that was in winter and it seems to follow coolant temps most of the time, around 80c. It is safe to say that i will rarely encounter extreme oil temps. Most of my driving is very relaxed, mostly 2,500 rpm highway cruising and hypermiling.

I just came accross this chart on the Driven Oil catalog, i've circled what corresponds to my engine's bearing clearances and oil temps.

View attachment 90590
View attachment 90591

Driven XP10 = 0W10
Driven XP2 = 0W20

Here's the chart on my (somewhat outdated?) owner's manual: The requirement was MB229.1 or API SH if not available.

View attachment 90598

Conclusion: It seems evident than running a low HTHS 5W30 (A5/B5 or ILSAC) should be harmless year round in my application, theoretically even a 20 but that raises others questions and a few concerns about other things likes piston rings etc. Is my logic skewed? please chime in!
These charts are interesting. Thanks. Hopefully, the more knowledgeable guys here can give us a general interpretation of these mechanical specs vs. oil vis.
 

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This is a follow up to another thread i made a while back asking people about their experience running 0/5W20 in old engines.

I've been leaning towards thick oil since i know what oil is and only cared about xW40 ones. Probably because i'm european and have been told about the inevitable disasters that will happen if 5W30 is used in an engine because it's like water. I am more and more interested in experimenting with thinner oils in my application as i am learning about the possible benefits they can offer as well as how bearing clearances and oil pressure work. I've established that running a synthetic ressource conserving 5W30 is in my engine is in fact more than safe.
What are these possible benefits? Thinner oils are being chased primarily for fuel economy, not performance.
Here are the values found in the service manual for my engine:

Main bearing clearance: between .025 and .045mm = between .00098 and .00177 in inch.
Rod bearing clearance: between .030 and .050mm = between .00118 and .00197 in inch.

Mininum oil pressure at hot idle: .3 bar = 4.35 psi.
Minimum oil pressure at 3,000 rpm : 3 bar = 43.51 psi.
And what does your manufacturer spec for viscosity for the above dimensions?
I've heard about the 10 psi per 1,000 rpm rule and from experience these engines run much higher pressure than that even if MB says 4.35 is acceptable at hot idle (that seems extremely low). The typical pressure is more like 1.5 bar (14.5 psi) at hot idle and the gauge usually pegs at 3 bar (43.5 psi) between 1,500 and 2,000 rpm when hot on all the M1xx gas and OM6xx diesel engines.
The 10psi per 1,000RPM rule is a rough rule of thumb for building a Small Block Chevy. It is NOT a universal constant across brands, it was to aide people in determining, roughly, what the appropriate grade to use was when hot rodding an SBC, where bearing clearances would deviate from stock.
I've never been able to get my oil temp higher than 95c (203f) after an italian tune up but that was in winter and it seems to follow coolant temps most of the time, around 80c. It is safe to say that i will rarely encounter extreme oil temps. Most of my driving is very relaxed, mostly 2,500 rpm highway cruising and hypermiling.
80C sounds low for coolant temp, might want to look up what your thermostat is supposed to open at.
I just came accross this chart on the Driven Oil catalog, i've circled what corresponds to my engine's bearing clearances and oil temps.

View attachment 90590
View attachment 90591

Driven XP10 = 0W10
Driven XP2 = 0W20
A chart made up of grades that don't exist (0w-10, 0w-5) in J300 isn't a great starting point here. I'm going to go out on a limb and suggest that Mercedes knows more about your engine and what it needs than Gibbs.
Here's the chart on my (somewhat outdated?) owner's manual: The requirement was MB229.1 or API SH if not available.

View attachment 90598

Conclusion: It seems evident than running a low HTHS 5W30 (A5/B5 or ILSAC) should be harmless year round in my application, theoretically even a 20 but that raises others questions and a few concerns about other things likes piston rings etc. Is my logic skewed? please chime in!
229.1 has a minimum HTHS of 3.5cP:
Screen Shot 2022-02-27 at 2.04.33 PM.jpg


That is the "in the bearings" (high temp, high shear) viscosity that Mercedes stipulates as a minimum.

I mean at this point, with all your waffling on the subject, you might as well just locate some 0w-8, throw it in and see if you can put a rod through the side of the block, which will end the experiment and leave you with a conclusion, vs what appears to be this incessant waffling over something that really doesn't require the scrutiny you are giving it.
 
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What are these possible benefits? Thinner oils are being chased primarily for fuel economy, not performance.

And what does your manufacturer spec for viscosity for the above dimensions?

The 10psi per 1,000RPM rule is a rough rule of thumb for building a Small Block Chevy. It is NOT a universal constant across brands, it was to aide people in determining, roughly, what the appropriate grade to use was when hot rodding an SBC, where bearing clearances would deviate from stock.

80C sounds low for coolant temp, might want to look up what your thermostat is supposed to open at.

A chart made up of grades that don't exist (0w-10, 0w-5) in J300 isn't a great starting point here. I'm going to go out on a limb and suggest that Mercedes knows more about your engine and what it needs than Gibbs.

229.1 has a minimum HTHS of 3.5cP:
View attachment 90648

That is the "in the bearings" (high temp, high shear) viscosity that Mercedes stipulates as a minimum.

I mean at this point, with all your waffling on the subject, you might as well just locate some 0w-8, throw it in and see if you can put a rod through the side of the block, which will end the experiment and leave you with a conclusion, vs what appears to be this incessant waffling over something that really doesn't require the scrutiny you are giving it.
Interesting that Daimler specs 3.5 HTHS across the board for everything. Not sure if a 5W20 can meet that, most of them are ~2.6-3.1. Many ILSAC 5W30s are lower than 3.5 too, that’s Euro 5W30 territory.
 

M119

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Thanks. The experiment won't go further however. I knew it would be okay because tons of cars with the same engine are running something like an ILSAC 5/10W30 in north america, some with very high mileage and i've seen similar or better UOAs on Mercedes forums compared to Mobil 1 0W40. I just wanted to see by myself what i keep hearing on bitog about improved gas mileage and better throttle response. It definitely seems less sluggish when cold. I'll probably go back to a 40 anyway after a short OCI. This oil cost me next to nothing anyway... The question was also for me to find out what in these engine would require a higher HTHS compared to a similar japanese, american and every other european engine and i still don't find anything at all. The specified oil for similar engines of the same era is always a A5/B5 5W30 when i look at any oil recommendation tool from Motul, Total, Shell etc. Even for a Volvo red block.
 
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OVERKILL

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Interesting that Daimler specs 3.5 HTHS across the board for everything. Not sure if a 5W20 can meet that, most of them are ~2.6-3.1. Many ILSAC 5W30s are lower than 3.5 too, that’s Euro 5W30 territory.
Gotta get into the newer Mercedes approvals to get away from the minimum 3.5cP limit. 229.6 and 229.71 both have lower limits:
Screen Shot 2022-02-27 at 2.39.36 PM.jpg
 
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