Turbocharger oiling - how thick is too thick?

MolaKule

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...On a different note - I don't see this mentioned yet, but 75w90 Gear oil is a similar viscosity to a 10w30-10w40 Motor oil. I'll include the graph below for reference...
Each turbo manf. will specify a range of suitable viscosities based on the expected bearing temperatures, the volumetric flow rate of the lubricant, and the oil pressure as discussed in this paper posted above and below.


The read-across viscosity on the charts is immaterial; the point is the additive chemistry in an engine oil is very different than the chemistry in a GL-5 differential lube.

Read across viscosity charts can be seen here: https://bobistheoilguy.com/viscosity-charts/
 

OVERKILL

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The cold weather issue is pressure related. 0w40 mobil 1, for example, will give you a lifter tick in cold weather. Porsche actually redesigned the pressure release valve to combat this issue in later models, but a lot of people (me included) found that 10w eliminated the issue. Kinda crazy that they would redesign an engine part rather than change the recommendation, but that would tick off the company that paid to have their emblem stamped in the trunk since they only offer a high mileage version and a motorcycle version of 10w.

Those things are unrelated. A 0w-40 is thicker at 0C than a 10w-30. Where a 0w-40 gets "less thick" is down well below 0C, and it just means that its rate of thickening is slower because it has passed the cold temperature requirements at -35C and -40C respectively.

ALL oil gets thicker as it gets colder. The Winter rating is just a qualification for the oil to still be both pumpable, and have a limited impact on cranking speed by way of viscosity ceilings for both parameters.

The pressure relief valve simply works to limit overall system pressure, which means at say -10C while both a 0w-40 and 10w-40 might have the pump leaning on the relief, bypassing that oil back to the feed-side, it may be bypassing less of the 0w-40 because it would be a bit thinner. Follow?
 

OVERKILL

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Vladiator! Where did you find these charts! Holy **** I have looked for weeks trying to find this information! Tranny oil is back in the list! Now just gotta find a gear oil that will jive with the 01a and not eat a turbo from the inside out...

Seriously, if you're ever in the lake cumberland area PM me and I will buy you a beer (or 6 lol)

Please don't take his posting of the charts as his recommendation of you using a gear oil in your turbo's, he's simply pointing out that viscosity-wise, they are similar. A lot of people think gear oil is massively thicker than engine oil, but it isn't. It is however, designed completely differently, and not an appropriate product for use in a turbo.
 

MolaKule

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Thanks again for all the replies. After understanding more about gear oil additives, I'll cross this off the list. There are so few manual transmissions anymore that detailed discussion about the stuff rarely ever comes up.

Sorry for talking out of turn on the oil list, I didn't mean to tick anyone off. The list is fine, and the testing behind it is great. If you start running a 20year old 986 though, please come to the forum and read what a lot of really experienced guys have to say about some of these.

The cold weather issue is pressure related. 0w40 mobil 1, for example, will give you a lifter tick in cold weather. Porsche actually redesigned the pressure release valve to combat this issue in later models, but a lot of people (me included) found that 10w eliminated the issue. Kinda crazy that they would redesign an engine part rather than change the recommendation, but that would tick off the company that paid to have their emblem stamped in the trunk since they only offer a high mileage version and a motorcycle version of 10w.

Speaking of mobil 1 (putting fire suit on now), the comment I made was based on info from this site. I'm not a "back in the good ol day" person, the comment was based on base group iii being the mainstay of their formulas. My understanding of oils (yes it is basic) is that it's better to start with better base group and need fewer additives then to just rely on additives to meet the needed specs. Please correct me if this is not accurate though.

The oil starvation issue - that's a doozy. People have tried everything under the sun and still have failures - accusumps, deep sumps, improved baffles. You could write a book on the issue, but the problem is purely mathematical - over 6k rpm the oil pump is moving over 20L per min and when the scavenge pumps cant get the oil back to the pickup during a long sweeping high g turn (porsche cheaped out and only put scavenge pumps in two corners of the case instead of all 4 and remember that this is a horizontal setup so gravity doesn't factor in) there's nothing that will save you.

Anyway, thanks again for all the replies!
Now you are going off the original Turbo subject. Let's try and stay with that topic.

Is there anything in this paper that you found to be incorrect? Did you read it?

 
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Vladiator! Where did you find these charts! Holy **** I have looked for weeks trying to find this information! Tranny oil is back in the list! Now just gotta find a gear oil that will jive with the 01a and not eat a turbo from the inside out...

Seriously, if you're ever in the lake cumberland area PM me and I will buy you a beer (or 6 lol)

Never in my life have I heard of anyone using gear oil for lubrication for a turbo or supercharger unbelievable.
 
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Maybe out of turn here - but the Mercedes-Benz 229.5 seems a more stringent standard to meet than the Porsche A40
- if we get down to specifics.
 

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Never in my life have I heard of anyone using gear oil for lubrication for a turbo or supercharger unbelievable.
Yes, it does seem counterintuitive.

But then, many of us are learning new and better understanding lubrication concepts, usage techniques, and schedule considerations everyday.

I'm sure the poster is as well. He or she is new here. Be firm but gentle. :)
 

OVERKILL

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Maybe out of turn here - but the Mercedes-Benz 229.5 seems a more stringent standard to meet than the Porsche A40
- if we get down to specifics.

That tool is not designed to compare different certifications to each other, it even says so in the bottom, lol. To determine how it compares, you'd need to know the entire sequence of 229.5.
 
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That tool is not designed to compare different certifications to each other, it even says so in the bottom, lol. To determine how it compares, you'd need to know the entire sequence of 229.5.
You're going to make me go read that! We're back to learning something new everyday.

Ah yes, see the Note's last sentence in the lower-right. That whole Lubrizol endeavor reminds me of interesting marketing in so many ways. :cool: :)
 
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Please don't take his posting of the charts as his recommendation of you using a gear oil in your turbo's, he's simply pointing out that viscosity-wise, they are similar. A lot of people think gear oil is massively thicker than engine oil, but it isn't. It is however, designed completely differently, and not an appropriate product for use in a turbo.
Yes, I only posted the charts for ^that exact reason. Should've clarified that, my apologies.

Gear oil should NEVER be used for turbocharger lubrication, or engine lubrication. Motor oil is meant for that.
 
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On a different note - I don't see this mentioned yet, but 75w90 Gear oil is a similar viscosity to a 10w30-10w40 Motor oil. I'll include the graph below for reference.

View attachment 54032
Gear oils defined by SAE J306 shows that the low temperature cut-offs are at a viscosity of 150,000 cP instead of 60,000 cP as shown in SAE J300 for motor oils. That's a big difference. If a turbo system is going to be lubricated with gear oil, it's going to need its own independent oiling system with a pump (preferably a PD pump) that will ensure adequate lubrication pumpability and flow, and proper filtration and pressure relief. Seems way too complicated and open to multiple failure avenues, even if gear oil was suitable for turbo bearing lubrication.

And what spec (SAE or otherwise) defines the HTHS of gear oils? I doubt if gear oil manufactures even show a HTHS spec. Turbo bearing are spinning at insane speeds, and therefore if gear oils have less than stellar HTHS viscosity, it's a disaster waiting to happen.
 
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4WD

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Gear oils defined by SAE J306 shows that the low temperature cut-offs are at a viscosity of 150,000 cP instead of 60,000 cP as shown in SAE J300 for motor oils. That's a big difference. If a turbo system is going to be lubricated with gear oil, it's going to need its own independent oiling system with a pump (preferably a PD pump) that will ensure adequate lubrication pumpability and flow, and proper filtration and pressure relief. Seems way too complicated and open to multiple failure avenues, even if gear oil was suitable for turbo bearing lubrication.

And what spec (SAE or otherwise) defines the HTHS of gear oils? I doubt if gear oil manufactures even show a HTHS spec. Turbo bearing are spinning at insane speeds, and therefore if gear oils have less than stellar HTHS viscosity, it's a disaster waiting to happen.
Yeah, with turbo coking already a challenge for motor oil formulator types … seems gear oil = rum & coke
I still say robust cooling of the motor oil supports longer life for all wear parts …
 
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IMG_20210414_201410314.jpg


Schaeffer's oil 10w30 engine oil!!

I use it in my dust covered Vortech supercharged mustang.These head units are spinning around 55,000 rpm depends on the pulley set-up being used.

Just saying 😉
 
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What turbos are you using? It sounds like some type of BW?

i was just reading the other day that the EFR’s are very sensative to oil pressure. To much and they stop spinning freely.
 
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@MolaKule, I don't think he is, but lets say that he was using a stand-alone pump/cooler just for the turbo bearings, and the oil in no way mixed with anything else in the car. Would an aviation/turbine oil make any sense in this case? (Putting aside the cost of the oil)
 
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