Turbocharger oiling - how thick is too thick?

Messages
11
I am in the process of installing a remote twin turbo setup (journal bearing style) on a 00 boxster 2.7L H6 5 speed manual transmission (01a model for those familiar with german automotives). I have a transmission cooler setup that I could very easily use to supply oil to my turbos but I am unsure if it is too heavy - royal purple 75w90 max gear.

I have read bobs post about turbo oiling, the advantanges of full synthetic, the need to avoid lightweight oils ( <= 30), and that there is theoretically too heavy of an oil to create a sufficient float layer of the bearing. However, I have not seen anyone who has ever attempted such a system before documented online and I have not been able to find any hard cutoffs for what is too thick. I've reached out to Garrett and BW with this question and have not gotten an answer from either (Garrett never responded, BW refers you to local installers who told me just that they had never done it). I even posted on theturboforums hoping to find someone who has at least tried but no luck there either.

So, does anyone have something objective to contribute? I am tempted to try it and see but that such a huge gamble that the proposition doesn't excite me.

Comments and criticisms welcome.

Best, Ike
 
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Messages
184
Location
WI
I would think that gear oil is definitely too thick an oil to be pumped through the turbos.

The other issue I'm seeing potentially is the high temps generated by turbos would likely shorten the life of that gear oil, thereby compromising your transmission life as well.

Not to mention, with a one-off system such as this, you run the risk of leaks and again, transmission failure.

I'm interested in seeing your progress nonetheless :) and good luck! I'm trying to convince my better half that I need a weekend track car!
 
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18,142
Location
Upper Midwest
Why would you think that a gear oil (Royal Purple or not) would be a more appropriate lubricant for the turbocharger over a properly rated motor oil that has a specification or approval that is specific to turbocharger longevity and deposit control?
 

MolaKule

Staff member
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22,102
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Iowegia - USA
So you want to cool the turbo bearings with an external transmission cooler system?

Does the external transmission cooler system have a pump?

Any gear lube with an EP additive would probably take out the turbo bearings in short order.

I would try a synthetic 10W30 engine oil and an oiling system separate and apart from the transmission..

I think what is critical here is the amount of fluid flow that is available to the Turbo bearings to keep them cool.
 
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Ike84

Thread starter
Messages
11
The setup for the transmission cooler was designed by myself - transmission to pump to cooler and back to transmission. I can very easily put a filter in line and then plumb into the turbos.

No, I do not think that the gear oil is necessarily better than motor oil. The motivation for using the tranny setup is twofold - first, the plumbing is already there and would be very simple to do. Second, the engine in this car has issues with oil starvation in high g turns and I do not want to aggravate that.

The flashpoint of RP is 191C, compared to my 20w50 motor oil which is 210C, so I'm not sure that the temp will play a huge factor here.

The importance of the turbo oiling is cooling related in turbos without a water jacket, which mine do not, but more importantly is the hydrodynamic layer that supports the bearing. Without that layer, the bearing becomes off balance and given a little bit of time the whole appartus goes kaboom. Hence my concern with the viscosity.

Anyway, thanks for all the repliesn. This is a great forum with a ton of useful knowledge.
 

Ike84

Thread starter
Messages
11
Any gear lube with an EP additive would probably take out the turbo bearings in short order
Can you elaborate on this point a bit? I am still very new to learning about oils, and dditives and metal compatibilities are still a bit of a mystery.
 
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16,159
Location
NE,Ohio
the EP additives in gear oil will trash your turbos. 5w30 to 20w50 motor oil would be more appropriate the viscosity based on the oil temp.

Can you elaborate on this point a bit? I am still very new to learning about oils, and dditives and metal compatibilities are still a bit of a mystery.

Have you ever smelled gear oil.. esp hot gear oil. That right there will tell you how different it is from motor oil.
 

4WD

Messages
17,367
Location
Texas
Regardless of easy … gear oil is not what you want in those snails.
Do you have a spin on oil filter and room to sandwich in a better oil cooler?
 
Messages
249
Location
Central US
I am in the process of installing a remote twin turbo setup (journal bearing style) on a 00 boxster 2.7L H6 5 speed manual transmission (01a model for those familiar with german automotives). I have a transmission cooler setup that I could very easily use to supply oil to my turbos but I am unsure if it is too heavy - royal purple 75w90 max gear.

I have read bobs post about turbo oiling, the advantanges of full synthetic, the need to avoid lightweight oils ( <= 30), and that there is theoretically too heavy of an oil to create a sufficient float layer of the bearing. However, I have not seen anyone who has ever attempted such a system before documented online and I have not been able to find any hard cutoffs for what is too thick. I've reached out to Garrett and BW with this question and have not gotten an answer from either (Garrett never responded, BW refers you to local installers who told me just that they had never done it). I even posted on theturboforums hoping to find someone who has at least tried but no luck there either.

So, does anyone have something objective to contribute? I am tempted to try it and see but that such a huge gamble that the proposition doesn't excite me.

Comments and criticisms welcome.

Best, Ike
What exactly do you mean by remote twin turbos? Are you trying to mount them in the front of the car? I'm having trouble computing this in my head on a MR-layout car. Why not just hang them off the back in the typical location?

I would venture to say that Corvette forums would be a resource for how to plumb remote turbos. I wouldn't mess with a self-contained oiling system running on gear oil, that sounds like a good recipe to blow out seals.
 

MolaKule

Staff member
Messages
22,102
Location
Iowegia - USA
Any gear lube with an EP additive would probably take out the turbo bearings in short order.

I would try a synthetic 10W30 engine oil.

I think what is critical here is the amount of fluid flow that is available for the bearings to keep them cool.
Gear Lubes contain sulfur-phosphorus extreme-pressure (EP) additive chemistry that decompose into acids at high temperatures, so gear oils are not suitable as Turbo lubricants OR as cooling fluid.
 
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MolaKule

Staff member
Messages
22,102
Location
Iowegia - USA
The setup for the transmission cooler was designed by myself - transmission to pump to cooler and back to transmission. I can very easily put a filter in line and then plumb into the turbos.

No, I do not think that the gear oil is necessarily better than motor oil. The motivation for using the tranny setup is twofold - first, the plumbing is already there and would be very simple to do. Second, the engine in this car has issues with oil starvation in high g turns and I do not want to aggravate that.

The flashpoint of RP is 191C, compared to my 20w50 motor oil which is 210C, so I'm not sure that the temp will play a huge factor here.

The importance of the turbo oiling is cooling related in turbos without a water jacket, which mine do not, but more importantly is the hydrodynamic layer that supports the bearing. Without that layer, the bearing becomes off balance and given a little bit of time the whole appartus goes kaboom. Hence my concern with the viscosity.

Anyway, thanks for all the repliesn. This is a great forum with a ton of useful knowledge.
Keeping the oil cool at the bearing inlet, with the proper rate of oil flow and temperature drop through the heat exchanger, will keep the viscosity from thinning out.

Here are some technical data on the topic of turbocharger bearing cooling:


 
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Ike84

Thread starter
Messages
11
Holy cow, tons of replies!

That's a sweet video, it always amazes me how hot this stuff runs. 1400 on paper is just a number, in real life it's horrifying!

The RP maxgear does not contain the sulfur compounds which become acidic at high temps. My gearbox has quite a bit of bronze in the synchros and will not tolerate that formulation. I never realized it was because of the EP additives until reading specifically about this, so many thanks for the knowledge!

In turbo speak, a "remote setup" refers to where the turbos aren't mounted to the exhaust headers. I don't have room to do so because of structural components, so the exhaust will go to manifold - collector - 2.5" piping - turbo - cats/muffler.

Yes, there is a sandwich plate adapter for this vehicle. No one makes one with outlet/inlet ports though, so it gets complicated from there (I will need to run to a remote filter and then have to T off those lines). This would lend itself to a bigger oil cooler install, but the oem spec is actually water cooled and I am upgrading my stock to one from a 3.4L motor so cooling shouldn't be an issue there. Again though, I am concerned about worsening the oil starvation scenario. I have contemplated fabbing up a dry sump system but to do it right would take A LOT.

Unfortunately, most turbo manufactures don't actually endorse a specific brand or weight of oil! The company line is "use high quality oem recommended oil for your motor". I am actually a certified garrett installer (not bragging here, it's quite a joke of a process to obtain that certification) and trust me when I say that I have tried every way I know to get this info out of them (and BW) but no go.

As for the A40 list, I will say one thing - a lot of things about porsche are great, but there are plenty of things that are total garbage. I am a pretty outspoken about porsche's flaws, the company makes far from perfect vehicles. The A40 list is no exception to this. While motor oils are debated pretty heavily in the boxster and 996 forums, the one thing that most agree on is nature of that list.

Anyway, thanks again for all the replies! And as always, comments and criticisms are welcomed.

Best, Ike
 
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