Turbocharger oiling - how thick is too thick?

I

Ike84

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Apr 12, 2021
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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 (
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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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!
 
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?
 
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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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.
 
MolaKule said:
Any gear lube with an EP additive would probably take out the turbo bearings in short order
Click to expand...
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.
 
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.

Ike84 said:
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.
Click to expand...

Have you ever smelled gear oil.. esp hot gear oil. That right there will tell you how different it is from motor oil.
 
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?
 
Ike84 said:
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 (
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
Click to expand...
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 said:
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.
Click to expand...
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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Ike84 said:
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.
Click to expand...
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:


www.garrettmotion.com

Turbo System Optimization

Turbo System Optimization covers the auxiliary systems and how to properly calculate, install, identify problems, as well as tips for how to correct
www.garrettmotion.com www.garrettmotion.com
 
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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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