Why not separate lubrication for a turbo?

[y_p_w]

Has anyone ever thought of it? It occurs to me that turbos share the same oil as the engine because it's convenient, but does it have to be that way? Couldn't there be a better way? Perhaps sealed bearings? Or a separate oiling system? Maybe some specific lubricant just for turbos - possibly even grease. I mean - there are diffs that use a different lubricant than the same transaxle, so why not a turbo?

You're basically dealing with a system that could be sealed and wouldn't otherwise be subject to contamination. Most are also water cooled, so oil wouldn't necessarily be needed to cool the bearings if the flow of coolant is increased. I keep on hearing about turbos that were oil starved because a screen got plugged up or where the oil used was insufficient to protect the turbo.

 

[itguy08]

My guess is because they spin so fast (couple hundred thousand RPM) grease would get beaten up almost immediately, same with any other oil that would exist as a sealed unit.

I think the simplest and best method is to tap off the 5+ qts of oil in the sump. That way it gets filtered, cooled, and is fresh to lubricate those high speed bearings.

Turbo failures seem to be occurring less these days despite them being used in more and more applications.

 

[skyactiv]

VW has the best solution on the new 2014 Jetta. The models with the 1.8L turbo engine are not the ones from 10 years ago. The new 1.8L Turbo engine has an oil cooler and holds get this, 6.75 quarts of oil.

 

[MolaKule]

Quote:
Has anyone ever thought of it? It occurs to me that turbos share the same oil as the engine because it's convenient, but does it have to be that way? Couldn't there be a better way?


The shared oil system is there for cost reasons.

A separate pump, filter, and oil cooler could be designed for a custom turbo. Sounds like another market for an enterprising entrepeneur.

 

[Hyde244]

Originally Posted By: y_p_w
Has anyone ever thought of it? It occurs to me that turbos share the same oil as the engine because it's convenient, but does it have to be that way? Couldn't there be a better way? Perhaps sealed bearings? Or a separate oiling system? Maybe some specific lubricant just for turbos - possibly even grease. I mean - there are diffs that use a different lubricant than the same transaxle, so why not a turbo?

You're basically dealing with a system that could be sealed and wouldn't otherwise be subject to contamination. Most are also water cooled, so oil wouldn't necessarily be needed to cool the bearings if the flow of coolant is increased. I keep on hearing about turbos that were oil starved because a screen got plugged up or where the oil used was insufficient to protect the turbo.
One word: money.

It is far cheaper to have a shared oil system than a dedicated turbo system. What's more, if no significant performance/maintenance benefit can be derived, there is even less incentive to consider having a dedicated turbo oil lubrication.

There is also a simplicity in having only one oil pump that applies the same oil to all of the engine. Less moving parts/complexity means less things that can go wrong. It is for this reason as well that the same oil is used in variable cam timing instead of having a dedicated fluid.

 

[JHZR2]

Thermal mass is critical. Id much prefer to have the turbo sharing a many, many liter sump of oil than having its own, smaller sump. The turbo is much hotter than many locations in the engine that oil contact, so Id rather have as efficient a means of shedding heat. Sometimes larger sump with more volume and more other things to contact with is the best bet...

 

[y_p_w]

I did a search and did find some turbos are available with sealed bearings.

Quote:
http://aerocharger.com/aerochargers/#technology

BEARING DESIGN & LUBRICATION

A unique self-contained oil system was also created for the Aerocharger® which lubricates the ball bearings in a fine mist of oil. Since the oiling system is separate from the engine, a proper lubricant can be used for the precision ball bearings instead of using oil formulated for engines. This differs from conventional turbochargers that use a flooded bearing system which rely upon the engine’s lubrication system. By avoiding the use of a flooded design a virtually frictionless, self-contained bearing lubrication system was achieved.

So apparently they constantly spray a mist of oil on the bearings, and as long as the bearings are spinning, the mister is engaged. They claim it also has less drag since it isn't spinning in an oil bath with large parasitic losses.

 

[Shannow]

The big emergency diesels at work (1,000, and 1,250hp) have separate oil systems for the turbochargers that comprise great big baths of oil, and not much else.

As per molakule's post, a car would need a whole lube/cooling system for the temperatures involved.

 

[Ken2]

Diesels I've worked with up to 2700 hp have a shared oil system. Very large diesels have separate systems for the turbochargers.

 

[supercity]

Not only cost but added weight, complexity and reliability would make it unviable for a passenger car IMO.

 

[eljefino]

SUPERchargers sometimes (often?) have their own oil system.

 

[hardcore302]

Many aftermarket supercharger manufacturers went from an oil line to a sealed unit with a separate oil. It smells horrible when you drain it. Have you ever smelled the oil in an old GTP?

I'm not sure if the supercharger gears spin as fast as a turbo, though.

 

[threeputtpar]

In my particular application, there are two turbos so there would need to be a seperate supply for each one.

Any where they are located in the engine bay (completely inaccessable unless the engine is removed) would make it nearly impossible to service the oil. I don't think they'd last very long with the ever popular "lifetime fill".

 

[artificialist]

The oil seals aren't 100% perfect in a turbo, so if it was sealed, who knows when the turbo would run dry and be destroyed?

 

[KrisZ]

If the turbo had its own oiling system, what would be the chances that the average knucklehead would change, or even check the oil level? I would guess they would be near zero.
That is why RX-8 did not use a separate oil tank for the apex seal lubrication system.

Combine all the things mentioned already and it’s easy to see that the existing solution is the best compromise between cost, maintenance and reliability point of view.

 

[Shannow]

Originally Posted By: KrisZ
If the turbo had its own oiling system, what would be the chances that the average knucklehead would change, or even check the oil level? I would guess they would be near zero.


Pretty much what happens with the supercharged L67s...no-one checks it...my local holden dealer hadn't sold a bottle of oil in 10 years..

 

[il_signore97]

Originally Posted By: Shannow
Originally Posted By: KrisZ
If the turbo had its own oiling system, what would be the chances that the average knucklehead would change, or even check the oil level? I would guess they would be near zero.


Pretty much what happens with the supercharged L67s...no-one checks it...my local holden dealer hadn't sold a bottle of oil in 10 years..



Probably very true for most people. My friend had a 2001 Pontiac GP with one of these engines and I helped him change the supercharger oil twice over the car's life. But we were typically anal with stuff like that, and he drove that car to almost 650,000 km before he lost compression in one of his cylinders lol. That supercharger oil stinks though!

I would imagine that a stand-alone turbo lubrication system would have to be a lot more sophisticated then supercharger lubrication (temperature, speed of rotation, oil flow, cooling, etc). As far as I understand, the supercharger simply has a small sump of oil for splash lubrication. A stand-alone lubricant for the turbo would need some kind of flow and cooling, no?

 

[y_p_w]

I was thinking about this because Subaru turbo cars sold in the US have a recommendation for oil changes on a severe service schedule of 3750 miles. And the main reason is because the oil and filter pick up contaminants and eventually the little screen can plug up - possibly starving the turbo of oil. The engine itself isn't particularly hard on the oil, but the turbo is.

A sealed system wouldn't get contaminated and could be a specialty lubricant that could last a lot longer than motor oil. Motor oil is a compromise, and in order to get it to work the bearings have to be drowned in oil,

In any case I found a turbo setup with its own oiling system. Apparently one of this company's keys is that they place the bearings closer to the air intake so it doesn't get too hot. And the oiling system they use constantly mists the turbo rather than an oil bath.

 

[y_p_w]

Originally Posted By: il_signore97

A stand-alone lubricant for the turbo would need some kind of flow and cooling, no?

Not really if it's water cooled. Still - the turbo system I found with its own oiling system doesn't even have coolant lines.