Published by Tim Scott on Jul 30, 2016

In this video, we demonstrate the five biggest mistakes people make when dealing with a turbo leaking oil.  Examples shown include incorrect turbocharger mounting orientation and improper return line size.  Click the video below to learn more:


Hello everybody. Thanks for coming back to Tim’s Turbos Information Center.

What I would like to try today is to simulate why a new turbo or rebuild turbo can leak oil, even if everything is in perfect shape.

So what we have here – this is the inboard side of the oil seal holder.

Inboard Side of an Oil Seal Holder

You can see when you pop it out, there is a very little piston ring right in there. That’s what holds in all the oil, but really it’s not designed for that. It’s actually designed to keep boost pressure and dirt from entering the inside of the turbocharger.

Oil Seal Holder Part

Simulating What It’s Like in a Car

So what I did here is I loaded up a rotor group in here and you can see this is where the compressor will be and this is the oil seal holder and bore. This one was actually built without a seal in there and so there is nothing to keep the oil in. Just to show you that, there is no pressure on any of the seals and they don’t have any contact with oil as well.

So I’m going to simulate what it will be like in the car. I have it set up here on the VSR machine and I got the pump set up at about 60 PSI. I’m gonna show you a little further view. This is just a clear tube return line. We’re gonna turn the pump on. You can see the oil coming out here.

Oil Seal in Simulation

Why Turbochargers Leak Oil, Even When Everything is in Perfect Shape

Now as you can see, there’s no oil coming out of that seal. It still can rotate – there’s no pressure on it, nothing – so you don’t even need to have an oil seal in there to keep the oil in.

But, what I can show you is, when you move the return line in an upward position, you’ll instantly see the oil starts to come out of the seal.

Moving the Return Line into an Upward Position

Leaking Oil

So, what I would simulate here is if you had a bad return line or if you had a kink in it, or you had exhaust pressure, not exhaust pressure but more crankcase pressure getting into the crankcase, it’ll come back up the return line of your turbocharger. If you have any type of back pressure, it will come up here.

If you have, you know, cheap fittings and all different types of angles, or if this turbocharger is even clocked in a certain way, like if it’s angled like that, it’s gonna leak oil out there too. You need to make sure that these components are all set up right. This should be at 12 o’clock, this should be at 6 o’clock, and you should have all the right fittings in there.

Fittings for a Turbo

If you’re using 10 AN fittings, it’s gonna be pretty small – you can hardly fit a pinky through those. Just about every manufacturer uses tube type fittings and you can pretty much fit your whole thumb in there.


So, this just goes to show you that even with the oil pressure on the turbocharger, it’s not gonna leak, even without a seal.

If you got any other questions, send me a message and I’ll go over a few different topics for you.

Thanks a lot.