Why turbos need oil (and sometimes water, too)
If you WATCHED THE LATEST EPISODE where the lads solve an oiling issue with #science - but it has raised a few questions from people wondering why turbochargers need oil (or coolant... or both!) in the first place. And how do you fix a problem where you can't get high-pressure oil?
Turbochargers spin around and make boost, right? Which means that we need to keep the spinny bits spinning freely and easily, so they can do their choo-choo thang and make our cars rad and fast. The compressor and turbine wheels are mounted to a shaft that runs through the middle of the turbocharger, and this shaft sits in bearings, which allows it all to spin, as you can see below.
Here is a close-up of a turbocharger bearing cartridge. Now you need to lubricate these bearings as they spin, because otherwise they will get hot and sieze or even melt. We lubricate wheel bearings with grease, but the heat loads in a turbo are way, way higher than a wheel bearing so for this we need something better.
Bearing technology has come a long way in the decades since turbochargers were first invented, and their cooling requirements are all different - you might hear about "journal bearing" and "ball-bearing" turbos - which is why some turbos are only cooled with oil, but others also have engine coolant running through them.
One of the trickiest hurdles to overcome when strapping a spoolyboi onto your pUrItY chariot is working out how to get the high-pressure oil jamming into the turbo, and how to drain it out after it has done its job.
On a car the easiest way to sort your turbo oiling is to find an oil gallery in the block which has a screw-in fitting to plug it from the factory. This way you can simply replace the blanking plug with a fitting you can then connect an oil feed line to - oil feed sorted!
For the drain the optimal solution is to run it directly down to just above the "tide line" in your sump, where you can drill a hole to plug a fitting in (either threaded into thick alloy, or welded into a steel oil pan). Keeping this line as vertically-located as possible is important, to ensure good drainage, as the oil needs to go back to the sump so it can cool down before being sucked back through the oil pump to lubricate everything once more.
Thanks to MX-5Miata.net for this pic!
If you can't position your turbo in this way, then don't despair as there are other ways to tickle this riddle, and this solution is where the below image of an Aussie V8 Supercar engine comes in.
You can learn more about the ultimate oil system, the dry sump, HERE as there are some concepts and theories to take away from these motorsport-qualified ways to keep your spinny bits happy. And isn't that what we all want at the end of the day?
Basically they use a multi-stage oil pump mounted outside the engine, driven off a big drive belt (another name for the fat rubber jigger what looks like Ye Olde Timmy the Timing Belt in the above pic). This can push oil into the engine, and suck (scavenge) it out after it is used, and so "scavenge systems" are sometimes used on low-mount or rear-mount turbo installs, where the oil drains are actually lower than the engine oil pan.
The downside to these set-ups is the complexity and the extra expense that incurs. But the upside is your car can then go pssh-pssh, and that is worth all the headaches and dollars spent, right? Right!