Published by Tim Scott on Jul 6, 2015

Keep your turbo cool in the summerWith summer here you need to think about keeping your turbo running cool. Proper oil flow is needed to maintain lubrication and cooling of turbo bearings.  Insufficient lubrication can lead to costly premature turbo failure.

OK, Keep it COOL! Give it the oil!

Here are some good starting points when considering oil line size. The three most popular line sizes are -3AN, -4AN, and -6AN lines. Also keep in mind that the oil needs to flow through at least two fittings.

  • 3AN (line) I.D. is about .145″ or 3.68mm
  • 4AN (line) I.D. is about .187″ or 4.75mm
  • 6AN (line) I.D. is about .375″ or 9.5mm

This is just the measurement I took by putting a drill bit into the lines. Actual specs will very from brand to brand.

So those are the line sizes, not the orifice going through the fitting. The fitting that presses into the line has a much smaller inner diameter.

For example my Porsche runs 6 bar of oil pressure. So we are at almost 90psi. I am running a S256 Borg Warner turbo. I know it will fill the turbo up with more oil than can properly drain out in time (overcoming the seals, not blowing them out). So instead of using a -4AN line with a restrictor, I can use a 3AN line. This should keep adequate flow to the turbocharger. A lot of small and mid frame turbos can get away with a -3AN line when the oil pressure is high.

Now, running a larger frame turbo for racing and what not. You need a lot of oil flow for cooling. This would be s400’s HT3B’s, S500, HX50’s, Gt40’s. These are big boys! I would not use ANYTHING under a -4AN line. And if you can use a -6AN, use it! Even the G forces can cause loss of oil flow to these turbochargers. I can go on all day with this stuff. And there is much more I could cover. I don’t want to go into detail overload because everyone has a different set-up.

Feel free to call or email for help!