Smoking Turbos - EXPLAINED Check Valves, Oil Drains, Crankcase Ventilation
If you have a car that resembles a James Bond tricked out SRT-4, please take the time and check this out.
A turbo drains its oil from gravity, nothing more and nothing less. If there is any restriction in the turbo's drain path back to the pan, oil will build up in the center housing. This oil is going to take the path of least resistance and will leak out of the turbine's side piston ring and turn into blue smoke coming out of the exhaust.
Most of your friends are going to tell you that you have a blown seal, and that your turbo needs to be rebuilt. 99% of the time, there is nothing wrong with the turbo. We get turbos in the shop everyday for rebuild because of the mysterious "blown seal" theory that lingers around every intarweb forum that deals with any turbo vehicle. These turbos are perfectly fine, and don't need a rebuild 99% of the time.
I'm putting this explaination together to help all of you save time and energy before you feel the need to send a turbo back to us for rebuild.
Lately, we've noticed a trend with some of the available "check valves" in this market that some shops are selling. Moreso, there are part numbers floating around this forum from industrial supply companies that many people are buying and installing. Most of these check valves will not work properly to allow enough crankcase venting so the turbo can sufficiently drain.
We've done some testing here with a local car and we were able to figure out what was going on. The very popular 1/4"NPT check valve has a .200" valve that is insufficient in allowing the engine to pull enough crankcase pressure when in vacuum. This extra crankcase pressure under vacuum conditions will cause the turbo to leak oil past the piston ring and results in blue smoke out your exhaust. Get rid of this size check valve as all your are doing are causing more problems for yourself.
That same company offers a check valve with 3/8" NPT ports and the valve size is .460". This valve is FTW, period.
We put the 1/4"NPT check valve on the car, let it sit at idle for 30 minutes. After about 20 minutes, the car started smoking, and got progressively worse over the next 10 minutes. Keep in mind, this is on a car that never smoked before. We then installed the 3/8" NPT check valve on the car and let it idle for 30 minutes. No smoke at all. We then put the smaller check valve back in, and instantly started smoking again.
Please make sure you know what you're doing, and don't just listen to everyone else. If you have questions, any of us here at AGP can answer them.