Sale ends todayGet 30% off any course (excluding packages)

Ends in --- --- ---

Excess blue smoke on Deceleration

General Engine Building Discussion

Forum Posts



Tech Articles

Talk about engine building here. New products, tricky questions or showcase your work - If it's engine building related it's welcome here.

= Resolved threads


Hi Guys

I have an ongoing issue with my turbo 4 cylinder; an excessive amount of blue smoke is seen on deceleration only. Things i have changed so far..

- brand new turbo core (brand new, not refurb. changed due to turbine wheel copped some damaged),

- valve stem seals, i've already pulled the head off last month and had them replaced because of this issue.

The engine is in a car that i have just finished a ground up resto on. Currently has 1900km on clock.

Any other uncommon issues that would cause this? I've been told about one other cause, but doesn't add up with me.

I have a video on the dyno showing this issue, if anyone wants to view.


Have you done any work on the pistons? In my experience I have seen this due to several reasons. Most common for me has been valve stem seal, but you already replaced them. Is your coolant reservoir getting full unexpectedly? Could be your ring pack on the piston allowing for excessive oil to make its way into the cylinder. When you decelerate or engine break you basically scavenge any oil on the cylinder (important during engine breaking) causing this condition. And lastly for me i would probably say you could be having an extremely rich condition on decel. Does the smoke has a strong fuel odor? There are just so many variables to pinpoint this. Hope I could shed some light.

Low tension oil rings or incorrectly fitted?

Drawing excessive amount of crankcase fumes through PCV?

You may be able to narrow it down by checking for oil leaks in the turbocharger - may leave an oil trail in the ilet tract and/or burned deposits in the turbine housing?

Any sign of plug fouling?

If an oil restriction was recommended for the tubo' oil feed, was it used? Is there an adaquate oil drain/return and is it correctly oriented?

Oh, are you sure it is actually oil smoke - as in the above post?

Its a hard question with lots of variables, you'd really need to see the video. Send me a pm to organise. Answers to questions:

- they were pistons made to suit engine build, increased compression. Not touched since engine was finished

- no to coolant reservoir filling

- couldn't comment on smell of smoke, all you can smell in the dyno room is e85 hahaha

- surely i would have some signs of smoke on accel or idle with piston ring issues?

- regarding my pcv, i run x2 dash 12 lines from factory ports on rocker to a steel wool filled reservoir in corner of engine bay. A further -6 line runs from this reservoir to a fitting after air filter. We did one run on the dyno with air box removed (with this -6 line now venting to atmo, still smoking). I havent drained the reservoir yet, its wet with e85 but smoke still present with it disconnected.

- Plugs are dry (which could almost prove turbo oil seals and theory below?)

- turbo oil feed is dash 3 hose with 1mm restrictor. The drain is (assuming) using correct size, 3/4 hose which fits factory barb on block. I wanted to expand on the orientation.. the turbo core is orientated roughly 30 odd degrees from centre, does it need to be straight? This is done to stop drain hose fouling on turbo flange.

- the other theory i was asked to check was the turbo drain blocked due to crankcase pressure, forcing oil out turbo seals. Would turbo drain line orientation or hose too large in diameter cause this?

Picture is to show breather lines, there is no actual pcv valve in ths circuit

Lastly, i spoke to Garrett, they recommend 65psi to the turbo core, i have a solid 70psi throughout rev range. Would the 1mm restrictor deal with this effectively?

There's a few clues you can use to help zero in on the cause:

1. If it's oil leaking past the turbine ring in the turbocharger then the smoking won't start until there's some heat in the exhaust to burn off the oil. You'll likely find the smoking won't start for several minutes after a cold start and will get worse as the exhaust heats up. You'll also find that once you come to a stop, the smoke may continue for some time.

2. If it's valve guide seals then this won't generally cause excessive smoking on over run, but you'll get a large cloud of smoke when you re-open the throttle. This will be worse the longer you're on over run.

3. The other option and the one I'd suspect given what you've mentioned, is ring seal. On over run oil can be drawn past the rings into the combustion chamber due to the low pressure created during the intake stroke.

Wouldn't dry plugs in all cylinders prove this is not an internal issue such as worn rings?

Not necessarily. It's dependent on the amount of oil being consumed. Generally you'll see the oil burning indicated on the plugs by deposits but this doesn't necessarily mean the plugs will be wet with oil.

Gentlemen -

Having similar issues as DB510 - Fresh hone, new rings on reused pistons, and a new turbo on a nissan 350z.

I am about 50miles into a engine break-in and my exhaust is clear (hood exit 24” off the turbo) on anything acceleration (whether in boost or vac). I am varying RPM from 2500 to 4k rpm and engine braking when not accelerating. Getting oil smoke on mostly on decel - whether in gear or in neutral coast(which I dont do often). Using Driven Racing Oil BR40 Convention 40wt

Just today got into light boost (3psi to 5psi) but I am getting light to moderate amounts of blue smoke on decel

I disconnected my catch can and plugged the manifold source, vented everything to atmosphere and no change

I need to note if I am getting the smoke on the cold/cooler engine

My turbo oil return line is NOT optimal and it may need to get re-routed - does not have great downward slope back to the sump.

5 out of the 6 plugs were dry with the exception of cylinder #3 had oil on it.

any further recommendations are welcome - thank you in-advance

We usually reply within 12hrs (often sooner)

Need Help?

Need help choosing a course?

Experiencing website difficulties?

Or need to contact us for any other reason?