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I couldn't find a thread that lists it under the search function, but I apologise if this topic has been covered elsewhere.

As the header says, I've got blue smoke coming from my exhaust from 5000rpm upward. I've read and been told that it could either be rings or seals, but nobody has been able to tell me how to properly diagnose the problem. How can I determine which is the culprit?

I found another 2.5 that has documents proving a bottom end rebuild less than 20,000km ago, however that also blew a small amount of blue smoke of start-up. Does anyone know what the likely cause of this is?

Any help would be greatly appreciated!

Generally blue smoke on acceleration is from the rings, on decelleration is from the valve stems/seals.

A leak down test can help check the ability of the rings to seal. It is more informative then a compression test. (But a compression test is usually easier to perform.) Adding about 20-30 ml of engine oil to the cylinder and repeating the test can check the rings (the oil temporarily increases the sealing ability of the rings but not the valves).

Another item to check is the brake fluid. Have you been needing to add any? If the brake master cylinder is leaking into the vacuum booster the fluid will get sucked into the intake and then burned. Usually that shows as more of a white smoke but it could be bluish-white.

Thanks, ghnl. I know I had a small fluid leak back into the booster due to a failed master cylnder. I never thought of that. I have since replaced the MC, so I assume that is no longer an issue. I'll get my mechanic to have a proper look.

Any thoughts on blue smoke at startup on a recently rebuilt engine? It sat in a paddock for years after 20000km on the 'new' motor.

Also make sure that the crank case breather isn't gunked up. More blow-by at higher rpm might choke the breather and produce smoke.

check the big intake hose for oil

If it sat around in a paddock, it could have corrosion in some combustion chambers,eg. pitting causing blow by.

Thanks for the help, guys.

Xrad, it would appear you're on the money. There's a fair bit of oil in the intake hose. What are my options? I assume that would be caused by a leak somewhere?

Cheers

I assume that would be caused by a leak somewhere

Not necessarily. These engines tend to put a fair bit of oil in the intake hose.

Try claning out the oil breather on the valve cover and the intake hose and see if that helps you out.

you may still have a case of excessive blowby causing the oil to get into the hose, but running the car should help this.


hth,

Will do, thanks Zig.

What causes this characteristic? I have oil as far down as the air filter, which is slighty concerning to me. I don't know.

Cheers

The crancase breather there on the valve cover is the problem...to a degree. There isn't a baffle to keep oil from being thrown off the valvetrain into it, the hole in the valve cover is kind of small (though this shouldn't matter a bigger hole would let the vapor escape and let the oil drain back into the crankcase better), and there is a fair bit of vaccum as it is connected downstream of the AFM (would be less if it was plumbed into the airbox between the air filter and AFM).

Run a compression test with the engine at normal operating temperature. You should see about 170psi and no more than 5psi difference between cylinders. If the compression test comes up low on one or all then do a leakdown test. That will tell you weather your problem is valves or pistons/rings.

The above is right...if you have "leaky" rings you have blowby and too much of that will put a bunch of oil in the intake.

hth,

Good news! I have perfect compression... In two cylinders.
The other four show 90, 110, 50 & 50 respectively. Sounds like the perfect reason to chuck a 3.0L in.

Thanks all the advice, guys.

Those are rather low. Are you certain you don't have any bent valves or a busted head gasket as well?

Don't toss the 2.5. They'll get rare and people here sometimes get nostalgic and want the 2.5 back in their car.

keep the 2.5. a quick hone, set of rings and valve seals, crank and rod bearings , reshim, new belts, and back in for another 50,000+ miles....

pop in a set of verde cams for that extra little ooommph...

xrad wrote:keep the 2.5. a quick hone, set of rings and valve seals, crank and rod bearings , reshim, new belts, and back in for another 50,000+ miles....

pop in a set of verde cams for that extra little ooommph...

That is, assuming the problem is in the lower block, not in the heads. Best to check/fix those too. Verde cams are nice, but work much better with 3.0 inlet valves in the 2.5

You could use the 3.0 inlet valves but how much will that help when the aluminium runners coming from the heads and going to the inlet chamber are the same diameter on the 2.5 and 3.0?