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Blue Exhaust

My 1997 Toyota Rav-4 has 133,000 miles on it and runs great. Recently, I have noticed it gives off a cloud of blue exhaust when started cold. This lasts for about 5 seconds, then the exhaust becomes colorless. Any idea why this happens and what to do about it? Thanks.

This typically occurs when oil leaks past the valve guide seals into the cylinders when the car is shut off for some time. When you start up, this oil in the cylinders burns (gives off blue smoke) and after a short time it’s gone and the exhaust is a normal color.

The fix for this is not too expensive and can be done without taking the engine apart. A good mechanic can confirm my diagnosis and give you a price.

You’re burning oil. If it goes away like you said, most likely oil is leaking past the valve guides. Only real way to fix it is to replace the valve guides in the heads. Not sure on the design of your engine but it could possibly be done without pulling the cylinder heads. I would suggest getting a compression leakdown test first to see the condition of the piston rings, intake/exhaust valves. If those check out good and they quote you a lot on a repair, I honestly wouldnt worry about it. If you drive short distances it may foul out the plugs sooner than normal. A heavier weight oil may also help clear it up.

You may have some leakage past the valve stem seals.

The oil that lubricates your valvetrain collects in “galleys” in the head and drains back to the crankcase via return passages. It’s prevented frm getting into the cylinders by seals around the valve stems. If there’s some leakage, a bit can drain past when the engine is shut down and sit either on the valves’ rear surfaces or in the chamber and get burned when you start the engine up.

Often there’ll be some smoke on deceleration also, as that’s a time of very high vacuum in the cylinders, and that can pull some oil past worn seals, but it’ll dissipate behind you as you’re moving down the road and unless it’s real bad yo won’t see it.

You need do nothing. Eventually enough of it may coat the catalytic surfaces in the cat cnverter and render it ineffective, but I honestly would do nothing except monitor the oil level.

You can if you like have the seals replced, but whether it’s worth it is a personal choice.

By the way, water vapor is normal on a cool day on startup and could be mistaken for a gray cloud. If it’s dipping water, that’s perfectly normal. It’s a byproduct of combustion and can condense inside cold pipes.

Agree with oil leaking past valve guides as likely cause. It is also possible you are getting some oil blowing by the rings, which means the engine is showing its age internally. If this is the case you’ll see puffs of blue smoke when you get back on the gas after going down a large hill. Sometimes if friends are following you in another car and they tell you there is blue smoke now and again it is likely the rings. A compression test can help confirm this diagnosis.

Another possibility is if the engine is sludged up in the top end. If this problem exists oil return holes may be clogged up and this allows oil to pool around the valve guide bosses. This in turn causes oil to seep past the valve seals and guides.

Removal of the valve cover could determine if this is the case or not. If not, then it could be valve seals and or valve guides; likely the former.
An engine that has ever been overheated can suffer valve seal problems also.

Another less likely possibility is that could be caused by a leaking injector. Normally blue is a sign of oil but not always. If the car runs fine when started cold this would not apply.