blowing smoke on startup

[larry emrick]

I am getting a lot of blue smoke on startup on my series 3 2.5 petrol, but does not seem to smoke after startup.
Valves, pistons and rings, or both?
Larry

[radio_05]

How would anyone know what the defect is without troubleshooting? What compression numbers are you getting on all cylinders? Usually cylinder #1 and #4 are the worst.

Is the air intake after filter clean, or full of soot?


What engine oil are you running?

[Rob]

One important question: What color is the smoke? If it is black it is likely over-fueling, grey with a "sweet" smell is anti-freeze and bluish is oil burning.

Assuming it is bluish (oil): smoke all the time is often related to the engine being worn-out (oil getting past the rings while the pistons are moving, pressurized oil getting past a damaged head gasket into a combustion chamber, etc) but If you are just getting smoke on start-up that suggests that oil has collected in the cylinders while the engine is stationary. The valve stem oil seals are the usual suspect for start-up smoke as the are basically rubber o-rings that wear out and allow oil to leak down the valve stems into the cylinder while the motor is sitting or to collect on the closed intake valves. The valve stem seals are not related to engine compression so any compression testing won't help you much to determine if the valve stem seals are the oil source. The series 3 has a rudimentary pollution control system that draws oil fumes from the crankcase into the intake. I would also check that system for any signs of oil pooling in the intake which could also cause smoking on start-up. Lots of good info out there on valve seal replacements... can be quite a bit of work though for such a small seal. The recommended solution includes pulling the head (the upside being you get a good look inside the engine).

There are a few basic steps you can use to help you get a general sense of the over-all condition of the motor. To check for blow-by (gives you an idea about the condition of the rings) have the motor running and unscrew the oil filler pipe cap and let it rest on top of the pipe. If it "dances" a little that is normal as the crank case is venting a bit from the movement of the pistons... if the caps is bouncing around or there is smoke coming out of the pipe that is a good indicator of the crank case pressurizing (likely worn rings). So if it passes the "dance" audition next thing to check is the spark plugs. Pull each one and see if they are showing signs of oil burn. Normal is a brownish discoloration on the tips, oil burn is obvious with soot and black encrusting on the spark plug. This is also a good time to do a compression test and a leak down test. Here's a link to a good article about those sorts of tests: https://mobiloil.com/en/article/car-mai ... kdown-test

Smoking from really worn rings is usually continuous but if the wear isn't too severe you might just get smoke when the engine is running in a "vacuum" state (when it is trying to draw in a lot of air but the intake is constricted... usually when starting on "full choke" or also when using the engine for compression-braking down a steep hill). Does it smoke in those situations?

Good luck, hope this is of use to you.

Cheers, Rob

[larry emrick]

Hi Rob:
Thanks for all that. It is much as I thought.
Larry

[island dormy]

Hi Larry

Great advise from the other guys. A compression test will give you all kinds of useful info.

I have a rover that puffs blue smoke on start up (worse when its cold or has been sitting for 2 hours or more) it has done it for 20,000 miles, it does not use any oil between oil changes its just annoying. Since it does not use any oil between oil changes and runs good with good power (it will hit 70 Mph on the flat) I just ignore it. The likely cause is either the little rubber valve guide seals are worn out or were poor quality to start with (guess which color box they came in) or the metal valve guides the valves run in were too loose and worn out to start with. In my case I do not know I did not do the rebuild.
The cure is to remove the head and change the seals and at the same time check the valves and see how loose they are in their guides.
Supposedly you can use compressed air or a rope jammed down the spark plug hole to keep the valves from falling down and change the seals with out removing the head but taking the head off these engines is so easy its not worth the bother.

Good luck Victor

[harv]

If it's not using much oil, the most likely cause of blue smoke on start up only is worn valve guide seals. Unless this really annoys you, it's not worth all the effort to replace them.