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Blue smoke vs gray smoke - oil vs fuel

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Old 01-24-2018, 10:10 AM
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Default Blue smoke vs gray smoke - oil vs fuel

Have a '00 S2000, 158k miles (4.56 gears for 90k miles). Have had the car since it had 31 miles on it!

Couple of years ago, Greg (tr6greg) started to notice blue smoke out of my exhaust pipes. Seems to only happen after I have been engine braking, and then accelerating slowly. If I accelerate hard, no smoke.

Changed PCV valve, installed a catch can (never has more than a drop of oil in it), had the valve guide seals replaced..... and the blue smoke continues. Greg is always the person behind me, so he knows what to look for!

Billman recently suggested to add a qt of 15w50 oil and see what happens (as he thinks it may be the rings). Did this, and the smoke continued.

His second thought was to add a 2nd qt.... here is the strange part.... now it is still smoking after engine braking, but the smoke is gray!

Why would the smoke change from blue to gray, after adding the 2nd quart of a higher viscosity oil??????

Also.... my exhaust tips really get sooted up after 100 miles or so.... doesn't seem to be oil on them, wipes off nice and clean with a wet paper towel.

Since now thinking its a possible fuel issue, have swapped injectors (thanks Andy for the injectors!) to see what happens. Weather has been sh*tty, so haven't been able to get the car out of the garage to see if the borrowed injectors help out!

Another thing that you should know... last year, was throwing P300/301/302/303/304/1399 codes - cylinder misfires. Sent the injectors out for cleaning last winter... and all came back cleaned and supposedly OK... still had the misfire. Swapped out injectors and found the injector in cylinder 2 was bad. Replaced it, and car hasn't thrown a code since.

Appreciate any and all thoughts or suggestions on what my smoking issue may be.... Thanks!!!!!
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Old 01-24-2018, 11:05 AM
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Sounds like worn rings/cylinder walls to me. I'd like to do a compression test and look at the plugs.
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Old 01-24-2018, 12:23 PM
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Ive heard of a few times a bad injector may wash out a cylinder, which is what may have happend in your case and caused some scaring to the cylinder walls allowing some oil to get by maybe. Dunno that there is anything you can do about it.Quick Reply
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Old 01-24-2018, 03:37 PM
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Originally Posted by rpg51 View Post
Sounds like worn rings/cylinder walls to me. I'd like to do a compression test and look at the plugs.
When I pulled the injectors, replaced plugs in 3&4 as they were dirty...

Recent compression test was 205/195/210/205. Leakdown test was done last year, 3%-5%...

I have to add a quart of oil maybe every 2k-4k miles... Seems like I use less oil than others I
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Old 01-24-2018, 03:38 PM
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But why the change in the color of the smoke?

That is one of the things driving me crazy...

Thinking if I can get rid of the gray smoke.... might only have a little blue smoke which I can live with.
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Old 01-24-2018, 04:02 PM
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"now it is still smoking after engine braking."

Sounds like this could be a valve seal issue, too. Does the exhaust pass more smoke the higher the RPM's, during engine braking. Esp, the first throttle application --- after this engine braking?
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Old 01-25-2018, 03:19 AM
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Seems like the longer you engine brake, the more smoke when you start up. Already replaced the valve guide seals, with little to no improvement.

When we came down Mt. Washington this past summer.... engine breaking all the way down. At the bottom, after we stopped for 15-20 minutes, then started back up, looked like I was blowing a smoke screen that would have been in a James Bond movie!


No visible smoke during regular driving.
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Old 01-31-2018, 10:46 AM
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interested to know if you find out what is causing this.
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Old 01-31-2018, 10:57 AM
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If the valve guides are worn, new valve seals likely wont help, or if they do it will be very temporary. Did you replace the guides? Or were they found to be good upon inspection? It would not surprise me to find you have worn oil rings. 1 quart of usage per 2-4k miles is a pretty broad window. If you could narrow that down it would be better. If its every 2k id say for sure your burning it through the oil rings. At 4k it could be isolated, or mostly isolated to the guides/seals. It may just be what it is/not worth fixing if its the rings, and to continue to run the car keeping the oil topped off until it gets worse or you get sick of it and then replace the engine. Once you have to get into the bottom end, it doesn't become cost effective anymore, unless you are doing all your own rebuild work.

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Old 01-31-2018, 04:06 PM
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OK.... I use maybe a qt every 3k miles if that.

Valve guide seals were replaced, no difference in amount of smoke... was still blue.

Here is the big question....

Why did the color of the smoke change when I went to a heavier oil?

Blue smoke is oil, grey is fuel, white is antifreeze.

So why would the color of the smoke change after adding the heavier oil?

Just to keep this up to date... finally got the car out today, the different injectors or MAP sensor did not help. Still bowing grey smoke after engine braking, and accelerating gently....
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