blue smoke at startup - The 1947 - Present Chevrolet & GMC Truck Message Board Network

gman · 06-06-2003, 05:45 PM

Just wondering what the likely culprit might be of my mild blue smoke at startup. It always does it after sitting overnight but not during normal stop and go daily driving. Is it bad oil seals causing oil to run down valve guide into combustion chamber? Doesn't smell during normal driving, just at startup. Tuned using vacuum guage, 18 inches of vacuum at 5000 feet elevation. Runs well and starts everytime (knock-on-wood).

Any other ideas or disagreements on the valve seals. 170K on original motor. Thanks.

Class of 69 · 06-06-2003, 05:49 PM

Yup, seals, and loose guides. As long as everything else is still running great, nothing to worry about. You could have the seals replaced with the head on the engine, but usually don't gain much on the smoke, as the loose guide still lets oil down the valve stem.

**Stocker** · 06-06-2003, 07:24 PM

I agree competely with Class of 69! I might add that this is very, very common. Many engines have this happen far before 170K miles.

krue · 06-06-2003, 09:41 PM

Seals and guides would be my bet, also!

Gordo · 06-06-2003, 09:56 PM

I don't know the condition of the engine, but I have seen the oil return holes in the back of the heads plug up with crud and allow oil to back up and run down the guides. Just a thought.

*dtlilly* · 06-07-2003, 12:28 AM

I too agree that the valve stem seals are leaking oil back. I let a car sit too long after a fresh rebuild, and the seals dried up causing that problem. That was back in 1986, and the car is still on the road today running good (but smokes at initial start).

71-longbed · 06-07-2003, 02:12 AM

mine does that too ..not always ...the 350 has 239K on it...

ChevLoRay · 06-07-2003, 12:45 PM

An old-school trick is to use Studebaker "Umbrella type" valve stem seals. Never did have to do it, but old shade-tree hot rodders used to do it. You can do it without removing the heads if you get an adapter that will let you remove the plug, and pressurize the cylinder with air, while you compress the valve spring and remove the keepers to enable the installation of the stem seals.

oldsub86 · 06-07-2003, 01:10 PM

I agree with the suggestion to use the umbrella seals. I did my old suburban a few years back and it improved things dramatically. No more blue smoke on startup and over time the fuel mileage improved a bit. I guess it must have been bad enough to foul the plugs a bit.

06-06-2003, 05:45 PM	#1
gman Registered User Join Date: Nov 2000 Location: Ogden, Utah Posts: 290	blue smoke at startup Just wondering what the likely culprit might be of my mild blue smoke at startup. It always does it after sitting overnight but not during normal stop and go daily driving. Is it bad oil seals causing oil to run down valve guide into combustion chamber? Doesn't smell during normal driving, just at startup. Tuned using vacuum guage, 18 inches of vacuum at 5000 feet elevation. Runs well and starts everytime (knock-on-wood). Any other ideas or disagreements on the valve seals. 170K on original motor. Thanks. __________________ 72 Chevy SWB Custom Deluxe K10, 350/SM465, PS, PB, Fact. Air 2000 Harley...Wide Glide

06-06-2003, 05:49 PM	#2
Class of 69 Registered User Join Date: Mar 2003 Location: Stillwater MN Posts: 1,166	Yup, seals, and loose guides. As long as everything else is still running great, nothing to worry about. You could have the seals replaced with the head on the engine, but usually don't gain much on the smoke, as the loose guide still lets oil down the valve stem. __________________ 69 GMC K10 ..some restoration required....still..

06-06-2003, 07:24 PM	#3
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,814	I agree competely with Class of 69! I might add that this is very, very common. Many engines have this happen far before 170K miles. __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

06-06-2003, 09:41 PM	#4
krue Designated A-hole! Join Date: Mar 2003 Location: South Mississippi Posts: 36,448	Seals and guides would be my bet, also! __________________ "If it ain't broke, fix it 'til it is!" Being stupid ain't illegal. We're Still Debt Free Except for the House!!! www.daveramsey.com 70 GMC SWB Stepside project "Green Booger" soon to be 6.0l/4l80e 93 S-10 "Poppaw's Truck"

06-06-2003, 09:56 PM	#5
Gordo Registered User Join Date: Jan 2001 Location: Killingworth, CT. USA Posts: 3,378	I don't know the condition of the engine, but I have seen the oil return holes in the back of the heads plug up with crud and allow oil to back up and run down the guides. Just a thought. __________________ 1971 C10 swb stepside 350/700R4/3.73posi (retired as of 4/22/03) 1998 S10 short bed 2002 S10 Blazer 1942 Oldsmobile 1958 Massey Harris Pony 1951 Wife Killingworth, Connecticut May those who love us, love us, any of those who do not love us, may God turn their hearts. And if God is unable to turn their hearts, may he turn their ankles so we may know them by their limping. A man who works with his hands is a laborer; a man who works with his hands and his brain is a craftsman; but a man who works with his hands and his brain and his heart is an artist.

06-07-2003, 12:28 AM	#6
dtlilly Account Suspended Join Date: Jan 2003 Location: Shadow of Lambeau Field Posts: 5,597	I too agree that the valve stem seals are leaking oil back. I let a car sit too long after a fresh rebuild, and the seals dried up causing that problem. That was back in 1986, and the car is still on the road today running good (but smokes at initial start).

06-07-2003, 02:12 AM	#7
71-longbed Its Magically Delicious Join Date: Jan 2003 Location: oregon Posts: 2,398	mine does that too ..not always ...the 350 has 239K on it... __________________ 71 C10 LWB 350sbc -TH350 12 bolt 3.42 Posi Of all my favorite things to do, The utmost is to have a brew. My love grows for my foamy friend, with each thirst-quenching elbow bend. Beer so frosty, smooth, and cold it's paradise pure liquid gold. Yes beer means many things to me that's all for now cus I gotta pee.

06-07-2003, 12:45 PM	#8
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	An old-school trick is to use Studebaker "Umbrella type" valve stem seals. Never did have to do it, but old shade-tree hot rodders used to do it. You can do it without removing the heads if you get an adapter that will let you remove the plug, and pressurize the cylinder with air, while you compress the valve spring and remove the keepers to enable the installation of the stem seals. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

06-07-2003, 01:10 PM	#9
oldsub86 Registered User Join Date: Dec 2002 Location: Canada Posts: 695	I agree with the suggestion to use the umbrella seals. I did my old suburban a few years back and it improved things dramatically. No more blue smoke on startup and over time the fuel mileage improved a bit. I guess it must have been bad enough to foul the plugs a bit. __________________ 1968 Chevy - 292 with a powerglide

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