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| | | | Joined: Jan 2009 Posts: 54 'Bolter | | 'Bolter Joined: Jan 2009 Posts: 54 | I have a 1969 chevy c10 that uses oil badly, probably a quart to 700 miles. It has about 130000 miles on the 250 6 cyl. It does not smoke when running or driving but on start up it blows black moisture out the tailpipe. Does this need an overhaul? It doesn't get driven much anymore. Any advice? | | | | | Joined: Jan 2019 Posts: 2,242 Herder of Cats, Goats, and Sheep (moderator) | | Herder of Cats, Goats, and Sheep (moderator) Joined: Jan 2019 Posts: 2,242 | I'd recommend you start with a leakdown test. If it is coming out the tailpipe then it is getting into the combustion chamber(s). That is valves or rings. A leakdown test can help ID if the rings are good or not.
There can be assembly issues (incorrect rockers, incorrect oiling setup, valve seals, valve guides, etc) that lead to oil down through the valves and a decent number of them are fixable without a full teardown.
With that many miles on a 250, if it has not beem rebuilt before then it is probably due. Worth doing some checking first though. | | | | | Joined: Jan 2009 Posts: 54 'Bolter | | 'Bolter Joined: Jan 2009 Posts: 54 | What is a leak down test? | | | | | Joined: Feb 2004 Posts: 29,749 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,749 | Check the PCV valve and the crankcase ventilating system. If pressure is building up in the crankcase from a malfunctioning vent system it can cause excessive oil consumption on an otherwise good engine. Also look for oil leaks from the timing cover, valve cover, and bell housing- - - -high crankcase pressure can cause those places to leak. It's not uncommon for sludge to build up in the vacuum line between the PCV and the intake which prevents good ventilation air flow.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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| | | | | Joined: Jun 2004 Posts: 8,597 Riding in the Passing Lane | | Riding in the Passing Lane Joined: Jun 2004 Posts: 8,597 | Check out the simple things. If any of them don't solve the problem, I would not worry about it. One qt. every 700 miles was not considered excessive back years ago. The manufactures would not warranty if that's what it used. You don't drive it much so a qt. in about a month is not to bad.
Try using 10w40 oil in the winter & 15w40 in the summer.
That black moisture coming out the tail pipe could indicate a rich carb &/or choke.
George
Last edited by Phak1; 10/11/2023 12:23 PM. Reason: By Moderator for spelling
They say money can't buy happiness. It can buy old Chevy trucks though. Same thing. 1972 Chevy c10 Cheyenne SuperIn the Gallery Forum | | | | | Joined: Sep 2009 Posts: 5,777 Gearhead, Stovebolt Tech and Parts Tracker, Mod for Swap Meet and GTT | | Gearhead, Stovebolt Tech and Parts Tracker, Mod for Swap Meet and GTT Joined: Sep 2009 Posts: 5,777 | What is a leak down test? Give this web page a read (video included). Pretty much thoroughly explain what a leak down test is and how to get 'r done. 
~ Dan 1951 Chevy 3 window 3100Follow this story in the DITY Gallery"My Grandpa Carl's Truck and How it Became Mine"1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
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