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Jul 21st, 2025 | | | | Joined: Jan 2015 Posts: 22 New Guy | | New Guy Joined: Jan 2015 Posts: 22 | I've got a '48 low pressure 216 in my truck. Runs fine, but I'm getting blue smoke under harder acceleration, but only when the engine is warm. At idle it's clear. When it is cool or warming up, no smoke either. I did a compression test. Results as follows: 1-111, 2-110, 3-90, 4-110, 5-107, 6-100. Not horrible, but not great either. I haven't noticed any big blow by. Wondering if it's just valve seals. Thoughts? | | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | How much oil is it using? A little smoke is no big deal, as long as it's not using a lot of oil or losing power. It's just showing its age a little. Oil is a lot cheaper than engine parts, especially on a 216. Leaky valve seals tend to blow a little blue smoke on a cold start, and/or you'll get a puff of smoke after coasting for a distance and getting back on the throttle. Your symptoms sound a lot more like the piston rings are getting a little tired.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Jan 2015 Posts: 22 New Guy | | New Guy Joined: Jan 2015 Posts: 22 | Thanks for the feedback. It's not burning a lot of oil, and it's not getting dirty too quickly, which I'd expect if there was a lot of blow by. Obviously a ring/piston job is a big deal. Is there a way to test if the valve seals are contributing without ripping it all apart? Valve seals are dirt cheap, and it's just my time to do it. | | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | Go ahead and change the valve seals- - - - -it won't make any difference, but if it makes you feel better, do it.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | When you do your next compression test, squirt some oil in the spark plug hole, if the compression gets better, rings; often can hear valves leaking by listening in manifold.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
| | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | Do a cylinder leakdown test to confirm where the pressure loss is going.
Hint: It's the piston rings!
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Jan 2016 Posts: 631 'Bolter | | 'Bolter Joined: Jan 2016 Posts: 631 | When you do your next compression test, squirt some oil in the spark plug hole, if the compression gets better, rings; often can hear valves leaking by listening in manifold.
Ed Suspect his oil burning (smoking) ...........his rings are already sealed with excessive oil. If the oil was not the there the true compression would be far less than the 100-110 PSI previously meausred. Cylinder leak down test is the preferred test........ as mentioned. | | |
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