1991 Chevrolet K1500, 4.3 V6, 116k miles (estimated, due to broken odometer). Has had bad valve stem seals since I purchased it five years ago with 89k miles. Always a blue puff of smoke on startup. I can't tell if it is smoking badly now. Lately, it is starting to use a lot of oil. A quart every few months. I don't know if this could be from the bad stem seals, or if rings are getting worn? I might mention that this vehicle is a short tripper. I was doing once-per-year oil changes. Thinking I am doing about 6k miles per year or less. Decided I will start doing twice-per-year oil changes due to the short trips. Wondering if a 40 weight oil will reduce consumption. I've been using a 5w/30 as spec'd (although I put 5w/20 this last oil changed because that's what I had on hand). Thinking of going to a 5w/40 or 10W/40, for summer. Maybe even a 15W/40. Thoughts and suggestions welcome.
Heavier oil?
- Thread starter otis24
- Start date
Do a wet and a dry compression test .
You have nothing to lose by trying a 10w40 year round or the 15w40 in the summer. 
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Couldn't hurt...
Look, if you're driving 6,000 miles/year, and you're adding a quart every "couple" of months, then you're adding a quart every thousand miles or so, which isn't terrible.
In fact, with blue smoke on startup, it's probably just the valve stem seals...nothing else...and heavier oil may help with that.
Valve stem seals aren't a hard job on this. But heavier oil is cheap. Might as well see how it works.
Nope on the 40. Garbage oil.
Run the 5W30, your hydraulic lifters need a certain leakdown rate. to give you good torque and fuel economy.
You should NOT have run the 20 grade oil!
Just do the Stem seals if the compression test points that way, easy enough job.
but is suspect it was just a neglected and carboned up
rings and pistons.
Thicker oil is usually never the solution unless t you have big miles, and you dont.
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Originally Posted by Astro14
Couldn't hurt...
.....
Valve stem seals aren't a hard job on this. But heavier oil is cheap. Might as well see how it works.
a leakdown test will tell you where the oil is leaking into the cylinder.
replace the worn/faulty component.
Sounds like valve stem seals also to me. If your not gonna replace those -- move to a 10W30 or 10W40 High Mileage motor oil during summer months.
Triple_Se7en
$50 Site Donor 2023
Sometimes we are better off donating 5w20 oil to the Vietnam Vets Club, than use it because it's sitting in the garage.
I once put 5w20 in my 4.3 S10 and when I changed the oil 5K later, the magnetic drain plug was loaded with shiny silver shavings.
The idea to move up to 10w40 in South Dakota is your best idea, if you are not mechanically-inclined to fix the oil loss yourself.
Originally Posted by otis24
1991 Chevrolet K1500, 4.3 V6, 116k miles (estimated, due to broken odometer). Has had bad valve stem seals since I purchased it five years ago with 89k miles. Always a blue puff of smoke on startup. I can't tell if it is smoking badly now. Lately, it is starting to use a lot of oil. A quart every few months. I don't know if this could be from the bad stem seals, or if rings are getting worn? I might mention that this vehicle is a short tripper. I was doing once-per-year oil changes. Thinking I am doing about 6k miles per year or less. Decided I will start doing twice-per-year oil changes due to the short trips. Wondering if a 40 weight oil will reduce consumption. I've been using a 5w/30 as spec'd (although I put 5w/20 this last oil changed because that's what I had on hand). Thinking of going to a 5w/40 or 10W/40, for summer. Maybe even a 15W/40. Thoughts and suggestions welcome.
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Originally Posted by 53' Stude
Originally Posted by otis24
1991 Chevrolet K1500, 4.3 V6, 116k miles (estimated, due to broken odometer). Has had bad valve stem seals since I purchased it five years ago with 89k miles. Always a blue puff of smoke on startup. I can't tell if it is smoking badly now. Lately, it is starting to use a lot of oil. A quart every few months. I don't know if this could be from the bad stem seals, or if rings are getting worn? I might mention that this vehicle is a short tripper. I was doing once-per-year oil changes. Thinking I am doing about 6k miles per year or less. Decided I will start doing twice-per-year oil changes due to the short trips. Wondering if a 40 weight oil will reduce consumption. I've been using a 5w/30 as spec'd (although I put 5w/20 this last oil changed because that's what I had on hand). Thinking of going to a 5w/40 or 10W/40, for summer. Maybe even a 15W/40. Thoughts and suggestions welcome.
when the spec 5-20 went thu girlfriends 2.5L 13 oil burning malibu i switched to 10-30 which helped a while, then to a 5-40 + as it was using over a qt on a thou at only 60 thou she dumped it for a preowned optima 2.4 L that uses NONE. sooner or later yo might need to trade or fix or just keep dumping in the oil!! i was using 20-50 in my 72 nova, ok until it got cold + would not crank fast enough to start!!
Worn valve stem seals are common on 4.3's, but very easy to replace with proper tools. Small tidbit on a truck my dad once owned:
https://www.bobistheoilguy.com/forums/ubbthreads.php/ubb/showflat/Number/5096175/Searchpage/1/Main/308717/Words/4%5C.3+/Search/true/re-my-auction-find-1996-chevrolet-c1500-w-t#Post5096175
Originally Posted by skyactiv
Worn valve stem seals are common on 4.3's, but very easy to replace with proper tools. Small tidbit on a truck my dad once owned:
https://www.bobistheoilguy.com/forums/ubbthreads.php/ubb/showflat/Number/5096175/Searchpage/1/Main/308717/Words/4%5C.3+/Search/true/re-my-auction-find-1996-chevrolet-c1500-w-t#Post5096175
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Had a fleet of C1500 Chevys with 4.3 engines. Use the GM style o ring valve seal along with the umbrella seal over the valve guide boss. Double protection especially if there are worn guides. The umbrellas alone won't stop the oil usage on any SBC V8 or V6.
I plan on running this truck another ten years, unless I hit the lottery. The body is more likely to fall apart before the engine goes, even with some oil consumption. This truck has been a short-tripper for the last twenty years. The school I work for purchased it with 56k miles on it when it was five years old. They put less than 2000 miles per year on the vehicle, driving it around campus. The oil was changed once per year with about 1200 miles average on the oil. Mobil bulk conventional oil. I am guessing that the short tripping wasn't good for this vehicle. I just need to keep a closer check on the oil. If I can't find a good deal on a 5w/40, I may try adding a straight 30 wt for a while then move to a 10W/30 or 10W/40 next oil change. Current fill is Havoline 5W/20 HM. Will have to try to thicken that up a bit as it with a heavy top off oil as it consumes.
Triple_Se7en
$50 Site Donor 2023
Sit down with the Campus Board of Trustees and tell them longetivity for this vehicle depends on someone taking the truck off-campus and on the freeway every two weeks for at least 15-20 minutes of higher speeds driving. Tell them you will do it and not leave any McDonald's wrappers on the backseat floor.....lol
Originally Posted by otis24
I plan on running this truck another ten years, unless I hit the lottery. The body is more likely to fall apart before the engine goes, even with some oil consumption. This truck has been a short-tripper for the last twenty years. The school I work for purchased it with 56k miles on it when it was five years old. They put less than 2000 miles per year on the vehicle, driving it around campus. The oil was changed once per year with about 1200 miles average on the oil. Mobil bulk conventional oil. I am guessing that the short tripping wasn't good for this vehicle. I just need to keep a closer check on the oil. If I can't find a good deal on a 5w/40, I may try adding a straight 30 wt for a while then move to a 10W/30 or 10W/40 next oil change. Current fill is Havoline 5W/20 HM. Will have to try to thicken that up a bit as it with a heavy top off oil as it consumes.
Originally Posted by otis24
I plan on running this truck another ten years, unless I hit the lottery. The body is more likely to fall apart before the engine goes, even with some oil consumption. This truck has been a short-tripper for the last twenty years. The school I work for purchased it with 56k miles on it when it was five years old. They put less than 2000 miles per year on the vehicle, driving it around campus. The oil was changed once per year with about 1200 miles average on the oil. Mobil bulk conventional oil. I am guessing that the short tripping wasn't good for this vehicle. I just need to keep a closer check on the oil. If I can't find a good deal on a 5w/40, I may try adding a straight 30 wt for a while then move to a 10W/30 or 10W/40 next oil change. Current fill is Havoline 5W/20 HM. Will have to try to thicken that up a bit as it with a heavy top off oil as it consumes.
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