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I have a 91 Chevy C1500 with a 4.3l out of a 93 astro van that burns oil badly, it smokes upon start up and I just noticed tonight that it was smoking when I was driving. I've got oil all over the underside of the engine, the trans and almost everything in between. Just did an oil change and put Lucas in and still smokes. I've looked it up and the only thing I can find is to check/replace the valve stem seals or guides but it is having a slight problem driving now where it will stop at 30mph when my foot is down and then itll just jump as of it got a boost of power and so now I'm thinking its the piston ring, (because my plugs arent firing off properly due to oil goop build up) but I'm not sure. I normally dont mess with 4.3l engines as much as i do a sbc (my mom has a 99 tahoe I work on and it's got a 5.7l sbc 350) and I cant figure it out. I just check the oil after letting it sit for an hr (8:30pm) and the dip stick is dry and I did an oil change 5 hrs ago (3:15pm). I'm now thinking it's the rings but I dont have a garage to work in and I'm working as a manager for little Caesars making (7.75/hr) little over minimum wage (7.25/hr) and working on a budget living in the truck. So any advice would help tremendously.
 

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Is it smoking out of the exhaust? If so how is the oil all over the engine and tranny? How far did you drive it after the oil change ? or did it just sit there and somehow lose over 1qt of oil. What kind of oil pressure do you have?
 

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Lifelong S-10 Owner
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Valve stem seals are probably leaking but you have a engine gasket leaking very bad if the bottom side of the vehicle is covered in oil. Have you checked the oil sending switch also to see if it has blown and is pouring oil down the back of the engine? You may have to power wash the engine clean at the car wash and then look for oil leaking after driving it home. Working on the 4.3 is very similiar to working on your mom's 5.7 V8 as they are both the same design minus 2 cylinders.
 

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Been there Done it
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Sounds like a gasket or seal or pressure sensor leak and the smoke is a result of the oil burning off the hot exhaust.
 

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Registered Hoosier
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Check your PCV system. The passage in the tbi used to plug up. Next, check for plugged oil drain back holes in head.
 

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the new guy
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that's not oil leaking under the truck, that's corrosion protection.

a quart in an hour is unbelievable. you need to put some card board under it and see where the drips are showing up and trace up to find out what needs replacing. yes, you are burning oil but the leaks need addressing first so you aren't putting another astro or s10 engine in your full size, because you are heading that way right now
 

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On a full size truck the best way to fix a leaking 4.3 is with a 5.7 that doesn't leak. That would have to be the easiest engine swap ever.

Find a rusty or wrecked 88-93 C1500 and buy the whole truck. You'd have every part you'll need. Those 5.7 TBI's last forever and rarely need anything fixed, as long as you do an oil change occasionally.

EPA says the 5.7 gets 2 mpg less than the 4.3, but users report it's closer to the same as the 4.3. Around 17 mixed city/hwy.
 
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Probably rings and valve seals if it's a high mileage vin z 4.3tbi. It is very common. You can drive it for a long, long time like that. Just top up the oil every once in a while.
 

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Boozebag
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If you were to use a quart in 5 hours and didn't do a lot of driving... You have an oil gusher.
As was said earlier, you need to locate the oil leak first.
Does this truck have a remote oil filter?
I am pretty sure you will find that the oil feed lines to the filter assembly are leaking like a water fall. A super common problem.

If the engine was burning that much oil, you wouldn't be rolling coal... you'd be rolling petroleum...
o_O
 

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Does a 91 C1500 have a remote filter?
 
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