CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

1979 chevy c-10 burning oil

Hello, I have a 1979 chevy c-10 with a 350. It is burning oil and I am not sure why. I had a my regulator mechinac took a lot at it and he could not figure out what is wrong with it. Some of the mechinacs I work with (I am not a mechanic) say its the valves causing the problem. The milage on it say about 85,000. But I am pretty sure it have rolled over and was not told when I bought it about 3 months ago and I have been using sae 30 heavy weight oil.

How many miles on the engine? Has the right oil been used, and has it been changed on schedule? Engines do burn oil as they age and wear - mostly when the piston rings don’t seal against the bores in the engine block as well as they used to.

One thing you can do that might make a difference: use Marvel Mystery Oil in the gasoline. It can free up stuck piston rings, so the rings do a better job of flexing against the cylinder bores and keeping oil from migrating up into the combustion chambers. I used it in my 1984 Chevy Cavalier when it started using more oil somewhere in the high 100,000 mile range, and the oil usage dropped.

1 Like

Check the oil level and top it off early one morning then drive for 15 minutes and when you stop immediately check the dipstick. If the dipstick indicates that the oil is more than a quart low it is likely that one or both the heads have sludge blocking the drain back holes which is allowing the oil to puddle up to the valve stems where it is drawn into the the cylinders.

One quick way to check the valve guides is to drive at highway speed and the let your foot off the gas pedal. Look in your rear view mirror and if you see smoke it’s the vacuum of the engine drawing oil though the worn valve guides! This is not an expensive repair. I had two small block GM engines that developed excessive valve guide wear at high mileage.

You could also be leaking a small amount of oil at highway speed which would not be noticed by checking your drive way or garage floor.

Please tell us the mileage on the engine.

the miles say 85,xxx but I think it has been rolled over. I only had the truck for about 2 or 3 month about now. I been using sae 30 heavy duty oil in it. If it helps.

Sorry, I missed that you had told about mileage in your original post.

A 1979 anything is not required to certify mileage. None of these mechanics has suggested a compression test or pulled valve covers to look for sludge? I assume you have changed the oil since you bought it so change it again and add some kind of additive and high mileage oil and hope for the best.

I have change the oil twice since I got it. First, when I got it home and the second time was one thosand miles later. I am not sure if my regular mechanic did a compression test. I did not see signs of tool marks or smugging around the valve covers like the covers have been removed since owning it. I think I put sea foam in the oil and I put some in the gas tank as well. But not one have said anything about sludge.

Is that straight 30 weight oil?

straight sae 30 traveler oil from tractor supply store. First time using that oil the and brand of oil

I presume you are you losing oil, probably more than 1 quart in 1000 miles right? How much exactly do you lose, what’s your oil consumption rate? Why do you think the engine is burning the oil rather than it leaking out? Are there any oil leaks on the ground where you park? If you are certain the missing oil is burned in the engine, next step is to find out if it is burning all the time, or only on start up. Ask somebody to watch the tailpipe as you start the engine after the truck has been sitting for several hours or even over night. If they see a black puff of smoke which quickly goes away, that’s consistent with a valve guide problem. If not, and they see a little black smoke out the tailpipe even after start up, a compression check would be next on the list.

If this truck’s engine has remained untouched all these years, I would expect the valve stem seals to be shot

1 Like

I always use MotorCraft or Penzoil branded oil in my Ford truck. Suggest to stick w/common name brand oils, as those oils will have the additives needed to keep the seals sealing.

Maybe more than once. :grin:
Hey, it’s old enough to smoke! What’s the problem?

Seriously, the way to start is to check the vacuum, run a wet/dry compression test and to pull the valvecovers and check out the valvetrain. My guess is that you’ll find the answers you seek. And my guess is that it’ll be wear and tired parts. Piston rings and valvesprings lose their “spring” over the years. And parts wear. Considering the millions of times they get pounded around, it’s no surprise that they do.

1 Like

I have not see any oil on the ground under the engine. My father and some one from work has seen smoke coming from the tailpipe. The smoke clears up soon after start up.

You have all the symptoms of a well worn engine. And on a 1979 I’d say you’re doing great!
Run the tests I suggested and post the results.

That’s a common problem with the valve guide seals on a GM engine of that vintage.

If you have a length of nylon rope, you can easily change the valve guide seals without removing the heads.

Tester

So is cylinder wear, tired piston rings, tired valve springs, and worn parts.

Valve guide seals.

Tester

1 Like

Classic symptom

valve stem seals