Engine using excessive oil "opinions wanted"

[Hondo78]

1986 c10 factory 305 engine 52,000 original miles. I bought the truck from PO he had it running but said it had been sitting in a barn for 7 years. The engine runs good but the oil usage is bad like a quart every 350 to 400 miles. Has no leaks no smoking on initial start up but you let it sit idling for 2 to 3 minutes and there's excessive smoke from the drivers side exhaust. Spark plugs on that side are oily with cylinder 5 and 7 being the worst. Compression on that side range from 145 to 155. What do you guys think? Broken rings? No smoke on start up kind of rules out valve seals?

This will not be well received but here goes,
1. Drive down your street in first gear to 25-30 mph and let off the throttle if it smokes you likely have valve seal issues. If you accelerate hard and it smokes you have ring issues.
2. I Bought a C10 new in 1985 with a 305 automatic, after 10,000 miles I returned to Parker Robb Chevrolet and asked for an engine evaluation as the truck would burn a quart of oil between oil changes, (1500-1600 miles). The truck was returned with a GM report, stating burning a quart by 1500 miles is within spec.
3. Valve seals are an easy weekend fix, rings can be reseated by putting a table spoon of baking soda into the intake and working the engine driving up a grade at a brisk pace. (Not recommended but common practice in 1985)

The 305 is not a worth while engine to rebuild unless you need a numbers matching engine; they do however wake up with matching pistons sizes and a balance, with a mild cam and better OEM 305 small chamber heads.

What I did in 1985?; I bought a balanced 350 with, small chamber small valve iron heads and installed a mild cam. Oil consumption issue was no longer an issue, the peddle feel improved and fuel economy picked up by 1.5 mpg highway.

Noteworthy: My 305, when disassembled had three different sized pistons installed directly from Chevrolet, so balance was not a concern at Chevrolet in 1985. The engine was produced in MX as were most of the common low performance small block line up after 1970. That's why we bought BMW 320I's for our spouses to drive, better build quality. GM was fat and happy.

 

[Mofarmer]

Thanks Hondo I will try the 25-30 mph test. I have had several 305s through the years in trucks and cars and I agree they were a total fail on GMs part.

 

[Grit dog]

Thanks Hondo I will try the 25-30 mph test. I have had several 305s through the years in trucks and cars and I agree they were a total fail on GMs part.

They were so bad, I think my Dad's 85 C10 had like 50k miles and the engine was shot. Dropped a 307 out of a, idk late 60s early 70s somethin or other in it (because it was what my parents could afford at the time) and IT lasted longer and ran better than the 305!

 

[AuroraGirl]

From personal experience, I do not recommend filling the crankcase with kerosene as a test unless you install a valve on the drain plug spot and also plan on buying at least 15 gallons if you want to fill her to the top.

on a serious note, my square burned a LOT of oil when the timing was super retarded, the plugs were colder than it “should “ have, and the fuel mixture was rich

adter sorting that out it barely does. Probably leaking it tbh.
Is it running in tip top shape?

 

[SquareRoot]

Shitcan it. Duramax swap.

 

[AuroraGirl]

Dirty max boo, I want to see a Saturn 4 cylinder and 5 speed manual or I’m going home

 

[AKguy]

Heck, some of the airplanes I have flown use waaaaay more oil than that! We use to joke about topping off the oil tank and checking the fuel.

 

[SirRobyn0]

on a serious note, my square burned a LOT of oil when the timing was super retarded, the plugs were colder than it “should “ have, and the fuel mixture was rich

adter sorting that out it barely does. Probably leaking it tbh.
Is it running in tip top shape?

You do have point there. I'm not sure retarded timing alone would do it, but an engine running rich enough to dump unburned fuel past the rings into the crankcase will dilute the oil with gas, after that it'll definitely burn more oil because it's thinned out. I do not think that this is the OPs problem though, but it's something to keep in mind.

Heck, some of the airplanes I have flown use waaaaay more oil than that! We use to joke about topping off the oil tank and checking the fuel.

Seems to me there was a car joke in 70's, fill the oil and check the gas cause here comes a....... To bad I can't remember what the car was anymore.....

 

[AuroraGirl]

You do have point there. I'm not sure retarded timing alone would do it, but an engine running rich enough to dump unburned fuel past the rings into the crankcase will dilute the oil with gas, after that it'll definitely burn more oil because it's thinned out. I do not think that this is the OPs problem though, but it's something to keep in mind. I only said timing because I fixed all three issues close to eachother and I quote literally moved the distributor at least 20 degrees in position and cleaned the centrifugal weights(they would stick out sometimes)
I haven’t even taken a timing light go yet I just put it where it sounded good for the mean time.




Seems to me there was a car joke in 70's, fill the oil and check the gas cause here comes a....... To bad I can't remember what the car was anymore.....

Yes I was perplexed at how quickly the gas diluted the oil because I thought it had internal damage or tolerances because it would take minutes after an oil change but as soon as I got it running properly the gas evaporated and blue smoke stopped and with a fresh oil change an a winter of snow plowing I only adddd a part of a quart but the engine leaked pretty good on the valve covers and the oil pan so it as hard to tell how much was from combustion. I bet there is a tiny bit but for all I know it’s literally tip top shape. I want to install an hour meter gauge on my truck since that would help gauge use better than miles since I have no Speedo or road use lol

 

[idahovette]

Brand new in May 1970, LS6 Chevelle, used a quart every 150 miles, Ran like a banshee, but oil consumption was terrible. Was working at the Chevrolet store and the Factory Rep came around. Told him what it was doing, he said "They are built loose, that's the way they are". Kept on him every month he came around, finally after me pissing and moaning for 4 months, he relented and we ordered a fitted block for it. Got the new parts and put it together and what a difference!!!!!! Now it only used a quart every 300 miles, and this is with Valvoline 40 weight and GM EOS additive. Lived with it. Tried to keep the old block, but he showed up the next month with his briefcase and a BIG hammer, whacked the side of the block and DONE!!!!....He enjoyed it, too!!

 

[Raider L]

When we were putting my new engine in I later found out that the guy who was checking the engine machine work specified to have the guides over reamed for racing purposes. After the first year I got tired of all the oil it was burning and I asked him what he had done to it when it was built. He said he had the guides over reamed because he thought I was going to be racing it. I said no and I took the heads off and had new guides put in that were much closer to what kind of driving I was going to be doing, and for the fact the guides were silicone bronze guides I could run a couple of thousands clearance instead of the .015" clearance he had them. Now I was at .002-.004" and no oil consumption! Stainless valves to.

 

[Matt69olds]

I never understood the thinking behind MMO in the fuel tank to help with rings ?? Its just going to get burned during combustion and in my opinion just make matters worse. We used to use the GM Top engine cleaner back when it was still potent. I would take all the plugs out, pour about a cup in each cylinder and let it sit overnight. Then crank it over to get any leftover out, put the plugs in and fire it up. I have fixed a couple of stuck ring cases that way.

I thought I was the only one who thought this way. My personal favorite is the fuel additive that’s supposed to clean up carbon deposits on the back side of intake valves. That stuff is hard to remove with a wire wheel, I have a hard time believing any fuel additive will dissolve that crud!!!

 

[Matt69olds]

Personally, before adding anything to the engine oil, I’d take it for a long drive. Give it a few full throttle acceleration pulls, work the engine hard. If the rings are sticky, some hard work and heat will clean things out.

Run a compression and leak down test. This will give you a good idea as to how well the engine is sealed up, in addition it gives you a perfect opportunity to check the condition of the plugs.

Does it smoke after sitting overnight? If so, classic symptom of valve seals. Those are fairly easy to change without engine or head removal.


If it doesn’t fog for mosquitoes going down the road, doesn’t leak, the plugs look good, and is otherwise an ok engine, I’d run some 10w40 or 15w40 Rotella and drive it until your ready for the engine swap. Maybe the thicker oil will slow down the consumption?

 

[Ricko1966]

A cheap one is with the engine running trickle a garden hose down the throttle keep it running with the throttle the water turns to steam in the combustion chamber and cleans up the top end. You will need new plugs afterwards. Justice Brothers came up with a similiar treatment we used at a couple of shops I worked at pull a vacuum hose connect manifold vacuum to a small tank with a valve attached put a stick on the throttle about 1500 rpm open the valve and let the mystery cleaner get sucked into the running cylinders. I think the cleaner was mostly acetone. Either way it's the most direct way of cleaning the combustion chamber and rings without a tear down. I still have a J.B. tank and valve if you want to borrow it.

 

[80BrownK10]

1986 c10 factory 305 engine 52,000 original miles. I bought the truck from PO he had it running but said it had been sitting in a barn for 7 years. The engine runs good but the oil usage is bad like a quart every 350 to 400 miles. Has no leaks no smoking on initial start up but you let it sit idling for 2 to 3 minutes and there's excessive smoke from the drivers side exhaust. Spark plugs on that side are oily with cylinder 5 and 7 being the worst. Compression on that side range from 145 to 155. What do you guys think? Broken rings? No smoke on start up kind of rules out valve seals?

Stuck rings. Add a ton of seafoam or Berrymans to the fuel and then do an I-talion tune up. Look up a guy if you need to know how. And then run that thing like you stole it for several hundred miles. I bet those rings come around.