Technical How to Diagnose Oil Consumption Issue

SBC 350. Using between 1/2 and 1 full quart in about 40 miles of driving, highway or in town. I'm pretty new to working on cars, and I'm trying to make this a bit of a daily driver. I'm not sure where to go next. I want to find the problem and fix it. Thanks.

No obvious major oil leaks. Not a dop under the truck in its parking spot. Exhaust has no obvious color or smoke. Some smoke under initial hard acceleration, which I would think is normal. My exhaust goes straight back then out the sides a little behind the cab. The end of the pipes have a black sooty oily coating on the inside.

I've done:
New PCV valve
Added a 1 inch spacer to Holley 650DP with a port for PCV
Added baffles to valve covers
Tried 3 different oils
Mobil 1 10w-30
Carquest 10w-30 (seemed to show some improvement but not convincing)
Valvoline VR1 conventional 20w-50
Had the bowtie heads re-done at local shop for a separate problem (two bent valves)
Basic compression test
1 - Dry 144 Wet 144
2 - Dry 118 Wet 122
3 - Dry 141 Wet 145
4 - Dry 145 Wet 151
5 - Dry 145 Wet 147
6 - Dry 126 Wet 129
7 - Dry 148 Wet 149
8 - Dry 131 Wet 134
New spark plugs (ones with about 2,000 miles on them looked terrible
Retarded the timing some

I did not build the engine, but talked to the builder. He says:
6000 miles on it or less
Bored 0.40 Over
Flat top Pistons
High Volume Oil Pump
X Rods
Hardened Push Rods
Harland Sharp Roller Rockers
305/25 Comp Cam
Double Roller Timing Chain

Holley 650 DP
Victor Jr Intake

With the new plugs and retarded timing, it's running great, but still "using" a lot of oil. I would gess the plugs are going to foul and it'll start running worse again.

What should I do next to find my problem?
Straight 40 weight oil?
Buy and use a leak down compression kit?
How do I check that the valve guides were done correctly?

 

Sounds like time to tear the motor down....

 

Oil rings aren't doing their job would be my ass umption.

 

Man, you must get great gas mileage (LOL) or one of your kids has got a siphon.

 

I tore down a '71 307 and oil rings were froze to the piston.....

 

If no leaks
Oil rings or valve stem seals and or guide issues
Got to be smoking

 

This thing's got to be smoking like a freight train doesn't have blow-by

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One more thing
Look at the bores with a scope
I seen a guy polish all the scratches out
Polished the cyl walls like a crank journal.
Not good

 

Do a leak down test

 

Leak down for sure....#2 is low for some reason for compression. Did the guides get checked when head work was done? Stuck oil rings or compression ring in upside down. Bore finish wrong. Leak down will help pinpoint

 

I saw something similar back in the 1970's, the rings were in upside down.

 

A leak down test won't always detect bad oil rings....or loose valve guides for that matter. If the top rings are seated and working fine, but the oil rings aren't right, they won't show on the test. If the valves are OK and sealing, loose guides won't show either.

 

another vote foe second ring upside down , you have to wonder what thye cyl walls look like w lousy compression like that.....could be valve guides (doubtful) or leaking (being sucked) from the valley to intake ports . what did the intake gasket look like when you pulled the heads ??

 

Wind that sucker up tight in low gear. and let off the gas. bet you see a huge cloud of blue smoke. something wrong with the piston rings or no valve seals and badly worn intake valves or guides.

 

Least if you leak it down you'll hear air blowing in the crankcase rings are leaking

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or drive down a steep hill and let off gas

 

Did the shop replace the valve seals when they worked on the heads? The plugs all look about the same so it’s not just one hole using oil. In general the compression test results sound low and the wide range of readings suggest that it’s sick. It could be from improper machining, improper assembly, improper break in, whatever. Experience has taught me that when buying a used engine, you are essentially buying a core.

 

My vote is oil rings. Chances are the oil ring expander ends could have jumped over them selves on assembly, easy to have happen if not careful or just don't know. Another issue you may have created is the fitting of the PCV in a spacer under the carb, IF the carb is NOT metered for a pcv system it will now be running lean. Time for a tear down and renew what is required. JW

 

Tear it down the only way.....if valve guides good and positive seals then its got to be rings......pull the pistons and see whats going on

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What do you have for baffles? Look inside of the pcv hose and see if it is wet. You can suck a lot of oil through the pcv with bad baffles.
If you pull the pcv start it up and see if you have a bunch of crankcase pressure. That is usually from rings.
Also make sure the oil level is correct. To much oil can cause oil consumption .

 

Sniff test the dipstick. If it smells like gas, that thins out the oil and it blows past everything. The dry to wet numbers are well under 10%, you're at 4-5 %.

 

The easy way to check for gas in the oil is to warm up the engine. then pull a plug wire and stick it in the oil fill. Start it up. If a big explosion blows the oil pan & valve cover off there was gas in the crankcase!

 

or you have a bad mismatch between the heads/intake manifold. "redone" heads, did they take some material off (how much material came off) then not true up the surface that contacts the intake manifold gasket?

 

You've said you've tried 3 oils but to me it's unclear whether the engine was broken in after the rebuild with regular mineral oil allowing the rings to initially bed in. Although I have no first hand experience of this my understanding that bore glazing will occur if synthetic or overly slippery oil (additives?) is used for initial break in, with an attendant loss of oil control. Fix probably entails honing? Might get away with a temporary change of oil though?

I do however have first hand experience of a used, believed good, new to me engine that revealed on first start up that the block was indeed split, probably from freezing, but cleverly disguised and painted over. Grrr! Replacement block, bored to match existing, all used parts transplanted, new gaskets naturally. Man that thing used some oil but other than plug fouling there was no real sign. I'd have expected huge smoking to accord with the truly colossal oil loss. Decided it must have been the heads. My schedule didn't allow for the time for a rebuild (and the valves were tiddly) so I bought new 'stock replacement' Dart items, and the oil loss thankfully disappeared. Phew!

Chris

 

Not sure on what you did to your heads but older SBC's did not have valve seals ...They had a square o ring under the valve keepers and a steel umbrella over the valve springs and without putting them back on they really used oil. SBC heads needed to be machined to accept valve seals but some guys used Ford umbrella seals over their guide to help oil consumption if they were unable to get knurled guide work or false guides installed.

 

My SBC daily puts out blue smoke when started after sitting overnight, for about 5-10 seconds maybe, or long enough to burn the oil sitting in the cylinders I assume. It's an open top (old Blazer) and I have to back right through it getting out the driveway, for a tasty aroma. After that it does not visibly smoke and doesn't use a tremendous amount of oil. I figure the oil is going past the guides when sitting. As I recall the guides have been knurled and it has the stock o rings in the retainers.

 

Pull of the carb and look for oil in the intake manifold. If there is oil there, you may have a miss routed vacuum line sucking oil. If the intake is dry, get a USB scope if you don't have one (like this: https://www.amazon.com/Endoscope-Se...ds=borescope&qid=1560520451&s=gateway&sr=8-20 ) and look down the runners to the intake ports and see if there is oil there. The ports should be dry and clean on an engine with only a few thousand miles. If they are wet and oily, then the intake is not seating properly and you are pulling oil from the valley into the engine.

If the intake and ports are dry of oil (and assuming that the shop did a proper job on the heads) the only other option is rings.

 

Give us a rundown was this a rebuilt motor Why was it rebuilt what's the history

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Thanks for all the thoughts so far! I appreciate it.

Sounds like I should do a leak down test and have a look inside the intake. Last time I had the intake off it was pretty dry inside, and I had the oil consumption problem prior to that. Hopefully, I can get some useable information from doing that. If not, then its tear down time.

Here are some replies to your questions, and some more info if you're still interested.

I took the heads to a local shop because I had a miss and a bent valve in 5 and 7. The shop said the problem was too weak of springs. It had only 63lb springs and they put it 85lb ones. I talked for a bit with the guy who did the work and he assured me everything was great now, for whatever that's worth. He clearly knew more than me anyhow. He said they were flat and didn't need any material taken off to level them. He had a number written on the heads at each valve, but I can't remember what that indicated. Each bent valve had contacted the piston and left some marks. I'm not sure how big of a deal that is.

I was told by the guy who built the engine, that he had an engine from a Chevy truck, (confirmed to be a block from a 1979 C10/Suburban via stamped numbers). He then rebuilt it to drag-race in an S10. He had some success drag-racing and sold the truck to someone whom he beat, and was impressed. I bought the running driving S10 from that guy and pulled the engine and several other things to put in my ratrod. Seems unlikely that the rings were never given a chance to seat, but maybe I'm wrong assuming that. When I put the "repaired" heads back on, I also replaced two lifters and used a high zinc oil. Then followed their instructions to hold the RPM at 2,000 for 10 to 15 minutes. I've also either used high zinc oil, or an additive with zinc at each oil change since then.

I'm really puzzled about not having much smoke. However, the inside of my exhaust is a little oily. And also, how could I have a terrible oil leak that doesn't drip while idling, nor drip once parked after driving. The bottom of the engine and chassis are not covered in oil. The oil has to be going through the engine, right?

Do the cylinder bores look too smooth, or do you see any obvious issues in these pictures? They were taken when I had the heads off.


I added the new PCV and baffles because I was getting a fair bit of oil spray out of my breather. Previously, there was a PCV but it just had a short hose pointing down the side of the engine attached to it. Essentially doing nothing. Now I have no oil spray from my breather. I had the oil consumption issue prior to my work with the PCV. I will, however, check the hose going to my carb spacer for oil. I did re-tune the carb after adding the spacer.

Do you agree that my compression numbers show low compression in all cylinders, compared to what a newly rebuilt engine should have?

Thanks again!

 

You mentioned adding a PCV valve to the engine. From the intake spacer, where is the hose routed and where is the PCV valve? Where is the crankcase vented to atmospheric pressure?