When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
My SBO consumes oil, I've been willing to deal with it for a while, but I'd like to finally put some effort into fixing it.
The past few years I've simply ran some top end cleaner through it after winter storage, along with a fresh set of plugs, and it runs fine all year.
I have about 1,000 miles on it this year and it used about 1/2-3/4 qt of oil. Images below are what #1 & 2 plugs look like after the same 1,000 miles. I get occasional blue smoke after starting it, but not all the time. Occasional smell as well. No smoke while driving (that I can notice), but I do sometimes notice smoke when I come to a stop. When I had the PCV system hooked up, it would use more oil. I now just run open breathers and the oil consumption has gone down.
The short block was rebuilt over 10 years ago with ported iron heads. I had Edelbrock heads added a while ago, which were rebuilt with different hardware including Viton seals.
All plugs look similar, so the oil is getting into all the chambers. Leads to me think it's either valve seals or piston rings. I suppose the intake manifold could be leaking from the valley? No external leaks, just a light oil mist near the breathers, which is to be expected.
What is the best way to begin investigating this issue?
Do a compression test and do dry and oil added to the cylinders. If that passes, a leak down test and pulling valve covers to make sure the valve seals are still intact. My Olds 350 I had in the 4x4 used a similar amount. I noticed melted and broken valve seals plus a couple of cylinders were lower than the others. I changed some valve seals and used combustion chamber cleaner left in the cylinders overnight. The compression raised 25 to 30 psi in those two cylinders and the oil consumption was cut in half easy.
Nick,
An easy way to check for the intake leaking in the valley is to
1. Take both the breathers out of the valve covers.
2. Block off the hole in one valve cover, duct tape works good
3. Start the engine and let it idle.
3. Take a can of Gumout carburetor cleaner and shoot about a 5 second blast into the open valve cover hole.
If the intake is leaking it will suck the fumes in from the crankcase and the idle will change noticeably in a few seconds.
Thanks for the replies guys, I'd be thrilled if it was valve stem seals causing the oil consumption. That's a job I'd be willing to tackle myself and not have to pull the engine. I'll do dry/wet compression test and then investigate the seals.
Originally Posted by BillK
Nick,
An easy way to check for the intake leaking in the valley is to
1. Take both the breathers out of the valve covers.
2. Block off the hole in one valve cover, duct tape works good
3. Start the engine and let it idle.
3. Take a can of Gumout carburetor cleaner and shoot about a 5 second blast into the open valve cover hole.
If the intake is leaking it will suck the fumes in from the crankcase and the idle will change noticeably in a few seconds.
Is spraying carb cleaner into the crankcase a good idea? And I have EFI, so I'm not sure the change in idle RPM would be that noticeable as the computer would just cut fuel to maintain AFR and idle speed.
Is spraying carb cleaner into the crankcase a good idea? And I have EFI, so I'm not sure the change in idle RPM would be that noticeable as the computer would just cut fuel to maintain AFR and idle speed.
The carb cleaner wont hurt a thing. It will end up being fumes pretty quick. Have never tried it on an efi engine so I dont know if the computer will react quick enough so that you wouldnt notice it or not ? Good question.
The carb cleaner wont hurt a thing. It will end up being fumes pretty quick. Have never tried it on an efi engine so I dont know if the computer will react quick enough so that you wouldnt notice it or not ? Good question.
The IAC will most likely respond and make any change virtually undetectable. You’ll need to disable it to get a a reliable response.
If the carb cleaner test won't work, what about looking into the intake runners with a borescope where the intake meets the cylinder head for oil at the intake gasket? I have not done this but don't see why it wouldn't work. Anyone here tried it?
The IAC will most likely respond and make any change virtually undetectable. You’ll need to disable it to get a a reliable response.
Originally Posted by Sugar Bear
If the carb cleaner test won't work, what about looking into the intake runners with a borescope where the intake meets the cylinder head for oil at the intake gasket? I have not done this but don't see why it wouldn't work. Anyone here tried it?
Was able to perform a compression test today. Ran it up to operating temp and the results were all between 195-200, higher than I was expecting but at least they are consistent.
Here is a high res image of all spark plugs, you can zoom in on each one. 1, 3, 7 & 8 are the darkest, and #8 was wet as well. #4 looks hardly used. Keep in mind the engine was just idling for 10 minutes to warm up for the compression test, so it was running a bit rich during this time.
Sounds like valve guides, seals, or possibly intake gaskets on the valley side.
I started doing the compression test with the throttle closed, which is why the lower numbers are crossed off.
Those compression numbers look great. I don't see where you performed both a dry & a wet compression test since I see only one set of numbers and I'm going to assume you performed the compression test 'dry' w/o injecting oil into the cylinders. None-the-less, a compression test yielding 195-200 across all cylinders is excellent. You'd have had a much better chance of determining it it were rings had you performed a wet compression test after the dry compression test on each cylinder.
Regarding the spark plugs and the oil consumption. The spark plugs appear to demonstrate the engine is burning rich, IMO. The first thing I would do is set your A/F mixture screws to the absolute highest vacuum you can achieve on your engine. I understand you now have EFI, set your mixture correctly - appears to me you're burning rich.
Regarding the other possibility of oil consumption and (perhaps) the dark visualization of the spark plugs. Are you running the standard oil pump in this vehicle or did you change out the standard oil pump to a newer/upgraded high volume/high pressure oil pump?
Was able to perform a compression test today. Ran it up to operating temp and the results were all between 195-200, higher than I was expecting but at least they are consistent.
Here is a high res image of all spark plugs, you can zoom in on each one. 1, 3, 7 & 8 are the darkest, and #8 was wet as well. #4 looks hardly used. Keep in mind the engine was just idling for 10 minutes to warm up for the compression test, so it was running a bit rich during this time.
Sounds like valve guides, seals, or possibly intake gaskets on the valley side.
I started doing the compression test with the throttle closed, which is why the lower numbers are crossed off.
This was a dry compression test done at operating temperature. I did not follow it up with a wet test, didn't think it was necessary.
Oil pump is a blueprinted pump by Precision Oil Pumps. At temp I have 20-22# at idle and 45# at higher RPM.
Plugs are NGK BKR6E-11
AFR targets are: Idle 14.4, WOT 12.7, Cruise 14.5
Timing targets: Idle 22*, WOT 35*, Cruise 42*
Tuned by seat of the pants dyno, still messing with the Sniper software.
I got 15 MPG on the Power Tour this June which included a mix of high speed highway driving, backroad cruising and idling in traffic. 3.90 gears and a 5-speed transmission. I'm confident my AFR targets are good, but there is always the chance I have an exhaust leak upstream of the O2 sensor.
Reminder that I do get an occasional cloud of blue smoke at start up, happened last week actually. It was a breezy day and I saw the smoke floating across my neighbors front lawn.
This was a dry compression test done at operating temperature. I did not follow it up with a wet test, didn't think it was necessary.
Oil pump is a blueprinted pump by Precision Oil Pumps. At temp I have 20-22# at idle and 45# at higher RPM.
If you didn't think it was necessary - that's certainly your call. If there is a change in the compression reading on each cylinder between the dry reading and the wet reading it will demonstrate (most of the time) the general health of the piston rings. Since you didn't perform a wet test, you don't know if there is a delta.
I have no idea whether the blueprinted pump by Precision Oil Pump is a high volume oil pump. The reason for my asking was because (in general), and in particular, a high volume oil pump will most often scavenge far more oil volume from the oil pan up into the engine and you often end up with more oil than a standard oil pump would furnish leaking back down the valve guides causing more blue smoke the following morning during the initial startup. I was just curious if it was a high volume oil pump which might be resulting in more oil in general than a standard oil pump would provide.
The reason for my asking was because (in general), and in particular, a high volume oil pump will most often scavenge far more oil volume from the oil pan up into the engine and you often end up with more oil than a standard oil pump would furnish leaking back down the valve guides causing more blue smoke the following morning during the initial startup. I was just curious if it was a high volume oil pump which might be resulting in more oil in general than a standard oil pump would provide.
That’s pretty much an old wives tale. Any idea of just how much oil you would need to have in the head for it to reach the valve guides?
Take a cyl Head and lay it 45* just like as its installed on a V8. Then plug the return holes along with fastening a valve cover to it and see just how much oil you’ll have to put it in for it to reach the tops of the guides. It’s more than you might think.
Nick if you’re getting puffs on start up then it’s most likely guides and/or seals, but not for the reason given above.
Hope this helps.
Last edited by cutlassefi; July 14th, 2019 at 12:14 PM.
How many miles on the engine since it was originally built ? How was the oil consumption when it was new ? Valve seals really have to be bad to cause a lot of oil use and even then I really wonder. All of the early Chevy V-8s really did not have much of a seal at all but they didn't use much oil. When I rebuilt the 307 in my Wifes Riviera last year all I put back on it was the stock umbrellas and it basically has not used a drop of oil in 3500 miles.
If you have Edelbrock heads on it with the positive type seals, I really doubt that is the problem. Those seals last forever unless they were not installed properly and have come off the guide.
The plugs don't look all that terrible especially for a car that probably has a lot of short trips. I bet one of the best things you could do is go take it for a good 100 mile highway cruise. Like Mark said It might be a little rich too which will affect oil consumption.
This car was still in "project" status when the engine was originally built, so mileage is a best guess. I'd say the short block has 15,000 on it and the top end around 12,000 miles. I didn't drive it very much for the first few years with a solid cam & iron heads, and I don't know how much (if any) oil consumption there was. I didn't really start driving it consistently and on a more regular basis till I did the roller cam swap and Edelbrock heads. This is when I started to notice the oil consumption and occasional smoke. I had the PCV functioning when the Edelbrock heads were first installed, I removed it and now just run open breathers, and oil consumption has gone down.
The heads were purchased used, and then rebuild with springs provided by Mark to match the cam I got from him as well. They were rebuilt by a local shop that was highly recommended and he used Viton seals.
Actually most of my driving this year has been longer trips. Four days of Hot Rod Power Tour, trip to family cottage two hours away, Sunday afternoon cruises... etc.
If you can find out if it burned oil from the previous owner then backtrack to work subsequent to the sale you might be able to narrow the potential problem.
Is spraying carb cleaner into the crankcase a good idea? And I have EFI, so I'm not sure the change in idle RPM would be that noticeable as the computer would just cut fuel to maintain AFR and idle speed.[/QUOTE]
Block off one valve cover port, put your thumb over the other port with the engine running and see if pressure or vacuum builds under your thumb. If pressure builds you are ok. If vacuum builds up you have a leak on the bottom of the intake. Spraying brake clean in the crankcase is not necessary.
Funny somebody replied to this. I actually pulled the intake this winter. I was hoping to inspect the gaskets to see if they were not "pinched" evenly, but they tore when I removed them and I couldn't determine anything from that. I had the intake surfaces checked for flatness, and they were all good. Reinstalled and fired up, but no miles yet.
If the oil consumption has not gone away, I may consider replacing the valve seals and see if that resolves the problem. If the issue is internal (rings), then I'm going to just live with it till I get a new engine.
June 30th, 2019, 07:43 AM
