Q&A / Tech

Ask Away! with Jeff Smith: What’s Causing Excessive Oil Consumption in My Engine?

I’m having a problem with the small block 383 in my Impala. The engine was new about two years ago, but I keep having problems with the spark plugs loading up with oil. Some of my friends say it’s a valve guide seal problem but the heads were new when we put the engine together. Others say the rings never seated. If the rings never seated, wouldn’t the engine smoke all the time? The engine doesn’t seem to smoke either accelerating or coming down in gear. It uses about a quart of oil every 500 miles and it keeps fouling the spark plugs. Do you have any ideas?


Jeff Smith: You’re right, a quart every 500 miles is way too much, especially for a relatively new engine. At first, I was in agreement with your friends who suggested valve guide seals, but if you don’t see clouds of blue smoke from the exhaust on deceleration, then likely there is another situation. The above can often happen when the valve guides are worn or when improper valve guide seals are used. I still see unenlightened engine builders using those old, hard plastic PC seals. The problem with these seals is they are very stiff. Even normal valve guide clearance can quickly elongate these seals allowing oil to leak past – especially on intake valves that see manifold vacuum. That’s why the engine will smoke on deceleration –the high manifold vacuum pulls the oil right past the guide seals.

The better valve guide seals are the ones made with Viton or other fluoresastomeric synthetic seals that remain pliable under high temperatures. These can often be metal bodies that fit over the guide bonded with a rubber seal. The more pliable material will allow the valve to move inside the guide yet maintain a proper seal.

But assuming that your valve guide seals and the rest of your engine is in good shape, there could be another explanation. I actually had this same high oil use problem happen to me many years ago and I at first assumed it was poor valve guide seals. I replaced the seals with high quality Fel-Pro pieces but the problem persisted. Like your engine, I did not notice any telltale blue smoke on deceleration yet the engine continued to burn oil at a prodigious rate.

Eventually, I yanked the intake manifold and discovered small dots of oil on the floor of nearly all the intake ports. It was clear that the engine was suffering from a vacuum leak and the air was pulling oil from the lifter valley into the intake ports anytime the engine was running at high vacuum. For a street engine, this is just about 100 percent of the time!

At first, I blamed the Fel-Pro Print-O-Seal intake gaskets – the ones with the silicone seal around the perimeter of the port. I tried a different, paper style gasket but met with the same result – the engine continued to use oil. Finally, after a discussion with now-retired Fel-Pro gasket engineer Greg West, I discovered that my intake manifold was the real culprit.

My friend Wes Drellesheck sent me this photo awhile back of his intake port when the intake was first removed. His small-block suffered a similar problem of oil-fouled spark plugs and higher than normal oil usage.

My friend Wes Drellesheck sent me this photo awhile back of his intake port when the intake was first removed. His small-block suffered a similar problem of oil-fouled spark plugs and higher than normal oil usage.

After carefully measuring the angle of the heads and the corresponding angle of the intake manifold, we discovered that the intake created a diverging angle at the bottom on the intake ports which meant the gasket was not sufficiently preloaded at the bottom to prevent oil migration into the intake port. Subsequently, Greg developed an interesting test that I have outlined in a story in Power & Performance News. This story covers in detail how to do your own testing with no specialty tools required. All you need are some soft, lead shot gun pellets and a dial caliper.

After we measured the mismatch, we discovered the intake needed to be machined, removing roughly 0.015-inch from the top of the manifold at a tapered angle to zero at the bottom. I took the intake manifold to my machine shop and they milled the intake to create more preload on the gasket at the bottom of the port than at the top. Once that was completed, we re-assembled the intake manifold with those same Print-O-Seal intake gaskets and a new set of spark plugs and the engine immediately stopped using oil. Then I dribbled about 16 ounces of water through the carburetor at fast idle which steam-cleaned the chambers to eliminate all the carbon buildup on the pistons. Eventually, we were able to also add a degree or two of part-throttle timing that beforehand had only resulted in a bad case of detonation. Oil has a nasty habit of creating detonation so our now-clean chambers could accept a little more timing and the engine immediately responded with crisper throttle response and slightly better fuel mileage.

So the point is that even a small thing like a leaking intake gaskets can have a big effect on the performance of your engine. It’s worth checking if your engine uses oil. While small block Chevy was the engine in our case, we’ve seen this same problem with small block Fords as well. This will be true with any engine that has a common area between the lifter valley and the intake ports. Pontiacs or LS engines, for example, will not suffer this problem because the lifter valley is separated from the intake ports. However, they may still have a problem that will show up as a simple vacuum leak.

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  1. I had two engines do that, both with edelbrock intake manifolds, both brand new, the machining process at the factory was obviously not up to par, i checked my third one before installing it, no more problem, i would assume a batch made it past QA checks

  2. Chaz7799@yahoo.com says:

    Replace the valve guides and make sure they are right for the valves you have….

  3. Had exactly this problem in my small block Mopar…turned out that the very stiff Teflon positive seal guides just couldn’t control the oil well enough. I went to CompCams viton based seals (part# 529-16) which completely cured my problem!

  4. I had the same problem with my new 383 that I built in 1990. I was a poor airman and didn’t have enough money for a new intake do I used the stock cast iron. It didn’t take long to find it was leaking at the intake gaskets. I had already ordered and msd 6al and it burned up the oil nicely. Anyway I picked up an aluminum intake and the problem went away.
    I still have that same 383 and it still runs mid 12’s in my Camaro! 26 years old!

  5. Professional products is the absolute worst

  6. billy hathorn says:

    seen this problem alot with secondary rings being put on pistons up side down as well. see if there is alot of excessive blow from valve cover where pvc goes when its removed

  7. I would have guessed a pcv problem.

  8. The 383 Stroker using the 6” rods require a shorter piston, that shorter piston puts the wrist pin further up into the oil ring which can allow for oil vapor to escape the crankcase into the chamber and cause oil burning issues, oil consumption and oil coated plugs… I ran into this problem once and I will never use the 6” rod stroker combination ever again.

    The 3.75 stroke and 5.7 I beam rod is the best combination for the 383 build and the only one I would recommend doing… using an AFR 195 head…

  9. Does Gen IV bbc have same problems?
    I have same type problems with my new build up.

  10. hi, I have a honda city type3{wiki} with b15c2 engine and face similar issue. new sleeves were put in to the block in Dec 2018 and necessary things were taken care of such as main/ rod bearings etc but issue persists. Can you please advice on what could be the issue?

  11. Pingback: Ask Away with Jeff Smith: Lining Up Intake Manifold Bolt Holes on a 427 Chevy

  12. I had a 350 put in but oil is coming out of tapet covers and dipstick way too much oil pressure can you please tell me your recommendation on problems

  13. Rick Kannon says:

    I had this problem with oil with a new 406 Chevy SB I went to my head guy GUESS WHAT He showed me that Edlebrock manifolds are not square to the block and heads. The engine was sucking up oil into the runners. UNREAL quality of parts are crap now a days. Steve showed me here lets try this one. GUESS WHAT IT STOPPED no more oil problems.

  14. The paper composition intake gaskets with raised embossing around each port is the best gasket and will seal just about everything. They also are the least expensive.

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