I read here that a bad valve cover gasket can cause low engine pressure which will cause oil to be burnt.
Is this true? Exactly how would that work?
asked May 11, 2015 at 18:47
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3 Answers
In the video, when they are talking about "burning oil", they mean it is physically running off of the valve cover gasket and down onto the exhaust manifold, which burns outside of the engine. This happens when the gasket fails. Changing the valve cover gasket will cure this exterior seepage from occurring, which will solve this issue. This will not affect oil pressure, though if too much oil seeps out and you don't have any oil in the crankcase, this can ultimately cause your oil pressure to drop.
When a mechanic talks about an engine burning oil, they are talking about oil passing by the oil control rings, causing the oil to burn inside the cylinders. This happens when an engine gets old and tired. Changing the valve cover gasket will not cure this interior oil usage issue. Only an engine overhaul will fix this issue.
answered May 11, 2015 at 18:58
In my opinion, that's not true: the valves cover have an exhaust outlet to vent any combustion gases leaked from the valves operation, which is normal. That always happens, no matter how new or good an engine is, it is part of its design. So these gases are routed to the intake manifold to eliminate them. This means the valves cover is not part of a pressurized system, and therefore doesn't have an influence over cylinders pressure. In fact, all the contrary. If its exhaust vent gets clogged or blocked then that whole zone will get some pressure because minimal but continuous gas leak will build up. Eventually the valves cover gasket will start to leak out, or if the valves system has rubber bushes, they will get damaged.
Now: oil burning from valves cover is always because the gasket is gone, or the rubber seal in the refill cap is damaged. When the engine is running, there is a lot of oil spraying in there, remember the valves, the camshaft and the rest of the things inside needs lubrication. In some engines that's so evident that if you remove the refill cap you can actually see oil spitted out. Oil will leak from gaskets to outside the engine where it is hot, then it will reach more hot zones, like the exhaust manifold and there it will burn even with smoke.
Oil consumption and burning (related with valves cover) have nothing to do with engine pressure. Only the head gasket could make that, but then, comes together with many other symptoms.
answered Jul 14, 2016 at 23:24
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There is, on some engines "PCV" positive crankcase ventilation which means that the crankcase is part of a closed system either above or below atmospheric. Commented Mar 13, 2017 at 8:27
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@Solar Mike is correct. If such a system misbehaves (as from age, or lack of required maintenance), the air pressure under the valve covers can increase, thus forcing oil out of otherwise-good gaskets. In those cars, replacing the valve cover gaskets will work only temporarily, as the PCV system will continue to overpressure the interior of the motor, and force oil out of the new good gaskets, too. To solve valve cover leaks on such motors, one must fix the underlying cause: the PCV system. Commented Jun 10, 2018 at 21:18
additional info
Internal oil blow by might be a result of a failing piston ring and will cause( oil to burn in combustion chamber. Fouling the plugs. Also losing power. Eventually that plug will fill with oil crud. Causing a dead cylinder. You also risk scoring the cylinder walls causing piston Slap. Eventually burning up bearing. Exhaust gas blown into sump oil also ruins oil. Then you know the rest
Mike M 4x4 mechanic and diagnostic tech R and R offroad.
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Yes, exactly...and it is the most frequent problem. Two things are to blame directly on "silent" oil burning/consumption. I mean silent because the lack of smoke under the hood: bad piston rings or bad valves retaining bushes, or both :) Commented Jul 15, 2016 at 15:47