Rick's Free Auto Repair Advice

Car losing oil but no leak or smoke

Car losing oil but no leak or smoke

Why is your car losing oil?

All engines burn some oil between oil changes. That’s why carmakers recommend checking the oil level at least once a month and topping off when necessary.

Some engines burn more oil than others; it all depends on the engine design and the condition of the engine. It is a fact that most engines will burn some oil. Most carmakers consider one quart of oil consumption in 1,500 miles to be acceptable oil usage.

If you’re not leaking oil but feel that you’re losing too much oil, here are some other reasons that cause an engine to lose more oil.

WARNING: If you drive when your engine is low on oil, you’re decreasing the life of the remaining oil. One quart low? You’ve just decreased the life of the remaining oil by around 25%.

Mechanical reasons why a car loses oil

• Clogged PCV valve. The PCV valve is a one-way

PCV valves

Find the correct PCV valve for your engine and replace it.

valve that allows crankcase blowby gasses to flow to the intake manifold to be burned, but not allow backfire heat to enter the crankcase. The valve is constantly exposed to oil vapor and that can buildup and clog the small PCV orifice. If that happens, crankcase pressure builds to the point where oil gets pushed past the piston’s oil control rings and gets burned in the combustion chamber. So a clogged PCV valve can cause an engine to burn more oil than normal.

• Stuck oil control rings. Oil control rings are designed to wipe oil film on the cylinder walls on the upstroke and then squeegee off the excess oil on the downstroke. If the oil control rings get carbon buildup and stick, they will wipe oil up, but not squeegee it off, causing excessive engine oil consumption.

• Worn piston rings. Worn piston rings, like worn oil rings allow too much oil to burn off the walls of the cylinder.

Worn piston rings can cause engine oil consumption issues

• Hardened or cracked valve stem seals. The rubber valve stem sealvalve stem seals squeegee oil off the valve stem. When they age, they harden and develop cracks. Oil splash from inside the valve cover gets sucked past the worn valve stem seals and gets burned in the cylinder.

• Worn valve guides. Valve guides keep the valve stems straight. As the guides wear, the valve stem wobbles, allowing intake vacuum to suck oil down into the cylinder.

Driving habits that use more oil

• Engine braking. An engine creates high manifold vacuum any time the engine rotates with the throttle closed. That high engine vacuum occurs any time you take your foot off the gas pedal. However, if you use you downshift your transmission to help stop your car, you cause the engine to rotate even faster, creating maximum engine vacuum that sucks oil past the valve stem seals, valve guides, piston rings and oil control rings. As a general rule, engine rule, drivers that downshift to engine brake experience more oil consumption.

• Hard acceleration. Any time you put an engine under load, you increase combustion temperatures and those higher temperatures can burn off more oil.

• Driving with heavy loads or towing. Again, this puts a load on the engine with causes more oil consumption.Idling. With your foot off the gas, your engine is running at high vacuum which can pull extra oil into the combustion chamber.

• Stop and go traffic. This is a combination of heavy load during acceleration followed by high vacuum when you take your foot off the gas.

• Remote start. Using a remote start and letting your engine idle to warm up burns more oil.

• Using the wrong oil. Contrary to popular belief, using a heavier weight oil can actually increase oil consumption. This is due to added burden placed on the oil control rings which have to squeegee off a thicker oil film.

©, 2022 Rick Muscoplat


Posted on by Rick Muscoplat

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