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Can too much oil hurt an engine?

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Updated 11 Oct 2019

Jason Unrau

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Your car’s engine oil dipstick has a mark for ‘FULL’ and ‘ADD’.

If the engine oil level measures anywhere in between the two, you’re in fine shape.

But if you notice that the engine oil is too full, what should you do?

Is it okay to drive like that, or does it require attention?

What Do You Consider ‘Too Much Oil’?

It’s important to know what the oil level on the dipstick means.

It varies by vehicle but generally, a half-litre of engine oil beyond full will be about two centimetres above the ‘FULL’ mark on the dipstick.

A full litre will be about 4cm high.

Now, there’s some tolerance for the oil level in your engine.

After all, parking on an incline will change the oil level in the crankcase.

If the engine oil is reading just slightly higher than the ‘FULL’ mark on the dipstick, it’s likely not going to cause any problems whatsoever, but it should still be adjusted when you get the opportunity.

Anything more than that should be dealt with right away.

What Happens If I Drive with an Overfilled Engine?

Maybe your engine burns a bit of oil and you want to add a reserve.

Or maybe you just weren’t careful when finishing your oil change.

If you decide to drive with your engine overfilled with oil, it’s asking for trouble. Here’s why.

Frothy Oil

When too much oil is in the engine, the crankshaft’s rotation whips the oil up, mixing air into it.

It causes the oil to be bubbly or frothy, and the oil pump pickup tube can’t draw oil in properly.

The result can be low oil pressure – kind of ironic, isn’t it?

Engine Oil Leaks

Too much oil can also cause excessive oil pressure.

And when oil pressure is too high, it has to go somewhere.

That ends up being the weakest point in your engine – one of several gaskets or seals like the crankshaft oil seal, head gasket, or valve cover gasket.

Blue Exhaust Smoke

Also, when the crankshaft is rotating in engine oil, it splashes it up into the cylinders more than normal.

The oil eventually works its way into the combustion chambers where it burns and goes out the tailpipe.

A clear sign of an engine burning oil is smelly blue smoke from the exhaust.

Burned Out Catalytic Converter

Oily exhaust coats the catalytic converter inside too.

The catalytic converter isn’t designed to superheat oil, and that can lead to a converter melting down inside or becoming contaminated.

Serious Engine Damage

Too much oil can create resistance against moving parts like pistons and connecting rods.

Too much resistance will result in catastrophic engine failure, often beyond what can be repaired, and the engine needs to be replaced.

The moral of the story is this: too much engine oil will hurt an engine.

If you notice the oil level is too high, have some removed to prevent one of these serious problems from occurring.

A local mechanic can help you with your excess oil dramas, and luckily you can quickly and easily book yourself in online through AutoGuru.

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Written By

Jason Unrau

Jason is a Canadian automotive content writer with a background in the auto service industry, but he’s been hooked on cars and mechanics since childhood.

One of his first cars was an ’80 Mazda RX-7 that’s sorely missed to this day. A ’68 Ford Torino GT, a ’66 Ford Country Squire Woodie station wagon, and a ’96 Suzuki GSX-R 750 have spent time in his fleet of cars, bikes, and trucks over the past two decades.

Jason’s pride and joy is under construction – a turbocharged ’88 Mazda RX-7 convertible. Also on his resume is CASCAR official certification.