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Choosing Engine Oil

Today on Repairs101 I’m going to show you choosing engine oil for your vehicle.

Most frequently asked question

 Alright, here we go. Today on Repairs101 I thought I’d try and answer the question that I get asked more than any other question – and that is “What kind of oil should I put in my engine?”  Now it’s a really good question and it’s really worth looking into. So today I thought I would try and teach you how to decide for yourself what kind of engine oil to put in your engine. Using the wrong motor oil can lead to poor performance, premature wear and ultimately it could lead to failure.

Here’s the chart given in my Buick Century’s owner’s manual. You can see, very similar in the owner’s manual for my Blazer.

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So maybe the first question you’ve got to ask yourself is “What am I burning? Am I burning gas or diesel?” There’s a big difference between oils designed for gasoline engines and oils designed for diesel engines.

Service classifications

So the API – the American Petroleum Institute is the system that’s in use here in Canada and the US. So the API classifications start off as SA, then SB, SC, SD… you get the idea, right? Around the world there are other systems in use. OK you can see here right in the opening pages of the book – of the service manual – you can see that they are telling you that they want engine oils that are labelled by the API.

OK so they call this “the API Gasoline Engines Starburst”. Oils made specifically and exclusively for gasoline engines will have the starburst on them.

OK now this little symbol here is called “the API Donut” and this donut gives you all the information you need to know about the oil. It says that it’s API service SL, in the middle of the donut it says that it’s SAE 5W-30 viscosity and underneath it tells you that it’s an energy conserving oil.

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Here’s a list of API Service Classifications for gasoline engines and here’s a list of API Service Classifications for diesel engines. Now, of course the reason I’m flashing through this quickly is because, for most people, it’s really not that important. A real Gearhead might want to study these charts and understand them. Now most people just aren’t going to need to know every service classification on the chart, OK? We’re going to go to the store we’re going to pick up what’s on the shelf. It’s going to be fairly current if not the most current oil available and it’s going to match our fairly new to used vehicles.

Whether you think the “S” is for “Spark” or “Service” and whether you think the “C” is for “Compression” or “Commercial” – it doesn’t matter, as long as you learn that “C” is for diesel burning engines and “S” is for gasoline burning engines. If you have a brand new vehicle I definitely recommend checking and seeing that the Service Classification called for by the engine manufacturer matches the service classification of the engine oil you intend to use.


OK so viscosity – now that’s another issue. Viscosity is the measure of how thick an oil is. Think of molasses in February, now that’s going to be really thick. Right? Whereas water is thin. The lower the number on the viscosity scale – the thinner it is. So it’s very simple. A five weight oil is going to be very thin compared to a forty weight oil, say. 

So keep in mind that when you’re considering viscosity for your vehicle. Really what you’re asking yourself is “Is it going to be thin enough to start in the coldest conditions that it’s going to be exposed to?”. So for instance, if you’re in the Yukon at Christmastime you’re going to need thin oil. You know a five weight oil or even a zero weight oil. If you’re in an Equatorial climate then for sure you’re not going to really need anything very thin. You could go with a straight forty weight oil or straight thirty weight oil. Probably and have no problems ever starting it because it’s not going to be thickening in the cold.

Multi grade oil

So Multi-grade oil is what they’ve come up with to address the problem of “cold starts”. And then being thick enough to protect the engine when it’s hot and running. When it’s cold it behaves differently than it behaves when it’s hot and the way they do that is… They introduce a polymer into the oil in order to make it behave differently at different temperature ranges. For instance, when it’s cold it will be much thinner than when it’s hot. Which is counter-intuitive, I understand.

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So what they’re saying here is if it’s below zero degrees Fahrenheit you’re going to need a 5W-30 oil. And if it’s above zero degrees Fahrenheit you’re going to be OK with a 10W-30 multi-grade oil. OK over on this page we’ve got another viscosity chart and this time it’s given like a bar-graph.

So most everybody uses multi-grade oils in the vehicles these days. With the exception of “extreme service” and collectors you know. The real hardcore Gearheads… They’re going to want to use single weight oils. Because they’re changing their oil three and four times a year. And they want to make sure that – no matter what the conditions are. They’ve got the absolute best performing oil in their crankcase. Most people are going to fall into the lower one or two of these categories. And be wanting to use either single-weight oils from this column here or multi-grade oils here and here, OK?

Synthetic oils

Compared to conventional oils, synthetic oils last a lot longer. They can withstand a lot more heavy duty applications, extreme duty applications, more continuous service. They’re better in turbo-charged systems, super-charged systems – anywhere again where there is extreme service. OK some examples of extreme service would be – continuous service. Say an engine that’s running twenty-four hours a day like a Taxicab or a Police vehicle. Say a forklift that’s running commercial duty. Race-cars, high performance vehicles… Or how about say a tugboat that’s running twenty-four hours a day pulling a load through the inside passage. Something like that, you know? That’s extreme service.

Now synthetic oils will last longer because they resist degradation through oxidization. In other words they don’t oxidize quite as rapidly as conventional oils.

OK so after you decide what you’re burning – gas or diesel. And which Service Classification of oil you need – is it a “C” class oil or an “S” class oil? Then the last thing you want to know is what viscosity you want. And the only thing you have to ask yourself is. “How cold is it going to get when I start this thing?”. And, like I said, the lower the temperature, the lower the number viscosity you want. And if it’s real, real cold out there you want something as low as 5W. Or even 0W to get her started.

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