Synthetic Oil..color..longevity

When it comes to oil in all my past cars it’s always been the old trational oil we grew up using. NOW I own a car (2011 Cadillac CTS) that uses synthetic oils (5W30). Having never used this type of oils I had a couple of questions.

  1. With the old style oil you would usually go about 3,000-5,000 miles between changes depending on engine, milage driven and such. What is the mileage/time breakdown for Synthetics? I know my manual said basically my car will tell me when it needs to be changed but just wondering on average how long this synthetic stuff lasts.

  2. What are the advantages/disavantages of synthetic over old school type?

  3. When you would replace you oil with the old school stuff it was clear on the dipstick and would darken over time as it got “dirty” and used. Is that the same with synthetic? The car I just bought says the oil is at 98% and according to the manual you change it out when it gets down around 25%, yet when I pulled the dipstick it wasn’t clear, it was dark which I thought ment older dirty oil but wasn’t sure with synthetics if it looks different.

Oil lifetime is related more to the lifetime of the additives that’s the base oil. GM has a sophisticated oil lifetime algorithm developed over 20 years of use before your car was built. Depending on how you drive, it could last up to about 10,000 miles. We own three GM cars with the OLM and use it to determine when to change oil. The oldest car with OLM has 180,000 miles and runs fine.

It helps improve gas milage. This is the reason most car manufacturers are using it today

The only downside to synthetic oil is the cost. Too many up-sides to list!

The oil darkening is engine and use specific not oil specific. I’ve got cars that darken synthetic oil within weeks of a change and I’ve had 2 cars that would barely darken the oil between changes as called for with the OLM. And the mileage was 50,000 to over 100,000 on the cars amd as much as 10K on the oil itself. And I use nothing but synthetic oils and have for decades.

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Here’s a wiki article with a list of advantages:

Synthetic oil - Wikipedia

@Mustangman has it right, there are a ton of upsides to synthetic vs plain dino oil

That’s why I wait until Costco has a sale on Mobil-1, and then I stock-up. I recently bought 2 cases (6 bottles each) of Mobil-1 at Costco, and thanks to the sale price, the price per quart for Mobil-1 was the same as I would pay for conventional Castrol at Wal-Mart!


I can tell you based on experience that synthetic oil does darken as it is used and I have seen no dramatic difference in color over time, or miles, as it ages in the cars I have that use it. I did some research for a story recently on why it is being used more, and what the advantages are for BestRide, a partner site to CarTalk if you are interested. The typical time between oil changes is getting longer and varies by MFG, but 10,000 miles or more is now common. In addition to the type of oil, the volume of oil, the filtration methods and other factors can increase the time between changes.

You can’t extend oil changes because it’s a synthetic oil. I don’t use synthetic oil because of the cost. I might change my mind if the price goes down but I doubt it.

From reviewing the manual it appears that they “highly” suggest and recommend going with synthetic and if it lasts up to around 10,000 miles then for me that would equal out to basically 1 oil change per year because over the past 10+ years I have only put on average 10,000 miles per year on my car. Now probably 75% of that is city driving which I know is harder on engines but even if I drop down to 2 oil changes per year over the 4 I was on average getting then I would think the costs should be pretty close as I was paying $25 per oil change using the dino oil over the synthetic. Since I am not sure how “reliable” the car is for telling me when the last oil change was done I am trying to get documentation from the dealership on what work was done on the car during the time they took it in for trade and I purchased it to see if an oil change was done. If I can’t or it doesn’t show one I will get it in this weekend for a change.

If you look carefully, I’ll bet you lunch that the manual also says to change the oil at least once per year, regardless of mileage driven

So don’t just blindly wait until the message center . . . or whatever you have . . . notifies you an oil change is due

Since you don’t have documentation telling you when the last oil change was performed, consider it overdue.

Your Oil Life Monitor takes that into account. My GM truck has an OLM that always triggered the “change oil” much earlier when I’d been towing. It would go 7000 miles plus with just highway driving.

Your car is smart enough to know when it is time. Believe it. Use good quality oil and filters and you will be fine.

Your car has an oil life monitor, right? It’ll take your short trips into account, GM’s monitors are quite sophisticated. And yes, follow their recommendation to use synthetic, it’s important that you do. Of course, if you don’t know when an oil change was last done, do it so you’re starting ‘fresh’.

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Both car manufacturers and oil producers disagree with that statement.


Even the oil of 10-20 years ago is not the oil we grew up using. The American Petroleum Institute (API) standards for oil refining and additives have been increasing gradually throughout the years.

Some maintenance schedules called for conventional oil changes in the 7,500 mile range as long as 18-20 years ago. I’m still driving one of those cars, a 1998 Honda Civic with almost 300,000 miles, although I change my oil every 5,000 miles. The maintenance schedule calls for oil changed between 3,750 and 7,500 miles, depending on driving conditions and ambient temperatures.

I wouldn’t focus too much on the color of the oil. If you want to obsess about the condition of your oil, I recommend sending a sample of used oil to a lab, such as Blackstone Labs, for a used oil analysis. Otherwise, the smart thing to do is follow the car’s maintenance schedule. If you want to change your oil more often than is necessary for the sake of peace of paranoid mind, 5,000 miles between oil changes is a reasonable compromise.

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On the car that uses synthetic, I change at 5000 miles which is about 50% OLM. Why? Because the car is expensive and oil is cheap.


requires oil that meets GM standard GM4718M. not all synthetic oils will meet the spec. owners manual says so. it also does not say if ANY dino oil will meet this spec

The main reason Cadillac specifies synthetic oil for your engine is, the engine utilizes Variable Valve Timing.

And the variable valve timing solenoids rely on oil pressure and that the oil remain clean for them to operate properly.



Plus, the oil life monitor’s computations are based on the use of synthetic oil that meets specifications.

Are all synthetic oils the same? My manual says 5w30 only, does it matter brand or are there other classifications?

Not sure of what your definition of dark is but in your case, it could indicate that this vehicle was neglected in the past.

Synthetic oil pretty much acts the same way as conventional oil as far as color change goes, it just usually takes about twice as long to change. But since it lasts longer, it often contains more detergents and will clean out a dirty engine. If the oil is pretty dark at 98% oil life, then I’d suspect that the oil wasn’t changed as often as it should have been in the past or substandard oil was used.

The seller probably did an oil change just before putting it up for sale. If they used synthetic oil, it would start cleaning very quickly. They might have also used something like Auto-RX which has chemicals that turn the oil dark very quickly. In either case, I’d plan on changing the oil again real soon, and use a quality synthetic oil. You may need to do a couple of oil changes ahead of schedule until the oil stops turning dark to quickly.

It would also turn dark early if there is a lot of blow-by.

You want a synthetic oil that 5w30 with the letters SN in the grade circle. Look for API Service SN in a round circle about the size of a quarter somewhere on the bottle. If it has that, brand is just personal preference (or in my case, on sale).