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MECHANICS CORNER: Synthetic versus regular oil

Jim Schlund Published on 31 December 2009

 Mechanics Corner,
A friend and I had a discussion about synthetic motor oil.

We have different understandings as to whether or not it can be used for longer oil-change intervals than normal motor oil. I have not found any manufacturer blessing its use for longer-than-normal oil change intervals.

My friend understands that as one of its selling points – since it costs about twice what regular oil does, it should last longer than normal oil. He uses it, with extended oil change intervals. I cannot justify the cost without the manufacturer of my vehicle stating that it’s okay to exceed the regular oil change interval with synthetics. Jim, what’s your take on this?
—Brad Nelson

This is a good question. The two most frequent questions I get are: What vehicle/tractor is the best to buy? and What is the best oil for my engine?

Synthetic oils cost more because they have a high temperature rating and longer life. How much longer depends on usage. Here are a couple things to consider and then we will discuss when to change your oil.

1. Know when the manufacturer suggests changing your oil. They know the machine better than anyone, so their recommendations are a good place to start.

2. Read statements on synthetic oil. With those recommendations, many manufacturers will give statements about use of synthetic oil and how/when they can be used. Corvettes suggest starting with synthetic oil. Many car manufacturers say not to use synthetic oils until at least 30,000 miles. Most engines work well with regular oil and don’t need synthetic oil.

3. Consider cost. Not just the price of the oil but the cost of disposal. Synthetic oils won’t burn. A trucking company in Idaho’s Magic Valley uses natural oil because they can burn it off when it’s replaced. They can’t do that with synthetic oils.

4. Consider how the machine is being used. Operation is an important factor. How you use the equipment will have a big effect on when it should be changed.

If you are constantly starting and stopping or the engine isn’t on very long, you will need to change the oil sooner. If you cover long distances or the engine is running for extended periods of time, then you might be able to go a little longer between changes.

The simple fact is that without testing the oil, you are just guessing about your engine oil’s capabilities of protection. The great thing is that testing is easy and most of the time free (or low cost). Some oil manufacturers call it SOS: Scheduled Oil Sampling. This is how it works:

Get an oil testing kit from your local dealer. After reading the manufacturer’s recommendations, decide when you should probably be changing your oil.

Then when you change the oil take a small sample and send it to your dealer and they will send it to a lab for testing. According to some dealers, this test is free and they will usually have results within a couple days. The only cost is in mailing the small bottle to the dealer.

This is why you should check your oil. Money. You may change your oil around 5000 miles, but after testing your oil you find that the detergents and additives are all but gone, meaning your engine is not being protected and, therefore, won’t last as long. Then you change the oil at 4,000 miles and test the oil again.

This time the test comes back and you learn that it might have lasted longer. Then a third test might tell you that you can go 4,500 miles between oil changes and still give your engine adequate protection. Now you know the optimal interval to change your oil for your operation, which will save you money in cost of oil and wear and tear.  FG