Is it Safe to Put Synthetic Oil In My Older GM Truck?

It's long been rumored that switching to synthetic oil in an older truck will damage its engine. Is it true? Not anymore.

When synthetic oil was introduced about 50 years ago, it contained esters that later proved to wear down the seals in old engines and cause leaks. The masterminds behind synthetic oil addressed this issue by figuring out how to produce effective synthetic oil without needing esters. As a result, we no longer have to worry about synthetic oil damaging older engines.

However, it’s worth mentioning that switching to synthetic oil may lead to quicker oil consumption. Due to the smaller and more uniform size of the molecules, synthetic oil is more likely than conventional oil to slip through the rings and cylinder wall. This isn’t a big issue, though. You just have to watch the oil levels and consumption rate more closely.

Pouring oil

Photo credit: Dvortygirl

Benefits of Switching to Synthetic Oil

Some people may argue that cars manufactured before 1990 were built to run on conventional oil. They’re right, but conventional oil isn’t always the best option for fuel efficiency and engine protection. In fact, synthetic oil was developed to solve some problems created or neglected by conventional oil.

Compared to conventional oil, synthetic oil:

  • Lasts longer: You can go 5,000-10,000 miles between oil changes with synthetic oil.
  • Performs better in extreme temperatures: It flows better in cold weather. It also doesn’t break down or evaporate in hot weather or under trying conditions (such as towing or off-roading).
  • Helps clear out sludge in the engine: While some conventional oils are formulated to do this too, it’s a more common feature in synthetic oil.
  • Maximizes fuel economy: Synthetic oil is known to boost fuel economy by 2% or 3%.

Basically, synthetic oil prolongs your truck’s life, performs much better in abnormal situations, and is more versatile than conventional oil.

Is Synthetic Oil the Better Option for You?

All that being said, synthetic oil isn’t always the better option for older GM trucks. It depends on many different factors.

Use Synthetic Oil if You…

1. Idle your truck a lot. Your engine needs air flow to stay cool. When you idle your truck a lot, even in stop and go traffic, your engine isn’t getting enough air flow and may overheat. Unlike conventional oil, synthetic oil helps alleviate this problem.

2. Live in a desert, high altitude environment, or cold area. All three environments have conditions – such as hot weather, thin air, and freezing temperatures – that lead to either an overheated engine or decreased oil flow. Due to its versatile nature, synthetic oil is better equipped to perform optimally in these conditions.

3. Use your truck for anything other than regular day-to-day driving. For example, off-roading, racing, or even towing. Any kind of non-normal driving on a regular basis puts a strain on your engine, and synthetic oil is designed to protect it from long-term damage.

4. Wait more than 6 months between oil changes. Synthetic oil lasts much longer than conventional oil. If you drive your truck daily, the resiliency of synthetic oil makes it safe to push a few thousand miles past your suggested oil change mileage. Even if you drive only occasionally, it’s still a good idea to use synthetic oil because conventional oil will start to break down much earlier, even when not in use.

Older S10

If you drive your older GM truck, such as this 80s-era Chevy S-10, in a lot of stop-and-go traffic, synthetic oil is the better option. Photo credit: IFCAR

Use Conventional Oil if You…

1. Use your truck as a commuter vehicle. It takes a while for conventional oil to heat up and properly lubricate your engine, but when it’s in motion, it’s pretty darn effective. That’s why synthetic oil – which is made to lubricate and cycle faster – might be overkill if you drive your older GM truck from point A to point B every day without a lot of traffic or idling.

2. Your truck consumes at least 2 quarts of oil between oil changes. We mentioned earlier in this article that older trucks consume synthetic oil faster than conventional oil. If your truck already consumes more conventional oil than usual, then there’s no sense in splurging on synthetic oil if it’s just going to run right through your truck. (If you have a 5.3L V8 engine that consumes a lot of oil, here's a way to fix it).

3. Have an engine that’s prone to oil leaks. Synthetic oil is thinner and more likely to slip through the cracks. If your engine already has a leak, synthetic oil is just going to leak out faster. Conventional oil is the safer choice in this situation because it'll leak out slower.

Things to Keep in Mind Before Making the Big Switch

If you’ve determined that synthetic oil works better for your truck, the following two pieces of advice will come in handy:

  1. If you’re worried about your older GM engine being unable to run synthetic oil due to loose seals and components, bring your truck to an experienced technician and have him/her make the necessary repairs or replacements. Once the technician gives your truck the green light to run on synthetic oil, you should be good to go.
  2. Avoid synthetic blends! You may be tempted to save a few bucks on a synthetic blend, but synthetic blends aren’t regulated and you’d be taking a gamble on the quality of the oil. Also, you might be overpaying for the blend because it may contain 99% conventional oil and only 1% synthetic oil. Blends don’t offer the same kind of protection as pure synthetic oil does.

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