Can GM Cars Go a Full Year on Full Synthetic?

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Since we are on the subject of GM cars, I have a ‘15 GMC Sierra PU with the 6.2L. I have driven it only 1100 miles in the last year and am planning an OC myself soon. Now I am wondering do I need to? The manual says 1 year or what the OLM says. The OLM is around 80% the last time I looked. It has been previously serviced at the dealer, and the power train warranty expires at the end of this month. It seems wasteful to dump 8 qts. of barely used oil.
If your OLM is like my Duramax it will show 0% at a year. Been there twice.
 
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Yep new car costs are crazy. Over the long run a couple of UOAs can save a lot of money from wasting oil, too short a run, or in costly engine repairs, from too long a run. Why guess when a $10 UOA can take all the guessing out of the equation? And as an added bonus you'll know if you have excess fuel dilution and/or coolant finding its way into the oil. I've said it before, blanket statements can get you in trouble.
Well said, Sir.
 

ssalvat

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I'm reviving this thread as I'm over 6 months on both cars with 5w-30 full synthetic oil. Both cars have probably gone around 2,000 miles in this time. I don't think there are any engine issues, both seem to run fine, BUT both have developed very slow drips. Seems like both engines now have a very thin sheen of oil on them, which occasionally runs and drips. I know the Vibe didn't ever do this before, not sure on the Yukon since I bought it used last year, although the previous owner did explicitly say at one point that it had no leaks.

Since this is the first time the Vibe (and I think the Yukon) has used synthetic oil, and it's now dripping for the first time, I'm guessing the cause is the synthetic oil, so I'm considering going back to high mileage conventional. I'm curious to hear if others think this might help. I'm also curious if I can still get 5000 miles/1 year on conventional, or if I'd need to go back to every 6 months. Thoughts?
 
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I'm reviving this thread as I'm over 6 months on both cars with 5w-30 full synthetic oil. Both cars have probably gone around 2,000 miles in this time. I don't think there are any engine issues, both seem to run fine, BUT both have developed very slow drips. Seems like both engines now have a very thin sheen of oil on them, which occasionally runs and drips. I know the Vibe didn't ever do this before, not sure on the Yukon since I bought it used last year, although the previous owner did explicitly say at one point that it had no leaks.

Since this is the first time the Vibe (and I think the Yukon) has used synthetic oil, and it's now dripping for the first time, I'm guessing the cause is the synthetic oil, so I'm considering going back to high mileage conventional. I'm curious to hear if others think this might help. I'm also curious if I can still get 5000 miles/1 year on conventional, or if I'd need to go back to every 6 months. Thoughts?
To many variables to determine if the oil is the problem, and I wouldn't venture a guess. I would try a HM synthetic oil and skip the HM conventional oil..
 
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Synthetic oil doesn't cause leaks, but since synthetic oil flows more easily than conventional it will find its way out of any pre-existing, potential leak points easier than conventional oil. You might be better off sticking with conventional oil or trying a HM synthetic oil.

I had synthetic oil in my Equinox for over a year since the pandemic hit. Only drove 3,000 miles during that year. Oil Life monitor was still showing 44% after 12 months, however OnStar Diagnostics threw a fit that it had been more than 12 months since the last oil change (based on the last OLM reset.) Went ahead and changed the oil and filter anyway just because it was a year old and for general peace of mind. The oil that came out was pitch black, which kind of surprised me since it only had 3,000 miles on it.
 
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Palmer, Alaska, USA
Synthetic oil doesn't cause leaks, but since synthetic oil flows more easily than conventional it will find its way out of any pre-existing, potential leak points easier than conventional oil. You might be better off sticking with conventional oil or trying a HM synthetic oil.

I had synthetic oil in my Equinox for over a year since the pandemic hit. Only drove 3,000 miles during that year. Oil Life monitor was still showing 44% after 12 months, however OnStar Diagnostics threw a fit that it had been more than 12 months since the last oil change (based on the last OLM reset.) Went ahead and changed the oil and filter anyway just because it was a year old and for general peace of mind. The oil that came out was pitch black, which kind of surprised me since it only had 3,000 miles on it.
I also have an Equinox and mine is used as a commuter car -- 24 to 25 miles RT each day. As mine has the notorious 2.4L non-turbo DI engine with its poor piston rings, oil degradation, through contamination, dilution and shearing, prominently shows itself at around 3,000 miles. At around 2500 to 3K miles, it begins to burn this blow-by degraded oil at a much higher rate. Hence, I change it out when oil usage and or burning begins.

After discussions with the more experienced mechanics at a trusted local GM dealer, they're telling me what I'm now mentioning: these smaller displacement GM DI and turbo DI engines require consistent oil changes at or near 3K miles. If you plan to keep your vehicle for a long period of time (100,000 to 200,000+ miles), they do not recommend extending OCI's to 5K or 7K miles -- following your OLM display to 25%, 10%, or 0%. Ask me how they and I know... ask me about timing chain replacements.

Anymore, it's 3K OCI's for me in DI engines. Period. That equates to around 50% to 60% on the typical GM OLM.

...

OTOH, my Gen III 5.3L V8 truck engine is a different story!
 
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