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2007 Chevrolet Silverado 2500HD — accidentally used synthetic oil

I plow with a 2500 HD Chev Diesel 6.0 Ltr. I changed the oil yesterday rushing to get it done during a brief warmup here in northern Vermont. I didn’t realize the Valvoline Heavy Duty Diesel motor oil I bought also was labeled as Fully Synthetic. I had never used synthetic oil before. The truck has 105,000 miles and it is only used for plowing during the winter now. Should I drain the synthetic oil out right away and go back to regular diesel engine motor oil? Full disclosure, I got the wrong oil filter and did not swap that out when I changed the oil. I’m a cold idiot, I know.

The synthetic is not going to hurt anything, but I would change the filter as soon as possible, and top off the oil.

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+1. 100% agreement. The fully Synthetic may look a little more dirty next time you change it since it has more detergent than regular dino oil, but that’s about the extent of difference.


?? I’m seeing the 6L engine is gasoline and the 6.6 is a turbo-diesel for that year.

Presuming you have the 6.6 L turbo-diesel, I believe Chevy requires the oil spec meet API CJ-4, either 15w-40 or 5w-40. Make sure you see that spec printed on the bottle.


Yes. My mistake it is a 6.6L Duramax

The oil I used is 5W-40 API CJ-4 rated hvy duty diesel engine oil

Should be go to go. Any oil that meets or exceed manufacturers requirements is fine. Agree with pyrolord314 too.

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There are some people who believe that changing to synthetic oil late in a vehicle’s life can cause oil leaks…Or make small leaks worse.
I have actually experienced this on one of my own vehicles. Switched to Synthetic @ 130k mi. and soon after the valve covers started leaking…Maybe just coincidence…then again maybe there is some truth to the “myth”.

I’d prefer full syn for plowing duty in cold weather. I’d keep using it.

You got that right.

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Agree - Totally by coincidence.

These old wives-tales are so hard to kill (especially with the internet).

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I think it’s coincidence. I had a Corolla that I got with 120-130k miles on it (early 2000s model year), switched it to full synthetic after i got it…no problems. My 05 Town & Country I also switched to full synthetic after I got it (about 135k)…no problems (with oil consumption anyway, I had other problems with that beast…)

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Well maybe its not just coincidence.

  • Synthetics damage seals: “A synthetic oil won’t create a leak,” said David Canitz, technical services manager at Royal Purple, "but it will find any marginal seals due to lack of maintenance”

Which is why high mileage synthetic oil is always an option.

Agreed. And by the way I have no qualms with synthetics… they are almost certainly superior to a conventional mineral oil in most every way, no matter the mileage but the fact remains, in a high millage egine, it is plausible, they could cause or “ exacerbate” an oil leak… The reason, I have gathered, is that the molecules in a synthetic are smaller and can therefore get past a gap in a seal or gasket that a conventional may not physically be able to.
I would emphasize the word plausible.