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Discussion Starter #1
Quick question looking for a quick answer. I'm an idiot and accidentally bought 5 quarts of 5W-20 oil instead of the 5W-30 I normally use, as per spec. Old oil's already out of the car. New stuff's Valvoline SynPower full synthetic, same as the old.

Can I use the 5W-20? What adverse effects might there be? I'm changing it in the dealership I work at, so if I absolutely have to I can buy some semi-synth 5W-30 and change it again to full synth later.
 

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Should use 5w30 for the correct pressure on the chain tensioner. It's very picky about oils
 

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My saab calls for 0w20 or something like that and still uses the same tensioners and everything. I would still suggest running the 5w30 but short term it really shouldn't hurt anything. The oil will be a bit thinner though so if you have even a minor oil leak it could start leaking quite a bit
 

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You should be good with 5W-20 for the 10,000 Kms. The only thing that may be different is how fast the level goes down. Just check your oil every 1000 Kms or so and top it up. My 2010 Cobalt called for 5W-20 and it has the same engine except for Cam actuators which are a bit more sensitive to viscosity. Again I wouldn't worry about hurting your engine, it actually might do it a bit of good for a 10,000 Kms run.

---------- Post added at 04:05 PM ---------- Previous post was at 04:03 PM ----------

Forgot to mention, if you notice you have more valve clatter and it annoys you the go back to 5W-30 but only if it's loud and annoying.
 

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Discussion Starter #6
Alright, thanks everyone for the advice. It's running just fine for now, I'll probably leave it in there and keep an eye on the oil level. My engine's in great shape for it's mileage, no leaks whatsoever, so I'm not worried about that. The lighter oil should make it run a little bit more efficient too, and it'll help a bit with startups once the weather gets cold. If I notice any noises or difference in how it runs I'll switch it right back.
 

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What year is your Cobalt?

---------- Post added at 08:33 PM ---------- Previous post was at 08:28 PM ----------

Late 08 came with the revised timing chain tensioner if you have the earlier version I recommend You change it to the better version. If it has a bump on the head you're safe, if the head of the bolt is flat you are in danger of failure.

 

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I would not use 5W-20. GM rated these engines for 5W-30 and they have not been back spec'd for 5W-20 nor have they even hinted that 5w-20 is okay. It would be absolutely foolish to think you can run a 5W-20. If you live in a very cold area then GM recommends a synthetic 5W-30 or 0W-30. Simple as that.
 
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