So I purchased a 2006 Silverado with the 6.0 over the weekend. The previous owner had tons of documentation of using Mobil 1 high mileage full synthetic for the last 7 years and last 60 ish thousand miles. Would it be ok to go back to regular full synthetic? Truck has 160k on it.
Switching from high mile to synthetic
- Thread starter Wil90
- Start date
Definitely. No issue using a regular pcmo full syn 5w-30. I've been using 15w-40 in both of the gmt 800's in my sig for several years now which I've owned since new and have put almost 600k on combined with the original engines no metal inside either replaced. Not even the head gaskets have failed on either engine yet. They use minimal if any oil and run wonderfully to this day. Use 15w-40 as well if you want if it doesn't go close to 0f. You can also use a euro rated 30/40 grade. But a regular full syn 5w-30 is no issue.
Sure as long as you're okay with having to replace old gaskets/seals which may age because they're no longer receiving the "extra" seal conditioners which is so common with HM oils.
Triple_Se7en
$50 Site Donor 2024
Check the concrete for little black spots when into the next 2-3 OCIs.
Other than that, you should be fine, unless the engine gives you a shout-out audio / consumption difference.
Here are a few previous threads that may be helpful.
For what it's worth I have done this for hundreds of thousands of miles on my old vehicles.
https://bobistheoilguy.com/forums/threads/switching-from-high-mileage-to-non-high-mileage.376965/
https://bobistheoilguy.com/forums/threads/switching-back-from-high-mileage-to-regular.325022/
https://bobistheoilguy.com/forums/t...l-once-you-switch-to-it-no-turning-back.9259/
https://bobistheoilguy.com/forums/threads/switching-away-from-high-mileage-oil-safe.195024/
https://bobistheoilguy.com/forums/threads/late-switch-to-full-synthetic.323602/
https://bobistheoilguy.com/forums/threads/switching-from-high-mileage-oil-bad.166666/
https://bobistheoilguy.com/forums/threads/can-i-switch-back-to-non-high-mileage.269105/
https://bobistheoilguy.com/forums/t...ck-non-high-mileage-oil-full-syntheti.295702/
For what it's worth I have done this for hundreds of thousands of miles on my old vehicles.
https://bobistheoilguy.com/forums/threads/switching-from-high-mileage-to-non-high-mileage.376965/
https://bobistheoilguy.com/forums/threads/switching-back-from-high-mileage-to-regular.325022/
https://bobistheoilguy.com/forums/t...l-once-you-switch-to-it-no-turning-back.9259/
https://bobistheoilguy.com/forums/threads/switching-away-from-high-mileage-oil-safe.195024/
https://bobistheoilguy.com/forums/threads/late-switch-to-full-synthetic.323602/
https://bobistheoilguy.com/forums/threads/switching-from-high-mileage-oil-bad.166666/
https://bobistheoilguy.com/forums/threads/can-i-switch-back-to-non-high-mileage.269105/
https://bobistheoilguy.com/forums/t...ck-non-high-mileage-oil-full-syntheti.295702/
Thank you for the links ! Looks like the previous owner did the timing cover gasket and oil pan gasket in 2019 - 40k miles ago . Was just worried that the switch would cause a leak?
Thanks for the feedback, super helpful!
That’s a tuff call. What’s wrong continuing the HM oil? If you’re looking for extended oils. I believe M1 makes a 20K EP HM oil.
I was always under the impression that HM oil would swell seals etc and eventually cause them to fail due to making them “mushy”
wemay
Site Donor 2023
Being that it was on a lengthy diet of SYNTHETIC high mileage, i doubt using regular synthetic will free up carbon that would cause a leak. All oils have seal conditioners, hm just has more. I wouldn't worry one bit about switching.
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What have you learned since then?
High mileage oils do not cause seals to fail by making them "mushy" some of these higher performance style oils that are not high mileage oils have more "seal conditioners" than actual high mileage oils and nobody complains about issues out of them.
I run nothing but high mileage oils, never had an issue.
I’ve used HM oils in the past without issue. My last truck I didn’t use HM oil because there was no need too. 137K on my beloved 15 Tacoma.
Oil doesn't cause leaks, water does. An engine that sits for a year, never cranked or driven, will be more leak prone than one that's driven 100 miles daily no matter what oil you use.
High mileage oil stopped my truck from leaking so I would worry that it would start leaking again. Currently I have regular syn in it and it hasn't started leaking but I'm going back to HM next oil change.
Smile man, it's an Internet forum and sometimes folks can be light-hearted around here. You can switch without issue.
You'll be fine, the LS isn't really that picky about oil especially the Gen 3. I bought my 2004 w/ 42k miles and been using PP and RGT 5w30, I go through a quart between changes and it has 122k now. I think you'll find that most people use M1 0w40 in these.
The word "synthetic" means very little today.
