Should I continue using HM Oil after gaskets?

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Oct 23, 2015
Pulled my Grand Prix Engine to replace the rear cover seal. While it was out I changed pretty much ever gasket besides the front cover and head gaskets. Should I continue using high milage oil? I'm worried the additive in the HM that swells gaskets will hurt my new gaskets.
I don't think it will make any difference but I would probably just stick to the oil you were using before anyway. I like to keep an engine on one oil after I get it started.
Originally Posted By: Old Mustang Guy
If you like your HM oil I would say stick with. I personally think Maxlife is good for any car for which it has the proper rating.
+1 I had some MaxLife stashed for my previous vehicle which had 120K miles, so when I got the F-150 I decided I would use it in it anyway. MaxLife meets Ford & Chrysler specs for modern engines as well as GM DEXOS. If you get a synthetic blend oil change at a Valvoline dealer, you get MaxLife whether your vehicle has 5,000 miles or 500,000. The high mileage oil phobia about seal swellers & such is nothing but paranoia & false information.
Leaking about 2qts in 5k miles, most of that was from the valve covers which are a common failure point on GM 3800s. Pulled it for the rear cover seal that totally let go, coolant spraying everywhere. I use Mobile Super HM currently, still not sure what to put in it. Might pick up a jug of regular Super and see how it goes
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However, I remember reading that the additional additive packs in most HM oils (I'm specifically referring M1 HM, to be clear) protect many other aspects of a higher mileage engine. ZDDP and additional detergents are the primary reason that I'd choose a high quality HM synthetic even if I didn't have a seal or gasket leak. Also, I'd put a bit more faith in the oil than I would something like a typical ATF (actually Lucas Trans Fix comes to mind) where seals or gaskets are just "swollen", I'd like to think (hope) that lubricant engineers for SOPUS, Exxon, BP, C/P and the like have worked out the chemistry a bit further into more of a "conditioning" that the oil lends to the seals and gaskets.
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