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Thread: I'm topping up with Full Synthetic 10W-30; I don't remember exact range/grade of oil

  1. #1

    I'm topping up with Full Synthetic 10W-30; I don't remember exact range/grade of oil

    Hey All

    So I decided to pick up a quart of oil to top up my oil level in my other car, a 94 Impala SS, (which I've owned since new), as I've noticed the level dropping on the dipstick. There is a slight leak on the ground that gathers and I am presuming it's from the oil pressure lines that are near the front anti sway bar. They look sludgy and they've burst once before in 1999 and I will soon have that worked on. In the meantime, as I don't want the oil too low (the dipstick shows the level near the ADD line when I checked it on a level surface with the engine cool; the owner's manual states to check it when it's warm and not running although I've always checked oil when it's cool and not running) I picked up the quart of oil (it may not need that much), however, this is the first time I've topped up my oil, on this car, whereas otherwise I've always just changed the oil normally.

    What I'm not certain of is, which exact weight of oil I already have in there. I've always used Synthetic (or Semi-Synthetic possibly here and there) oil in this car since my first oil change after I bought it new. I picked up a quart (946mL) of Pennzoil Platinum Full Synthetic 10W-30. The manual says (of regular oil) 5W-30 ideally or that 10W-30 will be fine.

    I recall first using Castrol Syntec back in the 90s and for some reason I recall a crazy range of 5W-50 but now I'm not entirely sure. That being, since I'm just topping it up I'm thinking it's going to be ok if I mix weight specs (as I really don't know which range I have in there).

    That said, a number of other things are running through my mind now:

    -can one mix semi synthetic with full synthetic?

    -can one mix a different weight range with what's already in there?

    -can one mix semi synthetic (or full synthetic) with regular oil (I've seen people do that; someone I know replaces one quart with synthetic or semi synthetic with his regular oil)

    -if the manual states 5W-30 or 10W-30 does that mean we should use those same ranges for semi synth or full synth?

    -the car has about 80,000 miles (124,000km) on the stock LT1

    -I'm thinking, even if that 5W-50 I used to use is the ideal (which it may not be in hindsight), I think that the 10W-30 full synthetic's more-consistent-range-accuracy will protect to about at least 40 weight of what regular mineral oil would offer (however since the manual says 5 or 10W40 for mineral oil then I'm liking to think that I'm in the ballpark with Full Synth 10W-30).

    -I know that the LT1s inherently run hotter (due to the reverse flow cooling) and I always remember, since new, how the temp guage would fly to the high area which is normal, however I'm not in a desert either. The summers here don't yield more than 95 degrees F (35 degrees C) so I'm thinking 50 weight is a bit of a stretch. The temps here won't dip much below 10 degrees F (-12 C) either.

    so, any thoughts of my topping up with Full Synth' 10W-30 even if I don't remember what exactly I have in there?

    here's the details on the Pennzoil Platinum Full Synthetic 10W-30 I bought last night from Walmart ('interesting how it's derived from Natural Gas!)


    https://www.walmart.ca/en/ip/pennzoi.../6000016943506

    thanks everyone

  2. #2
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    Yes, you can mix viscosities and you can mix synthetic and non synthetic. Yes, the ranges are the same. I wouldn't waste my money on "semi-synthetic", I read the actual portion of synthetic in this can be very low. For me, I always run Walmart 5W-30 full synthetic oil in the 4.6L.

    from the bestoil.com:

    A semi-synthetic blend may have only 5% or 10% synthetic oil since there is no requirement as to what the mixture percentages should be. Therefore, the benefits received may be questionable for the increased price above conventional oils.

  3. #3
    Quote Originally Posted by Agent2006 View Post
    Yes, you can mix viscosities and you can mix synthetic and non synthetic. Yes, the ranges are the same. I wouldn't waste my money on "semi-synthetic", I read the actual portion of synthetic in this can be very low. For me, I always run Walmart 5W-30 full synthetic oil in the 4.6L.

    from the bestoil.com:

    A semi-synthetic blend may have only 5% or 10% synthetic oil since there is no requirement as to what the mixture percentages should be. Therefore, the benefits received may be questionable for the increased price above conventional oils.
    that's great information

    thank you Agent2006

    I really appreciate it

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