GTX HM has been doing very well in my ‘97 Suburban with 180K miles. The old girl has never even had the valve covers off and still doesn’t leak.
27 year old GMC Sierra 93,000 miles. Should I switch to full synthetic(Mobil 1)?
- Thread starter Chris B.
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If you are already buying M1 0W-40 for the other car, I would put that in the truck.
I switched my 2010 Hyundai Santa Fe over at 146,000 from qs all mileage to m1ep . Now at 186,000 no leaks no issues. I look at it like this. Full synthetic is a better oil and I want the better oil in the sump as I plan to drive this until the wheels fall off. 
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.If it's only seen conventional its whole life, just stick with it. Any API SP conventional/ blend will work just fine. Switching to a full syn after such a long time invites the possibility of leaks, especially the RMS if it's never been changed. I've seen many a leak develop on older small blocks that were run their whole lives on conventional. I'd stick with an SP conventional or blend. Why risk a leak developing?
Heck ya....dont hesitate to switch it to an oil of your choice. Very nice truck!
My brother has a 97 K1500 with the 350 Vortec, has over 250K on it and still runs great. Actually have to do the front brakes on it again this weekend and fix a couple of other minor issues. His is no where near as nice looking as yours is, his has been used an abused with lots of rust on the body panels. Frame is still in good shape though. I do all the maintenance on it and I've run everything from 5W30 to 10W40 in it without any issues, semi or full synthetic. Usually go around 5K miles before doing an oil change. Reality is these engines don't really care too much on what oil you run in them as long as you keep them full and don't neglect the oil changes. I usually put in whatever I managed to find on sale around here, which last time I did the oil change was with some full synthetic Pennzoil that I got from Menards for $17 for 5 quarts.
I start my 93 down to -3 to-7°f in PA just fine on 10w40 QS All mileage. Just let it warm up before driving off.
Yes, change to Mobil 1 HM or Castrol or Valvoline. Any HM oil or if money is no object then go HPL or Amsoil. All great choices.
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