Would syn be good for truck that sits a lot?

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Chris B.

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I have a 1997 GMC Sierra with the 5.7 Vortec V8 and 83,000 total miles on it. It has been on Castrol GTX and I'm thinking of switching it to a full synthetic. The truck sits a lot and I only put 1,000-1,500 miles a year on it. UOA's are decent and show plenty of TBN left after a year and 1,000ish miles. Iron is a little high so I'm thinking a synthetic might help with the micro corrosion that is causing the high iron from sitting. What do you guys think? Also what full synthetic oil and weight you can buy at Wal-Mart would be a good choice? Many thanks!
 
The use of synthetics will likely increase the iron count in a UOA that is nearly worthless in determining engine wear. I personally would not bother. Just buy whatever you can get for the least amount of money. The oil will not cause the engine to fail. For a truck that is about to enter her second decade she looks excellent I dare to say new! You have replaced the intake and head gaskets?
 
Hey that's a nice clean truck! You haven't said how you drive it only that you obviously don't drive it much. If you're just doing short trips with the engine rarely getting good and hot, then yes I'd suggest a synthetic 0W-20. On the other hand, if it just sits a lot but when you do drive it it gets a good run then any cheap API 5W-30 syn bought on sale would be a fine choice. You could also use an API dino 5W-30 as you are which quite frankly is fine as well.
 
Thanks guys! I drive it when I need a truck which is ever few weeks. When I do drive her it is for most of the day so she gets really hot and gets a work out! Then it gets parked in my garage till next time. I have to add about 4 to 12 oz of oil ever 1000 miles to keep her on the full line on the dip stick. Intake was done at 76,000 miles. Price of oil and filters is no concearn to me at all. I just want the best oil to protect the engine in these conditions. What weight would be best? I'm thinking the 20wt oils would be very bad for this engine as it was built for 5w30 and long before 20wt oils were even around. Thanks again for any more input and here are more pictures:
 
Given that it was neither Ford, Toyota, nor BMW who designed/tested your engine, I'd stick to what GM recommends. Porsche and Ferraris have backspecced to 40s these days, but that's no reason to got to a 40 either. Dave1251's point regarding synthetics, iron, and UOA is worthy of note, both in the effects of synthetic, and what the iron really means... If it were mine, I'd either go synthetic, and multi year oil changes, or GTX/PYB or something similar, and do it annually, and not worry about the top-ups.
 
What a nice, clean truck. I would use PYB 5w30 with one year OCI. No point using synthetics in this car if it's rarely driven.
 
Nice looking truck. Looks like it just left the factory. For me, I wouldn't use synthetic. I personally would just get Pennzoil conventional 5w30 and a Wix filter and change it once a year. $20 on a oil change for that condition of truck is nothing. I ran synthetic in mine for over 100,000 miles and then went back to conventional, not because of price but it sounded the same if not a bit quieter and the oil still looks clean after 5,000 miles or OLM. I'm not saying synthetic is better or worse, but I just didn't find any differences except price for my truck.
 
Is PYB better then Castrol GTX? My last Tahoe on GTX with the 5.7 liter had the lowest wearing 350 on file with Blackstone Labs. This Sierra has yet to show a UOA as good as my 1997 Tahoe did also.
 
Originally Posted By: chrisri
What a nice, clean truck. I would use PYB 5w30 with one year OCI. No point using synthetics in this car if it's rarely driven.
+1. Indeed a nice, clean truck. Your engine bay looks better than my 2012 car.
 
Originally Posted By: chrisri
I would use PYB 5w30 with one year OCI. No point using synthetics in this car if it's rarely driven.
+1. This is exactly what I am doing. I have an extra car that only gets < 2,000 mi /yr now. I always ran it on M1 or PP 5w30, but now that it is rarely used I changed over to PYB. I won't run the same oil for more than a year, and it would be ridiculous to drop M1 with 2,000 miles on it every autummn. On a < 2,000 mi. OCI the PYB is more than up to the task - there would be nothing to gain from a syn in this application IMO.
 
Originally Posted By: Chris B.
Is PYB better then Castrol GTX? My last Tahoe on GTX with the 5.7 liter had the lowest wearing 350 on file with Blackstone Labs. This Sierra has yet to show a UOA as good as my 1997 Tahoe did also.
FWIW, take a look at these: http://www.pqiamerica.com/CastrolGTX.htm http://www.pqiamerica.com/Pennzoil.htm Based on prior experience, as well as this information, I would use PYB over GTX...
 
Originally Posted By: Chris B.
Thanks guys! I drive it when I need a truck which is ever few weeks. When I do drive her it is for most of the day so she gets really hot and gets a work out! Then it gets parked in my garage till next time. I have to add about 4 to 12 oz of oil ever 1000 miles to keep her on the full line on the dip stick. Intake was done at 76,000 miles. Price of oil and filters is no concearn to me at all. I just want the best oil to protect the engine in these conditions. What weight would be best? I'm thinking the 20wt oils would be very bad for this engine as it was built for 5w30 and long before 20wt oils were even around.
You must be a young guy, 20 grade oils have been around as long as the grading system and was the most commonly recommended grade in the 30's and 40's before the advent of multi-grade oils. But I agree since you're getting your giving the truck a good work-out the spec' 5W-30 is the way to go. Since you're not particularly concerned with cost of oil then I'd suggest start using a synthetic 5W-30 at the next oil change. And since you're getting the oil up to temp' every time you drive it you can extend your OCI to about three years if not longer. This may seem too long to you but it's not time that degrades oil it's actual usage or mileage. If you're uncomfortable about leaving the oil in that long have a UOA done before you change it; that will confirm how much approximate life is left in the oil.
 
Originally Posted By: CATERHAM
. . . . And since you're getting the oil up to temp' every time you drive it you can extend your OCI to about three years if not longer. This may seem too long to you but it's not time that degrades oil it's actual usage or mileage. If you're uncomfortable about leaving the oil in that long have a UOA done before you change it; that will confirm how much approximate life is left in the oil.
This is surprising shocked !
 
Use a quality synthetic 5W-30 - change it every 4 years. I use M1 in my '92 Suburban which also enjoys sitting in the garage for long periods. Only about 500 miles a year - I'll probably go 6 years on this OCI, I last changed it in 2010.
 
88-98 GMT's were one of my favorite 1/2 tons. A lot of modern stuff for reliability, but still easy to work on. Loved the styling. I had an 88 with over 265,000 miles. I replaced a door handle here and there and a few sensors, but nothing major til 250,000 miles when it needed a new transmission. The engine was still running strong. I'd still be driving it if it wasn't for an inattentive driver who hit it. Parts were dirt cheap for it. Id keep that truck as long as you can.
 
Just run a name brand 5-30 dino No need for syn Seems like you had rather wash it and look at it than drive it
 
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