Use the weight of oil specified in the owners manual for your climate. Doesn't need synthetic, but synthetic doesn't hurt. I change every 3000 miles, so full synthetic would be an expensive waste. I'm not going to use the extended oil change intervals you can get before synthetic goes bad because I like clean oil. Now if you are like my Mom was, and never even think about changing oil, then synthetic is a good bet. She once had a 1968 Fury III that ran over 25K miles on it's' break in oil (with additions). She traded it in 1971 without ever changing the oil - no problems yet. Just change it on a regular basis with the correct viscosity and you will be golden.

Myself I use 5W30 Quaker State dino oil from Walmart and Wix filters. Not the "for high mile" stuff. Inexpensive, good, and you get 5 quarts instead of 4 (like at Autozone and Advance Auto Parts). I've used Quaker State in everything since they gave me a 100K mile extended engine warranty when buying a new 1990 Pontiac. I don't think I have ever heard anyone question the quality of Wix filters and have only heard good things.

 

me really stupid,,had to look up dino...ha

 

I have used Penzoil Dino (PYB) for 210,000 miles with no issues in my Blazer. My change interval has been 10,000 - 15,000 miles. The change interval on my Toyota has been over 10,000 miles for 285,000 miles using semi synthetic. Approx 10,000 mile intervals on the Malibu at 110,000 miles with full synthetic (following the computer), same on the GMC. K & N and Mobil 1 filters. No oil related issues on any of them. My wife and I used to put about 25,000 miles a year on our vehicles with lots of highway miles.

Lools like I’m more like Les’ Mom than Les. Lol.

Modern oils are excellent. My dad told me that oil change intervals used to be around 500 miles back in the 1930s so things have improved quite a bit with both oil and engine design

George

 

I switched to Mobil1 synthetic and noticed the pressure went up. Which is a good thing, I think.

 

Your mileage is not too high but a switch to full synthetic in an older dirty engine can liberate a lot of "stuff" because of the extra solvent action so keep an eye on your change intervals for the first few and use a top shelf oil filter.

George

 

If you want to get into a serious discussion about oil, oil filters, oil change intervals/OCI, and anything to do with oil, go to the forum: bobistheoilguy.com. These guys cut oil filters open and count the no. of pleats and the type of springs and the material the anti drain back valve is made of. Grand new filters and filters that have been in service for 1,000's of miles. When I was a frequent visitor, they liked Pennzoil in the Yellow Bottle/PYB for petroleum or non syn oil. For synthetic oil, they had debates over Mobile 1, Pennzoil Platinum, and of course, they had those that preferred the Amsoil, Royal Purple, and Redline premium oils. OCI were another hot topic. Some were convinced 3K for non-syn and 5 K for syn. Now the oil change intervals have crept upwards. This has been pushed by car manufacturers and by oil companies. I think that is strange and ironic since the modern engines of today are VVT, DGI, turbo charged, and AFM and DFM which would cut off half the cylinders in a V8 to improve gas mileage. All these improvements and upgrades put additional stress on oil. These engines needed the best syn oil. Extended oil change intervals they didn't need. Our 4.3 L V6's don't have those advanced engineering upgrades, thank goodness. They do benefit from Synthetic oils and I like to use Pennzoil Platinum with a NAPA Gold oil filter. OCI ? I am old school with a 5K interval.

 

I forgot to add that I like the suggestion I have read about using 5w/30 weight in the winter months and 10w/30 in the summer months. I have seen that suggestion in some GM owner's manual. Not for the 2003 Blazer, mine didn't come with one. It was missing in action. The 5w/30 circulates quicker in the cold start ups. This is when most of the wear occurs.
I do like also like the suggestion to fill the new oil filter before installing it on an oil change. This is if the filter is mounted up right like on the Blazer /Jimmy. Some of the new cars have the oil filter mounted upside down so this is not possible.

 

I'm just curious why you wouldn't want the oil to circulate faster on cold startup in the summer. In theory, at least, 5W-30 and 10W-30 are the same viscosity when hot. The only difference is when they're cold. I don't see any downside to running 5W-30 all year (which is what I do).

I doubt the second or two it takes to fill an empty filter is really going to hurt anything, but I always pre-fill mine, anyway. It only takes a minute, and it certainly can't hurt. I used to work on trucks that had much bigger oil filters (held a full gallon of oil). I always pre-filled those, too.

 

I agree why wouldn't it always be better to have 5w- oil when you start up?
And it seems to me -w40 would always be better when the engine is hot.

What could be the advantage of 10w30 over 5w40? Just asking.

 

I had already hunted down this old response of mine to an older thread before realizing this was a 2019 thread that had been zombie'd, so I'll reply anyway and include the link because I'm hard-headed: https://blazerforum.com/forum/lounge...e2/#post704530

Really basically though, you should run 5w30 in these engines unless you live in a really warm climate, in which case you might get away with 10w30 if it's cheaper since you don't need the better cold start viscosity performance of 5w30 anyway. Since these engines were engineered for 30-weight though there aren't many good reasons to run something like 5w40 or 10w40 unless you're trying to cheat your way around an oil leak or two by using thicker oil, potentially at the risk of greater engine wear and reduced fuel economy from reduced oil circulation. And really generally, nowadays 5w30 oil with high-mileage additives might be a better choice in such situations anyway, just be sure to stick with high mileage oils from that point onward if you switch to HM.

Synthetic or conventional is kind of up to you and the costs you're facing in your area. Synthetic is better oil in plenty of ways, but these older engines can't take advantage of many of the benefits synthetic oils have for modern engines (esp. extended service intervals), so if you're keeping up with the oil change interval it just doesn't matter a whole damned lot.

Personally, these days I run Costco's Kirkland brand full synthetic 5w30 and stick to a 5-7k mile service interval. Major reason for this is that it's full synthetic, SAE SN-plus certified oil but still actually cheaper than generic parts-store brand conventional dino oil here anyway, so it's pretty much a win-win. Nicer stuff and cheaper too, and actually spec for the truck so I don't need to worry.