After changing my oil this weekend I noticed the pressure went up. On my gauge 12:00 high reads 40 lb. And my pressure using mobile one has been about 11:00 or 11:30, say, 35 lbs.. Shortly after putting in the new oil (Valvoline 10w-30 synthetic blend) it was about 50 lb, as high as it's ever been. After some highway miles though it dropped down to about 20 lb.
I'm not too worried, but I wonder if anyone else has noticed pressure changes with oil changes.

 

What weight was the former Mobile 1 oil?

 

also 10w-30. Could a bad filter cause movement like that? I used a Walmart Supertech short

 

Upon further driving I still have the ~50 psi but noticed the low psi only shows up when idling. drops to about 25. Normal?

 

Slightly higher pressure isn't 'bad enough' that I'd be too concerned about it but I'd probably stay away from the Walmart filters in the future. i prefer to stick with an AC Delco or Purolator Gold though, they're known quality filters, have the correct pressure bypass valves, and are cheap enough that you don't feel like you're wasting money having it sit on a shelf. Oil filters are one of those things that you know you're going to need in the future unless you plan on getting rid of a vehicle that I don't mind shopping around in advance for the best price online and having a few on hand in case I find myself with some of that elusive 'free time' on a nice day that's close enough to when it needs changed. That way, I don't spend half the day running around looking for what I already know I'm going to need to get the job done. Plus, it's never too late to start collecting RockAuto magnets for the garage fridge AND you'll save enough to throw in the PCV Valve and all the other things like light bulbs you've been meaning to pick up but forget to buy (or they don't have in stock) at the same time. Same goes for the oil but THAT I usually DO pick up at Walmart because they're cheaper and I don't pay shipping.

 

When you talk about the AC Delco oil filter, the 'oil filter reference' books list two sizes for the GM 4.3L. One is the PF47 and is listed for the two wheel drive Blazers. I think this is the one Puttster calls 'short'. The 4WD 4.3L calls for an AC Delco PF 52 oil filter. Now notice that the auto stores such as Walmart, AAP, AZ, and others charge the same for the 'short' PF-47 size and the 'taller' PF-52 sizes iwhether n AC Delco, Walmart brand Super Tech, Purolator , Wix, and so on.
I want to recommend that you use the taller PF-52 size rather than the shorter PF-47 size. Now I am not recommending that you use AC Delco oil filters. I am recommending the corresponding larger size of PF52. YOu can look in the provided oil filter reference books the retail stores provide. You culd also ask the parts guy with the computer to crossreference PF52 to your favl. oil filter. Look at the oil filter sizes recommended for your year Blazer /Jimmy and use the larger size filter in your favorite brand for the 4WD 4.3 engine. There is no conflict in the larger size fitting to the 2WD 4.3L engines verses the 4WD 4.3L engine compartments. That way, you get larger capacity and therefore better filtration for the same price ! Maybe cooler oil temp's. YOU should be sure to check your oil level carefully after your oil change and compensate for the 'taller' size oil filter capacity.