Oil Pressure Puzzle

Hi All...
I am talking about a 1989 Chevy K2500 4X4, 5.7 ltr. V8 (350 TBI), VIN code "K".
About two years ago, the truck started to have low oil pressure. Being a
pretty good wrench myself, I thought this was odd. Oil pumps generally don't go bad. At this point the motor had about 140,000 on it. I switched out the oil pressure sending unit, and bada bing... back to normal. Well, after about 6 months, the pressure drops again. I figure better safe then sorry, and switched the oil pump out, and a new sending unit. Holy cow.. pressure is way up now. Before the pressure trouble started, she ran between 32 and 45 PSI, hot or cold. With the new pump, the pressure pegs over out of sight (I figure 65 PSI) until it gets good and hot... then it'll settle down to about 50 to 55 PSI (Still almost out of site on the gauge). This still bothered me though, and I pulled off the oil filter housing to check the oil pressure relive valve. It wasn't stuck or anything, so now I'm stumped. Is it possible that I got the wrong pump? I got it from the dealership. I didn't pull apart the old pump to see if it was bad or not... dumb me I know...
Thanks in advanced.
HDS
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there's nothing wrong with 55psi oil pressure.... don't worry about it.
-Bret
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I've been experiencing extremely LOW oil pressure on my 93 K1500 5.7 ltr. pickup and I've been wondering if I should replace the oil pump.
Since you actually did it, how much of a project is it? Is it something that the "shade-tree mechanic" should avoid?
-Derek

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Have you guys checked the pressure with a mechanical gauge? The reason I ask is because I have had to replace my electric gauge sender twice and have gotten two different readings. With the mechanical gauge I got 50 when cold and 30 when hot. With the stock gauge I get 40ish when hot and peg the needle when cold

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No... I never did. Should have, but after the second sending unit said I was still having low oil pressure, I felt it was better safe then sorry. On top of not checking it with a mech gauge, I never bothered to open the old pump to see if it was OK or not. Live and learn I guess. Anyway... the new pump is doing what yours is right now. Pressure gauge pegs out of sight when cold, but only drops down to about 55 PSI when warm. I hate it, because it used to stay right at 32 to 40 PSI no matter how cold or hot it was. I think that might be because the brass tube that runs out of the block to the sending unit might be clogged up a little. It's too cold, and I'm to lazy to pull it off to check it right now thought.
HDS
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Sorry for the delay Derek:
It was a major cluster. You have to pull out the front drive axle... I mean the hole thing... in order to get the oil pan off. There are two ways of getting the front drive axle out on my truck (yours may vary). What looks like the easiest way, is to remove the 4 bolts that mount the drive axle tubes to the supports on the frame... But I think they used the super duper impact wrench on those. I took out the supports that are on the frame... top first, and swung it out of the way. You also have to drop down the tie rod from the idler arms. Oil pump is held in with only one bolt. Oil pan was simple, but I had to remove the clutch inspection cover, clutch slave, and starter (standard trans... not sure about auto trans set up). My pump came with a new pick up tube. That needs to be pressed in and spot welded in the same location as the old one. For me, it was a two day job with beer breaks on the 4X4 model.
HDS
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Cool, thanks for the input. It seems the older I get, the easier it is to just fork over the cash and have my mechanic do it. This is starting to sound like one of those projects that deserves a professional touch... :-)
And if beer is involved, it'd probably take me a week. I disassembled the engine in an old muscle car that I had sitting around, and after the beer was gone I lost interest in rebuiding the engine! It sat in pieces in the garage for 3 years before I just gave it all away to some other sucker who probably did the same thing...
Thanks, again! -Derek

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