I have a 98 1500 with a 5.7, it has 172k on the motor. I start it in the morning and it sounds like it has piston or rod noise for about a minute then it goes away for the rest of the day. It caries 60 psi oil pressure, i have heard other trucks sound the same too.. any ideas what it is? Also has anyone replaced an oil pump with the engine in the truck?

 

haven't done it on one that new it was a 77 1 ton 2wd .as long as you can drop the pan should work ! might have to undo the motor mounts to lift it a little bit . seam's they are building a lot of the newer engine's with looser tolerances to allow for the hotter temp's to get the cleaner emissions .and i think the shirt's on the pistons are shorter ,maybe good example forged piston will make more noise until up to temp and expands .

 

My truck's 5.7 and my Blazer's 4.3 do the same thing. I think the noise is there anyway on most engines when they get broke in, but the vortec design makes it more audible. As far as I know, theres nothing to worry about. My Blazer has done it since it hit 60,000 miles and I haven't had a problem at all.

 

you - and I - have pushrod engine. though those are very reliable, due to somplicity, they, also, feature long pushrods from cam to rockers. those are prone to having larger gaps, than OVC engines, between lobes and hydraulic lifters. thus, until oil pressure builds up, metal expends, and gaps close, they sound crappy in the morning.
this is infamous GM morning sickness for those engines.
suggested treatment: pour a can of Seafoam into the cranckcase, about 1000 miles before oil change, and drive on it. absolutely safe and will clean all the crap out of lifters. Flush engine with flush oil during oil change. If possible, switch to synth oil, as that one is less viscous and builds up pressure in lifters faster.

 

mad,

i use 1 qt of lucas oil stablizer at each oil change in my 350 engine, 84K.

was having a bit of tapping noise, it quieten it down.

I use valvoline 10w40 oil and wix oil filters.

However, after much research on an old jeep engine problem.

i do believe synthetic oil does have better lube properties than dino oil

i would not put the seafoam in the crankcase of a engine with your high miles,

seafoam is a great cleaner for fuel system, i use 2 cans in the old truck fuel tank per year and it runs great.

 

I would not use synthetic on a motor with that many miles.If it has not been using it all along. I use to use something called rislone for quieting a motor down. It worked real good on a 79 firebird with a 301 in it. That thing was always making some noise when first started.

 

I use Seafoam in mine ever 3000 to 4000 miles and it's just fine. My truck has 199k on it currently. It works just fine. Improves fuel economy and cleans the engine really well. Got rid of a lifter noise I had too.