97 GMC 350 Vortec

EMC'S Z · May 24, 2003

I bought a 97 GMC K1500 Z71 with a 350 about a month ago. It has 125000 +/- miles. Recently it started knocking when cold. I t only happens when the temps are below 50 deg, and the truck has been sitting over night or all day at work. It has 10w-30w oil (f'ing girl at sprint lube didn't even ask). Is this an oil problem or a bearing about to go? Oil Pressure cold: 60lbs. +/-, warm: 45lbs. +/-, at idle warm: about 20lbs. I have one of those penn warrentys. How good are they? If they tear the moter down and find no problem I eat the labor.

I know that the lifters are noisiy( they weren't when I first got it) when cold but the knock is new.

My 94 3/4 ton w/ a 350 had 270,000 miles(on the speedo and it had 33's for 190,000 of those miles) when I sold it. lifter tick but no knock.

I was hopeing to add power to this truck. do I need a crank First?

Is 125,000 miles to much to add a Whipple or something? Am I asking for trouble?

Little more info

New cap and roter just before it started,

1800 miles on oil

Reads just under full on dipstick

Radiator flush and fill when I got it a month ago.

Needs plugs and wires.

help me out please.

Thanks Eric

DaveD · May 28, 2003

A couple of thoughts:

If it started happening after the oil change the previous owner may have pulled a fast one on you by using a oil viscosity that hid the knock. Have also heard the some oil filters don't have a anti drainback valve in it and it causes noise at startup till you have oil pressure.

Consider sending the oil out for analysis (about 25$). I understand they can tell a lot about engine wear, etc. I'm about to try that for my infamous engine knock problem on my 2000 6.0 GM says is normal.

The dealer should be able to look at the cylinder wear with a borescope. Also find out the cost to drop the pan and look at the bearings. I would think it shouldn't be more than a few hours labor. Maybe 1 hour to look with the borescope and 2-3 hours to check the bearings. You would be gambling about $300 for this diagnosis (4x$75). Seems to me a 350 should be rock solid though.

Oh yeah, a old trick to stop lifer noise is to put a pint of marvel mystery oil in the oil. Stopped them for years for me on some older 350's I had. Maybe the previous owner did that too.

Let us know what you eventually find out.

EMC'S Z · May 28, 2003

I let the local dealer who I was going to PAY to diagnose the problem, hear it and he said it was normal sounds. He said a PF 52 filter might help, but it wasn't anything to worry about. It definetly has a ton of power when warmed up and gets 16-17 miles to the gallon. I think that I am just going to get another extended warenty. Plugs wires and cap seemed to quiet it down alot to. For what I piad for the truck I can afford to get a new motor if I had to In a year.