Cold Engine knock

[oafmanwpr]

96 k1500 with 56,000 miles. Used Mobil 1 from new. Having what sounds to me like a bad piston knock when engine us cold and under load. This is not to be confused with the usual piston slap. The knock goes up and down with RPM and eventually goes away once its fully warmed up. This appreared after the truck was parked at an airport for a week in cold weather and I noticed the noise at start up the next day. Any thoughts?

[chevy4x4trucks]

it's just what you said, a cold start knock. happens in all vehicles from chevy to ford to dodge to even rice burners. there are some technical explanations of the cause of this on the fourm somewhere.

[oafmanwpr]

To clarify, this never happened until recently and the knock continues for several miles. I am familiar with the typical cold start knock. This seems more significant of mechanical trouble to me. I have lived with this truck for 8 years and never heard this before

[PharmZ71]

I have a 97 with the 350 in it, and i have a god-awful engine knock. I've had it for about a year now. When I initially took it to my mechanic it had a real bad ticking all the time. They said I had a stuck valve, fixed that, and then I deveoloped an AWFUL cold start knock that quiets after a while, but is always there if you get close enough to the block.

 

I was furious, took it back to the mechanic. He said that the engine had been over-revved (because of the hypertech programmer) and it had misshaped one of the pistons and now I had a piston slap. When asked why it didn't happen before I brought it in he said the engine computer was retarding the spark when the valve was stuck. I don't know if he is feeding me bulls*** but I do trust the guy from past experiences and other people that have gone to him for years and years. He told me that he has seen this engine go 150k easily with a piston slap.

 

Dunno if this relates at all to your problem, but I thought I'd share my misadventure with you.

[robsawatsky]

Your mechanic is taking a wild guess.

 

A knock like that could be cylinder, piston or bearing damage.

[traxion]

I had that problem w/ my stang. Start and 'knock knock'. After a bit it would stop. My dad told me it was 'just piston slack'. So I ignored but notice quite a bit of performance degrade. I almost got whooped by a dakota crew cab 6 cyl. The night I raced the dakota was the night when it started knocking loud constant. So I killed the motor and loaded it on a trailer and took it home. After diving through the motor I found that I had spun a bearing on the crank shaft. Had to buy new bearings and a whole crankshaft. Cleaned everything up sealed it up, put it back in the car and no knock. Still running like a champ. Just some thought.

[asepgrad98]

could be main bearings.....

[PharmZ71]

Don't mean to take over this topic, but do you guys think I should go get a second opinion. My truck has been running with this knock for over a year now with no loss in power. Am I just buying time till something blows, or should I just weather the storm?

[traxion]

Don't mean to take over this topic, but do you guys think I should go get a second opinion. My truck has been running with this knock for over a year now with no loss in power. Am I just buying time till something blows, or should I just weather the storm?

 

Depends on a few things. Does it knock all the time? Is it just in the mornings?

I have a slight knock in the mornings sometimes when its cold. Its just the lifter giving a little 'chatter' until the oil pressure builds up and then its bueno. So dont get to worried if its mild in the mornings.

[PharmZ71]

It's LOUD in the morning when it's cold, a little tamer when its warmer out, but still noticeable. When the engine warms it quiets to the point where you can't hear it, unless you stick your head under the hood near the block, then you can hear a faint knock...but it never truly disappears.