I have a 98 3500HD with the 6.5 TD w 118,000 on the truck and only 35k on a goodwrench motor according to previous owner. My problem is the truck has a heavy knocking sound when started cold. It starts fine has some blue smoke while the knocking is at it's loudest and the sound steadily quiets as the truck gets warmer. This goes beyond normal diesel clatter the knock is very heavy and pronounced. With a metallic sound to it.the truck runs fine and doesn't smoke, no lights on on the dash, runs at a constant 180 to 185 oil pressure is good, injectors were just replaced, and compression checked. Noise never completely goes away, but is quiter when warm. also quiets signifigantly when you put your foot in it. One mechanic said it is normal, but I have friends with 6.5's and theirs don't do this. They think mine will fly apart any day but after months it still is the same. Please help, I can't afford to have this truck go down for something stupid, but if it is terminal I need to plan ahead. Thanks in advance for any help.

Well, I had a 94 that was alot quieter than my 98 now. I remember hearing my friends 98 start in sub zero temps and back then I remember thinking how it sounded like it was going to fly apart. It was so loud that it actually hurt your ears if you were standing near it when he started it cold. My 98 still isn't quite as loud as his but it is alot louder than my 94. Point being, yours is probably fine. Take it to another mechanic that you trust and have him listen to it too.

Sound's like a spun rod bearing or possibly wrist pin. The problem with internal problems is you can either spend a bunch of money and time getting it diagnosed and fixed now, or you could not spend any time or money and run it untill something fails, but this method could potentially cost you more money in the long run because a thrown rod COULD! ruin the entire engine. I personally can't afford the time to chase internal problems, I would have to run till failure than at least I would know what's wrong so I could fix it as fast as possible. I have heard many stories on this forum about people who bring their truck to a mechanic which just starts throwing the owners money into the truck and the end result is a "crap shoot" at best if the original problem is ever fixed. IMO

If my truck is outside overnight in cold weather,cold here is like in the 30's.In the morning when i start it, it will sound like a mack truck for about 5min then quiet down to normal.I think it has something to do with the timming.after about 5 min of warming up its normal.I wouldnt worry about it,unless it does that at every startup warm or cold.Also if i use the block heater it wont do it.




I have a 98 3500HD with the 6.5 TD w 118,000 on the truck and only 35k on a goodwrench motor according to previous owner. My problem is the truck has a heavy knocking sound when started cold. It starts fine has some blue smoke while the knocking is at it's loudest and the sound steadily quiets as the truck gets warmer. This goes beyond normal diesel clatter the knock is very heavy and pronounced. With a metallic sound to it.the truck runs fine and doesn't smoke, no lights on on the dash, runs at a constant 180 to 185 oil pressure is good, injectors were just replaced, and compression checked. Noise never completely goes away, but is quiter when warm. also quiets signifigantly when you put your foot in it. One mechanic said it is normal, but I have friends with 6.5's and theirs don't do this. They think mine will fly apart any day but after months it still is the same. Please help, I can't afford to have this truck go down for something stupid, but if it is terminal I need to plan ahead. Thanks in advance for any help.

My 98 heavy knocks to when cold.Had the dealer check it out which came out normal.

There's 3 major groups of different PCM programming, 94-95, 96-97, and 98-up. From what I've noticed, they get louder at cold start-up with each programming change, 98-up being the loudest with the most cold advance.

You want loud advance TDC offset GMCTD & I did that to -1.94 on mine when cold sounds like bottom is bout to knock out, once warm sounds like normal 6.5. Probably just cold, try plugging in block heater see if that helps, mechanical prblem caused noise will stay hot or cold condition. As TDG says cold advance on cold morning really agrivates the problem

Thanks alot for the input, I agree, I would have thought that a mechanical problem would not be affected by temp, or advance. I now noticed that at dead cold start knock is not there, it starts maybe 15-20 sec. later also with each knock you see a quick puff of change in exhaust smoke coming out of tailpipe which makes me think it is timing and or fuel related. Also noise gets faster as it warms up, and quieter until gone at operating temp. Truck runs at about 170 degrees according to guage.

Thanks again for any mor input you may have.

You wanna here knock at cold start-up, mine sounds like there's 8 rods about to fly out the oil pan when it first fires up cold, still knocks pretty loud even when warm until its hard under acceleration around 2000 rpm, normal cruising around streets at 30 MPH brings the knocking back, the only thing i can say it sounds like is 671 @ idle. It never did this before the chip so i'm not to worried about it.