rectoy
Junior Member
Good morning. I have a 1996 5.9 15004X4 with HD everything with 356,000 miles that I abuse as a work vehicle in my mobile marine mechanic business. There is a large difference between outboards and vehicles which is why I'm here. The engine has had only two thermostats replaced, qualifying my statement that it has never been apart. I change the oil & filter every 3000 miles. In-and around town gas mileage has been 15.2-16.1, highway loaded (55MPH) is 19.0 and highway unloaded (65mph) 22+mpg. All records kept for IRS!! Cold oil pressure is 70#, highway hot 55#, idle w/AC on, 105F outside, 38#. There are no knocks, no bangs. Recently I have started hearing a "thuck-thuck-thuck" noise coming from around the area of #6 & #8 rockers. It never happens when the engine is cold, never starts until there's an extended idle or most often when oil is warm, won't go away if I accelerate, but might if I shut down and restart. Or not. I might not hear it after an oil change, or might. There is no consistency to WHEN I'll hear it, just that I WILL, every day. I can hear it better in the cab than out. It is not an exhaust leak. The location is not exposed.The noise is NOT a knock, but more the sound of a plastic-head Snap On hammer tapping hard on a vice. It sounds about half-engine speed, leading me to think a lifter is beginning to collapse erratically, but there is no change in engine operation when it sounds off. As you can see by the above, I treat my transportation to steak while I eat burgers. It runs nicely, consistently (the kiss of death). Because there are no leaks, no internal problems(yet) the tech where I've taken my trucks the last 2 million miles hesitates to do anything other than say"Yup, there's a noise. Turn the radio up." At 73 I don't walk as much as I used to and would like to get this noise out of the engine or my head before I HAVE to walk. If I were to use Marvel Mystery Oil, Rislone, or Seafoam in the oil as directed, with the thought that there's a piece of trash stuck in a lifter, what % correct is my thinking? What % chance of success would you offer? Do you think I have a little man running through my head and there's something else to consider? Remember, it's 2 more cold months before boaters get off their wallets. Sorry about the length, just wanted to get as much as I could before you. Thanks for any help.