Last January, I bought a 2014 RAM 1500 Laramie Longhorn 5.7L with 100K miles on it. The engine had a bad head gasket by the #2 cylinder and the engine had obviously been badly overheated. I completely flushed the cooling system, sealed the gasket and completely replaced the cooling system; radiator, water pump, hoses, thermostat, fan clutch, etc. I also replaced the coil packs and plugs, and it's been fine. But, every time I start it up cold I have what sounds like a low-end rod knock, which seems to be coming from the right side. I know valve ticks and this ain't that. It's been doing this since I bought it.

The thing is, once the engine warms up, the knock totally goes away. I've only run Royal Purple since I've had it, the oil pressure is fine and the engine runs strong and smooth as silk. I'd really appreciate it if someone could tell me what's going on. Thanks.

P.S. I've put over 13,000 miles on the truck so far and nothing has changed; knocks when I start it up and totally goes away after the engine warms up.

 

Maybe a bearing got overheated as well..... Did coolant get into the oil at all? If you can, might drop the oil pan, and check rod/main bearing clearances.

 

Thanks so much for your quick response! - At some point I may do that in weighing whether to fix the problem or sell the truck. I'm just real curious as to what is knocking. Don't know if it's true or not, but I'd heard in years past that overheating could cause a rod to stretch and perhaps knock against the block. The thing there is that I know a little about metallurgy and once you've exceed the yield strength and stretch a piece metal, I've never heard of it coming back on its own. I guess it could be a main bearing problem, but either way, I 've never heard of these problems resolving themselves on their own and don't understand why once the truck warms up, the problem would go away.

 

I am thinkin' that if the rod got hot enough to alter its properties, just fixing the headgasket would not have solved the other problems. And it wouldn't be just one rod either. Also, if it were beating against the block, it would eventually provide it's own clearance, either that, or fail completely. Since the problem hasn't really changed in a significant period of time, I suspect just addressing bearing clearances will likely take care of it. Of course, that may mean replacing the rod/machining the crank... in which case, throwing another engine at it might be easier.