Viscosity and Rod Knock

[BBDartCA]

Have a neighbor with a 360 5.9l Dodge in a Durango with what sounds like a rod knock. Sound seems to come from the oil pan area. Its intermittant. Goes away when you rev engine. Maybe its something else, but soure sounds like you are hitting a piece of steel with a ball peen hammer (kinda has a ringing sound to it).

Whats odd is the sound was not noticed until the oil was changed from 10W30 dino (Chevron Supreme we think) to 5W30 M1. Thinking about going to a 5W40 or 5w50 to just see what happens to the sound.

Has anybody seen oil weight change how a rod knock or main bearing knock sounds?

 

[river_rat]

The ringing sound, and that it goes away with reving...except for the location...sounds to me like a collapsed pison skirt.

If you really do have rod knock, the oil viscosity will not quiet it much or save it from impending disaster.

My 2 cents.

 

[spasm3]

If the bearing has spun, switching back will not help. The bearing may have been close to failure anyway, and the thinner oil helped it along. It would have happened soon anyway. A thicker oil may quieten it down but only temporary.

 

[StevieC]

Try a different oil filter like a Mopar or Purolator and see how it is... If that doesn't fix it have the oil pressure checked (If there isn't a gauge) and the bottom end bearings.

Could also be a loose piston, I have seen this a few times in Dodge engines. Guess the guy was sleeping at the factory or the tool was out of calibration.

 

[BBDartCA]

I'm thinking its not rod or crank bearings. Sound, is not real steady with the RPMs and goes away when it revs. Maybe its a water pump bearing or something in the valve train (its got roller lifters I think).

Found this interesting video of rod knock. First video is engine running, second is result from tear down (yikes).

http://www.youtube.com/watch?v=zmVp8KBlMME

http://www.youtube.com/watch?v=oLYMApzEDaA

 

[xxch4osxx]

Could also be a wrist pin that is worn.

 

[JAG]

It would be a neat test to keep the same filter on, drain the oil and re-fill with previous brand/viscosity. If that made the noise go away it would make me think even less of M1 5w30 than I already do.

I was talking to a tractor trailer driver recently who had his engine running and it was knocking. I asked why and he said if he revved the engine a few time to build up oil pressure temporarily the sound would go away for a minute or so. He did this to prove it to me. I wonder if your friend's engine would do the same.

 

[mechtech2]

Switching oils is a lousy way to determine what this problem is.

 

[ItsuMitsubishi]

Originally Posted By: mechtech2
Switching oils is a lousy way to determine what this problem is.


yup it's also a really lousy way to find out your engine has a problem too.

 

[Gary Allan]

 

[Steve S]

One of the vans I had a work had a really worn engine with straight 30 at recommended idle speed the oil light would come on and you really could hear the knoce . I liked the van so I added 90wt gear oil to the crankcase and was able to keep the van for a couple of years till the owner of the company said the van is too old for the fleet. If the wear causes the viscosity of oil to leak out of the between the bearing surfaces too quickly there will not be the wedge of oil to seperate the parts. It is hard to diagnose noise by reading about it but usually certain noises are not good. Rebuilding an engine is expensive . Try a can of STP or some kind of motor honey to thicken the oil to see happens to the noise. It won't hurt anything and if it doesn't make a difference you won't be out of a bunch of $$$.

 

[BBDartCA]

Update - the knock is coming from the torque converter area (used a stethoscope to find the source). And it only knocks when warmed up. Changed to 15W40 Delo and of course nothing changed. Seems like a trans issue.

 

[StevieC]

Could it be a Flywheel?

 

[BBDartCA]

Could be. Will take the inspection cover off in a few days and check out. Making the sound only when its hot makes me think its a hydraulic issue.