7.4L Gen V knocking

[TBarCYa]

The Gen V 454 in my boat is knocking. I was headed to the marina whem I heard it and noticed the oil pressure was lower than usual at about 30psi running 4000rpms. I changed the oil and other than being low I didn't notice anything peculiar, not shiny or full of metal... But I wasn't looking for it either.

After the oil change the pressure is back to normal and she seems to run fine but the knock is still there. Fuel consumption and power may be a little low or the bottom may need to be cleaned.

Today I took the stethoscope to the valve covers and didn't hear the knock just the sound of the valves. The port rear cylinder was slightly louder than the rest but only slightly. I scoped the exhaust manifolds and heard the knock but it didn't sound like it was coming from the exhaust. I heard the knock in the intake manifold but it sounded consistent across all cylinders.

The last test was to pull the spark plug wires to see which cylinder would stop making the noise and none did.

Pulling the plug wires should have identified a rod knock and scoping the top end should have identified a bad valve/lifter/pushrod but didn't. Next time I get to the boat I'm going to pull the plugs and possibly do a compression test but is there anything else I should look for? Should I go old skool and put half a quart of transmission fluid in the oil to quiet it down and keep running it?

 

[alldodge]

If its a knock and not a tap/tick, then that would be a rod bearing and there is nothing you can put in the oil to make it better

If its a light tap, then it might be a lifter and trans fluid has been known to help, but I'm not a fan.

 

[GA_Boater]

Should I go old skool and put half a quart of transmission fluid in the oil to quiet it down and keep running it?

Not a smart idea. If you have a bearing problem and oil pressure problem, what will thinning the oil do for you except ID the reason quicker. Possibly by which rod aerates the block.

You should use an direct reading oil pressure gauge where the sender is. Dash gauges have been known to be way off and wrong.

BTW - How low was the oil?

 

[Scott Danforth]

if it spun a bearing, it will be cylinders 3 and 4. not sure why, however those appear to be the ones that go first. if its a bearing, there will be chips in the oil.

could simply be the coupler. pull the drive and fire it up. if the sound goes away, pull the motor and change coupler

 

[TBarCYa]

Not a smart idea. If you have a bearing problem and oil pressure problem, what will thinning the oil do for you except ID the reason quicker. Possibly by which rod aerates the block.

You should use an direct reading oil pressure gauge where the sender is. Dash gauges have been known to be way off and wrong.

BTW - How low was the oil?

I got 5 quarts out and it holds 7 so about 2qts low. Totally my fault for not checking it before heading out.

Since it has some hours after the oil change I'll pull the stick and see if there's any glitter next time I'm at the boat. When my Dodge Ram 5.7 spun a bearing it made a horrible sound that I'll never forget. This is definitely not that. Compared to that, this is a light tap / tick. Of course that engine destroyed itself in about 15 seconds.

 

[jakedaawg]

If you still have the old filter you can cut it open and see if it has a lot of metal...

 

[TBarCYa]

If you still have the old filter you can cut it open and see if it has a lot of metal...

Unfortunately I already disposed of the old filter.

 

[TBarCYa]

I was at the boat on Friday and pulled the dipstick and was pleased to find no glitter and no grit in the oil There's probably 5 hours on the engine since the oil change and it still seems really clean so I'll start poking around other places like the exhaust flappers (assuming I have those) and the coupler.