2004 4.8iS Bottom End Motor Knock

[BimmerE38E53]

Hi All,

So when I bought my X5 it was not apparent to me that there was a knock on startup. It's still fairly faint but it sounds deep!! By deep I mean bottom end. Not like a lifter tap. The strange thing for me is that it goes away after it has warmed up. Seems almost like the oil send unit or something may be getting slack. But that is a pure guess. I'm not very experienced with this motor but it's a very distinct sound that I have never heard before. Motor pulls extremely strong and runs solid. After it has warmed up its nice and quiet. Here is a small clip hopefully you can hear it. Trying to find some input on where to look to resolve this issue. I need to do the dreaded valve stem seals sometime this year and would like to fix this issue in parallel.

[itscoo2pyopants]

i have a similiar noise that goes away after it warms up. im at 120k miles. no other symptoms. curious as to what you find out.

how many miles do you have?

[David.X5]

I'm a m62 guy, but it sounds more like vanos startup rattle than rod knock.

The oil pump has a check valve I that keeps oil in the upper parts of the engine. If that stuck open, the oil would drain back and you might get more noises at startup until oil is distributed everywhere.

[upallnight]

Bottom ends knock are normally Rod knocks. You can isolate which cylinder has a rod knock by unplugging the cable to the spark plug coil. If the knock stops when the power to that cylinder is killed you just found the cylinder with the rod knock.

[BimmerE38E53]

Originally Posted by itscoo2pyopants

i have a similiar noise that goes away after it warms up. im at 120k miles. no other symptoms. curious as to what you find out.

how many miles do you have?

128k :/ I'm hoping it's not a rod.

[BimmerE38E53]

Originally Posted by David.X5

I'm a m62 guy, but it sounds more like vanos startup rattle than rod knock.

The oil pump has a check valve I that keeps oil in the upper parts of the engine. If that stuck open, the oil would drain back and you might get more noises at startup until oil is distributed everywhere.

I hoping that this is the case. I had one random startup that said turn engine off no oil pressure!!! Scared the hell outta me but after the noise and then that message I was hoping something like a check valve or just the oil pump itself was going and not a rod!!!

[BimmerE38E53]

Originally Posted by upallnight

Bottom ends knock are normally Rod knocks. You can isolate which cylinder has a rod knock by unplugging the cable to the spark plug coil. If the knock stops when the power to that cylinder is killed you just found the cylinder with the rod knock.

Yea unfortunately it does sound like a rod but I'm still hoping for it to turn out to be the lesser of all the evils!!!! Thanks for the input!!! I'll try unplugging the coils on a cold startup and see!!! Wouldn't rod knocks be constant? I have never known of a rod knock to ever go away. Maybe get quiet but never gone. Once mine is warm it's completely normal. This noise only lasts for maybe 5 minutes on cold starts.

[X53Jay4.8is]

Originally Posted by BimmerE38E53

Yea unfortunately it does sound like a rod but I'm still hoping for it to turn out to be the lesser of all the evils!!!! Thanks for the input!!! I'll try unplugging the coils on a cold startup and see!!! Wouldn't rod knocks be constant? I have never known of a rod knock to ever go away. Maybe get quiet but never gone. Once mine is warm it's completely normal. This noise only lasts for maybe 5 minutes on cold starts.

I would be very surprised if its a rod knock. Rod knocks as you have eluded to typically are there all the time and even at at higher RPM. You have much lesser problem I would imagine and since your noise goes away after 5 minutes.

[upallnight]

Originally Posted by BimmerE38E53

Hi All,

So when I bought my X5 it was not apparent to me that there was a knock on startup. It's still fairly faint but it sounds deep!! By deep I mean bottom end. Not like a lifter tap. The strange thing for me is that it goes away after it has warmed up. Seems almost like the oil send unit or something may be getting slack. But that is a pure guess. I'm not very experienced with this motor but it's a very distinct sound that I have never heard before. Motor pulls extremely strong and runs solid. After it has warmed up its nice and quiet. Here is a small clip hopefully you can hear it. Trying to find some input on where to look to resolve this issue. I need to do the dreaded valve stem seals sometime this year and would like to fix this issue in parallel.

Shady car dealers will use a thicker oil to disguise a rod knock, but as the oil is diluted with gasoline the oil will thin out and the knock will return.