06 Z4 3.0i knocking when engine is cold? No warning lights.

[Johnny87]

Quick question. It's my first BMW and everything with it is fine, drives great, No warning lights on the dash and everything is fine. I'm Chicago and right now it's really cold and when I start the car, The engine makes a knocking sound. It usually goes away when the car is warm and on the few warm days we had that were warm, I didn't hear the knocking when I started it up. I'm guessing its fine since it only knocks when its cold and I have no warning lights. I just need reassurance from maybe another Z4 owner, or someone with BMW experience to tell me Is this normal or should I have it check out? Was thinking of buying myself a diagnostic tool cause it cost as much as the BMW dealer charges for there diagnostic.

[JBasham]

So, you might run across more people that know about this issue in the E90 forums, or maybe even the original X3 forums.

Here's my 2 cents. I have used that 3.0l motor in 3 different cars, for over ten years now. It has a reputation for making ticking noises on start-up from the hydraulic valve lifters. It can be pretty random. The "cause" loosely put is an oil pressure issue in the head. It takes a certain amount of oil pressure to get the lifters pumped all the way up to full length. If there's not enough pressure, the lifter is a tad short, so there is a little space left between the rockers and the valves (etc) that makes sort of a tapping noise. Once things get going in the motor and warm the oil a tad, the lifters pump up, and the noise goes away.

Hydraulic lifters are kind of like a stiff spring in the valvetrain that's designed to keep the rocker arms adjusted snugly against the valve stem, without the need for periodic manual adjustment of each rocker arm. So by their nature they need to expand and contract a little, and the oil pressure making its way in and out of the lifter valves is the mechanism that makes it all happen.

I ignore it when I hear it on startup of the BMW N52 engine, as long as it goes away after a few minutes. Bad valvetrain noise in a motor can be a sign of trouble, since it means my valves are getting mildly hammered by the valvetrain, with excess wear on valve guides, springs, valve tips, and valve seats. In some engines I would feel the urge to dig into it right away. But a little ticking from a car with hydraulic lifters on cold start up? Doesn't really bother me.

One other point of automotive religion with me is taking it easy on start-up. I don't ask much of the motor or push it over 3K rpm for a bit while I let the oil get a little warm. With modern multi-grade oils things are better than they used to be on this front. But they keep building motors with tighter and tighter tolerances too, so it's harder for cool oil to get to the friction surfaces. But doing it this way is almost a matter of superstition, potentially. Once I get a motor good and warm, I rev the snot out of it, and I'm not afraid to hit RMPs that would make most daily drivers freak out. The motors hold up fine as long as I keep the oil reasonably clean and the engine temps under control. They aren't made of glass!

[Johnny87]

Thank you so much for your input, I do appreciate it. I'm not a mechanic, but I do basic work on my car and I was thinking the same thing about the oil and lifters etc. I'm just not educated enough about engines to really know for sure what it was. I had a mechanic that lives on my block ( alley mechanic so I took it with a grain of salt ) and he reassured me that it was normal, but to get a diagnostic anyways. But what you said makes sense. I can sleep a lot easier tonight, thank you.

[JBasham]

Wow, glad I could help. Nice car, BTW. Wish I had one.