labguy

Over the last couple of weeks, I have started noticing a knocking sound at start up that goes away completely after about 5 seconds. Car still runs and sounds great otherwise. My wife noticed it the other day when I started the car with the door open. She said, "What's that noise? You should go on that forum and ask what that sound is!"

So, any ideas?

Anker

Mine does the same thing. I believe it is the lifters and.or chain tensioners that have to come up to pressure. It has done it since i bought it 30K miles ago and it isn't getting any worse, The rest of the time the engine is quiet and smooth. No codes.

GaryVC

This is a noise that I've also noticed. It is more pronounced when I've not used the car for several days and is most apparent on the first start of the day. As Anker stated there haven't been any codes generated and the oil level is good. The source of the noise is speculation, it could well be engine assemblies that rely on oil pressure for adjustment. I've seen a couple of posts that mention ways of bringing up oil pressure just prior to starting the engine. I've never done that before nor had a car that seemed to need it, my RX7 was quiet from the first turn of the key. It would be nice to hear from someone who has installed an oil pressure system and how it worked out.

gregjc

My CLK 350 is the same - aware of this for a few seconds upon first start after several days since previous start. All quiet and smooth at all other times and no faults. I am running Penrite 5w40 full synthetic oil. I'm wondering if a 0w40 would make a significant difference (shorter time to pressure due to lower cold viscosity) - any ideas?

labguy

I use Mobile 1 0W40 full synthetic oil. Mine does it every time I start it up. It's been doing it for the last several months.