Noisy/rattling valves after parking for a long time?

[q45inca]

hi, my 2002 Q45 with about 140k miles and regular synthetic oil changes has noisy (rattle/knocking) valves on startup after longer parking - the longer it stays (several days/few weeks), the worse the noise. After idling for a few minutes the oil pressure or whatever must get to the right level in the valve lifts/valve train and the noise disappears - the car revs smoothly.

If the car is only parked for a few days there is no noise.

What exactly could be the problem and how to fix it? Thanks

[Q451990]

My Q (and the one before it) both do the same thing. When you say idling for a "few minutes" do you really mean several minutes? Mine will quiet down after maybe 5-10 seconds. If that's how yours is acting, I suspect is just the timing chain tensioners losing pressure over time. There's not much that can be done to fix it. One trick I use if it's been sitting for a week or more, is to pull the fuse for the injectors and then turn turn the engine over with the starter for about 5-10 seconds. That at least gets some oil moving in the engine before the start. I do this before the first start after an oil change too.

[q45inca]

Thanks, I should rather have said tens of seconds. It gets longer with time, so if the car has not run in a week it could be 10 seconds. After a month could be a minute. I could live with that except that my teenage daughter started driving the car and fine points of not flooring the accelerator if valves are rattling are lost on her. If there are no quick fixes short of replacing timing chain tensioners etc I will have to live with that and try to tune her ear into it...

[EdBwoy]

I too, think it's a severe case of the normal oil-gravity relationship and things taking a little while to build pressure.

What weight of oil do you use in the engine?
Out of curiosity, did it just recently start to do this or has it always happened since the car was younger?

[q45inca]

I use Mobil 1, 10W30 synthetic. The rattling has been going on for a few years, gradually getting worse and now with extended no-use periods and kid driving it the problem is becoming worrisome. Car also blows a blue smoke on startup occasionally, but after warming up was passing California smog tests without any problems (and with huge safety margin) when I lived there

[EdBwoy]

I was going to suggest a thick-ish oil but I'd say 10w-30 is good.

And you know, reading historic posts back when the oil consumption of the VK was shocking new owners, there were murmurs about the piston rings allowing excessive oil into the combustion chamber. Maybe your clearances have worn just that much more and you're collecting more oil.

However, I see that as more of a likelihood of puffing when punching the gas while already running.
I'd say your startup smoke could be from the PCV end of the business - oil collecting in the intake and cylinders then you burn it at startup.

If you want to, you could install a catch can to prevent the oil from making it into your combustion chamber.

[Q451990]

I'm not sure that even new timing chain tensioners would fix it... Mine were replaced when the guides were replaced, and I've always had the issue. It's a nasty annoyance of owning a garage queen. I would suggest that if you know that your daughter will be driving the car, try my "pull the injector fuse" trick, then start the car and let it warm up at some point not too long before she drives it. Although I don't have a teenage daughter, I bet it can be a lot like having a wife (which I do have) - and if there's no amount of discussion that will change the inevitable startup habits - a workaround is in order

[ZiprHead]

I hate to say it but I've heard of people having problems with Mobile 1 oil in the same manner. Mostly motorcyclists. They get a lot of engine clatter on startup with Mobile 1. Apparently it runs down to to bottom of the engine too "efficiently".

[EdBwoy]

...One trick I use if it's been sitting for a week or more, is to pull the fuse for the injectors and then turn turn the engine over with the starter for about 5-10 seconds. That at least gets some oil moving in the engine before the start. I do this before the first start after an oil change too.

Mr. Q45, I've got a question for you. In most fuel injected cars I've dealt with, when you push the gas pedal to the floor during startup, the engine cuts fuel. {Programmed as a flooded engine in most cars). This in effect achieves the same goal as pulling the fuse feeding the injectors... or pulling the fuel pump fuse.
Have you tried that in your car by chance?

[Q451990]

I haven't tried that... The Q is supposed to behave that way as well, because that's the way we tell people to deal with flooding issues. I suspect you'd have a quick high rev from whatever fuel pressure builds from the fuel pump cycling on to prime the system when you first turn they key on. Could work though. I'm just too much of a chicken to test it.

[EdBwoy]

If you have the pedal to the metal before turning the key, no fuel should go to the cylinders. The pump might prime, but the injectors won't release.
But... Fair enough. Nothing beats the certainty of a pulled fuse.