I had family mechanic replace the timing belt about 12 months ago, plus new accessory belts. Tensioner was as a bit rattly on cold starts for the first few days, but soon settled down okay.

In the last three months, it has intermittently had a loud rattle on cold starts in the morning. Sometimes nothing, sometimes quite loud for 5-8 seconds. I tried the stop, wait 10 seconds, restart thing - but it didn't seem a definitive improvement 100% of the time - and as often as not it didn't rattle anyway.

I checked the accessory belt tensions, thinking the new belts might have settled in and needed retensioning - but they were perfect. Had pretty much resigned myself to taking it in for a tensioner replacement with genuine and booked it in.

Before I took it in, I thought I'd replace the oil as it was due, and noticed family mechanic had used a Ryco filter last oil change (as he has done in the past). I always use a genuine filter and genuine parts, because I can't be bothered stuffing around with rubbish to save a few bucks. The oil was down a little, but not excessively.

So replaced the oil and used a genuine filter.

Every start since then - absolute silence on cold starts. Rattle is completely gone.

I can only assume the anti-drain back valve on the Ryco was insufficient (perhaps it's a multi fit filter), or the valve had failed completely. My oil was draining out of the top of the engine overnight, and rattling on startup because it was starved of oil until it was pumped up there.

If you have the cold start rattle, might be worth to consider replacing your oil filter with a genuine unit.

I never had a problem with Ryco oil filters for 10 years (4x a year) on my Camry, but my mechanic won't be using one again on my Mitsubishis. Almost dumped $400+ on a perfectly good tensioner.

Interesting. My mechanic uses some brand I've never heard of. So, from now on, I'll be buying genuine for him to fit. Thanks for the heads-up.

Interesting - I have a rattle just like that and It's not the tensioner - and I always use ryco - will get a genuine one and see what happens.

Uhhhh, I might be wrong, and please correct me if I am, but the oil draining out of the filter overnight wouldn't be an issue, because the oil filters screw on vertically, don't they? So oil can't drain out, even if the anti-drain back valve was faulty..??

As for the oil draining out of the top of the engine, isn't that going to happen regardless?

The only thing that I can think of that might cause the rattle at cold start up is the oil being too thick to get pumped there fast enough, but that's just my two cents worth

Reason for my thoughts is my use of Gulf Western 25w-50 previously in my KH, (cringe) the noise from the top of the motor on cold start ups, especially when left outside in the cold overnight was pretty awful, I imagine only because of the oil, despite being pumped up there eventually (oil light would sometimes take a second or two) the oil was still too thick to actually get in amongst the bits and bobs in the top of the engine that it needed too.. Needless to say a little warm-up was always required

Last service I bit the bullet and made the switch to Penrite HPR-10 Full Synthetic, and so far it seems to have made the engine a whole lot happier when its cold

It's not the oil draining "out" of the filter, it's the filter allowing oil to flow backwards through the filter and drain out of the head because of gravity when the car is at rest.

It was not caused by thick oil, it had 5w-30 full synth.

After months of cold start rattle, I changed the filter - and it has not happened in two weeks. I have no doubt the filter was responsible.