2.7L cold start rattle?

Ok so I’ve read a ton of people saying that they can’t figure this “rattle” out and recently I just started having this issue on my 01 Tacoma 2.7L 282,873 miles and what I found upon inspection is my exhaust manifold is cracked on two cylinders, front and 3rd from front. It’s not a real obvious crack, but it’s between the tube and mounting flange. I have not had a chance to get it fixed yet and will post an update when I do. I just wanted to post this because I’ve seen so many people having this problem without having any posts with what the problem is. Hope this helps some people! Cheers to busted knuckles and cold beer

 

My engine did do this but stopped knocking on start up when I used 10w30 because they were out of 5w30 when I was changing the oil. It had knocked for years before on start up. I haven't heard it knock in about 2 years using 10w30 pennzoil platinum. I could just be going deaf and Georgia hasn't had a very cold winter this year but jo knocking.
Also I worked at a place that had 2.7 tacomas all with less than 30-40k miles and I know several of them knocked on startup when it was cold outside so I'd say it's normal.

 

sounds like piston slap. In Vermont when it was in the negatives all the way up to the 30’s temp wise, it did that until it warmed up. Soobies are notorious for that as well, and I know of MANY that still knock when cold with over 200k. I’m pretty confident it’s not as bad for the engine as it sounds. Metal just shrinks when it’s cold. I’ve since moved from Vermont and doesn’t really do it much here in Virginia, unless it gets into the 30’s.

 

You're knock/rattle was piston slap. Mine had it at 119,000 and I fixed it the same way you did. I use 10-30 also. Rattling on start-up for a few seconds is almost always piston slap. 10's of thousands of new car from all brands have had it since the 90's. Thank the EPA. Hypertutectic pistons are the culprit. A few years ago I posted many posts on the subject here on this forum as to why they rattle. Believe it or not, it really doesn't hurt anything, so they say" but I solved the problem anyway.
No, I'm not a mechanic or technician. Just an information junkie.

 

I never understood how hypereutectic pistons cause piston slap. I have read that these pistons have higher silicon content which causes them to expand less at temperature, and this allows for tighter assembly tolerances between the piston and cylinder. So tighter tolerances should reduce piston slap, right? Is it possible that some manufacturers are using these pistons but not tightening up the tolerances allowed by these pistons?

 

The reason they slap is because the tolerances aren't right. They have to expand to seal the cylinder properly which is why the rattle only lasts a few seconds. They heat up pretty fast. Sometimes they get them right and sometimes they get them wrong. They have very short skirts for less drag and better MPG. The short skirts make them rock in the bore until they heat up. Look at all the new engines from the 90's on up and compare the piston skirts. Older engines from the 80's and back have far longer skirts than anything made since the 90's. It's been a huge problem since the 90's. Thank the EPA.

 

I was doing some reading on it my self since I only knew about cast/forged engine. I dont think the hypertutectic pistons are necessarily at fault. From what I've read about them they seem to be great material to use, especially for us naturally aspirated guys. Seems like toyota just didn't get the tolerances right or their design of the piston shape isn't optimal for longevity. But I dont think the material it self should be blamed, they have a lot of advantages and the disadvantages isn't really a big deal for us since we're not boosted from factory nor was it really intended to be.

 

Mine started early on around 30k, it still does it at 130k. It sounds like a little diesel in the morning cranking away. Just let it warm up and be nice to it. It did it when I lived in California during cold mornings and does it every morning during the winter in Alaska. I use 0W during the winter and 90+ octane, it doesn't matter.

 

I bought my regular cab 4wd with 100,000 on it in 2018 and it started this noise not long after I got it. I've cut the oil filter open multiple times and no metal so makes me feel better. Mine has gotten to where it does if if the sits all night in 50 degree weather or below. I've put 93 and sea foam in the has and it helped alot but was still there.

 

I have a 2003 base model Tacoma w/ the 2.4L 2Rz engine, 172k miles. Hard to tell from the video if the sound is the same, but mine also makes a rattle or clatter for maybe 30 seconds on cold startup. Seems like it's a Toyota thing, not limited to one engine.

 

I have an '04 3RZ with 276 on the clock.. just noticed this started happening over last winter. Only knocks for 3 seconds max on cold startup.. exactly like OP @kim414may.

I run 5w30 synthetic every 3500-4K miles. Don't see any loss in power, no oil burning, and just had the oil pressure switch changed out.. they hooked a gauge up to the block to make sure it was holding pressure and it did... So that hopefully rules out the main crank bearings going out (HOPEFULLY). I did change out the plugs and coils which didn't do anything (tried iridium first then switched back to stock copper)

What I can say is that I hear a very similar light rhythmic "knock" when driving under light load.. like let it hang in 3rd gear at 3K RPM and barely using any pressure on the gas pedal maintaining pace.. When accelerating or letting off to engine brake the noise is completely gone. I've tried taking recordings of the noise but it's drowned out by the background noise in the cab. Obv I'm not riding around at 3K on an almost 300K motor, but every now and then when making moves in rush hour traffic you gotta let the gears hang to get to where you wanna be.

My cat's been bad for a couple years.. so it could be that. I'm way overdue for a valve lash adjustment (doing that this weekend). I plan on peeking with a flashlight behind the timing cover to see if the guides are worn while I have the valve cover off. Who knows, maybe I have a crack in the exhaust manifold that's hiding under the heat shield. There is valve tick when accelerating under load, but it's been doing that since I had the headgasket done about 100K ago, when they supposedly adjusted the valves "as needed".. pretty sure the shop didn't do anything.

Will keep you all posted after the valve adjustment this weekend.. We will get to the bottom of this once and for all!