Piston rattle on cold starts - not on warm

Not a new thing but always wondered why, on cold winter mornings (In Atlanta, anything below 40) my '06 Tacoma has machine gun-like piston rattle for 5-10 seconds, then fades away. On warm summer days, no such noise at all. I'm using high mileage Castrol oil and the level is OK. Only other noise is a little knocking going up hills. I have the 4-cylendar engine.

 

What makes it one piston and not something else

 

Look up winter gas.

 

It's all the pistons. Remember when we used to put playing cards in the spokes of bicycles? Sound sort of like that for about ten seconds, then fades away but it's almost painful to listen to. Never happens in the summer. Might try an oil pan heater I have. It's just a brown, 4-inch square heating pad and I put it on top of a short section of stove pipe and slide it under the oil pan. I've noticed that if I have run the engine the night before, it's not as bad. Seems like oil isn't getting where it needs to be soon enough.

 

Does the engine have hydraulic or solid lifters? If hydraulic, the start-up noises could be dirty lifters. The feed holes get dirty and the lifters won't pump up with the oil.
Add a pint of Mystery-Oil (I know) before the next oil change and see if it quiets down. If they aren't too far gone (10-15k oil changes) the high detergents in it will usually clean them out pretty quickly. If you have solid lifters, they're always more noisy with a cold start.

I haven't had to use the Mystery-Oil fix for years: I think the credit for that goes to Synthetic oil.

 

What viscosity rating is your oil? That could possibly make a difference. Also, changing oil brands can sometimes have an affect.

 

This^

 

VVTI controller on 4 bangers typically.

Hard to find videos of the noise,

https://www.youtube.com/watch?v=FzzboZDObbs

 

OK, definitely not the lifters in that vid: VVT components. Makes sense with that flavor of noise and with a TSB documented fix.

 

Cold-weather startup noise is usually one or more of a few possibilities:

-Hydraulic lifters: usually accompanied by the engine running like crap for the duration of the noise as cold thick oil pushes into the lifters

-Timing chain slap: oil-pressure-actuated timing belt tensioner takes a few seconds to tension up as thick oil struggles to flow into it.

-VVTI or whatever your brand of variable valve timing is: cam phasers are oil-pressure-actuated. Without the oil flow they slap around a bit before stabilizing.

I’m sure there are others. But basically boils down to cold oil being thick and hard to pump. My taco hates super cold starts. Last 20-30° below zero snap we had made me really want to get a block and/or oil pan heater. Wouldn’t use it often but would give me a lotta peace of mind.

what weight oil are you running?