2000 Tundra Limited V8 - loud noise after shutoff - HELP

Hey guys,

My 2000 Tundra is making a loud knocking sound after I turn it off. Here is a video so you can hear it. It happens a few minutes after being shut off. It used to be 20ish minutes after turning it off, but it has gotten sooner and sooner. Now it is about 5 minutes after turning it off.

I already know there is some issue that needs to be addressed. It struggles to start sometimes, and sometimes it completely dies after a few seconds of running. The mechanic said he thinks that issue might be the fuel-pump, but he needs to hold it for a few days to see if he can catch the problem when it happens (it's inconsistent).

Anyway - the Tundra is my only vehicle, and I need to know if this knocking sound is an emergency or not. Like, do I need to stop driving it and take it to the mechanic today, or can it wait until later next week (Wednesday)? Either way, I know I need to take it to the mechanic, but I'm just wondering if I need to rush or not.

 

sounds like some sort of venting to me? Like gas pressure venting from the system or something.

There are many here with lots of experience with first gens, so someone will chime in

 

That's an interesting one. Don't think I've ever heard this one before.

 

You know it's extremely rare if shifty hasn't heard of it.

 

With how many different cars I've owned, across most of the modern post-50s manufacturers, it's crazy to me I've never encountered it with any of them. More than half of my vehicles were shitboxes someone else was tired of dealing with, and I got them for a great price as a result

I've heard stories of vehicles continuing to knock after shutoff. Normally older European cars though, all diesel.

I'm curious if there's any other information @Beeb can provide here. Was it ever overheated? Any recent noteworthy activity to share?

 

A couple minutes after shut off gives you enough time to get the hood popped, maybe after hearing it a couple times you can start to pinpoint where its coming from.

 

It almost sounds like a toaster oven ejecting, *CLANK*. Maybe OP had someone install a toaster in the engine bay?

The one thing that inevitably continues to "do stuff" after shutting off an engine is cooling. You can't stop a vehicle from cooling itself, and when cooling happens, things contract, both metal parts, and liquids.

It'd be interesting to know if the coolant reservoir is up to its standard fill line at cold and hot.
It'd be interesting to watch for a surge in the reservoir while the clanks are happening.
It'd be interesting to know if/when the coolant was most recently topped off, and if/when the thermostat was last replaced.
It'd be interesting to know what color coolant is used in the truck, it should be red/pink, but if someone installed something else, that's bad news.

If the thermostat was somehow loose (i.e. damaged guts or jiggle valve clocked incorrectly at install) and/or there were bubbles in the cooling system (i.e. air entry from a recent fill) I could see either one causing weird noises. I suppose if the truck overheated and the head gasket was cracked, maybe it's periodically farting steam bubbles? But OP would see smoke on startup, I'd think, or foamy oil.

Good time to check dipsticks and fluids.

I suppose check master cylinder too, all fluids for that matter.