'14 v, 216K, engine rattle upon startup

I've been cruising the threads and may have zeroed in on the cause of this, but I'd prefer to run my specific situation by everyone and see what they say.

This car has been awesome. I'm at just under 216,000 miles and haven't had to do anything to it except the recommended maintenance, tires, brakes, and a rear license plate light.

For the last 25,000 miles or so, the engine (ICE) has been rattling occasionally upon startup. I first noticed it happening after I'd been cruising on battery power for a while and the battery gauge had gotten down to two bars. It has always been an intermittent thing and I discovered that it would stop if I pushed the accelerator in harder to make the ICE work harder.

These days, sometimes it happens upon startup at rest, and it doesn't seem to matter how charged the traction battery is. I'd say that it happens more commonly after the car has been sitting for a bit, but not so much after it's been sitting overnight. It'll last for several seconds when it happens, and it feels like the ICE is going to shake itself loose from its mounts. I was able to pop the hood one time recently before it stopped, and I saw the ICE wobbling from front to back, and it seemed that the accompanying sound was coming mostly from the right side.

I am low on coolant; the overflow tank is almost empty. Sometimes I have been smelling coolant after turning off the engine and getting out around the car, but I've never seen dribbles. The "check engine" light has never come on.

I've had it since new, did dealership servicing for the first 25,000 miles with Toyota Care, then switched to mostly local-mechanic servicing except for the big one at around 110,000 miles. I know I knocked out two major servicings at once right there - I know that one was for 120,000 miles and the other was for either 100,000 or 110,000. Since 196,000, each servicing has been at the dealership because my local shop went out of business and I haven't chosen another local shop... plus the dealership does free oil changes for any Toyota or Lexus at 200,000 miles or more, so I can't argue with that. I mentioned the engine rattling issue at 196,000 miles and they said nothing about it.

Recently I've also noticed that when the ICE kicks on, sometimes I can hear a liquid sloshing sound, almost like when a window-unit air conditioner kicks on. This happens with or without the car A/C being engaged, and seems unrelated to the rattling because the ICE doesn't rattle at these times.

I guess the car doesn't owe me anything with this mileage, but everything else including the traction battery seems to be working well, and with just having put new tires on it maybe 20,000 miles ago, I'd rather not get rid of it. Do y'all think it's the head gasket? If yes, what would it likely set me back to get this done at the dealership? I'm somewhat mechanically inclined, though I've never done engine work more sophisticated than changing spark plugs. Could I execute this repair myself and not be likely to screw it up?

I also read about the EGR system potentially being clogged. Would that trigger the "check engine" light? If it has to be cleaned or replaced, would it be best that I get that done while they're doing the head gasket if that's what the car needs?

 

What's so much better about the Gen 4 engine compared to the Gen 3 engine? And what mods would be required?

I put more coolant in today and it was doing fine... but it's just a matter of time before the next rattling episode. For what it's worth, I should note that before my last oil change (by now almost 9,000 miles ago), I had checked the oil and noticed what looked like microscopic sediment in the sample at the bottom of the dipstick. They didn't tell me that they noticed anything weird about my oil when I asked the mechanics at the dealership about it.

Reading through more posts about similar problems, I can say that I noticed something else that others have noticed. Today as I went to put in coolant, as I unscrewed the cap, it released air pressure sort of like a beer can does when you pop the tab. I thought nothing of it, as the engine and cooling system were both around operating temperature by that time, but it happened.

This "catastrophic engine failure" of which you speak - would it damage the engine to the point that a replaced head gasket wouldn't fix it?

 

Man... that engine has been purring like a kitten since the day I got the car. Of all things to be my very first mechanical problem with it... major engine trouble. Any other car it'd be something like an alternator or windshield washer pump.

Those pictures looked like the engine on my lawn mower looked when, for unknown reasons, something blew through the block as it was running. Now I have to ask... is there a chance that such an occurrence with this engine could send metal flying into the passenger cabin?

Also - can this happen while the engine still has coolant and has not overheated?

 

Update: It was the head gasket. I got it replaced, along with the thermostat and radiator (they must've put in a radiator of questionable quality when repairing the most recent deer collision), and I'm at 226K+ now.

 

Yes. I caught it once in time to pop the hood and watch. It was rocking back and forth significantly.