2011 engine rattles HARD on startup after sitting a couple of days

Likely it is a problem. This is the major symptom of your head gasket leaking coolant into the cylinder ...a known problem on the 2010 through at least the 2014 Prius. it causes this rattle until the coolant is expelled from the cylinder a few moments later. It will likely get worse over time until you must replace the head gasket.

 

Probably the head gasket.

You did "EGR service several years ago": this was DIY? Did the intake manifold with it's EGR passages get cleaned as well? Can you recall the miles on the odometer?

To check head gasket, on the day after car's been driven, pressurize the engine coolant system (remove reservoir cap and install stopper of some sort and apply sustained air pressure), remove wipers/cowl and spark plugs*, and run borescope into combustion chambers, looking for exceptionally clean piston top(s), coolant weeping from head gasket seam.

diy coolant pressurizing gizmo:



* See video #13 here: Nutz About Bolts Prius Maintenance Videos | PriusChat

 

Sorry for the bad news but yeah, that's a primary symptom of head gasket failure.

The best test to confirm this is to remove the sparkplugs and use a video borescope to inspect the inside of the cylinders while the cooling system is pressurized with a test pump.

Good luck!

 

The next big problem will be replacing th hv battery. Nimh battery typically good for 10 years so I’ll
Let you do the math for 2011. And then brake booster replacemen if the brake fluid had never been changed.

Because saving gas cost a lot of money.

 

The real economic benefits of hybrid ownership go to those who buy new and unload it before its 15th birthday.

If the car is already burning oil, I'd go for the engine replacement... but honestly I think replacing the whole car is an even better move.

Sorry & good luck!

 

Just curious, which video?

 

Do you mean will a head gasket replacement prevent the EGR cooler from clogging up with carbon?

My hunch: it’s the carbon-clogged EGR system that’s causing the head gasket failures.

your head gasket has developed a path, or paths, allowing coolant to make it into the combustion chambers. Likely started at the wall between cylinders one and two, on the exhaust side. Leaving it thus is starting the cascade of subsequent failures.

 

A post-2014 engine should do better with all oil-control issues- they changed the rings. That's all 4th generation engines and the last of the 3rd.

There's no precise timeline for how long an engine with a leaky gasket lasts. Most of it comes down to how well you keep up with the coolant loss, which itself is variable. If you are very diligent about it, you can probably stretch it out quite a ways. Generally speaking, the coolant gets too low, engine overheats, burns a rod bearing and blows a hole through the block.

Some drivers have stayed ahead of it for many months.

Personally I'm not convinced that EGR clogging is doing that much to cause gasket failure. It's an interesting theory, but there's just no data.

Uneven heat distribution and thermal cycling has been popping head gaskets for 100+ years, so that's my own bet.

 

Neither gen “blows oil into the EGR cooler”. The cylinders are called combustion chambers for a reason: they incinerate anything combustible, hydrocarbons, oxygen.

the EGR system will clog with dry, powdery carbon, because that’s the nature of pre-catalytic exhaust, regardless of engine burning oil or not. Because Toyota (obviously in hindsight) designed a flawed system and compounded the error by neglecting to test it sufficiently.

Putting in a fourth gen salvage engine will not resolve the EGR system shortcomings, and will add compatibility issues. A common issue post-transplant is overheating.

where you’re at I would just replace the head gasket, using the Toyota gasket kit (includes head gasket and everything else pliable that you’ll encounter in the process. And use new head bolts. Those two parts are about $300~400 USD.

I can’t recall, did you mention moderate oil consumption as well? If it’s getting out of hand, replacement pistons/rings, the revised ones, is another $200~300 USD for the parts. If the cylinder walls are scored/scuffed, a new short block is around $2k USD.

Machine shop “may” be worthwhile, if any of the machined mating surfaces are distorted enough to be out of spec, specifically at head-to-block and head-to-exhaust. You need a machinist’s straight edge and feeler gauges for that. It’s also good to spray some sort of solvent on the underside of upside down head, see if it leaks through. Last link in my signature has all the specs for mating surfaces. (On a phone turn it landscape to see signatures)

 

What’s the oil consumption? I recall someone mentioning 2 quarts every 5k miles, but not sure if it was you. 2011 for sure will have the low-friction piston rings, prone to developing oil consumption issues. 10k oil changes don’t help either.

elephant in the room with a lot of this, the deadbeat company that built these cars, leaving owners to pick up the pieces when their mpg experiments implode.

you have to weigh and decide the viability of repairs. It’s especially tough if you’re paying someone market labour. Consider DIY’ing at least part will help.

 

Really I hate to be the rain on your parade, but I say no. Personally, I think a Prius is a phenomenally reliable vehicle for roughly the first 15 years of its life, and sometimes you can carry them out to year 20- your chances are best when you started from new and aged it yourself.

But I think yours has passed through that golden window and is now nosing down into money-pit mode.

I would not sink more money into that car. Top up the coolant and stretch it for a while, but put the money towards the replacement car.