All Mounts Replacement

I think you're going to find that mount replacement is going to be futile and not going to gain you much I can't see the mounts in a Prius really ever wearing out per se there's not enough engine nice person if you will or power to rip mounts off and we can these modern type mounts more than likely your engine's about to blow up just to be simple about it so your engine wobbling around in your engine compartment in this type of setup is almost guaranteed not to be mounts unless somebody's changed an engine before done something like that and literally tried to lift the engine off the mounts with them not unbolted and even then that's a stretch Good luck.

 

Is the engine coolant level stable in the reservoir? How about cold-starts, any knock/shake?

 

Maybe somebody worked on the car and has left something loose. The mount bolts and all that most of them are very easy to see so shouldn't be a problem You should be able to have somebody sit in the car and accelerators move the car with the hood up just a few feet you should be able to see it pretty smartly You might could duplicate some of it with a pry bar personally I've never seen a Prius with bad mounts where the engine was able to rock around like it did in the front end drive car with a dog bone. So it's hard to really imagine other than something being seriously out of balance and then you would have the clanking of the plate that's in between the engine and the transmission it's kind of like a flywheel but it's not I think it's a torque plate so it'll be interesting to see what this turns out to be.

 

Often we hear people thinking their motor mounts are bad when it was actually a leaky head gasket causing misfires. In a gen3 Prius this will severely shake the engine combined with a metallic rattling. Watch the coolant; if it drops again its head gasket or rebuilt engine time.

 

Yeah this.

If it’s the head gasket, follow up with a full EGR cleaning.

see first 2 links in my signature. On a phone you’ll need to hold it landscape orientation to see the signatures.

 

Two tests are commonly used:

A leak-down test will pressurize the cylinders, one at a time, at Top Dead Centre on the compression stroke, with a special gauge set. How well it holds pressure, and where it leaks, determine head gasket integrity.

Boroscope inspection of the cylinders, with the coolant system pressurized. If a particular cylinder looks much cleaner, that’s evidence coolant is leaking past the head gasket. There may also be tears of coolant evident.

 

1. Lose more coolant with continuing symptoms is definitive. #1 with a bullet.

2. A quality borescope with multiple views operated by an experienced operator can be definitive when a cleaner piston top (steam cleaned) is observed. It won't be easy with a cheap borescope and the piston won't look new, just cleaner than others.

3. Sometimes a pressurized coolant system with a borescope may detect the coolant drops when observing the head gasket. This is much harder but has been done. Its a test where false negatives are common.

4. Leakdown tests and coolant gas detectors almost always give false negatives unless the hg leak is massive. Massive is not typical on a Prius. Coolant in the oil is not typical. Both are old school conventional engine techniques.

Be aware flippers sometimes use short term sealers to mask the problem. When this has been done it can take weeks to months for the sealer to wearoff before pre-existing hg leaks reappear.

 

^ This. Buying a 2010 with 200K miles, there's a good likelyhood this was done. A 3rd gen with neglected EGR and those miles is almost guaranteed to have a blown head gasket.

Ever read about freeway pileups, the kind that never end, fresh cars keep plowing in? That's us...

 

You could baste/siphon out a bit of the coolant in the engine reservoir, look for goop.

 

I had the same issue, thinking it was motor mounts. It turns out it was clogged EGR passages on the intake manifold. Pretty easy job with the right tools and at that mileage it needs to be cleaned anyways so it's worth a try. I wouldn't rule out spark plugs either, the original ones will last forever but counterfeits are not uncommon and can last as little as 15k from my experience.