Blown head gasket?

If you open coolant reservoir and you hear air sucking in, that generally means the bad Gen3 design that causes failed headgaskets is upon you. However if it's not to severe and you're only driving around town some people can go years without having to replace the headgasket. But make sure you don't push it too far because if it starts running rough too much you may end up having to replace the dampener in the transmission: WTB - gen 3 damper / clutch | PriusChat

 

i think it is, how many miles on her?

 

yes, to a degree this sounds like a head gasket problem but there should also be some engine codes. I guess there are other things it can be as well.

I diagnosed the head gasket problem on my 2013 in the last few weeks.
first got p301
then it went away!
but it came back

- the center electrode of spark plug 1 was very clean, while the other 3 looked kind of normal. it was getting kind of steam-cleaned!
- coolant level was 3-4 inches low
- I used a test kit from Harbor Freight + my hand vacuum pump that would be used for brake bleeding and other tests.. to do a chemical test for combustion gasses in the coolant bottle. this was positive for a bad head gasket.

I am in the middle of the job now. there was a small ~1.5mm wide path from a coolant passage into cylinder 1.


so, you should also look through the forum to see if there are other conditions that cause poor running.
clogged EGR? bad MAF? etc. I am not super familiar with the symptom other than for a bad head gasket causing misfires due to the coolant getting into the cylinder.

 

90% + probability it is a blown head gasket. You can confirm with a block test or leakdown test. If the engine coolant is dingy brown and the inverter coolant is nice and pink I'd say 99% chance your head gasket is blown.

If you're a DIYer there are videos on youtube and write-ups here. Clean your intake & egr while in there... I was living in an apartment when mine blew so I had Maxat Hybrid in West Sacramento replace it and they did a good job. If you search "prius" on Sacramento Craigslist, you'll also see a bunch of ads from mobile mechanics that specialize in prius head gaskets (though I've never used one).

If you've got under 250,000 miles and aren't having to add oil between oil changes, I'd plan on replacing the head gasket since you stopped driving it and likely have not caused further damage. These engines will go 350,000+ miles when cared for...

I would not install a used engine unless you're super short on cash and were DIYing it (in which case I'd at least replace the head gasket on it). Unfortunately, many people used 10,000 mile oil changes and have clogged up their oil rings so you're gambling when you buy used.

If you're planning on replacing your engine, a brand new short block (block, rods, pistons, rings, crankshaft) costs $1800 from discount Toyota dealers (like Maita if you purchase online). Throw a rebuilt head on that and you'll have an engine that'll go hundreds of thousands of miles.

 

When you had your number two spark plug out all you had to do was stick it up to your nose and look at it with a magnifying glass do you smell coolant on the plug do you see little wet droplets they'll be microscopic hence the need for a glass. I'm so crazy I smell it and then I stick my tongue on the tip of the dirty plug and taste the antifreeze because I know what it tastes like and I go oh holy crap here we go. No need to stop driving it now The damage is probably pretty well done once you start having the stutters and what have you next is something letting go and a whole in the center or the lower oil pan or the girdle whatever you want to call it. Have pictures been there done that yeah. If you're stopping to drive the car in the hopes that you're going to fix this get ready to spend about 5 grand that's about 3,000 more dollars than a low mileage takeout from another country like Japan where the cars built. If you're going to go that way and be hard and keep it all in the States and I get a bunch of machine work done and all kinds of this and that probably find out it's not going to last very long generally speaking open deck design engines do not deserve your cash and machine shop hours and mechanic labor time it's basically a throwaway look at the Camry engines see Camry sitting around look like brand new all of them are engines are blown up.

 

98% its a head gasket and its been bad for awhile. Those occasional early morning rough starts that cleared in 3 seconds were the start of it. The gasket in the early stages seals off quickly, the fouled plug clears and it may run for weeks before it happens again. By the time you lose a lot of coolant and it is rattling at stop lights your whole engine is at risk. Hydrolock now is a possibility, broken rods and holes in the block happens.

Get it fixed now. A quality borescope is often definitive in the early stages.

 

The EGR and head gasket links in my signature may help. I wouldn't concentrate on the EGR if the head gasket has failed: address the HG first, and then the EGR.

Resist the siren call of Head Gasket sealer treatments, it's snake-oil that makes a mess of your coolant system.

Videos of interest: