Repair or engine swap

I would drive til it won't then swap with lower mileage motor

 

The dealership will think you should make them rich, that's what they'll think.

I think I'm with tankyuong, when the time comes it can be replaced with a lower-mileage one, whether from Japan or from a US wreck, but just using some oil and occasionally making the start-up noise doesn't necessarily mean the time has come yet.

Some members will reply on any thread about the start-up noise by saying the head gasket must be blown (and will often say further that it must be because of the EGR), but my 2001 made that same startup noise occasionally for its last few years. I never found out what it was, but there wasn't any head gasket leakage happening, and a 2001 has no EGR.

If you wanted to do a leakdown test and/or check the condition of the EGR circuit, nobody would call you crazy. It might give you some idea how soon the time might come, or reassure you that it's not right around the corner.

 

If I may...?

How’s the engine coolant level in the reservoir? Stable?

 

Time to pull this out again:

Mr. 2010-14 Prius
Knock Knock Who's There?

Stage 1
Spark Plug and Coil Change
Clean EGR
Monitor Coolant
Try Head Gasket Sealant

Stage 2
Order a Motor from Japan
Arrange Killer Install Deal

Stage 3
Question Motor from Japan

Stage 4
Decide to Change the Head Gasket

Stage 5
Reconsider Motor if yours might have a Bent Rod

 

Put a strip of masking tape vertically, mark current level (cold) with a sharpie, and keep an eye on it. Sounds ok, but good to verify.

 

Whatever causes it (and various things can), it makes a very unnerving loud clatter; speed variations of the misfiring engine get compounded by drive train clatter in the gearbox, as described on page 4 of this article.

Anything that might cause a startup misfire can cause it. The article above is interesting because it gives a good example of a methodical diagnosis, and in that case it all came down to one bad spark plug. But the sound was so awful the owner had already let the car go for scrap price before that could be diagnosed.

The TSB linked in #6 above has more to do with cases where Toyota apparently thought the cause was condensed water in the EGR passages being slurped into the cylinders right upon starting. Water does condense in those passages; I've never been quite sure how it gets slurped on startup, given the EGR valve should be closed then, but perhaps if it is fouled and not completely closing, enough airflow through the pipe can be developed to carry the water out. Toyota released a redesigned manifold with the EGR passages routed differently, but it didn't turn out to be a silver bullet.

Naturally, EGR as a cause is only possible for Prii that have EGR (2010 and later). Other causes (like the spark plug in the article) are possible in any Prius generation. As I mentioned earlier, I never did find the cause in my old 2001.

And yes, a faulty head gasket can cause misfiring, so it is also a candidate for the cause.

 

Normally a plug or coil that is the root cause of the misfire won't clear up so nicely after a few seconds. Plenty of head gaskets start out using minimal antifreeze. A dealer will normally recommend changing the engine for $5k up. Some report changing engines for $2k-$4k using independents, head gaskets alone from $1k-$3k. Obviously losing antifreeze and white smoke are late stage head gaskets symptoms.

 

You’ll see P03XX for misfire, with XX being 01 through 04, corresponding with cylinder numbers. Standing in front of engine compartment, cylinder 1 is at left end, aka the “front” end of engine.

 

An intermittent misfire won't always throw a code, especially if it clears quickly and the engine runs good for the rest of that trip. If it was a traditional plug or coil fail then a code would be expected. Many have been where you are and have found completely blocked egr coolers, a bad design on gen3s as are the pistons and piston rings, at least from 2010-14. The egr system was redesigned in gen4 engines and better piston rings were in place by 2015.

There is quite a debate on the root cause of head gasket failures with these engines including theories like blocked egrs, oil burning, high speed driving, thermal cycling during the drive cycle, oil pooling in the intake, head gasket materials, head gasket geometry, pinging caused by carbon buildup and most recently, a dealer mechanic who thinks it is chronic overfilling of the oil. Usually its high mileage engines that are arguably worn out anyway. Some buy time with head gasket sealants.

Getting an accurate diagnosis should be the first order of business.

 

+1

Definately don't assume it's a blown head gasket. My '13 had an intermittent knock on cold start -- mostly upon first start in the morning with cold winter ambient temperatures, but not every morning. It started around 100K miles. I now have almost 180K miles. I've installed an oil catch can, and cleaned the the EGR twice -- once at 115K and once at 172K -- both times the cooler and intake manifold passages were completely plugged allowing 0% flow. I can't say definatively that either of these maintenance items directly solved the knocking problem because both times the EGR service was done in the spring, when the knocking had already ceased due to seasonal weather change.

But this winter the knocking has not returned at all -- not once. My assessment is that there's no way the head gasket was leaking at 100K, and now at 180K it's miraculously fixed itself.

I guess that's just a long way of saying, we all know the knocking comes from a misfire. And while a leaking head gasket certainly can cause a misfire, not all misfires are caused by a leaking head gasket.

 

THIS.

 

A leak-down test will help.

 

Another head gasket data point, dealer mechanic's livestream from a couple of days ago acknowledges the rate of gen3 head gasket failures is "alarming" and they don't know why. Realize most dealers recommend replacing the engine which effectively junks these cars.

The question being answered asked if Toyota changed something in 2012 and the mechanic ran with that, but we know the rings and pistons changed by 2015.

Interestingly, the mechanic says the engine parts are rarely warped, suggesting overheating is not the prime suspect.

 

Interesting!