Loud rattle when engine kicked on

I agree with all that, but just doubt EGR is the sole culprit in rampant head gasket failures. Otherwise, why did they revise the block significantly for the 4th generation, especially regarding thermal management?

 

If the dealership was changing plugs around it would’ve taken 30 seconds to take a borescope and Look at the tops of the pistons. I think it’s ridiculous that they did not do that! I really dislike dealerships.

 

The dealer is going to look for low hanging fruit and try to reproduce the problem before listening to anyone's diagnosis, especially conflicting internet theories. Certainly they need to do their due diligence before recommending a $7,500 or higher engine rebuild. Which is their usual strategy rather than doing an engine out head gasket repair only to find out later the rings are bad or a rod is bent.

Remember this car was purchased not long ago with 195,000 miles. Plus the op spent a big chunk of change at the dealer having all the routine services performed. The dealer may feel a sense of responsibility. I know, it seems like magical thinking.

Head gasket problems in gen3s are now becoming more mainstream knowledge and is certainly not caused by egr clogging. Egr clogging is more of a poor engine design symptom than a root cause. Many cars have systemic head gasket failures, Subaru for example. We just were not ready for an advanced technology Toyota to fall that far.

Many Toyotas years and models have excessive oil burning. This was quickly recognized in gen3s by Toyota, with some getting a free rebuild.

Head gasket fails are much more likely to be a combination of bad design elements, primarily in the stop start thermal cycling Prius 1.8L. Poor pistons, rings, combustion chamber, intake, cylinder wall thermal cycling, egr size, egr placement, pcv location, intake design allowing fluid accumulation and who knows what else. All of which were reengineered in gen4.

So far we see very few head gasket fails in 2015-2017 gen3s but they are still relatively young. They do have better piston rings.

Gen4 cylinder insulator to even out cylinder wall temps

 

Your independent has never seen it. Sort of a flat earther in a kind way.

I would suggest a rebuilt engine. If necessary order from Hybrid Pit in California for $2300 and pay someone $1,200 to install it. Require complete cleaning of the intake and egr in the install price. The installation will require many bolt on parts to be reused but a good shop could do it in a day or two. The critical head, piston and timing work will be done by experienced rebuilders before you get it.

 

I know they have nice big pretty buildings and have the "halo" of being backed by Toyota Corporate, but a Toyota dealership is the last place you want to be. There is no diagnostic code for "blown head gasket," and dealership techs stick to rigid diagnostic flow charts. Everyone here was all but certain you had a blown head gasket and confirmation of it could have taken just a couple minutes, but Toyota wanted to waste a day swapping coils around because the computer said there was a misfire. On paper that seems like a reasonable thing to do, but for an experienced mechanic (mechanic - not parts changer) it is absurd. The 2010-2015 Prius is well known for blowing head gaskets and causing these exact symptoms. Severely bad ignition coils do not suddenly start working 10-30 seconds after restarting your engine. Swapping coils as a first diagnostic step was a waste of his time and your money.

Now this same mechanic wants to say that in "his experience" there is a 70% chance it is more than a blown head gasket. He obviously has little/no experience!!! He reads codes from a code reader and throws parts at the car hoping the codes go away. And for a 1-3 year old Toyota under warranty, that probably works okay most of the time. Blown head gaskets don't happen under warranty, so he doesn't see them often. When he (or his dealership) does see them, he quotes obscene prices to repair them so the customer almost always takes the car elsewhere.

There is probably a 90% chance it is just a head gasket right now. If you had a fleet of prii and 10 of them presented with these exact symptoms, replacing the head gasket and machining the head would fix 9 of them. It just sucks to have that 10th car and have to go further with an engine rebuild/replacement and lose some of your labor costs to wasted work on the head.

And it will come with a 10 year old head gasket just waiting to blow. If you do get a junkyard engine, you should at the very least replace all of the gaskets/seals (including the head gasket). If you're paying someone else to do this work, you're starting to reach the point where you could probably pay to rebuild your own engine.

Sounds like fixing your head gasket is more and more appealing under these circumstances. If you can get that rebuilt engine from hybrid pit for $2,300 I would jump on it, but with pandemic issues I would not be surprised if they can't supply them right now.

The noise and vibration DOES come from the hybrid system, but the noises & vibrations are not the problem - they are symptoms that will go away once the underlying problem is solved. That problem is a severe misfire caused by a blown head gasket. RJ explained this before:

I suspect some of the noise also comes from the drive chain rattling inside the "transmission" (power split device), but the fact is this hybrid system noise and vibration goes away when the engine is fixed even though the noise isn't coming from inside the engine.

I don't know that trying to relay this information to your mechanic is worth your while unless you really like him. You are probably just better off making an appointment with a hybrid specialist, even if that means taking your car 200 miles away and staying overnight in a hotel or airBnB.

 

One minor correction: Gen2s had a drive chain but that was updated to direct gearing in Gen3s.

 

I would check all the local shops and anyone else within a hundred mile radius. Call Hybrid Pit first. Often a small shop can be the best. Superior dealer mechanics graduate to their own shops. Places like Calif, Florida and Texas have more Prii running around so they have more resources.

I certainly would not put in a used 100k mile gen3 unless it was something like $2k all in and you plan to trade the car before the "warranty" expired. A lot of mechanics might say head gasket alone. If it was a Honda Civic I would say yes. These gen3 engines have issues. Again, if you are flipping the car as soon as it is repaired, go for it.

Your financial position makes all the difference. Paying $6,800 for a 40k engine is "ok" but I would ask for vin and carfax verification. A used engine might cost the dealer $1,500. US engines have a vin plate to the left of the timing chain cover. There are resellers of so called Japanese import used engines (JDM) that always say 40k-50k miles. With no US style vin they can not be verified. Most junkyard engines have their vin plates removed.

Trading up is a sure way of avoiding uncertainty.

 

Engine vin plates used in US Prius vehicles (typical)

 

I have no experience with either of these guys, but they have decent reviews on google.

Cincinnati Hybrid +1 513-271-1570
Pinpoint Auto (Buffalo, NY) +1 716-405-0698

I drove my Prius 100 miles to have its headgasket replaced. It was just starting to consume coolant regularly and have rough restarts, but it drove fine on flat highway at 60mph... I used a scangauge to keep an eye on coolant temperatures (you could just get a cheap OBD2 dongle and download a smartphone app).

 

Yes its a head gasket. The dealer confirmed it and it is common. 1. The spark plugs clear up and run decent preventing a code. It takes a longer period than you get. 2. No overheating until the reservoir is empty. Maybe not for a while after that. 3. At first you only lose a few drops each rattle until its really bad. Then you risk blowing a hole in the engine from hydrolock. 4. Coolant does mean a head gasket. The symptom alone is enough for anyone who has seen it before. If you recall several of us called it just from the description. I and others have seen it several times before.

In Calif there is a shop that is franchising, Gasketmasters, that makes a business out of this problem. They actually have mobile service and can change the head gasket, head or engine in your driveway. Kind of like the windshield replacement companies but at a higher level. They bring the gasket set and fluids, tear it down, check for serious warping and rod damage, have a machined head ready to go and usually carry an engine. Hybrid Pit is a similar operation without the mobile service.

In the context I suggested "trade up", it meant trade up to another car. If it is a Prius it should be a 2016 or newer excluding a Prius v wagon.

I would install a well rebuilt engine with new pistons and machined head. This is as close to a new engine you can get. Your dealer $6,800 used engine would be the second option I would consider. Dismissing a head gasket job alone is me being conservative, confident and secure the result will last years.

 

Just pull the engine to check the clutch damper. That is part of the process to install another engine, rebuilt or used.

 

There is no diagnostic trouble code for a blown head gasket. Most DTCs simply report electronic faults in the circuits of various sensors or unepected readings from those sensors. I assume you had a P0302 code (misfire cylinder #2). In most cars (and I assume for Toyota as well) this code is triggered when the crankshaft position sensor does not see the expected acceleration that would occur when cylinder #2 has its power stroke.

Random misfires occur all the time for all sorts of reasons, so you won't get a check engine light for 1 or 2 misfires. Instead you might have something like a pending code in the background if the computer detected 25 misfires out of the last 50 power strokes. It would illuminate the check engine light if it detects maybe 100 misfires out of the last 200 power strokes. It might even turn itself off if the engine runs smoothly for the next 1000 power strokes.

With an early Prius blown head gasket, a tiny bit of coolant seeps into the cylinder. When the engine is running at say 2,000 rpm, the coolant only has about 1/30th of 1 second to enter the chamber. That isn't enough time for enough coolant to cause a misfire. When your engine is stopped while you wait 2 minutes at a light, a moderately blown head gasket will allow enough coolant to cause a misfire. A newly-blown head gasket might not even allow that.

When you park overnight, you allow a lot more time for coolant to seep. The engine also cools and contracts so the breech in the head gasket is larger. So your first start of the day will usually be the roughest. Once the engine pumps the water out through the exhaust (and/or heats it enough to evaporate), the misfire will go away (usually before setting a solid check engine light).

Well first of all, how would you even know unless you are monitoring coolant temperature fluctuations with an aftermarket gauge? The prius overheat light comes on after the temperatures have already gotten too high.

Second, these early head gasket failures are fairly minor and Toyota's otherwise robust cooling system can generally keep total engine temperatures in a reasonable range. You probably have some localized overheating (which is why heads warp when it gets bad enough), but unless you are flooring it uphill with the AC on in 120F coming out of Death Valley Toyota's cooling system will still keep the average coolant temperature normalish.

A newly blown head gasket doesn't consume that much coolant. If you draw a line with a sharpie on your coolant tank, the coolant level might drop from the top of that line to the bottom of that line (i.e. the thickness of a sharpie) over a week. It might take a month or more to go from the "full" to the "low" mark on the coolant tank.

These start off as very minor blown head gaskets by the standards of most cars, but due to the hybrid drivetrain's rattle & shake they are extremely noticable so people don't ignore them for as long as they might in other cars.

In fact, this is why so many people are in denial when they have a blown head gasket in a Prius - you're not yet experiencing the "normal" symptoms that you would in a conventional car. If you keep driving it long enough, it will get bad enough that you will get those normal symptoms too (but by then the odds of being able to just change a head gasket have greatly diminished).

A little moisture on one particular morning might be condensation. When it happens multiple times per week, week after week, it is coolant.