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What I Learned From Fixing The Headgasket On My 2010 Toyota Prius

When I bought my 2010 Toyota Prius, I thought I had made a huge mistake. After the repair, I was surprised to learn these things every early 3rd Gen Prius owner should know.


If you have not read my other article, Did I make a mistake buying a 2010 Toyota Prius?, make sure you read that. It will help answer some questions you may have.

I have been dealing with hybrids now for quite some time. I have now owned nine hybrids. I have had 6 Prius and 3 Honda Civic Hybrids. Why would anyone own so many hybrids? Great question. I do it to learn so that I can help other people with their hybrids.

I had a lot of experience with Gen 2 Prius, but with Gen 3, I felt like a hypocrite not owning one but giving advice. Granted, I know enough about Gen 3 to guide any owner in the right direction safely, but I needed to have one for myself.

After searching everywhere, I finally came across one locally that needed some engine repair work. Many times the early Gen 3 Prius can be found with a lousy head gasket and picked up for cheap. This Prius was one of those.

After an initial inspection of the car, I found the critical signs to a blown head gasket. Coolant and oil mixed, knocking on startup, and losing coolant in the expansion tank. I knew that this was a common issue and did some research on what the best method of repair would be.

After exploring and researching, I had two options. Replace the head gasket or replace the engine. Here is what I learned from this experience and what I ended up doing.

Your Gen 3 Prius May Need An Engine Replacement
I spent a decent amount of time talking to other hybrid repair technicians. These guys have done many repairs on Gen 3, and all of them told me that just replacing the head gasket is a precarious move.

I have been wrenching for 15 years now and needed a deeper explanation of why this is. What was explained to me is that when the head gasket starts leaking into the cylinder, the liquid coolant has to be expelled somehow. On startup, this coolant cannot be compressed in the engine, and so what happens is this puts extra strain on the connecting rod and usually bends the rod. Thus killing the entire engine.

I was devastated when I found this out, but also it made sense to me. It was at this point I had to decide to either roll the dice and repair the head gasket or replace the entire engine. Replacement of the engine was something I did not want to do. I buy these cars for research, then once they are back to 100%, I sell them and move on. Hence, owning nine hybrids.

Your Prius may not need an engine; it depends on how long the issue has been going on. You will not know that until you pull the head and find out. That was my next step, and what I found out shocked me.

What I Found Upon Pulling The Head On My 2010 Prius
One of my hybrid friends who had been down this road before gave me some excellent guidance once I was able to get the head pulled from the car.

2010 Toyota Prius with cylinder head removed

He told me to check the depth of each piston compared to the one next to it. If I have a bent connecting rod, the measurements will not be the same. I dug in, pulling everything apart, and what I found was rather surprising. After pulling the head off and measuring the piston depth, mine were all fine. This comparison should be any owners deciding factor on what to do.

The reason this blew me away is that the Prius had been drinking coolant, the engine oil alone proved that. I decided at this point that if there were something I was missing, I would find out once the engine was back together.

I cleaned up all the parts as best I could, and reassembled the car.

The Aftermath Of Repairing the Prius Head Gasket
I was very nervous about turning the car on after the repair. Even though the block and the head are straight, the valves were seating, and I had gone exactly by the book, I still quivered.

The Prius rattled to life as oil pressure built up within the first few seconds of run time, and then it smoothed out and was quiet. I was very apprehensive about driving it, but I knew I needed to make sure the repair was trustworthy.

2010 Toyota Prius After The Head Gasket Repair

I gave the Prius a quick 5-mile test run down the local fuel station and picked up a soda for myself. Quiet, smooth, everything in order. Everything seemed okay until on the return trip. Check engine light. Lucky for me, I always carry my code reader with me on test drives.

I plugged in and saw a P0401, EGR Insufficient Flow Detected. Having this code is crazy because I cleaned every port and passage on the cooler and piping, so there should be no issue at all.

Other than that, I have had no problems at all with the Prius from the engine. It is running well, smooth, and quiet.

I think I got fortunate with this job. As stated before, I spoke with many different technicians about this repair before I ever attempted it. I knew the risks of only doing a head gasket. I knew to check for a bent connecting rod; I knew to flush the engine, clean the EGR system, and all the small things in between. I have been working on cars for 15 years now, so my experience doing this was straight forward.

I think that someone who can follow the OE procedures to do this repair can do it. I also believe that you are taking a considerable risk, only replacing the head gasket. My 2010 has 211,000 well-abused miles on it. I could instantly tell that the previous owners did not care about the car. The green coolant that had been run through the car was a big sign of that.

If you want to fix your 3rd Gen Prius head gasket, know the risk you are taking. Many other problems can show up afterward once the repair has been done. Other problems may not happen until thousands of miles down the road.

So, I think the question now is, Did I make a mistake buying a 2010 Toyota Prius? Time and miles will tell all, but for $500 and some of my time, I think for me, it was worth it. I learned a lot, even more than what I have shared with you here today.

If you have questions or want to discuss doing a head gasket repair on your 3rd Gen Toyota Prius, let me know I am happy to chat with you about it. Hit me up on Twitter or find me on Facebook. I am glad to share my knowledge on hybrids and save you money. See you in the next story. How Long Do Toyota Prius Engines Last?

Watch this Toyota Prius truck with a nice little bed and click to subscribe to Torque News Youtube for daily automotive news analysis.

Peter Neilson is an automotive consultant specializing in electric cars and hybrid battery technologies. He holds a Bachelor of Science in Automotive Service Technology from Weber State University. Peter is also an Instructor of Automotive Technology at Columbia Basin College. Peter can be reached on Linkedin and you can tweet him at The_hybrid_guy on Twitter. Find his page on Facebook at Certified Auto Consulting. Read more of Peter's stories at Toyota news coverage on Torque News. Search Toyota Prius Torque News for more in depth Prius coverage from our reporters.


Marshall Goldberg (not verified)    April 14, 2020 - 2:37PM

Has the Check Engine warning for Insufficient EGR flow gone away? A CEL illuminates only after a failure occurs several times. The light may be a remnant of an older problem, although you could use TechStream to cycle the EGR value to make sure it's opening and closing.

Tim Hunckler (not verified)    July 13, 2020 - 4:27PM


Great articles about EGR, 3 signs of head gasket failure and this one. Very helpful. I have 1/3 of the symptoms as described in the 3 signs of a head gasket failure article. Very occasionally I get the aggressive rattle in the engine. This has happened 10 or less times over 2 years. A previous mechanic said it happens when the oil gets low. I check the oil more often, add some if needed and that seems to stave off the rattle/knock.They last a short bit of time or I turn it off and usually starts up okay after that.

Would this still be a head gasket problem or something else? Coolant levels are good and oil change last weekend showed normal color oil.

I'm doing my research now on how to change a head gasket but want to make sure it's the right move to make. I'm not real experienced with cars I have a desire to learn and have been helping friends recently which inspires me to take that roll. I have a trusted and experienced friend who is and agreed to help.

Any advice would be welcomed! Thank you!

Calvin (not verified)    August 13, 2020 - 8:54AM

In reply to by Tim Hunckler (not verified)

The knock only means a cylinder is misfiring. When the Prius engine misfires, it sounds like a rod knock. The only time your Prius should knock is if you turn off the engine and start it right up again, a known oddity in the gen 3 Prius. But of the knocking happens more frequently, that would be abnormal. The problem usually happens once in a while at initial startup. It becomes more frequent, until every cold startup begins with a knock. Then, it progresses to happening in the middle of drives.

First watch your coolant level. If it's full one day and a few days later some of it has disappeared, suspect a head gasket leak. Your nose is more sensitive than any mechanic's "block tester" with the blue dye. While the engine is cold (so you don't get sprayed with hot coolant), unscrew the coolant cap and smell the air that comes out. If you if you have any hint of exhaust smell, your head gasket is faulty. Next would be spark plugs. If you're due for plugs, just replace them. For everything else, you'll need a diagnostic scanner that can monitor misfires in real time to test ignition coils and injectors. EGR valve ports and PCV valve dumping oil into the intake manifold are also things you cam check for without a scanner. I'd everything out in that order.

Al j (not verified)    May 9, 2023 - 10:55AM

In reply to by Calvin (not verified)

Most people are not aware the knock is not coming from the engine. When small amounts of coolant are in the cylinder on start up the misfire causes the hybrid torsion clutch to rattle super loud. I have changed 2 prius head gaskets for #2 cylinder coolant issues. When turning the crank by hand rock it back and forth and listen to the hybrid drive it knocks allot. Any cylinder misfire will sound like the engine is about to explode but is actually just the drive making a loud noise.

jeff bach (not verified)    July 21, 2020 - 11:41AM

Two things I regularly see on the gen 3s are coolant pump not functioning correctly and egr coolers that are plugged up. These are the contributing factors in the head gaskets letting go.

Alan (not verified)    July 1, 2023 - 1:48PM

In reply to by jeff bach (not verified)

How do I tell if either of these are the case? preferably without electronic tools? Does high mileage motor oil or Marvel Mystery oil help keep the EGR cooler clean? Does old coolant cause either head gasket or pump failure? How else might I preserve the pump?
I did notice on my friend's 2013 that the top interior of the engine coolant bottle was a bit dirtier than that of the trans coolant bottle. What might that mean?

Don Phillips (not verified)    August 15, 2020 - 12:05AM

Thank you much. Just purchased the 2010 prius solar. I have the strange misfire at start up. After the plugs, the misfire was gone until tonight. It has 192000, oil changed every 5000 or less, documented on carfax. Crystal clean valve train to include the entire car. This thing was well cared for. It runs smooth except for the start up misfire rattle. I have no milkstake or reduction in coolant, however, there is a coolant odor inside the cockpit. After reading all of the head gasket issues, I feel this would be a good subject for a head gasket. Do these engines live on after a head gasket or are they done at 200000? I've heard everyone replacing them. What do you think? Also, this will be my first engine with that cam phaser. Is there anything special to that, or just line everything up to TDC like usual? Thanks for any insight.

Jeremyhahn (not verified)    July 21, 2021 - 8:08PM

In reply to by Don Phillips (not verified)

On the gen3 theres small holes on the intake manifold that get clogged with carbon build up it takes about 45 min to remove the intake and take a can of carb cleaner and remove all the carbon in them it should take care of the death rattle

Calvin (not verified)    August 15, 2020 - 3:40AM

Peter, the mechanics that discouraged you from replacing the head gasket the gen 3 Prius sound like alarmists. If the engien runs fine at any time during your test, the main components are still good. A problem like a bent rod doesn't come and go. I've never seen a bent rod occur on startup. If enough coolant has leaked into the cylinder (hydrolock) to cause this kind of damage. The engine simply won't crank. It will just stop when it reaches the hydrolocked cylinder with its valves closed. The only time hydrolocking will bend a rod in a Prius engine is if a copious amount of coolant enters the cylinder while the engine is running and the piston has the momentum of the spinning crankshaft. And if a head gasket leak is so severe it could fill a cylinder within a few milliseconds, I doubt that engine would have been able to run at all. The only time this amount of coolant can enter the cylinder is while the engine is stopped and it slowly fills the cylinder. But again, the engine won't even crank. There are lots of mechanics who are afraid of head gasket jobs because of lack of confidence in their own ability. For some, it takes several dozen to gain that confidence. Some will never get over it. It's just easier on the brain to cover your butt and recommend an engine replacement. I've had old-timer mechanics who are so uncomfortable doing them, I'd have to reassign jobs.

Rj (not verified)    November 28, 2020 - 10:14PM

In reply to by Calvin (not verified)

The reason the engine can bend or break a rod when cranking is that it has a powerful electric motor generator running at 201vdc turning the engine over at higher torque and rpms than a common 12v starter motor. Typically then bend first then break while driving.

don hiebert (not verified)    July 22, 2021 - 11:44AM

In reply to by Calvin (not verified)

There's no way for a significant amount of coolant to get into a cylinder with the engine running, regardless of head gasket failure or cylinder head cracks. There might be enough to make white smoke though. The Prius HV battery will turn the crank with a great deal more force than a 12v battery will, and yes, it's plenty to damage a piston rod.

jeff bach (not verified)    August 22, 2020 - 9:11PM

It does happen more often than you'd think that the coolant causes the piston to break. I have one in my shop now that broke the piston then the rod punched out the block front and back. You can look straight through the engine.
Once that morning miss begins I wouldn't waste time getting the gasket replaced along with cleaning out the EGR heat exchange. I,ve gotten to where it's better for me to keep a few cleaned EGR coolers on hand and just exchange them when doing the head gasket job or....replacing the engine.

Douglas Rodriguez (not verified)    August 31, 2020 - 10:03AM

As an avid used Prius buyer from auction almost all Prius from 2010-2016 will Experience this head gasket failure. I am shocked no one has rattled Toyota corporate for this well known issue. Toyota doesn’t care as it’s out of warranty and gives two shits about it. I wonder if it’s happening to gen 4 as well and wonder when we will see a flood show up with the issue. You can fix the head gasket only and it will survive everyone I’ve done has worked great. My plugin is at 245k and my V is at 299k both with new HG. The main freaking issue you will have after this is oil consumption. Every dealer knows about the old xb rav4 Recalls for oil burning and the Prius is also one of those. You will have to fill you’re Prius every 3 days depending how bad you’re low tension rings are. Shame on you Toyota for not fixing such a simple issue. Then again I almost have 300k lol

Douglas Rodriguez (not verified)    August 31, 2020 - 10:05AM

As an avid used Prius buyer from auction almost all Prius from 2010-2016 will Experience this head gasket failure. I am shocked no one has rattled Toyota corporate for this well known issue. Toyota doesn’t care as it’s out of warranty and gives two shits about it. I wonder if it’s happening to gen 4 as well and wonder when we will see a flood show up with the issue. You can fix the head gasket only and it will survive everyone I’ve done has worked great. My plugin is at 245k and my V is at 299k both with new HG. The main freaking issue you will have after this is oil consumption. Every dealer knows about the old xb rav4 Recalls for oil burning and the Prius is also one of those. You will have to fill you’re Prius every 3 days depending how bad you’re low tension rings are. Shame on you Toyota for not fixing such a simple issue. Then again I almost have 300k lol

William Coté (not verified)    September 16, 2020 - 3:20AM

I have a question Peter.... My "NEW" 2010 JDM engine with 50k miles on it is due any day here... I am thinking about replacing the head gasket preventatively. Is the quality of the original head gasket the issue here on why I would replace it or is it something else? And what would I gain by changing the head gasket? Thanks for any advise you might offer.

Peter Neilson    September 16, 2020 - 11:57AM

In reply to by William Coté (not verified)

I wouldn't do that honestly. The engine is still very tight at 50k. Once you hit around 170k I would suggest looking into having it done. One of the reasons the HG fails is due to the heat cycling of the engine. It is not so much the quality of the original HG its mainly due to time and heat cycling.

Ron (not verified)    May 28, 2021 - 12:48PM

In reply to by Peter Neilson

I went replaced the HG on my 2010 Prius. It wasn't that bad but I am an expert. I have done on GMC Acadia 3.6 Prius is nothing in comparison. The only confusion was following Alldata instructions on some parts specially on applying silicon on left side of HG before and after laying it down. I never liked the idea of using silicon on head gaskets as some techs do.I cleaned up the EGR passages but still getting the insufficient code. I don't want to replace it if it does NOT damage the new HG. Do you think if it does?

Don hiebert (not verified)    May 29, 2021 - 12:38AM

In reply to by Ron (not verified)

I've didn't use any sealant on the Gen 3 Prius head gasket and I don't think the Felpro instructions said to. Maybe soak the complete EGR assembly? If you have a code you're not sure what to do with, I'd go to Priuschat with it. Those are the Prius experts.

Marc Hogan (not verified)    October 10, 2020 - 9:35AM

Wish I read your article a few months ago. Just purchased my second Prius (2013). Had it for approximately two months and now it's just sitting in my yard because I am not certain what to do after the dealer told me that it's leaking coolant in the Engine and they can't tell if it's the Eng valve ($2000) or in need of a new engine ($6000). I only paid $5000 for the car, so I just can't pay $6000. My problem sounds exact to your 3rd gen issue. Any advice on how to find someone in Pittsburgh WO can do the work. Dealer price is way too much!

don (not verified)    November 26, 2020 - 8:30AM

In reply to by Marc Hogan (not verified)

Look for a similar car on Row52 dot com that has some crash damage. Check under the oil cap and make sure it doesn’t look like a chocolate milkshake. Pull the motor or hire someone in the yard for 100 bucks. You’ll be out of there for 250 bucks. You can likely find a mobile mechanic near you that could swap engines for 1000 or so. I certainly would. If any coolant has leaked into the cylinders, I’d say the current motor is trash and likely has a bent connecting rod.

Patrick Byrne (not verified)    May 20, 2022 - 10:15PM

In reply to by Marc Hogan (not verified)

Dang, me too... But haven't taken to local stealer ship yet for the bad news...just week 1 of ownership an knowing I'm the sucker... anyways, love to hear how it turned out! Meanwhile I'll be reading ...

Jason (not verified)    October 18, 2020 - 5:41PM

I have a 2010 Prius with 185K miles on it, and after recently replacing the spark plugs, coils, fuel injectors, and servicing the EGR I still manage to have some miss firing going on. I noticed when's taking the spark plugs out of cylinder one that it was wet and my coolant level was lower. I am assuming my head gasket needs to be replaced. Where can I get a good set of instructions on changing out the head gasket as what's you followed? Thanks in advance

don (not verified)    November 29, 2020 - 7:36PM

I did the gen 3 head gasket and really thought it was pretty straightforward. The internal combustion section of the power train is found in many Corollas and a number of other similar cars. Unfortunately, the owner continued to drive it after the gasket failure for some time and complained that randomly, initial startup in the morning was difficult. And, coolant was being burned. Depending on the piston position in the affected cylinder, whether the piston was on the compression stroke, and amount of coolant, engine rotation can begin but then be abruptly halted. This, combined with the fact that electrically generated torque is well above what a normal car starter produces, IMHO could radically stress the piston rod. I'm not an engineer though. The affected cylinder had significantly higher compression than the other three. And, there was polishing in two areas instead of the cross hatching found elsewhere. This was caused by the bent rod and that eventually led to the break. My suggestion would be to inspect cylinders for any polishing and toss then engine if any is found. Also, compare all pistons at TDC and if there are any differences, toss it. I think a piston could also likely be replaced with the engine in the car but would require removal of oil pan, likely the oil pump, etc. Unfortunately, I didn't know enough to toss this one so wasted some time and effort on the gasket replacement.

Jesse (not verified)    February 7, 2021 - 9:31PM

Thanks for the article Peter. Wondering if you (or anyone following this article) has a parts list covering everything required for a full head gasket replacement job on the 2010 Prius so I can properly cost it out before setting out to do this on my own? Also, looking for recommendations for the best place to purchase reliable parts for a job this intense. Not looking to do this a second time because of inferior parts :) Thanks in advance.

don hiebert (not verified)    February 8, 2021 - 8:59AM

Jesse, I'd suggest you look through all the relevant info on If the car was producing which exhaust smoke, then coolant was being burned and there's a possibility of hydro locking where coolant enters a cylinder after engine shutdown. This can bend a piston rod and I'm not sure how to easily check that except when cylinder sidewalls have been made shiny/polished. Maybe measure piston height at TDC? If you do the head replacement, cleaning head bolt threads and properly torquing and de-torquing head bolts will be much more important than the quality of parts you use. I like FelPro gaskets and bolts. I'd suggest a water pump and/or a timing chain, depending on the mileage your car has. You can always get Toyota parts or you can get the cheapest ebay or amazon stuff you can find. The cars I work on are usually 10 or 20 years old so I focus on the cheaper parts. I also like to take pictures after each part I take off and put bolts and nuts with each part in a plastic shopping bag or ziploc bag, You might want to consider or used motors as it's really not that much more difficult to pull and replace the motor. You do need an engine hoist that you can rent or borrow though. Also, keep in mind you may need to surface the cylinder head, although I wouldn't if it has a flat surface. Also, make sure to get all the bolts and nuts holding the coolant tube on the driver's side of the cylinder head. I forgot one and the locating pins caused some scratches in the cylinder head face as I was trying to remove it. If you leave the exhaust studs in the head, you need to pull it off pretty much straight forward.

Jesse (not verified)    February 8, 2021 - 2:03PM

In reply to by don hiebert (not verified)

Don - thanks for all the info and experience you shared. Maybe I can get a peek at my piston heights by snaking a borescope down into the spark plug holes before tearing apart the entire cylinder head.

I've already replaced spark plugs, fuel injectors, swapped ignition coils, and cleaned the EGR return tube trying to diagnose the cause of the "Misfire on Cyl 2" that I've been getting. Those all seemed to improve the situation temporarily, but ultimately it's come down to missing coolant in my overflow reservoir :(

I haven't noticed significantly white exhaust, but I'm finally starting to see some evidence of coolant in my oil under my oil cap and on my dipstick.