2010 Toyota Prius Generation 3 Engine Bay
Peter Neilson's picture

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?

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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.

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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.