PRIUS & HYBRID HEAD GASKET REPAIR

GET YOUR VEHICLE REPAIRED NOW!

The head gasket on the Gen3 Prius is more likely to fail than on most other Toyota models. The affected years are 2010, 2011, 2012, 2013, 2014, and 2015. I’ve never seen a problem with the generations before, and so far there have been no issues with the Gen4 (2016 and newer). If you found this page, I’m guessing your mechanic found a leaking head gasket on your Prius.

What is a head gasket

Most gasoline engines have two main components: the cylinder head and the cylinder block. The head gasket seals three areas at the joint between the head and block:

Combustion chamber
Water jacket
Oil galley

Most cars use MLS (multi-layered-steel) gaskets these days, as does the Gen4 Prius. MLS gaskets have a few layers of thin carbon steel that are embossed and crimped in critical sealing areas. This type of head gasket is able to seal higher pressure than the older composite gaskets, but it’s not wMost cars use MLS (multi-layered-steel) gaskets these days, as does the Gen4 Prius. MLS gaskets have a few layers of thin carbon steel that are embossed and crimped in critical sealing areas. This type of head gasket is able to seal higher pressure than the older composite gaskets, but it’s not without faults. They aren’t very good at sealing less-than-perfect surfaces. Pits, scratches, or a rough surface will cause premature failure. To combat this, manufacturers often apply coatings and sealants to the gaskets.ithout faults. They aren’t very good at sealing less-than-perfect surfaces. Pits, scratches, or a rough surface will cause premature failure. To combat this, manufacturers often apply coatings and sealants to the gaskets.

modeS of failure

The head gasket seals the combustion chamber, coolant passages, and the oil galley. Usually a head gasket will develop one of the following types of leaks.

coolant passage to combustion chamber
coolant passage to oil galley
combustion chamber to combustion chamber
external coolant leak
external oil leak

The Prius head gasket usually develops a leak between a combustion chamber and a coolant passage. Coolant leaks into the combustion chamber and is then pumped out the exhaust as steam. When the engine isn’t running, coolant from the pressurized water jacket can leak into the combustion chamber. This is a big problem on the Prius since the engine stops running frequently.

SYMPTOMS OF A LEAKING HEAD GASKET

Often a misfire is one of the first symptoms you’ll notice on a Prius with a leaking head gasket. A misfire on a Prius usually fairly dramatic. The engine will knock, shake, and rattle when it starts up. The misfire is caused by coolant leaking into the combustion chamber and fouling the spark plug. The engine will continue to misfire until the plug dries off.

PRIUS SPECIFIC SYMTOMS

The car will shake and rattle when the engine starts.
The check engine light will flash while it’s running rough.
Then it will eventually smooth out.
However, the next time the engine stops for a while, the problem may return.

POSSIBLE ADDITIONAL DAMAGE

The other problem with coolant in the combustion chamber is this: coolant can’t be compressed. If there’s enough coolant in the combustion chamber, the powerful electric motor can actually bend the connecting rod while trying to push the piston into a space already occupied with a non-compressible liquid. This isn’t common on non-hybrid vehicles because the starter motor is so much less powerful. On a conventional car the engine usually just stops cranking.

Luckily, bent connecting rods are relatively rare, but we’re always sure to check. There’s no point in putting a new head gasket on a badly damaged engine! Checking for bent rods is easy. We check the piston heights relative the deck surface. If one piston is sitting lower than the others, there’s a bent rod. If not, we can reassemble with confidence.

WHAT CAUSED THE HEAD GASKET TO FAIL IN THE FIRST PLACE?

If the car over-heated, that’s a very likely cause. When aluminum gets hot, it expands and grows larger. The head and the block are bolted together tightly, so the head is constrained in some spots, and will buckle away in other spots. In areas where the head buckles away from the block, pressure on the head gasket is reduced, allowing it to get hot and fail.

The water pump on the 2010-2015 Prius is electric. If the water pump fails, the master warning indicator comes on. This is the same light that comes on for everything though. There’s also a small thermometer icon that appears on the dash, but many people miss it. Anyway, if you ever find a P261B, P261C, or P261D stored in your ECM, take it seriously.