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Understanding the Head Gasket

Hometown Hybrids Head Gasket-1

Knock Knock- who’s there? Your head gasket!

We’ve seen an increasing number of Prius and Lexus CT 200h owners contacting us concerning their engine knocking upon startup. This is a serious issue and shouldn’t be ignored-don’t cross your fingers and assume it will go away! The failure seems to start around 100,000 miles and peaks at 180,000. The repair can be very expensive depending on how long the failure has been happening.

A failing head gasket Prius can lead to severe engine damage if left unattended. It is essential to be vigilant about the signs and symptoms of head gasket failure, and if you suspect a problem, seek the advice of a professional mechanic. Regular maintenance and inspections can help prevent head gasket issues and keep your Prius running smoothly for years to come.

Understanding the Head Gasket

A head gasket is a crucial component of the engine, as it serves to seal the engine block and cylinder head (preventing coolant and oil from mixing). It also helps maintain the correct pressure within the combustion chamber. When the head gasket fails, it can cause a variety of issues, ranging from a simple loss of engine performance to catastrophic engine damage.

understanding your head gasket

Most Common Symptoms of a Failing Head Gasket:

 Low Engine Coolant: The engine coolant system is supposed to be sealed and never leak. If your coolant is low, its likely leaking into the combustion chamber. You can also check your engine oil to see if its contaminated.

Coolant and Oil Mixing: A tell-tale sign of a damaged head gasket is the presence of a milky, frothy substance on the engine oil dipstick or under the oil filler cap. This indicates that coolant and oil are mixing due to a breach in the head gasket. If your oil looks like a Whataburger chocolate milkshake, you have a problem!

White Smoke from the Exhaust: White smoke coming from the exhaust is often a sign of coolant leaking into the combustion chamber. This happens when the head gasket is compromised, leading to a mixture of coolant and exhaust gases.

Loss of Engine Performance: A failing head gasket can lead to a loss of compression in the combustion chamber. This results in reduced engine performance and can cause the car to feel sluggish or have difficulty accelerating. Poor engine performance can also affect your hybrid battery… yet another reason to have this repair done asap!


We recommend cleaning your EGR cooler system at 100,000 miles. The EGR can get plugged with carbon buildup and cause insufficient flow. This will affect the ability of the engine to release pressure, causing the head gasket to weaken over time. This is a slow process, which is why many owners don’t notice until it’s too late.

Repairing or Replacing a Head Gasket

Repairing or replacing a head gasket is a labor-intensive job. The process involves removing the cylinder head, cleaning the mating surfaces, and installing a new head gasket. The mechanic will also inspect the cylinder head for warping or cracks and, if necessary, send it to a machine shop for resurfacing or replacement. If the mechanic determines that the engine has a weak rod or is warped, head gasket replacement may not be a sufficient repair.


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