White Smoke from the Exhaust? Engine Overheating? How to Diagnose a Blown Head Gasket

An engine overheating and white smoke from the exhaust are signs of a blown head gasket. Find out how to check your engine for a blown head gasket with these tips from our expert mechanics.

What Is a Head Gasket?

Mechanic reviewing how a blown head gasket can cause an overheating engine and white smoke from the exhaust

The engine can be separated into a few sections. There is the engine block, which houses the pistons on the bottom. There is also a cylinder head at the top, which has valves that open and close. Between the cylinder head and engine block lays the head gasket.

The head gasket keeps coolant or oil away from the pistons or combustion chamber, and it keeps exhaust gases from mixing with the coolant.

Why Does My Car Have White Smoke from the Exhaust and an Overheating Engine?

White smoke from the exhaust

Coolant or Oil Is Leaking into the Combustion Chamber

Head gasket
Head gasket

Looking at the head gasket, the circles are where combustion chamber is. The side with the ports is where coolant will be flowing. The head gasket is the only part preventing the oil and coolant from mixing together and from coolant leaking into the combustion chamber.

The head gasket may or may not have an area where pressurized oil will flow through. If it does have this area, pressurized oil could also mix with the coolant or leak into the combustion chamber if the gasket fails.

Exhaust Fumes Are Leaking into the Cooling System

If a faulty head gasket is allowing coolant to leak into the combustion chamber, exhaust fume gases will leak into the cooling system. If the gasket breaks, you’ll have a misfire between the two cylinders because the compression ratios will not be accurate.

Symptoms of Bad Head Gasket

  • Engine overheating
  • White smoke from the exhaust
  • Sweet smell that’s similar to maple syrup
  • Coolant or engine oil leaking from the engine externally
  • Low coolant, but no signs of a coolant leak
  • Engine misfire

How to Diagnose a Blown Head Gasket

Steps to diagnose a blown head gasket

  1. Check the Coolant Level

    To check for a blown head gasket, make sure the engine is cool. Then open the hood and check the coolant level. Don’t open the coolant cap with the engine warm. If you find level is low, top off the coolant.

  2. Check for Coolant Leaks

    Check the water pump, coolant hoses, and radiator for coolant leaks.

    More on how to check your car for coolant leaks

    You can also check for coolant leaks beyond a visual inspection by marking the coolant reservoir. Mark a line on the reservoir when the engine is cold. As long as the engine isn’t overheating, drive like you normally would. Then check and see where the level is at. If you’re losing coolant, the fluid level will fall below the marked line quickly.

  3. Check for Signs of Exhaust Fumes Leaking into the Cooling System

    To check for exhaust fumes leaking into the coolant, remove the radiator cap or reservoir cap with the engine cool. Then run the engine. With the engine running, look for bubbles in the fluid. Burping bubbles are not an issue, but you’ll want to see if there are any major bubbles. That most likely means exhaust gases are coming through the reservoir or radiator.

    You can also use a block tester, which is a special tester you can use to confirm the engine has exhaust fumes in the cooling system.

  4. Check for Carbon Build-Up in the Engine

    Remove and inspect the spark plugs. If you have spark plug wires, disconnect them. If there’s a coil, remove the coil. Then remove the spark plug with a spark plug socket and check the spark plug for a white film or powder, which is a sign the engine is burning coolant.

    Check the spark plugs for build-up. It’s normal to see a little amount of carbon build-up on the spark plugs, but a lot is a sign the engine could be burning oil.

    Take a borescope and look into the spark plug hole. This will allow you to see inside the cylinder. It’s normal to have carbon build-up on the piston. If one piston looks shiny and brand new and cleaner than the other pistons, that’s a sign coolant is inside the engine and burning off the carbon. A lot of clean pistons is not a good sign.

  5. Check for Any Engine Cylinders Filling with Coolant

    You can pressurize the coolant system with a pressure tester.

    With the coolant pressure tester hooked up, if you have all the spark plugs removed and notice any cylinder filling up with coolant, that’s an indication you’ll need a new head gasket.

    More on how to pressurize the coolant system

Fix white smoke from the exhaust and an overheating engine in your car yourself with quality auto parts and tips at 1aauto.com

White Smoke from the Exhaust & Engine Overheating - Pro Tips - 1A Auto
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White Smoke from the Exhaust & Engine Overheating - Pro Tips - 1A Auto
If you have white smoke from the exhaust and an engine overheating, it's time to check for a blown head gasket. Find out how to diagnose this issue with these expert tips
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1A Auto
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One thought to “White Smoke from the Exhaust? Engine Overheating? How to Diagnose a Blown Head Gasket”

  1. tell me how Subarus have a 97% chance of still being on the road in ten years…..while being prone to head gasket leaks…….only certain engine types????

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