Head Gasket Symptoms, Tests and Fixes
Failed head gasket symptoms
Engine Overheats—When a head gasket fails, hot combustion gasses can leak into the coolant, pushing the cooling system beyond its design limits. Other failures can cause overheating (bad radiator fan, bad radiator fan relay, clogged radiator, bad water pump) but you should never ignore an overheating situation. If your temperature gauge rises into the danger zone, stop driving the car and get it towed to a shop. If the root cause is something small like a clogged radiator or bad radiator fan and you keep driving it in an overheated condition, you can cause the cylinder head to warp and leak. In that case, you’ll have saved $125 on a tow only to cost you $1,500 for a new head gasket.
Continually low coolant levels—If you coolant level drops after you’ve added coolant, you’ve got a problem. It could be something as simple as a leaking radiator hose. But it can also be a sign of a deteriorating head gasket that’s allowing coolant to enter the combustion chamber where it burns with the air/fuel mixture.
Engine Misfire—A leaking head gasket can’t contain the high pressures needed for proper combustion. That causes a misfire condition along with lower power, rough idle and hesitation during acceleration.
White smoke from exhaust—The leaking gasket allows coolant into the engine and the coolant turns to steam during combustion.
Coolant in oil — This is less common than the other symptoms. It’s caused by a breach in the head gasket between a coolant and oil passage. Even in an overheating situation, that’s not usually where cylinder heads warp. They usually warp near the cylinder. That causes coolant to burn in the combustion chamber or exhaust to flow into the coolant. However, neglecting coolant and oil changes can cause head gasket deterioration between an oil and coolant passage.
What causes head gasket failure?
Over heating causes blown head gaskets
If you drive while your engine is overheated, you can warp the cylinder head and blow the head gaskets. Overheating is caused by:
Low coolant level — A coolant leak will cause your cooling system to run low and that can cause overheating.
Neglecting coolant changes — Coolant contains anti-corrosive additives that prevent radiator degradation. If you don’t change your coolant, corrosion will build up in the cooling sytem and reduces the system’s ability to remove heat from the coolant.
Clogged radiator fins — Air must pass over the radiator fins in order to remove heat from the coolant. Bugs, leaves and other debris can clog the fins and reduce cooling.
Worn water pump — Some vehicle makes are more prone to this than others. Some car makers use plastic impellers on their water pumps and those impellers can just wear away over time.
Radiator fan(s) not working properly — If the thermostatic or electric clutch on an engine driven radiator fan fails, it will not draw in enough air and that can cause overheating. Electric fans and fan relays can also fail, resulting in engine overheating.
What are so many engines experiencing blown head gaskets?
Why are we seeing so many head gasket failures these days? Here are the root causes:
• Less under hood room and more heat—More late model cars have more standard features that require more components under the hood and those components not only take up space, but also generate more heat and require higher electrical output. That puts a higher load on the vehicle’s cooling system.
• Longer life coolant—Long life coolant is a great idea as long as car owners actually change it when it’s worn-out. The evidence shows that car owners are greatly extending coolant change intervals or ignoring them altogether. The result is cooling system corrosion that reduces overall engine cooling that puts more stress on the engine’s head gasket
• Longer oil change intervals—Again, great idea as long as you change your oil when it’s due. But the evidence shows that in many cases, oil change neglect can cause head gasket deterioration due to acids and corrosive materials in the worn oil.
• Multi-speed radiator fans—To compensate for the smaller radiators and lower cooling system capacities, car makers have turned to multi-speed and variable speed fans. Great idea as long as they’re working. But what happens when they start to fail? How can car owners possible know that their radiator fan’s high speed no longer works?
• Bad luck—That’s right. Some engines are more prone to head gasket failure than others. The Subaru Boxster engine is one example. You can maintain the vehicle perfectly and still find yourself looking at a huge repair bill for new head gaskets. This is one big reason why you should check out the reliability of a vehicle before buying.
Twenty years ago head gaskets rarely failed. Now they’re failing at a much higher rate. This article will discuss the different head gasket symptoms, tests and fixes. But first, let’s take a look at how we got to this point where head gasket failures are occurring more often.
Thirty years ago, car makers built their engine blocks and cast iron cylinder heads with cast iron. But they were under pressure to improve gas mileage and that meant they had to reduce vehicle weight. To lighten the load, they began making engine blocks from aluminum. Unfortunately, they mated their aluminum engine blocks with cast iron cylinder heads. The two metals expand and contract at different rates and that caused the head gaskets to fail. In many case the two expanding and contracting metals moved so much, they literally scrubbed the gasket away in spots, causing them to leak. Car makers and gasket manufacturers rushed to come up with new gasket designs that could handle the different expansion and contraction rates. Then, car makers switched to aluminum for both the engine block and cylinder head, causing a whole new set of problems—cylinder head-to-engine block torque issues. Car makers responded by torque-to-yield bolts (TTY).
What is a torque to yield head bolt?
All bolts stretch to some degree when temperatures change and the load on the bolt threads and bolt head change. If the bolt is tightened too much, it’ll break if the bolt is forced to stretch too far. If you under-torque the bolt to compensate, you risk a head gasket leak because the cylinder head and engine block aren’t mated properly. So car makers had to determine the exact “sweet spot” where the bolt would handle expansion, contraction and combustion pressures without breaking. The TTY bolts solved the problem. When a TTY bolt is installed, it’s torqued to a certain torque specification. Then, the installer turns the bolt a certain number of degrees, causing it to stretch slightly in the neck area. In some cases, the car maker requires a third rotation to bring the bolt to its maximum strength, yet allow the bolt to expand and contract.
Head Gasket tests
Check the oil dipstick—If the head gasket fails between a cooling passage and an oil passage, coolant can leak into the crankcase where it’ll be whipped into the engine oil. The result looks like chocolate milk. The contaminated oil can’t lubricate properly can continued driving in this state can destroy your engine.
Check the coolant—If the head gasket failure causes oil to leak into the coolant, you’ll see an oily film in the radiator and in the coolant reservoir.
Conduct a combustion gas leak test—The combustion gas tester attaches to your radiator and is filled with a blue fluid. If exhaust gases are leaking into the coolant, the fluid will turn yellow.
Conduct a cylinder leak down test—This requires a special tool that pressurizes the cylinder. If the head gasket is leaking, the cylinder will be unable to hold the pressure and the compressed air will leak through the intake, exhaust, or crankcase, depending on where the head gasket failed
Head gasket sealer
I regularly see auto forum users ask if head gasket sealer really works. The answer is a firm maybe. The older head gasket sealers worked by plugging the leak with wood pulp products. Those products only work on a head gasket leak that’s between a cooling passage and an oil passage, and even then they don’t work for very long. The newer style head gasket sealers work by solidifying a polymer into the gap using the heat of the engine. They can sometimes stop a very small head gasket leak between the combustion chamber and a cooling passage.
Should you try a head gasket sealer?
Here’s the big issue with telling people to try a head gasket sealer. You’ve already got a leak. If you try the head gasket sealer and the sealer doesn’t work, or works for only a few days, you could find yourself in a situation where you’ve caused even more engine damage. Let’s say you’ve got coolant leaking into the crankcase and you try a head gasket sealer and it seems to work. But the sealer fails in a week and dumps lots of coolant into the crankcase to the point where your bearings fail. Now, instead of a $1,500 head gasket repair, you’re looking at a $3,000 engine replacement.
So, on one hand you’ve got little to lose, because the cost of the head gasket sealer is so low. If you can’t justify spending $1,500 on a head gasket job, my advice is to try a head gasket sealer. If it doesn’t work and you destroy the engine, well, the car wasn’t worth fixing in the first place.
Which head gasket sealer works?
There’s lots of money to be made by manufacturing head gasket sealer. You simply price your product high and claim that it works better than all the others. I won’t mention any names, but my feeling is that you don’t have to spend more than $40 on a head gasket sealer. Either it’ll work or it won’t. Why spend $70 or $100 on a head gasket sealer when it’s most likely using the same technology as the $40 product? Here’s my recommendation for a head gasket sealer.
Can you replace the head gasket yourself?
Let’s say you have all the tools, great mechanical skills, a good shop manual and the time to devote to the project, should you try it? NO.
These newer aluminum engines are really tricky. You can damage the engine deck simply by scraping too hard when removing the old gasket. Make one small mistake in preparing the deck and cylinder head and the new gasket will fail. Even expert technicians that do this every day can mess up the job. Do a search for “replaced my head gasket and it’s leaking again.”
©, 2016 Rick Muscoplat
Posted on by Rick Muscoplat