Engine Maintenance: Head Gasket Failure Symptoms and Diagnosis – UnderhoodService

Engine Maintenance: Head Gasket Failure Symptoms and Diagnosis

Over the last decade, the engines that have been used in the Honda and Acura line of cars and SUVs not only deliver many miles of service, but their performance level sets a standard that few car makers in their class have been able to match. Additional proof of both the reliability and potential of these engines is the popularity they enjoy in the sport compact market. I think it’s safe to say that the popular B Series twin-cam Honda engine is the current-day small- block Chevy, enjoying great popularity among both tuners and vehicle owners in general.

That’s not to say there’s never been a problem, but they’ve certainly been few and far between. One such problem is head gasket failure on early ’90s Civics. Honda was quick to react to the problem and developed a gasket and hardware to remedy it. The TSB lists the updated gasket and head bolts that will prevent a recurring problem.

We won’t cover the nuts and bolts of head gasket replacement in this article, since your technical information system will walk you through those procedures. Instead, we’ll talk about head gasket failure symptoms and diagnostic strategies. It’s the slightest head gasket leaks that will present the biggest diagnostic challenges. In such cases, the customer usually will notice a symptom that results from lost coolant.

It may be an overheating issue but, many times, it’s a problem the customer doesn’t relate to low coolant. It might be a “no heat” or “the heat is coming and going” complaint, or the idle fluctuates as a result of the low coolant level not allowing good flow to the warm-up device. When you ask your customer if he/she has noticed a coolant leak, the answer will be “no.”

The more severe cases of head gasket failure will be easier for the customer to notice. It’s hard to miss the telltale white steam coming from the tailpipe in the morning and the accompanying odor of coolant burning. If they ignore it for just a couple of days, the overheating will bring them to your shop soon enough but, hopefully, not on a flatbed. There is always the threat of the engine hydrolocking as a result of the cylinder being filled with coolant, preventing it from cranking over. When faced with this situation, don’t continue trying to start the car. Pull the plugs, cover the holes with a shop towel and crank the engine. There’s no missing the coolant escaping the cylinder.

With less obvious coolant loss (even though the customer noticed no leaks), our first step is to check for external leaks. Put the pressure tester on the car and check the usual suspects, like the radiator. Look at the bottom of the timing cover for evidence of a water pump leak, take a good look at the thermostat housing area and move the hoses around. Be patient; sometimes there will be only a slight leak, so give it time to surface.

While external head gasket leaks aren’t common on Hondas, they can occur and should be no problem to diagnose. Most will leave evidence and can be confirmed with the pressure test. But make sure that the leak isn’t originating elsewhere. You don’t want to replace a good head gasket if the leak is actually the thermostat housing disguising itself, with the coolant traveling down the head-to-the-block seam. Also be aware of the oil-to-coolant oil coolers used on some models. This “sandwich-plate” device mounted between the filter and the block has coolant running through it to maintain a stable oil temperature based on coolant temperature. As these vehicles get older, we’ve seen the effects of road salt and rust end up as pin holes in these units, easily mistaken for a coolant leak at the head gasket.

If no external leak turns up, check for an internal one. There are a couple of ways to proceed ‹ two tests that are each performed with the engine running. One is a dye test where the air that’s at the top of radiator tank is drawn into a turkey baster-type device fitted with a check valve, and then passes through a dye that changes color if exhaust gases are present. This is a reliable test as long as the chemicals are fresh (the dye has a relatively short shelf life). A variation to this test is to use your exhaust analyzer to sniff the same air that the dye is analyzing.

When performing these tests, take caution to avoid coolant contamination. If contamination mistakenly happens with the dye, it will cost you some chemicals. But, needless to say, the consequences are much greater if you suck coolant into the exhaust analyzer.

The most accurate and our preferred test method is a cylinder leak-down test. This test involves bringing the cylinder to be tested to TDC and introducing compressed air into the cylinder, while observing the coolant level in the radiator. A leak-down tester lets you see how much the cylinder is leaking in percentage points. We use a dual gauge tester where you set the regulator for 100 psi going into the cylinder, while the second gauge will show what the cylinder will hold. This is very useful information to determine how well the valves and rings can control the cylinder pressure. Always make note of the readings as they give you great insight into the engine (more on this later).

But when testing for head gasket leakage, we’re more concerned with the reaction of the coolant in the radiator to the pressure. When the offending cylinder is pressurized, it’s hard to miss the reaction of the coolant. I’ll give what looks like good cylinders a couple of minutes just to be sure. If you find high leakage, it takes only a couple of minutes to determine what’s leaking. Using a stethoscope, listen for escaping air in the spark plug holes and dipstick tube, checking how well the valves and compression rings are sealing.

While you can check the valves by listening in the intake manifold and exhaust pipe, I’ve found that it’s easier to hear the air that escapes from the tested cylinder into the manifolds and finds its way into the cylinder that has the valves open.

Now, let’s go back to the head gasket test. If, after a couple of minutes, there is no reaction in the radiator, remove the pressure, turn the engine counterclockwise until the next cylinder in the firing order is at TDC and do it again. Follow the firing order and test all of the cylinders.

The final gasket failure to consider is compression leakage between cylinders. This failure, and the resulting poor-run condition, is hard for a customer to miss. And, if it’s overlooked for any length of time, it will result in a very expensive repair. The aluminum cylinder head has little tolerance for those hot gases and extreme pressures passing over the mating surface, and it doesn’t take long for the casting to be damaged, resulting in the need for a rebuilt head to be installed.

In severe cases, the block will also be damaged. This failure will be evident with a compression test and will certainly be evident during a leak-down test. Be sure to remove all of the spark plugs before the compression test. This type of failure is rare on Hondas, and is often the result of the extreme cylinder pressures caused by detonation.

Don’t return the car without determining the cause. While it’s a good practice on all cylinder head service, be certain that the EGR ports are clear and the system functions as designed. Check exhaust backpressure, making sure a restriction there isn’t increasing cylinder temperature.

Damaged valves are another problem that will require you to remove the cylinder head. Whether the valves are burnt or bent, these problems will result in a misfire condition that won’t take long to confirm. Both can be quickly identified with a compression test. Checking the valve lash will further confirm the condition.

As a rule of thumb, a burnt valve will have tight lash while the bent valve will be wide. Keep in mind that bent valves are the result of timing belt failure. If you find an engine that has bent valve symptoms, and no recent belt failure is reported or evident, consider carbon buildup on the valves and stems as a cause for the wide lash and lack of compression.

There have been cases reported where the combination of low compression and the absorbent nature of the carbon will cause a “no start” condition that disguises itself as a bad timing belt. If you’re checking the valve lash, you already know the belt didn’t break. In some cases, you can get the valve to seat by pushing the valve open and letting it “snap” shut.

Another strategy is to put top-end cleaner into the manifold and let the car sit overnight so the chemical can soften the carbon. Be sure to crank the engine in the morning without the spark plugs installed to prevent hydrolocking the engine and the resulting damage. Whatever method you use, when you get the car running, a good top-end cleaning is certainly in order. Once a problem is confirmed and the head comes off, there are a couple of other tests to perform and decisions to be made before the head is reinstalled.

Whenever a head is removed, spend a few minutes with a flashlight looking closely at the head and ports. Carbon buildup should be easy to detect. Inspect the valves for any signs of overheating at the edges of the valve face. Look at the valves and seats that are being held open by the cam. Badly pitted, poorly seating valves should be serviced. If you did a leak-down test, pay particular attention to any cylinders that showed high leakage. Check the head for flatness using a straightedge. More than 0.003-in. of warpage should trigger a head resurface, while heads that have experienced extreme heat and the damage that comes with it may require replacement with a rebuilt unit to ensure a quality repair.

If you feel additional service is required, don’t hesitate to inform the customer. You’re doing him/her a favor by anticipating a problem that will require taking off the head again. When estimating an engine repair, it’s a good idea to explain that other problems could show up, so this situation won’t be a surprise. This is particularly important on engines damaged by overheating.

Your service information will provide the nuts and bolts of reassembly procedures, but there are a couple things to keep in mind. When cleaning the gasket surfaces, it’s tempting to grab the offset die grinder and use surface refinishing discs. I suggest resisting the temptation. While “sanding off” the gasket may save some time, the resulting dust and material removal could compromise an otherwise first-class job.

There’s no reason this open engine doesn’t deserve the same treatment that you would give an engine you were rebuilding on a stand. The discs can also remove enough material from the edges of the gasket surfaces that sealing could be compromised. That doesn’t mean that traditional gasket removal doesn’t require care to avoid damaging parts or keeping debris out of the engine. It’s just less likely to be a problem.

When the surfaces are clean, be sure to check that the oil passage that brings oil to the camshaft and valvetrain is free of debris and clear on both the block and head.

I would say the only time you’ll get away with a simple gasket replacement is when you’re dealing with a lower-mileage car that hasn’t had the updated gasket installed. If the gasket failure is the result of an overheating situation, you’ll find the head is warped as a result of the heat. If it got really hot, it’s a safe bet that the valve seals felt it and should be replaced. At that point, a valve job seems like the way to go. Of course, it’s most important that the cause of the overheating is identified and repaired.

Hopefully you included a timing belt, water pump and thermostat in your estimate that will cover you there, but be sure to check the radiator and hose condition before you finish the estimate. Check the condition of the radiator cooling fins. On some models, you can get an idea of the internal condition by simply removing the cap, while others won’t afford that option. Have the radiator checked on a high-mileage car where there is no obvious cause for the overheating. When the car is done, pressure test it for leaks and make sure the cooling fans are working properly. It’s important that you let the customer know the head gasket failure was the result of an overheating problem and not the cause. Make them aware of the temperature gauge and how important it is that the engine runs at a stable temperature within the operating range.

This brings us to the great ring debate. Hondas seem to have a problem with excessive oil consumption and the smoking that comes with it after a valve job has been performed. There are a couple of theories to support why this happens, but there is no disagreement that it does take place. It’s our policy to replace the piston rings whenever a valve job is performed. The good news is on the four-cylinder cars, this doesn’t make the job so expensive that it becomes out of the question for even an older car that’s in good shape.

Certain models have had problems with oil consumption without the heads being removed. The most common is the early- to mid-’90s Prelude. While some techs have blamed and replaced valve seals to solve this problem, it’s usually piston ring replacement that will fix the car. I mentioned earlier that a leak-down test is a good way to check the integrity of the compression rings and valves, but that’s not the case for the oil rings. As far as I know, there is no test for the oil rings. I suspect the rings over the valve seals if the smoking persists longer than it would take to clear out the cylinders after start up. I’d still do a leak-down test on the engine before disassembly to check the sealing capabilities. When replacing rings with the engine in the car, honing is not required or recommended. It comes down to the same issue as with gasket removal – the threat presented by the grinding dust outweighs any benefit that honing offers. If the cylinders are damaged, the engine will need to be replaced or a full rebuild with a bore job and oversized pistons is in order.

Other than the problems already mentioned, most engine problems you’ll see on Hondas will be the result of poor maintenance practices. Whether it’s a bent valve, burnt valve or a blown head gasket, it’s a safe bet that it could have been avoided with proper maintenance.

I still believe that valve adjustment should be part of a 60,000-mile service. Honda has changed the valve adjustment interval on its cars to include the wording “audible inspection only; adjust only if noisy.” The problem is that we are more concerned about a tight, rather than loose, valve. This is critical on the popular CR-V model where the specs are a tight 0.003-0.006-in. for the intake and 0.006-0.007-in. on the exhaust side. There is little room to compensate for wear before the valve is being held off the seat, resulting in a misfire or, if ignored, a burnt valve.

If you’re faced with a “poor run when cold” condition or a mysterious misfire code, suspect a tight valve. You may be wondering why it would present itself as a cold-run problem. It’s the result of the aluminum head expanding at a greater rate than the steel valve. As the engine heats up, the head will grow, moving the rocker away from the valve stem. This will result in valve lash and sealing of the cylinder. It’s further proof of why it’s important to adjust the valves with the engine temperature as specified by the manufacturer. Thankfully, Honda uses a cold setting, which makes the job much easier.

In addition to allowing the cylinder to seal, valve lash is important to allow the valve to transfer heat to the cylinder head. Without the opportunity to spend some time on the seat, it doesn’t take long for the 1,400° F exhaust gases passing by to burn the valve and damage the seat, resulting in an expensive valve job. While regular valve adjustment is critical on the CR-V, it’s a good practice on all of the four-cylinder Hondas. While the larger specs are more forgiving than the CR-V, they will tend to tighten up. This is most important on cars that are driven hard, and a good practice on all models.

We’re well aware that regular cooling system maintenance will prevent overheating problems and the radiator blockage that leads to head gasket failure. It’s important that we continue to educate our customers on the value of cooling system maintenance.

We all should be recommending water pump and drive belt replacement with a timing belt job, but consider adding a thermostat to the list. It’s a good time to replace it while the system is empty, it doesn’t add much to the price and, when you’re done, you and the customer can be confident that the cooling system is in good shape.

The final maintenance item to consider is regular top-end cleaning to prevent the carbon buildup on the valves. In my opinion, this procedure is dependent on how frequently you see the problem. If it’s a problem you’ve seen in your area, it makes a lot of sense to do the job, not only to prevent it from becoming a problem, but also to ensure the car performs as it should. Carbon buildup will cause driveability problems that the customer may not notice since they tend to come on gradually. But most will notice the increased performance and smoother running when it’s removed.

I hope you feel more confident that you’re ready to diagnose and tackle top-end service on four-cylinder Honda and Acura engines, and will continue to educate your customers on the benefits of preventive maintenance that will safeguard their vehicle from needing these repairs in the first place. As import specialists, we win either way.

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