Replacing a head gasket is one of the most complicated jobs you can do on an engine, so it doesn’t surprise that a lot of problems can arise after the replacement. Some of them are fairly simple to fix, while others will call for another engine rebuild, but more on fixing them later; for now, here are all the problems you might encounter.
The most common problems after head gasket replacement include misfires, coolant mixing with engine oil, engine overheating, and random coolant leaks.
Most Common Problems After Head Gasket Replacement
Here we will cover all the common problems after head gasket replacement in more detail, including what’s causing them. After that, we will go into how you can fix each of those issues.
If your engine runs rough after head gasket replacement, chances are it has developed a misfire. If that’s the case, the engine sound will resemble a lawn mower, or at least that’s how most people describe it. Furthermore, the check engine light will be on or flashing, the car will stutter when accelerating, shake while idling, and have overall poor performance and fuel economy. In any case, it’s impossible to miss.
A misfire means that one or more cylinders are not firing or is firing at the wrong time, which can lead to backfires or detonation. And one of the leading causes of misfires right after head gasket replacement is bad camshaft/crankshaft timing.
In other words, the timing belt is not installed correctly, resulting in the camshaft and crankshaft being out of sync. However, if the misfires started happening a couple of miles or days down the road, it’s possible that the timing belt was installed correctly, but it jumped a tooth or two later on.
The second possible cause of misfires under these circumstances, although not very likely, is mismatched connectors. Meaning you may have plugged the exhaust camshaft connector into the intake camshaft plug and vice versa. But that can only happen in newer cars that have one cam sensor per camshaft.
2. Coolant Mixing With Oil
Coolant mixing with oil is the number one symptom of a blown head gasket and may well be the reason why you replaced it. Alongside the coolant mixing with oil, you will almost certainly notice blue smoke coming out of the exhaust, which is oil and coolant burning in the combustion chamber.
The main causes of this are an improperly installed head gasket or wrong head gasket orientation. The second cause is a warped cylinder head which is why it has to be resurfaced every time you replace a head gasket. That resurfacing may not have been done at all or was done poorly, both of which will produce the same outcome as a blown head gasket.
Also, the engine block and cylinder head mating surfaces must be completely clean before installing the head gasket. That means it’s possible some debris or dirt was left under the new head gasket or on the cylinder head. And lastly, the cylinder head bolt torque and tightening sequence could be incorrect.
Each engine has its own specific head bolt torque specs and sequence, which, if you ignore it, will warp the cylinder head or back out the bolts. Moreover, some engines use torque to yield cylinder head bolts which must be replaced every time they are removed, and failing to do so will leave the cylinder head loose or warped.
3. Coolant Leaks
By coolant leaks, we don’t mean the coolant leaking into the combustion chamber but rather leaking outside the engine. A coolant leak after head gasket replacement can often happen because a lot of coolant hoses need to come off, and possibly the water pump and thermostat housing too.
That’s unless you see coolant foaming on the side of the engine just under the cylinder head, in which case the same causes we mentioned previously apply. Those include a warped cylinder head, dirty mating surfaces, wrong head bolt torque specs or sequence, and an improperly installed head gasket.
Although overheating is one of the leading symptoms of a blown head gasket, the reasons it happens after a replacement are much fewer. And the main cause is air in the coolant system or, in other words, an improperly bled coolant system.
Every time the coolant is flushed from an engine, you must bleed air out of the system after adding fresh coolant. Air in the system can lock the coolant in place and prevent it from flowing, plus it can create hot pockets of air near the cylinder head, causing it to warp fairly quickly. It also doesn’t help that a lot of cars have special coolant bleeding procedures that many people are unaware of, but more on that later.
The second possible reason your car is still overheating after replacing the head gasket is a stuck thermostat. Although the chances are somewhat low that the thermostat fails right after you replace the head gasket, it’s still worth checking, and it’s always a good idea to replace it together with the head gasket if the engine was previously overheating or mixing coolant with oil.
Fixing the Problems Caused by Head Gasket Replacement
As for fixing the previous potential problems, it’s important to mention that very few of them can be fixed by someone who doesn’t have much car repair experience. If you would describe yourself like that, it’s best to take your car in for an inspection where they can determine what’s causing each problem very effectively and fix it safely.
Misfires – Fixes
We already mentioned that the leading cause of major misfires after a head gasket replacement is camshaft timing. So, the first thing you should do is check whether the timing belt is installed correctly and reinstall it if it’s not. Also, if you notice the timing belt teeth are damaged or worn out, it means it has jumped, and it’s a good idea to replace it while you are there because it can destroy the engine if it breaks.
Next, recheck all the camshaft connectors. Make sure they are not damaged and that they are plugged in correctly. The best way to do that is to check a vehicle-specific service manual that you can find online reasonably easily. And while you are at it, check the spark plug leads and make sure they are snug over the spark plugs.
Coolant Mixing With Oil – Fixes
In case the coolant is mixed with oil, the only solution, unfortunately, is to replace the cylinder head gasket again. But once you remove the cylinder head, send it in for resurfacing and check the cylinder walls for cracks. But make sure you look closely because those cracks are hair thin at room temperature, and if you find any, you will have to replace the engine as well.
Once the cylinder head is back from resurfacing, buy a new head gasket and make sure you know the orientation. Even though some gaskets fit both ways, sometimes there could be two-millimeter-wide holes for oil or coolant passages that don’t line up.
Next, make sure the cylinder head and engine block mating surfaces are spotless and dry. Any kind of grease, fleece, and nearly microscopic debris on them can cause major problems. And lastly, find and print out the correct head bolt torque specs and tightening sequence for your specific engine.
Also, make sure you have the sequence in front of you while tightening to avoid making a mistake. Other than that, it also doesn’t hurt to have your torque wrench calibrated because, after a while, they will begin to click or beep too late or too early.
Coolant Leaks – Fixes
If you notice wet spots under the car or a smell of burning coolant inside the cabin after a head gasket replacement, there is no need to worry just yet. To start, check all the coolant hose clamps that came off during the head gasket replacement.
Those can be radiator hoses, thermostat housing hoses and gaskets, cylinder head hoses, etc. It’s also a good idea to look for leaks with the engine hot and running because the leak will be most pronounced under those conditions. And once you find the leak, retighten the hose, replace it if it’s broken, or replace whatever gasket or o ting might be leaking.
However, if you find burnt coolant on the side of the engine right under the cylinder head, I’m afraid you will have to replace the head gasket again. Also, refer to the previous section about coolant mixing with oil to see what you should keep a close eye on to avoid that from happening again.
The first thing you should do after a head gasket replacement is bleed the coolant system. The problem here is that some cars only require that you remove a bleed screw and wait for the coolant to start pouring out without any air bubbles. However, some cars require that you set the AC to hot and the blower on while bleeding, while others require that you enter the ECU (engine control unit) and set it to coolant bleeding mode.
The point is that many car models have special and unique procedures for bleeding the coolant properly. To check if your car has them, try and find some good model-specific forums and post a question, or get yourself a service manual where you will find the whole procedure with step-by-step guides.
On the other hand, if you are certain the bleeding procedure was done properly, it doesn’t hurt to replace the thermostat or at least test it to see if it’s working. That said, thermostats are fairly easy to replace and cost no more than $50 in most cases, so I would go with the first option.
Startup after Head Gasket Replacement YouTube Video
Q: What should I check after replacing the head gasket?
After replacing the head gasket, you should check if the car is overheating, if there are any coolant leaks, if smoke is coming out of the exhaust, and check the overall performance of the engine. And after a couple of days, check if any coolant is missing and whether or not the coolant is mixing with engine oil.
Q: How long will a car last after replacing the head gasket?
How long a car will last after replacing the head gasket depends on the overall condition, age of the car, mileage, and how well it has been maintained up until that point. But we can say that the head gasket will last at least 100,000 miles.
Q: Why would a new head gasket fail?
A new gasket could fail if it wasn’t installed correctly, the cylinder head was warped, the engine block or cylinder head mating surfaces weren’t clean, or the cylinder head wasn’t torqued properly. Also, it could be that the head gasket is good, but one of the cylinder walls is cracked.
Q: What is the aftermath of a blown head gasket?
The aftermath of a blown head gasket is most commonly a warped cylinder head, but it can be resurfaced, so it’s not too big of a deal. However, if the engine had overheated multiple times or the coolant was mixing with oil for too long, the aftermath is often catastrophic engine failure.
Q: Is it worth getting a head gasket replaced?
Whether or not it’s worth getting a head gasket replaced depends on the value of the car. A head gasket replacement usually costs between $1,000 and $2,500, so for older cars, it could be cheaper to buy a used engine or to buy another car.
Q: Is white smoke normal after head gasket replacement?
Yes, white smoke can be normal after head gasket replacement because the coolant that ended up in the exhaust because of the previously leaking head gasket is burning off. However, if the smoke continues for too long, it means the new head gasket wasn’t installed properly.
Q: Is changing a head gasket a big job?
Yes, changing a head gasket is a big job. As a matter of fact, changing a head gasket in some cases can be more complicated and time-consuming than replacing a whole engine. The average time to replace a head gasket is roughly 12 hours.
To summarize, the most common problems after a head gasket replacement is misfiring, coolant ending up in the engine oil, overheating, and external coolant leaks. Misfiring and external coolant leaks are not huge problems because those problems are fixed on the outside of the engine. However, the rest of the problems indicate that something is wrong with the new head gasket, and you will have to replace it again.