The coolant inside the cylinder is a pretty serious condition, and if ignored, could grenade the motor. But, the problem may not be as severe as it first appears.
The top 3 reasons for coolant in ATV cylinder include:
- Blown head-gasket
- Loose cylinder head bolts
- Cylinder head fault
In this post, you’ll learn about the most common causes for coolant inside your ATV cylinder, how to diagnose them and what you’ll need to do to fix them.
1 Blown Head-gasket
A head gasket is a graphite material that’s sandwiched between your cylinder (Jug) and the cylinder head. Its function is to seal – seal the compression chamber, seal the coolant passages and seal the oil passages.
Head gaskets work super hard and are under extreme stress. It’s not surprising they’re a common failing component. Gaskets can fail in a few different ways.
Symptoms of a blown head gasket vary, depending on engine type and how the gasket fails. As you have found coolant inside the cylinder, it suggests the gasket failed between the cylinder and the coolant passage.
This type of failure allows compression gasses to escape into the coolant system, which may present itself as coolant blowing from the rad cap or a coolant hose pipe blowing off. Compression gases escaping into the coolant system can cause rad damage too. This type of failure conversely also causes the piston to suck coolant into the cylinder on the downstroke.
The engine tries to burn off the coolant with the fuel mix inside the combustion chamber. This often presents itself as white smoke from the tailpipe and also causes a telltale sweet smell in the air.
How to diagnose:
There are a few ways to diagnose a blown head gasket, a chemical test of the coolant system, a leak-down test, and a coolant system test.
I like to use a leak-down test kit. This is a simple test and involves removing the spark plug, fitting an adaptor, and compressing the cylinder with air at TDC (Top Dead Center).
A pair of gauges help add and gauge pressure loss, but you’ll usually hear where the problem is. In our case, we’ll expect to see or hear air coming from the radiator, so top up your rad and remove the rad cap.
The leaking compressed air will cause the coolant to bubble up.
What Causes Head-gasket Failure?
Overheating is one of the more usual and immediate causes of a blown head-gaskets. And while we know we’ll need to replace the gasket it is worth noting – unless we find the root cause of why the gasket failed in the first place we could be back visiting this problem again.
Here are all the most common causes of head gasket failure:
- Overheating coolant system
- Wear and tear – gaskets wear is proportional to use, the harder she works the sooner you’ll be replacing the gasket.
- Old age – even well maintained bikes will eventually need a gasket, just a matter of time.
- Old coolant – old coolant or worse using straight water promotes corrosion inside the coolant system. Materials like gaskets, rubber, and plastic components are under attack. In fact, some old coolant turns acidic and actually eats away at the cylinder head. Condition known as electrolysis.
- Warped cylinder head – incorrectly torqued cylinder head and contatant heating cycles will lead to warping of the cylinder head.
- Frozen engine – ineffective anitfreeze will allow an engines coolant to freeze in winter which may cause the head gasket to fail
But as you know, overheating the motor is by far the most common head gasket killer, and so next, we’ll look at what the most common causes of overheating are.
Common causes of overheating:
Your bike depends on air rushing past the radiator to cool the coolant. Slower-paced trail riding may lead to overheating where a bike’s coolant system is already compromised, such as a partially blocked radiator, sticking thermostat, low coolant, poor coolant quality, etc.
Here’s a list of the main causes of an overheating engine:
- Low coolant level
- Coolant leak
- Old coolant
- Air locked coolant system
- Faulty waterpump
- Faulty rad cap
- Blocked rad (muck etc)
- Faulty rad fan or switch
- Fuel type issue
- Faulty spark plug, incorrect gap, or incorrect plug heat range
- Piston carbon buildup
- 2-stroke oil quality or quantity issue
- Carburetor issue
- Head gasket issue
- Vacuum leak
- Ignition timing issue
Testing the coolant system
Using a coolant system test kit will help diagnose any issues with the coolant system.
It may also indicate a head gasket failure, but it is more common to use a different tool to check head gaskets and we’ll look at them below.
Of course, not all bikes come with a rad fan as standard, so if you do a lot of trail riding and your bike usually runs hot, (you notice your bike dripping coolant) then consider fitting a rad fan.
Old coolant or using straight water in your coolant system causes corrosion, and that can lead to early gasket failure and some other problems, like:
Premature gasket failure
- Water pump seal failure
- Frost plug failure
- Head gasket failure
How to fix blow head gasket:
The only fix here is to remove the cylinder head inspect all components and replace the gasket. It is a job you can take care of yourself, but you’ll need to be mindful of timing the engine correctly when reassembling.
You’ll need to consult a workshop manual as you’ll need to know the cylinder head torque specs and also the tightening sequence.
In addition, you’ll need to be clear about timing the engine, getting the timing wrong could cost you a top-end rebuild.
When a cylinder head is removed, it is customary to reseat the valves and replace the oil stem valve seals, neither jobs are complex or expensive but you’ll be glad you did it.
The only special tools needed are a good quality torque wrench.
2 Loose Cylinder Head Bolts
As you already know, as gaskets age, they degrade, and cylinder bolts can become loose. Loose bolts will reduce friction between the head and cylinder. And by loose, I don’t mean hand loose. I point out of specification.
Because the combustion chamber is under such pressure (about 200psi), it will find any weakness. Torque specifications are very particular to each manufacturer, and the sequence of tightening is particular too.
A new gasket must be replaced whenever the cylinder head is removed, and a torque wrench used to tighten the head bolts to spec.
Borrow or buy a torque wrench, get your engine torque specs and sequence and check your head bolts. You’ll likely need to remove some components to gain access to the bolts. Re-torquing the head may not be successful. The correct fix is to replace the gasket.
3 Cylinder Head Fault
Your engine may look pretty solid, but in fact, it’s hollow and not as strong as it may appear. Coolant moves around an engine in a circuit. The cylinder head and cylinder (Jug) contain hollowed-out passages that allow the coolant flow.
If an engine overheats, the walls of the water jacket or head passages can develop hairline cracks which will allow coolant to enter the cylinder, either directly or through the intake valve.
This is the worst possible scenario as this type of damage can’t be repaired. Another common failure is a warped cylinder head. The warping may be caused by overheating, broken head bolts, or incorrect torquing specification or sequence.
A warped head can be repaired, but it will need to go to a machine shop for analysis and skimming.
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