Better To Replace Head Gasket Or Engine? (Money saving info)


cylinder head

Traffic is bumper to bumper, the temp gauge is in the red S**t!!, this is so stressful.

It is better to replace the head gasket so long as the cylinder head and engine block are undamaged. The cost of replacing an engine is far greater than a head gasket. Removing the cylinder head to determine if it has been damaged is the correct course of action.

In this post, you’ll learn the symptoms of cylinder head gasket failure. You’ll also learn how a mechanic diagnoses, strips down, and inspects the cylinder head gasket.

Gasket or Engine?

Changing the engine generally will cost a ton more money than simply replacing the head gasket. So, unless your cylinder head is damaged beyond repair, and you won’t know that without stripping the cylinder head. Replacing the gasket is the most cost effective route.

But it is worth confirming the head gasket is at fault, no sense in spending money you don’t need to. You’ll learn in this post an overheating engine can be caused for lots of reasons, many of which are inexpensive and easy to fix.

Common Symptoms of Blown Head Gasket

A car that’s overheating is a real pain to drive, constantly watching the gauge, expecting it to crap a bag of bolts any minute.

Overheating coolant system and steam are the most common symptoms associated with a blown head gasket. But not all overheating is caused by a blown head gasket.

Symptoms of head gasket failure, include:

  • High temperature gauge
  • Steam from the hood area
  • Car using coolant
  • Coolant leaking on the ground
  • Sweet smell the air
  • Oil slick in the coolant
  • Coolant in the oil
  • White scum underside the oil cap
  • Coolant hose pipes blowing off
  • Engine stalls when hot
  • Cloud of white smoke from the tail pipe

All of these are consistent with a blown head gasket. However, before jumping the gun and spending dollars, it’s better to confirm your suspicions with a little further diagnostics.

7 Different Ways Head Gaskets Fail

A head gasket can blow in seven different ways, the most common is of course the compression to a coolant leak. But some engines are pronto different type gasket failures and they will exhibit different symptoms.

Head gasket failure chart

The seven head gasket failures and symptoms, include:

  1. Compression to external – Engine miss firing and escaping air sound.
  2. Coolant to external – Leak and overheating.
  3. Compression between cylinders – Cylinders miss firing.
  4. Compression to oil – Smoke and excessive oil consumption.
  5. Compression to coolant – Overheating and white smoke at tail pipe.
  6. Oil to external – Oil leaking and low oil pressure.
  7. Oil to coolant – Coolant in oil pan and or oil in the coolant reservoir.

High Temperature Gauge

The temperature gauge on the dashboard for good reason, it’s a reminder to shut down the engine if the temps climb into the red.

But what happens if you don’t? Driving a car in the red can cause some pretty catastrophic engine damage. Apart from the cylinder head gasket failure, the engine could seize solid, that’s bad for a couple of reasons. Your engine is now beyond repair and it could cause an accident at highway speeds as the engine simply locks up.

Other Causes Of Overheating

A high-temperature gauge isn’t only caused by a failed head gasket, here are some of the more common causes, some are a simple fix and others aren’t.

  • Low coolant – Top up coolant
  • Old coolant – Replace coolant
  • Air locked coolant system – Bleed air from system
  • Cooling fan not turning on – Check fan fuse, fan motor and fan thermo switch
  • Bad rad cap – Replace cap
  • Failed water pump – Replace pump
  • Faulty harmonic balancer – Replace pulley
  • Loose water pump drive belt – Tighten belt
  • Broken water pump drive belt – Replace belt
  • Faulty fan – Replace fan motor
  • Blocked rad – Back flush coolant system
  • Stuck closed thermostat – Replace Thermostat
  • Cracked Head – Replace head
  • Cracked block – Replace engine
  • Loose head bolts – Replace Head gasket and bolts
  • Warped cylinder head – Skim or replace cylinder or complete engine

Steam From Hood

Steam from under the hood is pretty reliable sign things are hot and a common cause here is a failed rad cap. A coolant system is a pressurized system of about 1 bar (15 psi). Pressurized coolant has a higher boiling point and that’s good.

A failed rad cap won’t seal correctly and allows air in which causes the coolant to boil and produce steam. It’s the same reason removing the cap from a hot radiator causes the coolant to instantly boil, opening the cap drops the pressure instantly.

Leaking Coolant

Coolant can and will leak from lots of components, some more serious than others. The less serious ones include:

  • Corroded or impact damaged radiator
  • Perished hose pipes
  • Loose clamps
  • Split heater core
  • Split expansion tank
  • Water pump seal or gaskets
  • Rad cap
  • Oil or fuel coolers

The more serious places a leak can develop, include:

  • Cylinder head
  • Engine block

Using Coolant

Car coolant

If you find you are constantly topping up the coolant, it could well be a failed head gasket but it could simply be a leak in the system. Not all leaks develop into a puddle on the ground.

Remember hot coolant turns to steam so a small leak may go undetected. Staining around hose pipe fittings or a sweat smell is a giveaway that the system isn’t sealing completely.

Sweet Smell

Wet car floor mats

Ah love the smell of sweet coolant in the morn…..if you can smell something sweet and it’s not the BBQ sauce between the seats, you may need to check your carpets.

Wet carpets and a sweet smell are a sign the car heater core (like a small radiator) has split and is allowing coolant to leak into the cabin. This needs to be fixed, leaking coolant is a health hazard.

Oil Slick

Check the coolant or rad for a slick of oil, this is an indicator the head gasket has failed between the oil and coolant passages. This is generally the reason for oil in the coolant. However, some utilize the coolant system to also cool the oil, transmission, and fuel through independent coolers or hybrids. If the coolers fail the fluids could mix.

Coolant In Oil

oil dip stick

Yea, this isn’t good at all. Coolant in the oil is usually a head gasket failure, internal engine failure is possible too but less likely. As said earlier, a failed water-cooled oil cooler could also cause the fluids to mix.

Scum On The Oil Cap

This is like a calibrated thumb, usually right or thereabout. Removing the oil cap and finding a white scum (actually more like coffee creme) is any indication there’s moisture inside the motor.

The moisture inside the engine could be caused by short driving cycles of course, but if say the coolant needed constant topping up also, you could lean towards a gasket issue with more confidence.

Hoses Blowing Off

Coolant hose

If your hoses are blowing off their fittings and the clamps and hoses are in great shape, you can bet your gasket has a hole in it.

The cylinder compression is entering the coolant system and the excessive pressure is finding a release through the hose pipes. I’d go ahead and replace the head gasket on this one.

Engine Stalls

When the engine gets super hot, its metal components expand. Under certain conditions, this can cause a weak gasket to allow ambient air into the cylinder. The combustion chamber no longer seals and so compression and fuel ratios are lost. You may find the engine starts again as it cools.

White Smoke

White smoke isn’t just for a new pope, it’s also a sign your engine is making steam. As coolant enters the combustion chamber, it’s mixed with the fuel and causes steam at the tailpipe. A diesel engine can make white smoke for fuelling issues so be sure to get confirmation of a blown head gasket before tearing her down.

Diagnoses Of Blown Head Gasket

An experienced tech will know that some cases won’t require any conformation, the evidence will be undeniable. However there may be cases where it’s not as clear cut and for those cases, we’ll need to run a test.

In order to confirm a head gasket failure, a few different approaches can be taken.

  1. Combustion leak test kit
  2. Coolant system test
  3. Compression test
  4. Leak-down test kit

Combustion leak test kit

A chemical kit is a popular test, it uses a chemical concoction to test the coolant system for the presence of exhaust gases in the coolant. It’s easy to use and very effective, however, if the gasket hasn’t failed at a coolant passage, this test won’t work.

The coolant test

This kit pressurises the coolant system and measures pressure loss over a given period. But simple observation of the coolant level while the engine is running will often give the game away.

This isn’t an ideal way to test either as it only measures a coolant passage-way gasket failure.

Compression

This test is sometimes performed to help identify a head gasket failure, it isn’t conclusive but it will at least point to the problematic cylinder or cylinders.

Compression test infographic

Examining and reading spark plug condition can help highlight the problem cylinder too.

The Leak Down Test

This is the test I run, it uses compressed air to pressurize the cylinders in turn. The kit employs a pair of gauges to monitor pressure loss, but mostly you’ll hear the air escaping. Where the air leaks from points to the likely point.

  • Air bubbles in the coolant system tells you, the gasket has failed at a coolant passage.
  • Air from the dip stick, usually indicates worn rings, but as we’re chasing a suspected head gasket failure, it’s likely the gasket has failed at an oil passage.
  • Air leaking out through the cylinder head is an obvious sign of a failed gasket.
  • Air rushing from the adjacent cylinder tells you the gasket has failed on the bridge between the cylinders.
  • Air from the exhaust indicates a valve or valve seat issue.
  • Air leaking from the intake suggests an intake valve or seat fault.
Engine leak down infographic

Stripping and Inspection

Engine stripping

Removing the cylinder head is relative straight forward. However, care will need to be taken and the process will differ slightly from model to model. As jobs go it is sizeable, it’s not an engine rebuild but you are going pretty deep into the motor.

Various components will need to be removed to gain access to the cylinder head. Various components bolted to the cylinder head will also need to be removed. Some of which may include:

  • Intake manifold
  • Exhaust manifold
  • EGR valve
  • Alternator
  • Power steering pump
  • Turbo charger
  • Motor mount

Pulling the head itself will require removing the cam cover and some vehicles will require cam removal also. But before we can do that we’ll need to release the timing belt or timing chain.

Engine timing

Getting this bit correct is mission critical, this procedure will differ between vehicles, but the principles are the same.

The timing is set at TDC (Top Dead Centre) on the compression stroke, often engine-specific locking tools are inserted to prevent movement. The belt or chain tension is then released and the belt or chain removed or set to one side.

With the timing gear safely out of the way, the head bolts can be removed. These guys will be tight and will likely be Torque To Yield (TTY, aka Stretch bolts), meaning they are one-time use. You will receive new bolts with your cylinder head kit.

Bolts out, the head is free, better to have a helper to lift the head upwards cleanly, dragging across dowel pins will score the cylinder head.

With the head off the gasket can be examined for the suspected failure. If your engine is more than ten years old, and long in the clock I’d go ahead and re-seat the valves and replace the valve stem seals.

Valves

You can check for cylinder head warping with a steel ruler and a feeler gauge, but pressure testing is the only way to tell for sure the head isn’t cracked.

It makes great sense to send the cylinder head out to an engineering shop to check for cracks. Sole destroying to rebuild only to find you still have an overheating issue. The engineering shop has specialized kit just for the job.

A cylinder head kit will include the head gasket and bolts, it may not include other gaskets such as manifold, exhaust, cam, etc. It makes sense to change out your timing belt and water pump if they were due in the near future, It is worth investing in a new thermostat also.

Related Question

When should a gasket be replaced? A gasket performs an important function. It seals systems, components and protects them. A gasket needs to be replaced whenever a component is removed. Reusing an old gasket may cause component failure.

John Cunningham

John Cunningham is an Automotive Technician and writer on Rustyautos.com. I've been a mechanic for over twenty years, I use my knowledge and experience to write articles that help fellow gear-heads with all aspects of classic car ownership, from tires to roof aerials and everything in between.

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