It’s a sickening feeling when your car stalls, even worse if you suspect the engine is blown. Although major engine failure is pretty rare these days, it can happen.
An engine may blow in many different ways, some will fail and allow the engine to crank and some won’t. Types of engine failures that will still allow the engine to crank, include:
- Blown head-gasket
- Burnt valve
- Broken timing belt (non interference)
- Bent con-rod
In this post you’ll learn the most common causes of a blown engine, and if they will allow the engine crank. You’ll also learn how to diagnose engine failure, and if replacing the engine is worth it.
Common Engine Failures
Engines are pretty durable these days, when I was a kid engine needed a ton more love. But as technology moved on the engines became pretty good, rebuilds are rare nowadays.
Most engines are capable of covering at least 200 thousand miles without a major issue. Of course, the engine will need to be maintained or at the very least a have a good oil change record.
The term Engine Blown generally means the engine has suffered a major component failure, but of course, you won’t know that for sure until you diagnose the failure.
An engine commonly stops for one of three reasons:
- Fault in lubrication system
- Fault in coolant system
- Fault in air/fuel mix
The most common more specific engine failures include:
- Head gasket failure – Engine will crank
- Broken timing belt/chain – Engine will crank (non interferance)
- Faulty valve – Engine will crank
- Crankshaft seizure – Engine won’t crank
- Camshaft seizure – Engine won’t crank
- Piston seizure – Engine won’t crank
- Bent con-rod – Engine will crank
- Broken con-rod & block – Engine won’t crank
Modern engines usually only fail because some other component has failed, misuse or poor maintenance. A blown engine is a symptom and not the root cause.
Head Gasket Failure
The engine will still crank if the head gasket is at fault. A head gasket failure isn’t the worst kind of problem, in fact as engine failures go, this is the one you want.
The head-gasket is a graphite material sandwiched between the cylinder head and block. Its function is to keep the compression within the cylinders and prevent oil and coolant mixing.
The gasket breaks down over time but overheating is a common cause too. A blown head gasket may also be a symptom of another problem.
Symptoms of blown head gasket include:
- Overheating engine
- Temperature gauge in the red
- No heat from the heater
- White smoke from the tailpipe
- Coolant leaking: Coolant in the oil
- Hose pipes blowing off
Causes of blown head gasket include:
- Warped cylinder head
- Faulty rad cap
- Faulty thermostat
- Faulty fan
- Faulty temperature switch
- Faulty water pump.
Broken Timing Belt/Chain
The timing belt helps keep the top and bottom engine components in time. The timing is mission-critical, if it’s out by even a few degrees, the engine won’t run right.
Neoprene toothed belts or timing chains and the most common method to time the engine. Older motors used a metal rod known as a push rod to time the opening of the valves. The pushrods were pronto bending.
Engines are either interference type or not. Interference simply means the valves and push-rods overlap, meaning if the timing is off the piston will collide with the valves.
Symptoms: Interference type – Metal sound on crank; No crank; Click sound from the starter without crank; Engine light on.
Non-interference – No start; Fast crank; Engine light on.
Valves open and close sequentially to allow fuel/air mix in and spent gases out. The whole process is driven as you know by the crankshaft. The valves must make an airtight seal, damage to the valve or the valve seat will cause compression loss.
Causes of valve damage: General wear and tear; Wrong fuel type; Prolonged vacuum leak; Wrong spark plug heat range; Faulty EGR valve; Faulty purge valve; Faulty coolant system; Impact from Turbo failure.
Symptoms include Constant or intermittent single cylinder misfire; MIL on; White or wet spark plug electrode; No start; Hard starting.
The crankshaft is at the heart of the motor, the pistons drive the crank and it’s under tremendous stress. It needs constant lubrication, or friction will very quickly heat the bearings and the engine stops dead.
Causes of failure: Low oil level; Poor oil quality; Wrong oil type; Failed oil pump; Faulty oil filter; Oil system pressure loss; Wear and tear on the crankshaft; Coolant system fault.
Symptoms include: Knocking noise; High pitched sequel; Clicking noise from the starter motor.
The camshaft lives at the top of your engine. Its job is to control the engine’s breathing. It opens inlet and exhaust valves.
Seizure is common as the camshaft is the farthest from the oil pump. When it seizes, its lobes hold some valves open which causes the pistons to strike and bend the valves.
Causes include Low oil level; Poor oil quality; Wrong oil type; Failed oil pump; Faulty oil filter; Oil system pressure loss; Wear and tear on the camshaft; Coolant system fault.
Symptoms include: High pitched sequel; Fast crank; No crank; MIL on; No start.
Piston seizure is as you’ve guessed pretty terminal. The piston creates friction and without proper cooling, heat fuses the piston and cylinder, together, the engine is toast.
Detonation is another common problem to affect pistons, it happens naturally, when cylinder temperatures rise the fuel mix ignites without the spark plug. The effect is felt by the pistons over time if not corrected. Detonation is caused by incorrect gas, wrong plugs, bad knock sensors, wrong plug types, vacuum leak.
Causes of failure: Low oil level; Poor oil quality; Wrong oil type; Failed oil pump; Faulty oil filter; Oil system pressure loss; Wear and tear on the camshaft; Coolant system fault, Vacuum leak; Wrong plug type; Wrong gas type; Bad EGR valve; Faulty turbo charger oil seal.
Symptoms include: Engine stalls; Loud noise; Mil on; Puff of white smoke; Wheels lock up on manual transmission.
A con-rod connects the piston to the crankshaft and is liable to bend under certain circumstances. The length of the con-rod is critical to how the engine performs. A bent con-rod is repairable but will require a bottom end strip down.
Con-rods are famous for bending when cars a driven into standing water like deep water splashes. The water fills the cylinder and as water won’t compress, the con rod bends. The condition is known as hydro-locking.
Causes of failure: Incorrect timing; Faulty EGR valve; Water ingestion.
Symptoms of failure: No start; MIL on; Rough idle; Stammer; Excessive engine vibration.
Broken Con-rod & Block
The broken con-rod is a worse version of a bent con-rod. In addition, however, the broken but attached con-rod end breaks through the engine block. This is a common result if the con-rod breaks, but con-rods are more likely to bend unless your Dale Earnhardt.
Diagnosing Engine Failure
Diagnosing engine failure isn’t that difficult, but you will require a few tools. A compression tester, plug socket and ratchet, a leak tester works even better but does require compressed air.
A scan tool is the usual starting point, checking for codes helps shorten the diagnostic time.
Anyway, I’ll explain both ways.
Compression test checks cylinder compression and allows for comparison between cylinders. A minimum spec must be achieved and a large difference in cylinder(s) readings indicates a problem.
A dry compression test is usually performed first and if a problem is suspected it is followed by a wet test. The wet test helps identify if the problem is in the bottom or top end of the motor.
A compression test is of course only useful if the engine is cranking over, if it isn’t, you’ll need to use the Leak-down test.
The leak down test is the test I use a lot to help find engine issues quickly. It does require a small compressor in addition to a test kit. The test simply involves setting the engine to TDC (Top Dead Center) on the compression stroke (valves closed) compressing the cylinder and finding the leak.
Is Fitting An Engine Worth It?
Fitting a brand new engine likely won’t make economical sense, a used but tested unit is more likely to make sense. An experienced mechanic will have no problem swapping an engine on a smaller car in about a day, larger vehicles may take a couple of days. Larger cars are harder to work on as engine bay space is usually tighter.
In addition, your replacement engine may come stripped of external components, if so, your mechanic will need to gather new parts such as gaskets and seals, etc before the fitting is complete.
Makes sense to replace the timing belt, water pump, and drive belt too. This work is a ton easier on a bench, the shop may discount the labor.
Your new engine will also require at the very least an oil and filter change. I’d go ahead and service it too, air filter, fuel filter, and transmission oil change.
- The replacement engine cost
- Labour to fit
- Additional parts
- Timing belt water pump
- Drive belt
- Oil and filter change
- A/C recharge
- Gaskets and seal
You’ll need to balance the resale value of your car before the engine failure. Check Craigslist for your model, see the average price for a realistic valuation.
If you are spending less than a third of the cost of replacement more than that and I’d consider looking for a replacement car with a mechanical warranty.
Will a car start with a blown engine? A blown engine may start, but will run erratically and often with many strange metallic or knocking sounds. Revving a blown engine may produce increased noise, smoke and vibration.
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John Cunningham is an Automotive Technician and writer on Rustyautos.com. He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.
John uses his know-how and experience to write fluff-free articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.