Radiator Hose Blew Off And Car Won’t Start? Reasons And Solutions To Fix It!

Ford F150 radiator fan runs constantly
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Several parts make up the cooling system that includes the coolant, thermostat, water pump, driving belt, coolant temperature sensor, radiator, and connecting hoses.

Radiator hose even though is just a connecting hose between the radiator and the engine, plays a major role in connecting parts to maintain the engine temperature within limits.

If the radiator hose blows off and car won’t start, then it is typically due to the damages introduced by the engine overheating conditions like engine head gasket damage, cylinder head warp or it would be accidental disconnection of some sensors while replacing the rubber hose or damaged sensors resulting from coolant spillover, etc.

In most cases, the radiator hose blew off issue happens due to issue related to one of the parts like an aged rubber hose, low coolant level, faulty radiator cap, blocked expansion tank hose, faulty thermostat, clogged radiator, malfunctioning CTS, failing water pump or belt and faulty radiator fan switch.

If you are also facing the issue of the car not starting after the radiator hose blows off, then you are at the right place. Stay tuned for details!

10 Reasons For Radiator Hose Blowing Off?

The heat produced during the engine operation needs to be dissipated otherwise the engine would cease to function.

The water pump circulates the coolant in the cooling system between the engine and the radiator.

The coolant gets circulated inside the water jacket provided on the cylinder block walls and absorbs heat from the engine.

The radiator hose takes the hot coolant from the engine cylinder and it reaches the radiator at the top portion wherein it exchanges heat with the ram air which is pulled by the radiator fan over the radiator fins.

The cold coolant leaves the radiator at the bottom portion and it again circulated inside the cylinder water jackets by the water pump driven by the engine crankshaft through the pulley and drive belt arrangement.

If your radiator hose blows off then you may be planning to replace the rubber hose, but before you do so it is worthwhile to first understand what would cause a radiator hose to blow off.

If you try to figure out the root cause for the radiator hose getting collapsed, it would help in preventing similar events in the future and also may help in surfacing out problems that could permanently damage the engine and probably could avoid costlier repair operations.

Below are a few causes for the issue of the radiator hose blowing off.

Aged radiator hose

The radiator hoses are typically made of rubber elastomer hence there are chances of it getting cracked due to either aging disintegration over time or wear and tear with surrounding parts.

Hence all hoses including the radiator hoses need to be inspected thoroughly during the vehicle’s scheduled maintenance for any cracks or leaks.

If we happen to miss the disintegration of the hose during the inspection, then there are chances of the failing radiator hose getting blown off while driving.

Low coolant levels

The root cause for the radiator hose blowing off could be that the radiator hose didn’t withstand the internal pressure of the coolant caused by engine overheating.

You may see the engine temperature gauge reaching alarming levels indicating engine overheating.

If you are maintaining a low coolant level in the engine coolant tank, then there are chances of overheating of coolant and that would increase the coolant pressure in the coolant flow circuit which may cause the radiator hose to blow off while driving.

An increased coolant pressure occurs when the rate at which the heat is generated by the engine offsets the rate at which it is dissipated from the coolant due to less coolant flow in circulation.

Hence it is necessary to keep the engine temperature within limits by properly maintaining the coolant levels within max. and min. working levels.

Faulty radiator cap

The radiator cap is the part that sits over the radiator and is connected to the expansion tank by a hose.

When the coolant temperature increases, it gets pressurized and the valve inside the radiator cap opens and allows the hot coolant to reach the coolant expansion tank to maintain the coolant pressure within permissible limits.

But when the radiator cap seals and springs have large gummy deposits, then the valve won’t open and that would pressurize the coolant to an extent leading to radiator hose blow-off phenomena.

Ensure that the radiator cap seal is clean but remember not to open the radiator cap when the engine is hot, otherwise, the coolant will blow out due to working pressure.

Let the engine gets cool before you open the radiator cap for inspection.

Blocked expansion tank hose

The hose which is connecting the radiator cap to the coolant expansion tank sometimes gets blocked and it leads to pressurized coolant conditions similar to what happens when the radiator cap goes bad.

This increased coolant pressure causes the rupture of the radiator hose, especially at the vulnerable locations of the rubber hose.

When the engine gets cooled, the coolant temperature and pressure would reduce, hence the coolant returns from the expansion tank to the radiator due to vacuum generation in the cooling system.

A vent hose is connected to the expansion tank and the other end of it is left open to the atmosphere to allow air to enter the system to facilitate the return flow of coolant to the radiator.

When this vent hose gets blocked, the system vacuum would cause the collapse or burst of the radiator hose.

It is worthwhile to inspect the expansion tank connecting hoses to avoid repeat events.

Faulty thermostat

The thermostat is the part that sits at the outlet of the engine cylinder where the coolant exits the engine.

It senses the engine temperature and decides whether the coolant needs to be recirculated inside the engine when the coolant is cool enough or the coolant needs to be circulated inside the radiator for cooling off.

When the thermostat malfunctions, it would erratically restrict the coolant flow to the radiator when the engine is running hot.

This would increase the coolant temp and cause engine overheating since it is not exchanging heat with the airflow across the radiator and that would increase the coolant pressure and which would blow off the radiator hose while driving.

Clogged radiator

When the water pump pushes the coolant inside a clogged radiator, it would increase the back pressure in the cooling system and that would affect coolant circulation.

Anything that affects coolant circulation would result in engine overheating and put pressure on the radiator hose which eventually will come off as the pressure increases.

Hence it is essential to check the radiator and replace it if clogged.

Malfunctioning coolant temperature sensor (CTS)

The CTS acts like a fan switch. When the engine temperature increases, it sends signals to the ECU to switch ON the fan to pull more air flow across the radiator to cool off the hot coolant leaving the engine water jacket.  

But when the CTS malfunctions, it may not send proper signals to radiator fan when needed and that would increase the engine and coolant temperature.

The coolant remains hot due to insufficient heat exchange and increases the coolant pressure which would cause the radiator to get come off.

Failing water pump

The water pump is the part that pumps the coolant in the cooling circuit and ensures circulation of the same in the system.

But when the water pump goes bad, it would produce the typical sound, and many times the coolant leaks through the gasket seal in the water pump and deprives the coolant in the cooling system.

A low coolant level would increase the system pressure and make the radiator hose blow off.

Damaged driving belt

The engine crankshaft is connected to the water pump through drive belts. If the drive belts go bad it would affect the pressure of the water pump and hence the circulation of coolant.

This would probably lead to engine overheating and increase the coolant pressure sufficiently enough to blow off the radiator hose while driving.

Faulty coolant fan relay

Apart from the engine cooling system, if the air conditioning system is also not running efficiently, then the issue may be due to a faulty coolant fan relay.

Typically, in the car, the ECU gets a signal from the coolant temperature sensor and sends a signal to the coolant fan relay to switch on or OFF the coolant fan, but a malfunctioning coolant fan relay will not allow the fan to start or in some cases continuously run the fan even when the ignition is switched off.

As the radiator fan is switched off when it is desirable to cool the engine coolant, the coolant temperature and hence the pressure would increase and that would cause the radiator hose to blow off while driving.

Does The Radiator Hose Blew Off And Car Won’t Start? 7 Causes And Solutions To Fix It!

Now we know the causes for the radiator hose blowing off. When the car won’t start after the radiator hose blows off, before you start replacing the parts endlessly it is worthwhile to understand the reason for the car not starting condition.

Leaky cylinder head gasket

Have you checked the cylinder head gasket for any leaks? If not, it is time to do so.

In most cases, if the radiator hose blew off and the car is not starting, then it would mean that the engine might have got overheated sometime earlier and has damaged the coolant rubber hose.

The engine overheating could damage the cylinder head gasket to an extent that it would leak the gases, coolant, and oil that would start affecting the combustion process.

Often when the cylinder head gasket goes bad, it starts leaking the coolant through the sealing interface either into the cylinder where the combustion takes place or mixes with the oil lubrication circuit in the cylinder head.

If the coolant mixes with the fuel or oil lubrication circuit, you may also notice white smoke getting emitted from the exhaust tail pipe indicating vaporization of coolant when it combusts with the fuel in the cylinder or you may notice coolant seeping out of the cylinder head gasket area.

The damaged head gasket ultimately affects the engine combustion process and would prevent the car from starting when the rubber hose blows off.

Warped cylinder head

As already mentioned, when the rubber hose blew off and the car won’t start then there is a large chance that the cylinder head is warped due to engine overheating.

A warped cylinder head would affect the engine compression and won’t let the car start after an engine overheating phenomenon.

It is advisable to do a compression or leak-down test that indicates whether there is any issue with the engine compression or is there any other underlying serious engine problem.

Mount a compression tester on to spark plug socket of each cylinder and crank the engine a few times.

If the value is more than 100 lbs and there is not much difference in values between cylinders, then your engine is safe, you need to look for other problems.

If the cylinder condition has gone that bad preventing the car from starting, then you would notice that the engine makes huge noise after cranking.

Coolant spray over electrical parts

When the rubber hose blew off during driving, then it would spray the coolant all over the engine compartment and there is a possibility of coolant falling over nearby electrical parts especially the starter solenoid wiring harness or sensors which sit right beneath the engine coolant inlet point, or spill over maybe on other sensors like MAF, crankshaft position sensor, coil packs, TMap sensors, etc.

Since the electrical parts and sensors are sensitive to wet conditions, the car won’t start even after replacing the rubber hose once it blows off.

It is advisable to spray some WD40 over the distributor cap, surrounding electrical connections, leads, coils, etc, and wait until everything dries off.

Disconnected electrical connections

When the car won’t start after the radiator hose blew off and if you have not serviced any other parts nearby, then you need to check for disconnected electrical couplers.

It is possible that you might have unintentionally disconnected some electrical connections while adjusting or replacing the rubber hose or you might have disconnected some sensors and forgot to reassemble it back.

You need to carefully inspect beneath the car hood for a loose or disconnected electrical connector, especially the battery terminal connections, and reconnect the same and check whether the car starts.

If you observe any corrosion on battery terminals, then it is recommended to clean or replace the terminals.

Otherwise, the vehicle’s power supply to major engine parts may get disturbed and the car won’t start.

Malfunctioning thermostat

A malfunctioning thermostat would abruptly restrict the coolant circulation inside the engine cylinder water jacket and that would lead to the engine overheating and in worst cases, the piston may cease to move and get jammed.

When the oil which lubricates the engine moving parts get vaporized due to high temperature and the coolant which shall cool the engine is not available, then there is the possibility of the engine getting ceased.

The car won’t start when the engine gets jammed due to engine overheating followed by coolant rubber hose damage.

Hence check thermostat and replace it if required after inspection.

Fuel system vapor lock

The engine overheating also leads to increased fuel temperature.

Since gasoline is volatile, the increased temperature would increase the pressure and create a vapor lock inside the fuel supply hoses.

So, the next time when the coolant rubber hose blows off and the car is not starting even after replacing the rubber hose, then you need to inspect the fuel system for vapor lock caused by engine overheating.

To confirm that issue is related to fuel, you just need to spray some starting fluid into the intake system, if the car starts then you need to troubleshoot the fuel system.

If it doesn’t then the issue may be ignition spark related.

Discharged battery

When the rubber hose blew off and sprayed the coolant on the surrounding engine parts, you might have tried cranking the engine several times before the coolant gets dried off over the electrical connections or sensors nearby.

Multiple engine cranks would discharge the battery to an extent that the sensors that malfunctioned initially even if get recovered when it dries off, hence check for battery drain if your car is not starting.

Typically, when the car is not starting after rubber hose blew off and you are sure that nothing is touched except rubber hose replacement, then it is either the fuel, spark, or air intake system that needs to be looked into.

Final Thoughts

The coolant radiator hose even though seems just a connecting hose but when it gets blows off due to either engine overheating or improper cooling system ventilation through the overflow tank, it typically ends up with car starting problems.

The engine overheating issue can be due to malfunctioning of various parts which form the cooling system like the thermostat, water pump, driving belt, CTS, low coolant levels, coolant fan relay, and clogged radiator.

But when the radiator hose blows up and the car won’t start then apart from radiator hose replacement you need to look for the permanent damages left by engine overheating conditions like engine head gasket damage, cylinder head warpage, accidental disconnection of some sensors or damaged sensors resulting from coolant spillover, etc.

You can do simple compression or leak-down tests to confirm whether the car’s compression is intact or if there is any permanent engine damage.

It is necessary to understand the root cause of the car starting issue instead of endlessly replacing parts that may not be contributing to the problem and hoping that the car starts.

Happy Motoring!








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