My car is Skoda Rapid 1.6 litre petrol engine, 2013 model. It has ran about 140000 Kilometres.

Recently Smoke started coming out of my coolant reservoir and it was leaking not from the cap but from the mid of the coolant reservoir container.

So when we replaced it with a new coolant cap and new coolant reservoir container. Then we revved the engine just to check if radiator Fan is working properly.

Before the fan could have started the coolant reservoir cap blown up and coolant liquid came out like a fountain.

Seems like when coolant reservoir cap is removed then coolant circulation looks fine but when cap closed lots of pressure building inside coolant reservoir.

My old coolant reservoir was also replaced just an year ago, even it should have not broken so quickly.

What could be going wrong.

  • 1
    Welcome to Motor Vehicle Maintenance & Repair! Apr 15, 2023 at 15:32

1 Answer 1


You almost certainly have a blown head gasket.

The head gasket seals the joint between the engine block and the engine head. When there is a break or gap in the head gasket, hot combustion gases from a cylinder are forced into the coolant. The gases displace coolant and force it back into the coolant reservoir. The increased pressure in the cooling system can blow the reservoir cap off, as you observed, or crack the tank.

A mechanic with emission testing equipment can detect exhaust gases coming from the coolant tank, which will confirm the diagnosis. They can also do a compression test or cylinder leakdown test and will probably find that one cylinder has low compression or does not hold pressure.

Continuing to drive with a blown head gasket can damage the engine beyond repair. The escaping hot gases can cut a groove in the smooth mating faces between the engine block and the head. In addition, since gases are displacing coolant, there will be interruptions in coolant flow and overheating. The engine can develop internal hot spots that cause warping or other damage.

If the car was driven very little since the initial symptoms, it can be repaired with no drama by replacing the head gasket.

  • Thanks for the information, i have given the car to a mechanic will see what he updates me on the same.
    – mSatyam
    Apr 15, 2023 at 15:12
  • @mSatyam - If this post helps you, you should consider up-voting it so as to show your appreciation. Apr 15, 2023 at 15:34
  • In addition to blowing coolant out of the engine, there is another issue. When you stop the engine, the hot gasses in a cylinder will contract, and may suck coolant into the cylinder. Next time you try to start the engine, it will try to compress the liquid, and may break a piston, or contaminate the oil with coolant that gets forced past the piston rings. Also, you are lucky the coolant reservoir gave way: it could easily have also been the radiator, or the heater unit. Apr 15, 2023 at 22:20
  • Thanks all for your comments and suggestions, although the mechanic who is looking into my car is suggesting we check for any choking in the radiator first. There is a bit shortage of good garages in my area, I hope all goes well, will keep you guys posted.
    – mSatyam
    Apr 16, 2023 at 18:25
  • @Paul_Pedant I had got my car back from the mechanic, he has not replaced the head gasket. Instead the mechanic replaced the Actuator valve (valve that lets coolant go in radiator) and thermostat switch that switch radiator fan off/on. Now the coolant is not boiling as it was earlier. We did similar test as earlier to throttle high and now we see it does not boil neither the cap is bursting now. Will keep driving my car and inform how it goes in long run. Mechanic says engine is ok for now.
    – mSatyam
    May 4, 2023 at 10:55

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