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  • Writer's pictureTeam Vebo

Case Study #1: Hydrolocked Mini Cooper S (F56)

Recently, we received a distress call from our customer who claimed that his car died while trying to cross the flood and he could not start the car after the incident. He also reported that the water level was not 'that high'. So, after the call, we advise him to tow his car to our workshop so we can diagnose the car.

When the car arrived, first in our list is to check the engine oil cap to find any sign of water. Luckily, there was none, but now we wonder why does the engine refused to start? So, the next item in our list was to turn the crank shaft manually and we found out that the engine was jammed. So, this is the reason why the car refused to start.

The next step we did was to remove the spark plug and try to check if there is any water in the combustion chamber and viola! We found that there was a lot of water in the piston no.1 while blowing the high pressure gun into it. The video below shows how we checked this.

Since the engine is completely seized, the decision was to remove the valve cover and to check for any of abnormalities. We noted that there are no abnormalities here. However, after we open the valve cover, we start noticing that there's traces of water in the engine oil.

At this point, we're very curious because we would like to know how did the water enters the engine(Remember: The customer says the flood water is very low)? So we decided to open the charge-air duct. What is charge-air duct? It is the pipe that connects the turbo to the intercooler and from intercooler to the engine intake which connects directly to the combustion chamber. While removing the charge air-duct, we saw a lot of water pouring out. The video below shows how much water comes out from it.

We decided to investigate further by removing the engine to check in detail what causes it to be jammed? We started by removing the oil sump to check the crank shaft and piston from bottom, but nothing abnormal was noted again.

We continued to strip the entire engine, but the process was difficult as we can’t remove the torque converter due to jammed crank shaft. However we managed remove the piston out carefully and this is what we observed.

So by comparing all the conrod, it is obvious that this conrod no.1 was bent during the compression cycle after the water was ingested into the combustion chamber. This event is called hydrolocked and is explained in the next paragraph.

“Hydrolock (a shorthand notation for hydrostatic lock) is an abnormal condition of any device which is designed to compress a gas by mechanically restraining it; most commonly the reciprocating internal combustion engine. Hydrolock occurs when a volume of liquid greater than the volume of the cylinder at its minimum (end of the piston’s stroke) enters the cylinder. Since liquids are nearly incompressible the piston cannot complete its travel; either the engine must stop rotating or a mechanical failure must occur.”

So, how did the water actually gets in with such short period of time?

Point no.1 is highly suspected as there is where the water will get into the turbo and charge into the intercooler at point no.2. Point no. 3 is also another potential entry point of the water but this is quite unlikely as the air filter position is quite high which is nearly the top of the engine which is the top of front bonnet.

So lets measure how high are this point from the ground in actual.

This is point no.1 (41cm or 16 inches)

Point no. 2 (21cm or 8 inches)

Point no. 3 (73 cm or 28 inches)

So lets see this by comparing with the vehicle's front bumper.

Point no.2 is 21cm, which is slightly at the bottom part of the bumper.

Point no.1 is 41 cm, which is just above the front fog lamp.

We can see that the chances for the engine to hydrolock is extremely high for a Mini Cooper S(F56) even at a very low water level. We strongly advice our customers to avoid braving through flood water, especially when the car has a turbo system. As an ending note, lets respect the mother nature don’t take any chances to avoid such catastrophic disaster to our beloved drive.

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