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Old 20th May 2017, 03:34   #1
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Post Hydrostatic Lock - How to avoid it in an Automatic car

In the days of yore; when all cars /jeeps used to come with manual shifters; the words of wisdom that were bequeathed upon us were that if you were to find yourself in the unfortunate situation of trying to navigate a flooded road, here is what you would do.

Shift the car to a low gear (typically 1), slip the clutch if needed to keep the revs high and wade slowly (but not crawl) through water till you find higher ground!

Unfortunately, in modern cars with auto trannys and fancy electronics, doing the above may not be the most feasible option:

In addition, I have heard of several myths/incorrect Dos and DONTs from colleagues and even on TBHP that I felt it may be worthwhile to clear a few misconceptions

(For context, I have been in the unfortunate situation of driving the much maligned for hydrolock brand (BMW) through a fair amount of water on a bunch of occasions but have escaped unharmed each time)

1) Please remember that hydrolocks almost always happen because water ingressed through the air intake (which sits near the top of the bonnet) and not because water ingressed thorugh the exhaust pipe (which sits much lower down) - There is an exception to this norm , please read 7 (b) to find out what it is

2) If the water level is above your wheel (esp if you drive a sedan with 19" wheels), it is almost a given that water will reach up to the air intake - DO NOT attempt crossing in such a case - Take a look at the top level of your wheel and the air intake under the bonnet to get a sense of where it sits relative to the top of the wheel

3) Shift the vehicle transmission to 1 if you have paddle /manual shifters or the low/hill setting on the shifter- The intent is to keep the engine revving as high as possible while maintaining very slow speeds

4) Wait for the path to clear - you want to maintain continuous high rev on the engine - something you can't do if the car in front of you stalls

5) If at all you must stop in the middle of water, press the brake firmly with the left foot and keep the engine revving well over the idling rev count (say 1.5-2K for diesels that idle at 800 or 2-2.5K for petrols that idle at 1-1.2K)

6) Keep In mind that vehicles driving next to you can create waves in the water that can reach up to your air intake - which is why (4) is all the more important. Try avoiding driving side by side or very close to other vehicles in front

6) If by any chance your vehicle does stall, DO NOT attempt to crank it ; I repeat, do not attempt to crank it. If you don't, the worst possible outcome is that you will need to get your feet wet and get your car towed out . If you do, please read (8)

7) Your vehicle may have stalled because

a) despite your best attempt, some water may have gone inside the cylinder - The water sitting there won't harm a stalled engine and your engine will be back to normal once the water is drained

b) Water may have hit the engine electronics thereby shutting down the engine. While the engine got shut down, water could have back flowed through the exhaust into the cylinder (since there is no positive pressure of the exhaust gases coming out of the tail)
If you leave the vehicle uncranked, the worst outcome is that you will need to get the control circuits repaired

8) If however you do decide to crank an engine that stalled in water, you would be subjecting your engine to the worst possible scenario i.e. trying to compress an incompressible fluid (i.e. water) within the small confines of its cylinder - and that is what leads to the dreaded hydrolock (bent rods/ messed up piston/ deformed head/ even cylinder damage) because your engine tried to run with all its might against an immovable object

9) Driving too fast through water can also lead to a hydrolock even before your car stalls because your engine may end up damaging the rods even before it gets a chance to shut down safely

10) Whenever possible, opt for a hydrostatic lock cover (also known as engine cover) since the pricing premium isn't much. If at all you think it's too much, please opt for this as the additional cover rather than the much more popular zero depreciation add-on since the cost to risk hedge ratio for this is a lot more than a zero dep

That's all folks - Happy to hear any contrarian view points or any pointers towards any gap in my understanding

Last edited by abhi182 : 20th May 2017 at 03:39.
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Old 20th May 2017, 07:56   #2
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Default re: Hydrostatic Lock - How to avoid it in an Automatic car

Thank you for the useful post! It will be very informative to the readers and will also help avoid the common mistakes you've stated.

Overlooking the water splashing from other vehicles is one mistake that many people do.
My 2 cents : I usually wait sometime before attempting to drive through water. This is to see how other vehicles cross the area. If at all there are any gutters, (especially when attempting to cross an unfamiliar area) one can get an idea of the surface and also the depth of water which would help to visualize the safe path you should drive over.

One day, when I was in a fix whether to wade through water, I was looking at the vehicles ahead of me. I saw an 800 attempting to cross the water. I too was driving an 800 that day, so i thought to wait and watch. He had almost made it when I saw his front right wheel go into some hole ( a man hole cover got displaced) and he got stuck there.

Gokul

Last edited by --gKrish-- : 20th May 2017 at 07:58.
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Old 20th May 2017, 08:44   #3
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Default re: Hydrostatic Lock - How to avoid it in an Automatic car

Quote:
Originally Posted by abhi182 View Post

5) If at all you must stop in the middle of water, press the brake firmly with the left foot and keep the engine revving well over the idling rev count (say 1.5-2K for diesels that idle at 800 or 2-2.5K for petrols that idle at 1-1.2K)
Great post abhi182! Considering that the monsoons are soon to come (My favourite weather for a long drive. )

Well I don't know but that's kind of counter intuitive thing to do in my opinion. Wouldn't higher engine RPM result in greater damage if water does manage to get to the engine right at that moment?


Quote:
Originally Posted by --gKrish-- View Post

One day, when I was in a fix whether to wade through water, I was looking at the vehicles ahead of me. I saw an 800 attempting to cross the water. I too was driving an 800 that day, so i thought to wait and watch. He had almost made it when I saw his front right wheel go into some hole ( a man hole cover got displaced) and he got stuck there.

Gokul
Well if one gets stuck while wading through deep water, then the best thing to do is to turn off the engine right at that moment and instead get help to pull you out. Keeping the engine running only increases the chance of water getting to the engine and getting hydrolocked.
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Old 20th May 2017, 09:45   #4
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Default re: Hydrostatic Lock - How to avoid it in an Automatic car

I consider driving through water more than 12" deep a risky move with cars. I know I would never risk driving my car through a puddle of water unless I am sure it is shallow. How would I know that? Watch other vehicles. People carriers (Tata Sumos et al) and SUVs have higher ground clearances and can easily 'wade' through giving a car owner a good indication of how deep the water is.

IMO it's better to wait on the side of the road and wait for the water to drain away or levels to subside instead of taking a risk with the engine. Or, simply take an alternative route.

Last edited by R2D2 : 20th May 2017 at 09:49. Reason: Typo & additions
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Old 20th May 2017, 10:59   #5
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Default re: Hydrostatic Lock - How to avoid it in an Automatic car

Quote:
Originally Posted by abhi182 View Post
Please remember that hydrolocks almost always happen because water ingressed through the air intake (which sits near the top of the bonnet) and not because water ingressed thorugh the exhaust pipe (which sits much lower down) - There is an exception to this norm , please read 7 (b) to find out what it is
Aah OK. I always used to wonder how water traverses all the way from exhaust pipe into the engine.

Quote:
Shift the vehicle transmission to 1 if you have paddle /manual shifters or the low/hill setting on the shifter- The intent is to keep the engine revving as high as possible while maintaining very slow speeds
But this doesn't make any sense. Why do you need to rev the engine, if water is not entering from the exhaust pipe?

I'm just putting 2 and 2 together here -

In a MT car, you might need to rev the engine. Because if you are crawling at 10 kmph at 1200 RPM, the wall of water will slow down the car. The engine might stall when the revs drop below 900 RPM. That's why in a MT car, it seems to be a good idea to rev the engine while entering the water world. Even if the car slows down (engine RPM drops) because of water resistance, the car won't stall because you will still be at around 1500 RPM.

No such issues in an AT car right? The car will not stall even if engine speed drops when you hit the water. So why rev when all we need to make sure is that water does not enter the engine intake?

Last edited by smartcat : 20th May 2017 at 11:05.
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Old 20th May 2017, 15:18   #6
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Default re: Hydrostatic Lock - How to avoid it in an Automatic car

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Originally Posted by smartcat View Post
Aah OK. I always used to wonder how water traverses all the way from exhaust pipe into the engine.



But this doesn't make any sense. Why do you need to rev the engine, if water is not entering from the exhaust pipe?

I'm just putting 2 and 2 together here -

In a MT car, you might need to rev the engine. Because if you are crawling at 10 kmph at 1200 RPM, the wall of water will slow down the car. The engine might stall when the revs drop below 900 RPM. That's why in a MT car, it seems to be a good idea to rev the engine while entering the water world. Even if the car slows down (engine RPM drops) because of water resistance, the car won't stall because you will still be at around 1500 RPM.

No such issues in an AT car right? The car will not stall even if engine speed drops when you hit the water. So why rev when all we need to make sure is that water does not enter the engine intake?
Water does not enter from the exhaust pipe due to the positive pressure of the exhaust gases emanating from the pipe
Its more of a precaution to keep the pressure high enough .
Of course, the excpetion being that you release the accelerator or even shut down the engine at the first sign of trouble (engine misfires/loses power) so that any water that may have gone in does not cause permanent damage

Quote:
Originally Posted by R2D2 View Post
I consider driving through water more than 12" deep a risky move with cars. I know I would never risk driving my car through a puddle of water unless I am sure it is shallow. How would I know that? Watch other vehicles. People carriers (Tata Sumos et al) and SUVs have higher ground clearances and can easily 'wade' through giving a car owner a good indication of how deep the water is.

IMO it's better to wait on the side of the road and wait for the water to drain away or levels to subside instead of taking a risk with the engine. Or, simply take an alternative route.
12" is a high for a sedan or even a x-over!
I would be wary attempting 12" over anything more than a few feet distance even on a XUV
The upper threshold for me is water beyond the center of the rim for big tyred vehicles (which would be 9" for 18" tyres). or between center and top of the rim for small tyred vehicles...
DO remember there are a bunch of sensors in new cars sitting quite close to the underbody.. damages to those may not be as bad as a borked engine but even those can be quite expensive

I presume Punya Nagari means Pune?
We are a bit lucky in that water does not tend to stay for long in most areas because of the natural elevation of the city
As you rightly said, waiting it out or taking an alternate route would be preferable for those days when water does get logged

Last edited by abhi182 : 20th May 2017 at 15:25.
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Old 20th May 2017, 16:42   #7
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Default re: Hydrostatic Lock - How to avoid it in an Automatic car

Quote:
Originally Posted by abhi182 View Post
12" is a high for a sedan or even a x-over!
I would be wary attempting 12" over anything more than a few feet distance even on a XUV
Believe it or not I have driven my cars through a foot of water. Now one of the cars (a 9th gen Toyota Corolla) had good ground clearance with a tail pipe that sits high in the underbody and then curves downwards making it difficult for water ingress. It had absolutely no issues. A low slung car would be in deep (no pun intended) trouble. Since you're from Pune just saying this was at the Sangamwadi RTO underpass (railway tracks overhead) which is quite famous for flooding during heavy rains.

Quote:
The upper threshold for me is water beyond the center of the rim for big tyred vehicles (which would be 9" for 18" tyres).
Tyre size is the inner diameter of the tyre. The tyre itself will add another couple of inches to the overall height from the centre of the axle to the ground. So for e.g. with a car that has 15" rims the tyre adds 2-3 inches to the overall height (axle to ground) making it approx 7.5" (radius) + 2-3" which is about 9.5-10.5 inches right there. 1 foot will take the water level (when standing still) about 1.5-2.5" over the mid point. Not dangerous just yet.

More important than the tyre size is the ground clearance and design which will determine how high up in the body critical parts including electronic sensors are located. I certainly would not recommend any low slung car, especially one from the luxury European marques, being driven through a puddle of over 6".

Quote:
I presume Punya Nagari means Pune? We are a bit lucky in that water does not tend to stay for long in most areas because of the natural elevation of the city
Yep, it's Pune's classical name . More than the elevation what saves us Punekars is the rare instances of very heavy rainfall (compared to coastal cities like Mumbai) plus the city's location on the Deccan plateau where the natural lay of the land has mild slopes which causes accumalated water to drain/runoff towards rivers running through the city. It is a saviour because the PMC, as with many municipalities in this country, has barely provided for an effective storm water drainage system.

Last edited by R2D2 : 20th May 2017 at 16:44. Reason: typos
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Old 23rd May 2017, 16:24   #8
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Default Re: Hydrostatic Lock - How to avoid it in an Automatic car

Informative post, thanks.

OT: Maybe.
I've seen almost all car wash centers washing engine bays with high pressure water jets, what are the chances of water entering the cylinders through air intake or any other places? So can this too cause hydrostatic lock?

I strictly say no to engine bay wash always in any case
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Old 23rd May 2017, 17:03   #9
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Default Re: Hydrostatic Lock - How to avoid it in an Automatic car

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I've seen almost all car wash centers washing engine bays with high pressure water jets, what are the chances of water entering the cylinders through air intake or any other places? So can this too cause hydrostatic lock?
Wash the engine bay with low pressure only. If the washing centres cannot control the flow it's better not to wash the engine.

The hose should be handled in such a way that there is no direct stream of high pressure water on electrical connectors, the alternator, the brake fluid reservoir, the ECU (if under the bonnet), spark plug HT cables/caps or igniters (if a petrol), ABS controller and most certainly the air cleaner intake.

You can use plastic kitchen wrap to protect the connectors, air intake, and other components (if engine is cold) or kitchen aluminium foil wrap if the engine is warm. Never wash when the engine is hot.

The connectors are water resistant but not water proof i.e. they'll resist mild water spray and moisture but not a high pressure stream of water.

Last edited by R2D2 : 23rd May 2017 at 17:05.
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Old 23rd May 2017, 18:25   #10
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Default Re: Hydrostatic Lock - How to avoid it in an Automatic car

Great post by OP.
Living in and around Calcutta, certain areas of which are VERY prone to water-logging, I am well accustomed to driving , or avoiding driving through waterlogged roads.

One important aspect is to know multiple routes to reach your destination, and if possible, avoid driving on waterlogged roads altogether.

Couple of years back, it rained for about 48 hours constantly, and certain parts of my daily route was heavily waterlogged (water reaching till the mid of a bus tire).
Quite a few people tried to drive their sedans / hatchbacks / suvs through the waves, and immediately regretted as they shelled out thousands to push their stalled cars out of water (some people made fat bucks quickly that day!).
I , on the other hand, chose to drive 30 mins extra and took a l-o-n-g but drier detour, and reached my office without a hiccup.

So if you have already left for your destination in a car, do keep in mind that there may be longer but safer routes to your destination. If there are none, better to leave your car at home that day, and take the bus/train.
Off-course this excludes catastrophic events like the Chennai floods of last year.
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Old 23rd May 2017, 19:49   #11
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Default Re: Hydrostatic Lock - How to avoid it in an Automatic car

The other things to remember after going through a water hole is"

1. Heat up the brakes/motor/slave to get back that bite while braking.
2. Check for under-body stuck elements like branches, leaves, etc.
3. See if any of the body parts are prone for rusting or corroding.

Its a good practice to get a thorough wash from the friendly neighborhood petrol bunk along with a spray of diesel and oil during the monsoons. Always has worked out for me.
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