2012 Audi A6: Drove through modest puddle and now New Engine?


It doesn’t take much waster to cause hydro-lock to occur, the combustion chamber on a 2.0 liter engine is less than 1.7 ounces in volume.

The roads here flood with heavy rain, most streets here don’t have storm sewers. With flooded roads comes damaged engines, traffic doesn’t stop when there is 6" of water in the road and someones luck will run out.

We call that flood water, a puddle is something you step in, not something that submerges a car.



I’ve confirmed that the location is correct. Another co-worker actually towed him to the shoulder while he waited an eternity for AAA to show up.


I didn’t get the sense he was “embarrassed”, just surprised (like me) at the diagnosis.


I think I’ll know enough to not drive through the water.


As I’ve stated above, I’m very skeptical of the diagnosis (of a new engine). The co-worker told me the vehicle did not leak any fluids, so that rules out a rod through the block or out the bottom of the engine. But assuming there was damage to one or more connecting rods (internally), isn’t that something that could’ve been repaired (as opposed to throwing in another used engine with who knows how many issues it might have?). Only a day or two later, the dealership was informing him he needed a new engine (for $20,000). But then, once Insurance got involved, that became a used engine (w/60,000 miles) for $11,000 installed! At that point, I would’ve been looking more closely at the actual damage to MY engine (if there was any at all), and estimating the cost to repair it, because there was only 70,000 on his engine.

Are the connecting rods fabricated to deform to save the crankshaft in cases like this? You’d think they would be…


Yiyiyi…here we go again. This is a very unusual thing to happen overall, it would make no sense to design an engine for this. And the connecting rods carry perhaps the greatest load of any part in the entire car, no way they should (or could) be designed to deform easily.

The fact that insurance paid up $11k is VERY strong evidence the damage was real. Has your friend asked for the evidence? It’s there if he wants it.


The connecting rids are high strength steel… but the pistons are high strength aluminum, less strong than steel and they may have a hole through the collapsed center of the piston while the connecting rod is OK. Not impossibly hard to fix but a hydrolock can bend the connecting rod a little and the crankshaft a little and measuring that requires a lot of labor in disassembly and reassembly. That makes $11K for a used engine look pretty good.


If they were designed to deform under high shock loads, they wouldn’t make very good connecting rods. They need to NOT deform when the compressed fuel in the cylinder explodes!

What they’re designed to do is push the piston to effectively compress the fuel and to transfer as efficiently as possible (no bending) the forces of the combustion’s explosion to the crank shaft. They’re designed to do so without undue excess weight. Remember that it’s a “reciprocating mass” and constantly changing the direction of excess weight thousands of times a minute wastes energy that should be going to the crankshaft.

In short, they’re designed to do a specific job as efficiently as possible. That job does not include trying to compress water while being forced up by the explosions in the other cylinders and the inertia of the flywheel. Etc.


I was just trying to think of a way to detect this problem and quickly shut down the engine to minimize (or even eliminate) any damage. In software, you write ‘defensive code’ to protect against unusual situations that could cause a crash. Engine designers should have the same mindset. If a loophole exists where someone can drive a rather expensive 2012 Audi A6 into some pooled up water on a Mall exit ramp and destroy the engine, then that’s an unacceptable design, in my opinion. We’re not talking about driving the vehicle into Lake Superior. We’re talking about a modest amount of water on a heavily traveled road in a city with storm water drainage systems underground. This is just ridiculous!

But, OK - maybe deforming the connecting rod is a bad idea, but Mustangman’s suggestion that the piston might give way sounds like a good start. Now the connecting rod is inside (or through to top of ?) the piston? At that point, can’t the computer detect this and turn the engine off to minimize the damage?

Also - what about some kind of water detector on the intake? If you already have Mass Air Flow Sensors, why couldn’t you detect (substantial) water? Seems doable to me. Might have to be redundant to avoid false positives, though …


One doesn’t spend $10 million to save one person $10,000. It’s that simple.


Mr. Hero , I have said this before, I don’t understand your insistence about this incident. Adding a water detection system is silly. That is the drivers responsibility. I am beginning to think it is you with the problem and not a co worker.


At that point the engine has stopped, there is no need for the computer to stop the engine. Replacing broken pistons and bent connecting rods is an expensive repair, that is why the insurance company chose to pay for a used engine.

Perhaps someday the forward collision system will stop people from racing though deep water.


Let’s hypothetically say that you figure out a way to add an H2O detection sensor in the air intake. It cuts the engine out, but the stored momentum means the engine won’t immediately drop to 0 RPMs so water could still get in. Also as I mentioned in my earlier post:


I wonder if the self driving cars have a do not drive through water feature. :vertical_traffic_light:


Barkydog: very good question. Ask Elon Musk.

But I doubt the computer could tell the difference between wet asphalt and a deep puddle.


One accident I saw reported by a self driving car was it did not see a white semi and plowed into it.


It’s an interesting thought experiment, but remember that the connecting rods are going up and down thousands of times a minute. If you’re on the highway on-ramp and running it up to 6,000 rpm (I do it often) to merge into traffic, that connecting rod is going up & down what, 100 times a second? Imagine if you will the inertial forces that would have to be suddenly stopped, in addition to the stopping of the other cylinders mid-power-stroke and of the spinning flywheel. That too is an interesting thought experiment, suddenly stopping a piston being pushed by an explosion and by the inertia of the flywheel in mid-stroke. What would happen to that piston’s connecting rod and to the crankshaft boggles the imagination. You’d have what we call a “yard sale”… a pile of busted parts!


Don’t want to hydrolock an engine with water? Don’t drive through pooled water more than an inch deep. Of course that might involve someone having to wait things out (horrors…) or finding another route. (horrors also…)

A few years ago when a huge tornado tore up El Reno, OK this was accompanied by torrential rains which caused massive flooding on into Ok City.

At an intersection on May Avenue near I-40 the water was probably 3 feet deep.
Did that stop anyone from plowing ahead and coming to a halt when the engine died? Nope.
Did that stop anyone from plowing ahead AFTER they stopped momentarily to eyeball a dozen other vehicles already flooded out? Nope.

One woman plowed ahead and her car died just as she came to edge of the water. The on-site news reporter walked over and asked her what happened.
Her response was “I think I’m out of gas”.
The reporter said “Don’t you think the deep water might have something to do with it?”.
She says, “No. It’s a new Jeep Liberty and has 4WD”.
Cut to reporter rolling his eyes and saying “There goes another one…” as yet another vehicle waded in and died.

I would love to have been a fly on the wall at the Jeep dealer the next day and listen to the conversation after the Jeep was towed in.
Even better would be to hear what’s said if the engine is wiped and she’s thinking warranty is going to replace it…


Car makers do try not to get the air intakes too low but sometimes that’s all the space that is left.

My wife’s Saab. Very low intake and air cleaner. Just above the body lines. Literally everywhere else in the engine bay is filled with engine, turbo, intake, exhaust battery ect. ect. ect. Heck, you have to remove a headlight to get to the AC high side port. You have to remove the bumper cover to service any of the 5 coolers in the front. Condenser, intercooler, radiator, transmission cooler, oil cooler. Crammed full.


Now I feel guilty for having laughed at this one. My sympathies to the lady, but it IS funny.


When I was younger, and briefly entertained the “import tuner” scene (or at least read a few magazines), I seem to recall they made something like this, for all those “dropped and slammed” cars with “cold air” snorkels 3" off the ground. The way I recall them working was, as the engine began to “suck” water instead of air, internal pressure would drop, allowing spring-loaded doors in the intake pipe (located in the engine bay) to open, and intake dry (albeit unfiltered) underhood air got ingestsed, instead.

If your friend insists on fording puddles, I suppose he could look into a setup like this.


Only way I know to stop an engine very quickly is to inject water into a cylinder.

Oops, that is what he is trying to prevent…


Unfortunately these days when something bad happens fault must be assigned to someone or something other than the person actually responsible. I suspect there is some sort of warning in the Audi operator manual concerning driving through water. Of course it is obvious on this forum that operators rarely open it. Ignorance can be significantly eliminated through education. This incident is a very expensive lesson for whoever owns the Audi. The solution is simply never drive through water again, not trying to transfer blame to the manufacturer or somehow prevent hydrolock damage when driving through water.