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

This is a co-worker’s vehicle. I had heard he had his engine replaced, and that some dealer wanted $20,000 to do it, but insurance forced him to install a used engine for $11,000. Anyway, when I heard why he needed his engine replaced, I couldn’t believe it!

Says he hit some ponded water at a stop light in town (exit “ramp” out of the mall here). The engine stalled out and wouldn’t re-start. So he called AAA to be towed home, and then ended up at a dealership the next day (or two) where they said his engine was history because it had ingested water (and hydrolocked, I guess?).

How the heck is this possible? I know where this happened, and yeah - the road dips a little bit as you come up to the traffic light, but I can’t imagine that taking out a vehicle’s engine like his dealership claimed.

Was this just the perfect storm here - vehicle with very low clearance, low air intake capable of ingesting water, and a big enough downpour to make it all happen? I still don’t believe it. I think the dealership took him (and his insurance company) for a ride.

Perfect enough storm I guess, more info is better but one has to guess hydrolocked engine
More reading here, not the best but good enough

No way to tell over the internet. But such a thing could happen. Think of it like drinking coca cola from a straw. If the end of the straw is just barely above the level of the cola, little to no cola gets drawn into the straw no matter how hard you try to draw it in. But as soon as the end of the straw even barely touches the liquid surface, immediately you’ll get a whole lot of cola flowing in the straw. So if ever the air intake point gets below the water level, even briefly, a whole lot of water can get sucked into the engine, and yes, this can indeed happen. I wouldn’t guess that a big splash of water would be enough, but maybe w/some air intake designs, like for performance cars, even that could do it.

If he had one of those cone shaped “performance” type air intakes it would easily suck in enough water, it isn’t compressible you know so the only thing that can bend is the connecting rod.

So let that be a lesson to you; when going through a deep puddle, go SLOWLY!!!

I was unable to find a diagram of it, but I suspect the A6 draws its air from the duct under the headlight. That does make it susceptible to this possibility if an unknowing driver goes blasting through a deep puddle. You’ll find that many vehicles designed for serious off road travel including fording streams have their intakes elevated to above the hood to prevent water ingestion. Water ingestion can and will kill an engine. The pistons simply cannot compress it.


Since you weren’t driving, there is no telling how deep that puddle was and how fast he went through it.


+1 for mountainbike’s suggestion about air intake location. Lots of cars ingest air from below the engine, and that makes the likelihood of sucking in water from a puddle high. It is one of the reasons the State Police tell us to avoid standing water.


I’ll bet a dozen donuts the coworker isn’t telling the whole story regarding puddle depth and their speed. And for the insurance co. to pay $11k means it almost certainly did happen.


My moms old Mercury topaz (I think it was a 93) got hydrolocked when my sister was driving. Water rushed out the storm sewers and flooded the street. When I got there to push the car out of the water, it was probably 8" deep in the road. The water was not deep enough to get into the cabin. Sadly the car was only 6 months old.

I’d bet you’re right.

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The coworker was honing his story at work so that he’d be ready to take on his insurer.

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I’ve known this co-worker for 20+ years. He’s a good guy and a straight-arrow, but he may have been trying to beat that traffic light coming out of the Mall (it’s known for long delays as it intersects with the main drag). Since it was dark, he was probably focused on the light and didn’t see the water (and may have hit it hard, sending a wave over the hood). If the_same_mountainbik is right about intake ducts below the headlights, then maybe the engine did ingest enough water to cause hydrolock.

But it still surprises me for two reasons:

1.) I’ve been driving for over 30 years and I’d never heard of such a thing! Water ingested into the engine???

2.) You’d think the Germans would’ve done their typical “over-engineering” of their vehicle to protect against this somehow. After all, you’re building a low-clearance, high-performance vehicle and selling it to people who like to show that power off. If driving through a modest dip in the road (like my co-worker did) is enough to blow an engine up, you’d think this problem would be widespread and well-known by now.

What about the possibility the engine stalled to protect itself and the water could’ve been manually expelled to fix the problem? Before you say “How could the engine respond that quickly?”, watch that “This Old House” episode where a table saw blade, rotating at full speed, instantaneously stops (and drops below the table top) when a hot dog (simulating a human finger) touches the blade … leaving the hot dog unblemished!

You are giving “German engineering” WAY too much credit. This is not that uncommon, and I imagine German cars are just as likely to have it happen as any other.

As for the ‘engine stalled to protect itself’, nope, I don’t think any maker has a ‘stop the engine if you hit water’ system. Could they? Maybe, but they don’t.


I have. But, as Texases said, I doubt that the whole story is documented here.

These models aren’t designed for deep water operation… such as bombing through deep puddles. They’re designed for speed and handling on regular roads.

The Germans do design vehicles for deep water use, and their induction intakes are above the engines. Like the MB in the attached image.

Scotty Kilmer explains why its dumb to drive in deep water.

Where will the car draw air from? Cooler air is preferable, and most people don’t want an air intake stack sticking up next to the windshield. The other choice is down. Air drawn on top of the engine would be very hot, and there isn’t any room for an air intake up there anyway. Follow the intake tube from your air box to the inlet. It would only surprise me if it isn’t at the bottom of the engine bay.

I’m going to piggy back off of JT’s response here. Could they install a quick kill system? Sure they could, but I personally wouldn’t want one. Why build a system that could fail and kill the engine when nothing is wrong? Also, I would be worried that a system like that could be easily fooled by either high humidity or something as simple as washing my car. Honestly, if you go through puddles slowly, bypass them and go around them, or (very important!) not go through water where depth is unknown, you will likely never hydrolock your engine

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I’m not sure the engine could be shut down in time. The moving engine parts have a lot of momentum and I doubt it’s possible to stop them suddenly enough to prevent damage. At least with today’s engines. Possibly if you beefed up most of the parts and put in a mechanical mechanism to stop the rotation suddenly…

But it would cost a lot, and for what? to save 0.01% of the cars?

edit: on second thought, is it necessary to stop the engine, or just open all the valves and shut off the fuel? No, the valve openings are still smaller in area than the piston cross-section, and the piston is moving very fast, and I doubt the water would have time to flow out the open valves.

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In at least some, perhaps many, modern cars the snorkel for the air intake draws air from the cavity between the wheelwell outer liner and inner liner, the intake being about 2/3 of the way above the bottom of the wheelwell. Mine was in the fender cavity just below the parting line left of the headlight before I put in my custom ram air system. I designed the system to draw air from the (false in stock form) intake at the bottom of the valance panel (see image) and left of the lower grill, however I designed a relief drain for water into a chamber behind the intake to preclude any water-ingestion problem.

Hydro-locking is rare, but it does happen. I’ve know a couple of people over the years it’s happened to. Both were driving very aggressively at the time…

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