Could a two-inch deep puddle at 30 mpg hydrolock the motor of a Subaru Outback?

My car broke down yesterday and I had it towed to a garage that’s telling me I need a new motor. 2010 Outback, about 104,000 miles on it. Guy said I must have gotten water in the engine. I did hit a puddle earlier in the day but I was going maybe 30 mph max and it wasn’t more than 2-inches deep, probably not that deep. Is he feeding me a line of bull or what? He also said he had two other Subarus in the shop right now with the same problem. Looking at around $4,000 to replace the motor.

Anything is certainly possible… but given the circumstances (and the cost!), I’d definitely get a 2nd and 3rd opinion. It could be something simple as an electronic component getting wet.

Please provide more details, though.

Definitely get a second opinion. That’s an awful big expense to take one person’s opinion, unless that person has a long positive track record with you. If you had water in the intake filter housing or a wet engine air filter, that would support the water in the engine theory, but not definitively.

Water in the engine is bad, but it has a difficult pathway to get there. If you know where the air intake is and can remember where the splashing water got on your car, you can get some feel for whether the water could have gotten there. I can’t remember ever going through a 2" puddle at 30 mph so I don’t have a feel for how big the water gets.

Did you get a diagnostic report from this mechanic on what error codes you’re getting? I can’t interpret them, but there are real mechanics on this forum that can. Post the codes and you may get some useful next steps.

How long after hitting the puddle did the car run?


It is very easy for a mechanic to test for hydro lock. No codes will be set but stuff will certainly be broken.

It is simple, check the air filter for water, pull the spark plugs, bump the starter - water shoots out, then the engine is filled with water where air should be. Air can be compressed, water cannot.

The next step is to run a compression test, if no compression then replace motor.

I second the second opinion opinions.

I will note that some people like to install cold-air intakes that route the end down into the front bumper on the theory that they’ll get colder air there than in the engine bay. If you or whoever owned your car before you did this, it’s entirely plausible that you sucked up some water when you hit the puddle.

You may need a new motor, but I doubt that it’s because water got in your motor. The usual reason a motor goes bad is a lack of lubrication (an oil issue) that causes things like seized bearings, broken rods, cracked pistons, etc. Have someone else look at it.

Big question: did the engine die immediately after hitting the puddle? No? then it is not a hydrolock problem.

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That’s not true, I’ve seen engines operate for a period of time with bent rods after a hydro-lock occurred.

Thanks for your replies all. I hit a little bit of a puddle, from some melting snow. No bit deal, and I wasn’t going fast. The car ran fine for the 5 minutes it took to get home. Then a few hours later I drove a half-hour to a friend’s house, no problem. Then I drove somewhere for a 10 minute stop, no problem. Then I started driving home, about 10 minutes into that drive the car died. Sounded like a flat tire at first, kind of a flapping sound like I had cards on the spokes of a bike. Then it died and I had it towed. I haven’t had a chance to see what the codes were, etc., it broke down on a bridge with no breakdown lane and I was mostly concerned with getting out of there without someone crashing into my car!

I don’t see hitting a 2 inch deep puddle at 30 mph being a likely cause for engine hydro lock. Driving in 2 inches of water at 70 mph for a half mile maybe, even that seems unlikely, but not a small 2 inch deep puddle at 30 mph.

Are you sure OP that the puddle was only 2 inches deep? The entire puddle was at most 2 inches deep?

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Sounds more like the timing belt went.

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The 2010 OUtback came with either a F6 3.6L or F4 2.5 L. Only the F4 uses a timing belt from what I see. OP, is your engine the 2.5L F4? If so, at what mileage was the timing belt last replaced?

I’d say the 2nd opinion advice still stands. The amount of driving you did post-puddle suggests there is no connection between the puddle and the problem. It would be interesting to figure out the mechanic came to the conclusion that water got into the engine.

I agree that the timing belt is a likely suspect here. On an interference engine, that can result in serious internal engine damage.

Based on the information provided by the OP, I agree that the source of the problem is MUCH more likely to be a snapped timing belt, rather than hydrolock.

The interval for timing belt replacement on the 4-cylinder engine is 105 months or 105k miles–whichever comes first. So, if the engine in question is the standard 4-cylinder, and if the timing belt has never been replaced, then at 110k miles, the belt was overdue for changing and was in danger of failure.

The engine air intake on these cars is at the same level as the radiator cap, which is… quite high. So, unless someone modified the engine with a new–lower-mounted–air intake, it would be impossible for a 2 inch puddle to have thrown water high enough for water to have been ingested by the engine. If a 2 inch puddle could be ingested by that engine, then my Outback would have had its engine destroyed several times.

The most likely possibilities, as I see them, include…
A puddle that was much deeper than the OP believes it was.
The engine has a non-factory air intake.
The engine did not hydrolock, but instead was destroyed by failure to replace the timing belt on schedule.

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Agree with all you said but in my experience there’s leeway in replacing a timing belt. If a manufacturer says replace at 105K I would be very surprised if it broke at 110K. That would mean that at 105K it was already deteriorating which is unlikely.

If it was hydrolock, you couldn’t have driven it as far as you did. That would be an immediate stop and you couldn’t start the car.

If this happened to a 2010 Subaru Outback, then vehicle should never be driven as it was advertised.


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Suburu’s do have the problem of water finding it’s way to the cylinder, due to some breathers underneath, and the 2 inch puddle wasn’t it. Somehow it seems on your way back, there was a distraction, or it was not visible to see a large puddle. Your engine runs generally at 1200 degrees. Anything wet would dry in a minute. But the noise that sounds like a hydro lock (stopping the engine at 30mph or more) could cause engine parts to bend, if the engine stopped suddenly. And I would say that in the time it took the engine to cool, it would be likely hot enough to evaporate the water that was there. But the lock up, causing parts to bend could be the logically answer. I assume when you tried to start it, you couldn’t hear the engine noise at all.