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Backdrop

We had really heavy rains here today. I was in my '99 M5, idling in traffic when I noticed the brake pedal feel became really notchy. When I let go of the brakes the pedal would not travel back up easily and the engine started sputtering until I gave it a bootful of throttle. I also noticed a lot of steam coming out of the exhaust when adding copious amounts of throttle.

This kind of behavior is well-documented on M5 forums - basically the compartment containing the brake booster fills up with water when the drain plug gets clogged, which has the effect of ingesting water into the engine through the brake booster vacuum line (not to mention the booster itself). If enough water is ingested, it can result in hydrolock.

My Concern

I'm not concerned that the engine reached the stage of hydrolock while running, mainly because the engine would only idle poorly or stall whenever I pressed the brake pedal, and would idle well after the exhaust blew out a decent amount of steam via 5-10 seconds of high throttle.

What I'm concerned about is whether it is safe to turn the engine over now that it is cold, since steam may have condensed to form water in the combustion chambers.

I should mention that before turning the car off after reaching home, I pulled up the handbrake and gave the car 5-10 seconds' worth of sustained high throttle to blow out the steam, but have no way of telling if that was enough to make it "safe" for the engine.

Question

Is it possible to determine if the cylinders are too flooded to safely turn over?

In the absence of such a test, I was thinking of pulling the spark plugs, siphoning off any water using a vacuum line and cranking the engine over manually.

I'm open to suggestions.

Zaid
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3 Answers3

5

Given that there are no sensors inside the cylinders, I can't think of any way of doing so, other than Mauro's suggestion of removing the plugs and turning it over, which would spurt out any water in them.

You could try leaving it to evaporate, but if any cylinders are sitting with both sets of valves shut, any water in those pots won't evaporate off, so you'd have to turn the engine over part of a turn (by hand) to cover all of them...

Nick C
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4

If it is just condensation you are worried about, then I wouldn't worry. Water is produced normally by the combustion process. I would be more worried about water in the inlet tracts waiting to be sucked in. If it is too difficult to remove the plugs, I would turn the engine over with a wrench a few times, if there is significant water in the cylinders you will feel it.

I would also disconnect any ducting on the inlet manifold to make sure that there is nothing pooled in the pipes that could get sucked in, if I thought it was a possibility.

HandyHowie
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1

This particular problem has been a pain for many years in the industry, unfortunately there is no sure shot way of telling if the engine will hydro-lock on cranking.

Standard Solution is to remove the spark plugs and vacuum out the water basically not taking any chance.

That said, there are a few things which can be done to ascertain if its safe to crank the engine or not.

  • If you are in moving traffic with water level below your intake but above the silencer and your car stalls, you can push the car to a dry area and then crank it , it will take a few cranks but it should start in most cases.

  • if your car has been standing and water enters through silencer , same procedure as above, note that it should not be in water for too long probable a day or two with silencer underwater will not affect the car and its safe to crank.

  • HOWEVER , if water enters through the intake then you should Never try to crank the engine as it will definitely hydro-lock, removing the sparks and cranking is the best way to get rid of that water.

Shobin P
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