Where does the rain go?

[E63eeeeee...]

Just a random thought that's occurred to me a few times on long rainy drives. When you're driving through heavy rain or spray on the motorway, presumably quite a lot of water is coming into the air intakes on the front of the car. I've taken apart a few intakes and best I can remember they're essentially just tubes up to the filter. So what's actually happening? Is there some clever design in the intakes that diverts the water, or is the air filter just soaking wet? And presumably if that's the case, does the flow of air dry the filter by pulling water vapour into the engine? Obviously whatever is happening is OK, otherwise there'd be no working cars in Scotland, but is the difference between that and cars that conk out through ingesting deep water just volume? Or is something else going on?

[Krikkit]

They use airflow which has been turned or forced from high -> low pressure to remove the water droplets out - sometimes that's by hiding the inlet under a trim panel slightly, sometimes you have an inlet which has some sharp turns to fling the water out internally, then drain it out.

ZedLeg said:

A small amount of water going into your engine is fine, it’ll just vapourise against a hot surface somewhere.

ETA: This as well - humid air isn't an issue really, just condensed water droplets in large volumes

Edited by Krikkit on Saturday 25th March 15:44

[ZedLeg]

A small amount of water going into your engine is fine, it’ll just vapourise against a hot surface somewhere. If your engine gets flooded with either water or fuel it physically locks the engine as the pistons can’t compress the fluid. It’s called hydrolocking and if you try and turn the engine over without unsealing the head you’ll break something expensive to fix.

[ARHarh]

The reality is very little water will get anywhere near any intake, then any that may get past will get stopped by the filter. Don't think there will be anything anyone needs to worry about.

[Dannbodge]

Air filter are generally hydrophobic so water won't wet them out.
A lot of airboxes have drain holes in the bottom of them, so any droplets that get sucked up either evaporate as it's warm/hot or fall into the airbox the through the drain hole.

[Lester H]

ZedLeg said:

A small amount of water going into your engine is fine, it’ll just vapourise against a hot surface somewhere. If your engine gets flooded with either water or fuel it physically locks the engine as the pistons can’t compress the fluid. It’s called hydrolocking and if you try and turn the engine over without unsealing the head you’ll break something expensive to fix.

So, if you think you may have to drive through floods, locate the air intake on your vehicle. Most are at top of engine level, so OK but those just beneath the radiator in the front apron will need a home made snorkel leading well up in to the engine bay. Sounds like a bit of an extreme scenario but too many drivers go through floods at speed.

[Raccaccoonie]

More power

[ZedLeg]

Lester H said:

ZedLeg said:

A small amount of water going into your engine is fine, it’ll just vapourise against a hot surface somewhere. If your engine gets flooded with either water or fuel it physically locks the engine as the pistons can’t compress the fluid. It’s called hydrolocking and if you try and turn the engine over without unsealing the head you’ll break something expensive to fix.

So, if you think you may have to drive through floods, locate the air intake on your vehicle. Most are at top of engine level, so OK but those just beneath the radiator in the front apron will need a home made snorkel leading well up in to the engine bay. Sounds like a bit of an extreme scenario but too many drivers go through floods at speed.

Yeah, that’s the idea. Hence snorkels that go to the roofline on off roaders. It’s unlikely to be water in the engine that kills cars in floods these days anyway. IIRC once water has passed the door seals the whole wiring loom gets written off, which is why even mildly flooded cars will get scrapped.

[brisel]

Dannbodge said:

Air filter are generally hydrophobic so water won't wet them out.
A lot of airboxes have drain holes in the bottom of them, so any droplets that get sucked up either evaporate as it's warm/hot or fall into the airbox the through the drain hole.

What type of air filter are you referring to? Every vehicle I’ve driven in in my 34 year driving career has had a paper filter element, with the exception of very old Land Rovers and Eastern European tractors that have oil bath plus steel wire elements. Paper filters soak up water easily which severely restricts airflow, in extreme cases the vacuum pulls holes in the element.

As you say, many air intakes are designed to centrifuge coarse solids and liquids out before the paper element. When the fashion for low air intakes that used the ram effect to increase air pressure was thankfully over, air intakes were moved to above the radiators or behind the headlights where water ingress is much less likely though not impossible (see Rufford Ford Fails on YouTube).