Driving into water - Are you covered by insurance for damage. Rufford 29 August 2022 at 11:41AM in Motoring 44 replies 4.3K views

Car_54

mgfvvc said:

ontheroad1970 said:

If it's the high RPM that is stopping the water, then what's stopping you driving forward in a low gear and keeping the revs high?

Going backwards the exhaust is pushed through the water. The high RPM pushes exhaust gases down the exhaust and that stops water entering the exhaust. Going forward the air intake, in the front of the car, is getting pushed through the water. If you get it right the bonnet and bow wave keep water out of the air intake. If not, high revs will suck water in, resulting in terminal damage to the valves and other components.

Shirley, exhaust gases will stop water ingress, and the air intake will "suck" water in, regardless of engine speed?

mgfvvc

Car_54 said:

Shirley, exhaust gases will stop water ingress, and the air intake will "suck" water in, regardless of engine speed?

Higher revs give you more pressure or suction. I wouldn't expect it to make much difference in practice, but I couldn't say for sure.

And don't call me Shirley.

forgotmyname

Car_54 said:

Shirley, exhaust gases will stop water ingress, and the air intake will "suck" water in, regardless of engine speed?

If the exhaust tip is underwater and you switch the engine off the hot exhaust will cool and create a vacuum for the water.

When its running then it should not be an issue, got a 1L engine and a dustbin sized exhaust? Test it and tell us whether
that still applies. 

Ebe_Scrooge

forgotmyname said:

Car_54 said:

Shirley, exhaust gases will stop water ingress, and the air intake will "suck" water in, regardless of engine speed?

If the exhaust tip is underwater and you switch the engine off the hot exhaust will cool and create a vacuum for the water.

When its running then it should not be an issue, got a 1L engine and a dustbin sized exhaust? Test it and tell us whether
that still applies. 

I've heard this as well.  On the one hand it does sound perfectly logical - hot exhaust pipe, suddenly cools, creates a vacuum and sucks water back up into the engine.

But, to my mind, if you're driving through water that's deep enough to cover the exhaust pipe, surely the pipe is going to be pretty cold?  Yes, I know exhaust gasses are very hot, but if the pipe is submerged in water then it's going to be, at most, "a little bit warm".  Not hot enough to cause a sudden and very large vacuum if the engine stalls?

facade

Ebe_Scrooge said:

forgotmyname said:

Car_54 said:

Shirley, exhaust gases will stop water ingress, and the air intake will "suck" water in, regardless of engine speed?

If the exhaust tip is underwater and you switch the engine off the hot exhaust will cool and create a vacuum for the water.

When its running then it should not be an issue, got a 1L engine and a dustbin sized exhaust? Test it and tell us whether
that still applies. 

I've heard this as well.  On the one hand it does sound perfectly logical - hot exhaust pipe, suddenly cools, creates a vacuum and sucks water back up into the engine.

But, to my mind, if you're driving through water that's deep enough to cover the exhaust pipe, surely the pipe is going to be pretty cold?  Yes, I know exhaust gasses are very hot, but if the pipe is submerged in water then it's going to be, at most, "a little bit warm".  Not hot enough to cause a sudden and very large vacuum if the engine stalls?

I think that it is more a case of if the engine stalls, the exhaust fills with water, and then you can't restart the engine because at cranking speed there isn't sufficient gas flow to clear enough of the exhaust to reduce the back pressure.

 I suppose there is a remote possibility of the inrush surge* forcing some water all the way up the manifold and into a cylinder to get in the engine, but I doubt it.

Possibly the catalyst will shatter when cold water gets inside it, I don't know, they are very hot lumps of ceramic.

*The momentum of the water keeps it moving so it will climb higher than the level outside and then fall back.  It is what causes water hammer, when you quickly turn off a tap all the water in the pipe was moving and has to come to a sudden stop, so you get a pressure surge.

Car_54

Ebe_Scrooge said:

forgotmyname said:

Car_54 said:

Shirley, exhaust gases will stop water ingress, and the air intake will "suck" water in, regardless of engine speed?

If the exhaust tip is underwater and you switch the engine off the hot exhaust will cool and create a vacuum for the water.

When its running then it should not be an issue, got a 1L engine and a dustbin sized exhaust? Test it and tell us whether
that still applies. 

I've heard this as well.  On the one hand it does sound perfectly logical - hot exhaust pipe, suddenly cools, creates a vacuum and sucks water back up into the engine.

But, to my mind, if you're driving through water that's deep enough to cover the exhaust pipe, surely the pipe is going to be pretty cold?  Yes, I know exhaust gasses are very hot, but if the pipe is submerged in water then it's going to be, at most, "a little bit warm".  Not hot enough to cause a sudden and very large vacuum if the engine stalls?

But it won't create a vacuum. The exhaust gases may contract, but they won't disappear completely.

castle96

My Champ would be ideal here. Fully submersible to 6 feet (withthe snorkel on) All electrics/fuel fully protected

facade

castle96 said:

My Champ would be ideal here. Fully submersible to 6 feet (withthe snorkel on) All electrics/fuel fully protected

Nah, the idiots would try and drive it through at 60mph and roll it over probably.

NBLondon

There's a ford at Bourton on the Water which is clearly marked as not suitable for motor vehicles.
Bourton-on-the-Water Ford: English Fords   So would that give the insurers a getout?

Looking at it the other day; a competent driver with a proper off-roader could cross it safely but not a typical car.

Aretnap

NBLondon said:

There's a ford at Bourton on the Water which is clearly marked as not suitable for motor vehicles.
Bourton-on-the-Water Ford: English Fords   So would that give the insurers a getout?

Probably to about the same extent as disregarding or failing to see a no entry sign, a red traffic light or a speed limit sign gives insurers a get out, ie not at all really.