Does driving through flood water damage a hot cat converter? (1 Viewer)

Dec 24, 2014
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Hurstpierpoint. Mid Sussex.
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Ever since lighting was by Calor gas.
There has been frequent flooding in two of my unavoidable local lanes - for about 30 yds and up to about a foot deep at max points.
I drive at walking pace to avoid creating a bow wave and have never had any problem getting through, but in the back of my mind I seem to recall that cold water on a hot cat converter can damage it irrevocably (by shattering the internal ceramics I think).
Is this a fact or just a rural myth?
 
Jul 27, 2013
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Since childhood!
I hope not, but Iā€™ve heard the same.
What I do know is that doing a lengthy drive last week in torrential rain, involving going through two floods, has wrecked my parking sensors which now scream as soon as I select reverse. šŸ˜£
 
Oct 27, 2015
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I managed to crack a weld along the length of the thermal reactor (gets very hot - effectively its the exhaust manifold with additional air pumped in to burn off any polluting gasses) on my NSU Ro80 many years ago by driving through a deep puddle. It was under the floor. Just had it welded up and all was well.

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Minxy

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Aug 22, 2007
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I wouldn't drive any vehicle through that depth of water unless it was on very BIG wheels! It's not just the bow wave you need to be wary of but the water being pushed into areas it should be in the bodywork etc. I'd probably get my canoe out!
 
Apr 20, 2020
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When I see videos of people driving through floods I often wonder what it does to the wheel bearings.
Years ago I had a number of small boats and I often encountered problems with the trailer bearings
as they were submerged during launching.
The bearings were so called "sealed" bearings but still had issues.
 
OP
OP
Spriddler
Dec 24, 2014
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Ever since lighting was by Calor gas.
It's not just the bow wave you need to be wary of but the water being pushed into areas it should be in the bodywork etc.
I'm pretty sure it reaches the cat converter but on reflection it might not come as high as the door bottoms so maybe the deepest bits are only 7" or 8" but I've never stopped to get out and look and I don't keep a car long enough to worry about water splash or submersion causing corrosion.
I recall my Dad back in the 50's driving his 1936 Morris 8 through deep water in 1st gear and slipping the clutch to keep the revs up to avoid water going in the zorst pipe. There were gaps in the wooden floorboards and no carpet, just a small piece of rubber mat, so when going quickly through an isolated puddle the water would sometimes squirt up one's trouser leg. Corrosion wasn't an issue as it had a substantial 'proper' chassis.

When I see videos of people driving through floods I often wonder what it does to the wheel bearings.
Years ago I had a number of small boats and I often encountered problems with the trailer bearings
as they were submerged during launching.
The bearings were so called "sealed" bearings but still had issues.
I used to reverse my trailer down a slipway into the sea water to launch my dinghy and read in one of the boating magazines that it was important not to do it immediately after driving because the sudden cooling of the hubs could still cause water to be sucked into sealed bearings. I'm not sure how valid was that advice since the bearings shouldn't get particularly hot anyway.

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Oct 27, 2015
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Modern cars have 'close couple catalysers', directly after the exhaust manifold. They're usually in the downpipe from the exhaust manifold to the rest of the exhaust.
 
Jul 25, 2017
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I wouldnā€™t think it would be too much of a problem, would have thought it would have been part of endurance testing by the base vehicle manufacturers. Certainly on cars during pave testing( cobblestone surface to replicate rough terrain) they were put through water troughs every few laps or so to help cool down the shock absorbers as they were being subjected to far more abuse than would be seen on road

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Nanniemate

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Oct 1, 2019
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Still dropping clangers and making it up as I go along
I had to drive through flood water last week no option had to get out of a dead-end road I was more worried about water getting into the filters never considered the CAT. But it was cold as just left a hotel and it's a Vauxhall so it leaks like a sieve anyway ļæ¼:rofl:
 

andy63

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Jan 19, 2014
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I'm fairly new to owning a landy and this off road stuff..but in answer to the ops question I'd say that a cat could be damaged by sudden immersion in water due to the thermal shock..
You make the point about not creating a bow wave, but in fact that is just what you should be trying to achieve in deeper water... create the wave by gradually increasing speed then keep it going just in front of the vehicle... the engine compartment is then in the trough, just behind the wave and likely to be in less depth of water... dont increase speed and overtake the bow wave..
That is I believe the correct theory (y)
Andy
 
OP
OP
Spriddler
Dec 24, 2014
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Ever since lighting was by Calor gas.
Modern cars have 'close couple catalysers', directly after the exhaust manifold. They're usually in the downpipe from the exhaust manifold to the rest of the exhaust.
And yet apparently the cat thieves raise a car to cut it off from underneath. :unsure:
Presumably there's room to get an angle grinder up to the manifold area.

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Last edited:
Oct 2, 2008
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There is virtually no risk to cats , the main risks are water getting past seals in drive train especially if sudden cooling causes reduction in pressure in axle housings if not fitted with raised breather or if low level breather valve is blocked/stuck . quite common in Australia FMHE .
Then water into induction especially if air intake for filter is low down , or water goes over front and intake is just behind bonnet leading edge . If taken gently bottom of doors should be regarded as max . Water ingestion is pretty near 100% fatal for engine . If your handbook doesn't mention wading depth don't risk it JMHO
ps if manual select a low gear for a speed at which a small bow wave is created, do not disengage clutch as water can get into bell housing on most vehicles and will make plate slip , not what you want to get up other side if in a dip . Dont forget to gently apply brakes afterwards to dry them out , , although not as bad when it was drum front brakes.
 
Oct 9, 2019
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Itā€™s always worth looking at where the air intake is on your diesel engine as a number of cars have the scoop low down and will suck water into the engine if you go through a Ford such as Rufford, I seem to remember a few Citroens and BMWs had this problem, only way to fix it was new enginešŸ™€
 

andy63

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Jan 19, 2014
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I knew I had a photo..lol
This is a screenshot of a photo taken of of my landy on a recent trip to Wales..
I was told to try and get the bow wave going and just keep it in front of the vehicle..
You can clearly see the difference in water height so less water around the engine..(y)
Screenshot_20221020-095518_Samsung Internet.jpg

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Aug 6, 2013
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When I see videos of people driving through floods I often wonder what it does to the wheel bearings.
Years ago I had a number of small boats and I often encountered problems with the trailer bearings
as they were submerged during launching.
The bearings were so called "sealed" bearings but still had issues.
Hot hubs suddenly cooled will suck in water. As will transmission (and RWD differential) breathers.
 
Apr 27, 2008
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Eastbourne East Sussex
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4x4s often have breathers at a high level on gearbox and transmission components to avoid water being sucked in with cooling. I don't recall any special arrangements for cat converters though.
 
Oct 18, 2022
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Not sure about cat converters, but Iā€™ve experienced problems with diesel particulate filter after hitting deep puddles at speed. Shortly after the ECU would signal blocked filter and go into limp mode. Not unusual according to the VW mechanic.

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