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A few years ago I wrecked the engine of a Rover diesel, driving it thru stupidly deep water; now I read into todays's DT, of a driver who has ruined the engine of a Picasso in 2 inches of water. Why is this? All cars need air and one doesn't read about petrol engines sucking air thru their intakes so why do diesels have to have low set intakes and what is the alleged advantage?
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why do diesels have to have low set intakes and what is the alleged advantage?
It's to try and get cooler air rather than the air heated by the engine. Helps increase efficiency - allegedly.
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Thanks DD, I follow that but why don't petrol engines want cool air too? Also, many diesels have intercoolers to achieve a cooling effect.
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I worked for a major manufacturer and we were always getting claims from people who had driven thro' 1/2 inch of water at 1/2 mph!!! and their engine had blown-up.People used to claim escort air cleaner pick-ups came half-way down the grill-still a long way from the ground but a few seconds inspection would show that it was just a deflector with no back-the intake began at bonnet level.
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AS
Only TWO inches of water!! Really? The filter box on those would hold a couple of gallons, so a bit of spray wouldn't do any harm.
Just exactly how low is that air pick-up? What model is it; a Citroen Picasso Hoover HDi?
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Only TWO inches of water!! Really?
I suppose it all depends what speed the driver hit those 2" of water at. Was that mentioned in the DT article at all?
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I've never noticed them any lower on diesels than petrols, in fact they are usually in the same place on the same model regardless of fuel type.
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DD , my quote was wrong.! The text says roughly "Pembrokeshire heavy rain - surface water - driving very slowly thru a flooded section - sucked in water - bent con-rod - not a warranty job. Thus the water depth is not accurately known. However, I would still like to know why this seems to be exclusively a problem for diesel engines. I have never heard of a petrol engined car, being driven thru standing water, suffering water thru the intake and consuquent engine damage. Perhaps I should read more!
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I agree this seems to affect diesels more - although a friend's wife managed it on a petrol Laguna...!
I think this could be because of the two-and a half or 3 times greater compression ratio of CI engines - it doesn't need so much water in a diesel before the incompressibilty is apparent?
N
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>>I have never heard of a petrol engined car, being driven thru standing water, suffering water thru the intake and consuquent engine damage.
I have, but only on cars where the driver goes mad through the flood
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Steve
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People also tend to drive diesels faster thro' water because there is no ignition system to drown;wet ignition tends to stop petrols before they hydraulic!!
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AS
One difference between petrol and diesel damage might be that the initial spray of water into the cylinder might kill a petrol by wetting the plugs before the water can totally fill the combustion chamber. Diesels would just love it.
Older petrol engines would likely have cut-out from drowned engine electrics long before the air filter filled up. Diesel drivers seem to think that their vehicles are immune to water splash and consequently drive too fast. Not these days....
If memory serves; Picasso's take their intake air from the space between the N/S inner wing and the plastic arch liner. Maybe 12" from the ground? So just how fast was he going..... £6,000 too fast!
Personal tips based on seeing hundreds of flood breakdowns:-
Speed is everything. Walking pace is ten times too fast. Try not even to leave ripples. Forget all the balony about water getting sucked back up the exhaust; just a tickle of throttle and listen for the sound of rushing water - there shouldn't be one. At the right speed it's nearly silent.
Regardless of the vehicle; if the water level is getting much deeper than the centre of the wheels - back it out. Obviously keeping to the highest part of the road makes a big difference. Not much you can do about flying idiots coming the other way though.
Cars with fly-by-wire throttles can't dry-out the brakes by left-foot braking against the engine: ABS doesn't work with wet discs either.
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The compression ratio on a diesel is higher, the space above the piston when it is at TDC is very small on a diesel, it would take half as much water to hydraulic a diesel as it would the equivalent sized petrol. A diesel is usually turbocharged on top of that, so the amount of air is doubled again (if being boosted to say 15psi) so that is twice as much are going in and being compressed twice as much meaning 4 x more likely to hydraulic. (everything else equal)
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why cant fly by wirethrottles,dry out brakes,and abs doesnt work with wet discs,why not ,this is usefull information ,
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You can't brake with your left foot to dry the discs out while pushing the accelerator with your right foot. On all VAG diesels the brake light switch sends a signal to the engine ECU preventing the engine from accelerating while the car is braking. It's presumably to cope with people with a very wide right foot who could hit the brake and accelerator at the same time in an emergency braking situation. Not sure about abs; would be very surprised if abs doesn't work with wet discs.
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It's to try and get cooler air rather than the air heated by the engine. Helps increase efficiency - allegedly.
Why not just move the inlet to the front of the engine? I don't see how a low intake can make that much difference?
AS - intercooler only cools the air once it's been compressed by the turbocharger. If it's cold, dense air being compressed in the first place that helps a lot.
My dad drove through what must have been 5" of water (it found its way into the cabin!) in 1998. He still has the car, a Rover 400 Tourer. No harm done.
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Mike Farrow
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Most modern vehicles have the engine air intake forward of the radiator, condenser, intercooler but behind the grill. This ensures ambient air with a little ram effect to aid induction.
When driving through standing water the speed has a clear effect on the height that water is pushed up to. It wouldn't be difficult on most vehicles to get water up high enough go through the grill and enter the engine intake with dire consequences.
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>>My dad drove through what must have been 5" of water (it found its way into the cabin!) in 1998. He still has the car, a Rover 400 Tourer. No harm done.
As I mentioned,it only happens on driving too fast,water builds up in front of car ie wave. this makes water level higher still and gets into air intake,those that have any common sense drive slowly through flood or stream-I dont have any sympathies for those that go mad and wreck their engines
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Steve
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Steve some people may not know, my Mrs wouldn't for example.
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My girlfriend did exactly this last year in my 75 diesel picking me up from the pub. The car chugged and lost power as if it was going to stall. Was very very lucky no damage was done - next time I will get a taxi :-)
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Had this problem with an `84 Escort Diesel van. Wife drove thru flood, and big beastly 4x4 coming other way swamped engine which seized. Luckily she had stopped with prudence, and engine only ticking over when locked.
Towed home by VW T2 van (lots clearance), and took out injectors with suitable spanner. Turned over engine by starter - massive spray of water ex injector holes. Changed oil, replaced injectors, Escort ran another 100,000 miles no problems.
BUT! Asked postman (same van) if they knew answer?
Advice: remove pipe to air intake by LS headlight. Bend back, and fix to bulkhead top of engine compartment, where water would not get in. Easy Mod.
Postman quite right. Same mod for all diesels a good thing.
It`s only the petrol engines which benefit from air in from low front of car. Diesels don`t mind - they don`t get that hot anyway.
Any local garage would do this for you. As I said, that Escort diesel did another 100,000 miles. It got knicked, however in the end (inside job?) it was thought to get the engine for another van like that; without mod, another flood?
AS
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