Motoring Discussion > Scraping off the back window Miscellaneous
Thread Author: oilburner Replies: 42

 Scraping off the back window - oilburner
OK, I've seen three people in the last week scraping the ice off the *back* screen of the car.

All three were "proper" cars with heated rear screens, not 1980s Fiesta Populars or whatever. All had their engines running, so could have used the heater if they wanted to.

So, why do they do it? In every car I've ever owned I start the engine, press the button and the back screen is defrosted by the time I've got the scraper out and started hacking at the side windows.

Can anyone who does this enlighten me?

I also have a neighbour with a Ford and a heated windscreen that he refuses to use. Maybe related in mentality?
 Scraping off the back window - Bromptonaut
HRW on my Xantia has failed (again). Fuse OK so presumably another break in the wiring from body to tailhatch.

Just use either warm water or de-icer.
 Scraping off the back window - Old Navy
HRW scrapers, probably don't know it is heated or don't know where the button is.

Front screen, terrified it will flatten his battery. Is he of a certain age and not kept up with alternator introduction ? :-)
Last edited by: Old Navy on Wed 12 Dec 12 at 11:20
 Scraping off the back window - TeeCee
>> All three were "proper" cars with heated rear screens, not 1980s Fiesta Populars or whatever. All had their engines running, so could have used the heater if they wanted to.

Depends how it's parked. If they need to reverse out, the alternative is to sit with the engine idling from cold for 5-10 minutes while the screen does its stuff. Not good for the engine.

As for refusing to use it, I'm guessing he's an older chap? Back in the day use of the heated rear screen inevitably resulted in an eventual flat battery, as the juice used wouldn't be replenished by the dynamo or alternator in a short commuting run, especially when the headlamps were on and the heater blower was going at full chat.

My all-time favourite bit of cold morning lunacy was courtesy of a Greek gentleman who lived opposite my maths tutor. He owned a new Mercedes and the dealership had told him that sitting with a cold idling engine while it warmed up was detrimental to the car.
He'd interpreted that to mean that he should sit there revving the living jesus out of it while the thing warmed up, to the accompaniment of sheets of flame out of the exhausts.
I still pity the poor SOB who got that one secondhand.
 Scraping off the back window - oilburner
The guy not using the front screen is only middle aged, so I doubt he remembers the old days of dynamos. He is completely disinterested in cars though. More likely to wash and wax his 12ft wide plasma screen than the car.

>> Depends how it's parked. If they need to reverse out, the alternative is to sit with the
>> engine idling from cold for 5-10 minutes while the screen does its stuff. Not good for the engine.

Interesting point, however, all these cars were already sitting there idling. In one case, they scraped the rear screen first, which really foxed me. Like I say, do the side and windscreen first and you don't even have to touch the rear, it'll be done by then.

>>He'd interpreted that to mean that he should sit there revving the living jesus out of it while the thing warmed up, to the accompaniment of sheets of flame out of the exhausts.

lol! Brilliant! :)
 Scraping off the back window - henry k
>>As for refusing to use it, I'm guessing he's an older chap?
>>Back in the day use of the heated rear screen inevitably resulted in an eventual flat battery, as the juice used wouldn't be replenished by the dynamo or alternator in a short commuting run, especially when the headlamps were on and the heater blower was going at full chat.
>>
From one older chap.
When I bought my Fort Cortina MKII 1600E almost new I discovered that a limited batch of 200 HRW screens had been made so I had my rear screen replaced.
I never had any problems with battery/ charging.
The 1600E also came as standard with a couple of Wipac 55W spots that came on with the headlamps ( which I changed to Cibies) but still OK re volts.
 Scraping off the back window - Zero
I think churning the things over for 5 minutes before they fired up had more to do with flat batteries!
 Scraping off the back window - henry k
>> I think churning the things over for 5 minutes before they fired up had more to do with flat batteries!
>>
I totally agree.
The 1600E was always easy to start.
It had a 9V ( cold start) coil so turn the key and whatever volts were in the battery hit the coil. Relaese the key to running and a balast resistor reduced the feed to 9V
Simples and very effective.
 Scraping off the back window - rtj70
We had a VW Polo (1990 built I think) that went to the local indy for something. Don't remember what. They checked the battery and it was showing only 9v or something and said there's the cause of the problem (still don't remember what it was). Except it started every time, first time with that battery. Seem to think the problem we took it in for was mechanical anyway :-)
 Scraping off the back window - VxFan
>> So, why do they do it?

I do it to give the rear heated windscreen a hand getting rid of the ice and therefore don't have to leave the battery draining element on quite so long. That means more power available for my heated seats ;)
 Scraping off the back window - Dutchie
Young neighbours across the road from us throws a buckett of hot water across the frozen screen.I've mentioned to her that's
not a good idea.Up to now she got away with it.The Focus has a heated frontscreen its is clear in a few minutes.I clear most of the ice by hand from all the windows before starting the car.
 Scraping off the back window - John H
>> Young neighbours across the road from us throws a buckett of hot water across the
>> frozen screen.I've mentioned to her that's not a good idea.
>>

Why is not a good idea?

 Scraping off the back window - Maisie's Dad
>> >> Young neighbours across the road from us throws a buckett of hot water across
>> the
>> >> frozen screen.I've mentioned to her that's not a good idea.
>> >>
>>
>> Why is not a good idea?
>>
>>
>>

Do you throw buckets at your car then?

;o)
 Scraping off the back window - movilogo
I do it. Although I pour warm water rather than scraping it (sometimes just spray de-icer).

Because I have to reverse out of my parking space and can't wait long enough for heater to melt ice.

In case you ask why I don't park in reverse, this is because a road sign will prevent me opening driver's door if I do so.


 Scraping off the back window - Bromptonaut
>> >> Young neighbours across the road from us throws a buckett of hot water across
>> the
>> >> frozen screen.I've mentioned to her that's not a good idea.
>> >>
>>
>> Why is not a good idea?

I used to have Eyore tendencies about using water. Actually, provided it's warm not boiling, there's a very limited risk to the glass. Further advantage is that it stops glass inside steaming up for long enough for the aircon to get a grip.

Heater in the back is even more effective but that needs leads sorting the night before and time to sally forth 15 mins pre deprature to switch on.
 Scraping off the back window - John H
>> Heater in the back is even more effective but that needs leads sorting the night
>> before and time to sally forth 15 mins pre deprature to switch on.
>>

www.kenlowe.com/pre-heaters/cars/index.html

 Scraping off the back window - Dutchie
I was thinking of having the windscreen damaged by hot water Brompt.If it works fine.
 Scraping off the back window - oilburner
>> >> So, why do they do it?
>>
>> I do it to give the rear heated windscreen a hand getting rid of the
>> ice and therefore don't have to leave the battery draining element on quite so long.
>> That means more power available for my heated seats ;)
>>

Maybe I don't understand. Assuming you have the engine running, then what difference does it make? A car alternator should be able to pump out around 700-1200 watts of power. The heated rear screen takes around 150 watts or so.

More than enough left in the kitty for the heated seats at 15-50 watts each or so. :)

As long as you're not exceeding the alternators output, wouldn't the battery be increasing its charge, not draining it?
 Scraping off the back window - Skip
>> >> >> So, why do they do it?
>> >>
>> >> I do it to give the rear heated windscreen a hand getting rid of
>> the
>> >> ice and therefore don't have to leave the battery draining element on quite so
>> long.
>> >> That means more power available for my heated seats ;)
>> >>
>>
>> Maybe I don't understand. Assuming you have the engine running, then what difference does it
>> make? A car alternator should be able to pump out around 700-1200 watts of power.
>> The heated rear screen takes around 150 watts or so.
>>
>> More than enough left in the kitty for the heated seats at 15-50 watts each
>> or so. :)
>>
>> As long as you're not exceeding the alternators output, wouldn't the battery be increasing its
>> charge, not draining it?

>>

This is a Vauxhall we are talking about, it could be fitted with a 34amp Lucas 17ACR :-)
 Scraping off the back window - Duncan
>> I also have a neighbour with a Ford and a heated windscreen that he refuses
>> to use. Maybe related in mentality?


Why don't you ask him?
 Scraping off the back window - oilburner
>> >> I also have a neighbour with a Ford and a heated windscreen that he
>> refuses
>> >> to use. Maybe related in mentality?
>>
>>
>> Why don't you ask him?
>>

What and reveal that I'm a nosey so-and-so that's been spying on his defrosting techniques? ;)
 Scraping off the back window - WillDeBeest
Water poured over the car will freeze on the ground on a day like today, leave sheet ice to catch passing pedestrians - or you when you come home.

Anyway, who needs it? I found a good wheeze with the LEC. There's a button on the CC panel marked Rest which, as I understand it, distributes any residual warmth - or, erm, coolth - from the engine into the cabin after the engine is off. I pressed it last night as I got out, not expecting much but curious to see if there was any effect.

This morning the Volvo was iced up like the Pink Panther - barely recognizable - although admittedly it hadn't been out yesterday. But the LEC had barely a trace of frost on it, so while the neighbours scrubbed and scraped (or stayed in bed counting their empty bedrooms) I gave it two squirts of deicer on the windscreen, started up, turned the seat heater up full and set off to work. Heated jets meant the washers worked first time too. Smug, me? Oh yes!

May have been a fluke, of course, but I'll be trying it again tonight.
 Scraping off the back window - oilburner
>> Anyway, who needs it? I found a good wheeze with the LEC. There's a button
>> on the CC panel marked Rest which, as I understand it, distributes any residual warmth
>> - or, erm, coolth - from the engine into the cabin after the engine is
>> off. I pressed it last night as I got out, not expecting much but curious
>> to see if there was any effect.

There was something similar on Vauxhalls with climate when the Auto button was pressed after switching off. They called it Residual Climate Control or something.

Probably my favourite feature of the car when just parked up with sleeping toddlers in the back!

I shall have to see if our Ford or Citroën systems are as clever.

I'd be surprised if it was enough to stop the frost though. On the Zafira it was pretty much out of heat and switched off after about 20 mins.
 Scraping off the back window - Ted

SWM asked me to get a screen cover for her Note.....don't know why, it's me wot does the defrosting. I'd forgotten until I saw them in Aldi at about 30 shillings a few weeks ago.

Very effective and surprisingly good quality bit of kit. Trap the ends in the doors and it stays put. Easy to fold and stick in the boot. Might get one for meself.

I put the Suzuki down between the house and the 6 ft fence and it seems to keep clear of frost most nights . I noticed the other morning that the rear heater on the Note had only partially shifted the ice. I think they have limitations...I know it had little or no effect on the snow.

Ted
 Scraping off the back window - Old Navy
My car has three PTC heaters built into the climate control system so it gives warm air almost immediately.
Last edited by: Old Navy on Wed 12 Dec 12 at 14:48
 Scraping off the back window - R.P.
The 3 Series has one of these residual heat heaters - the X1 didn't but had heated seats and they were better at keeping your bum warm !
 Scraping off the back window - WillDeBeest
Well, the second night of residual heat didn't keep the car as frost-free as the first but it still seemed to help. But then Mrs Beest announced that she needed the LEC to fetch something bulky, so I had to spend 15 minutes chipping the Volvo out of its shell of ice before I could go to work. That has seat heaters too, of course, so no great hardship once I got inside.
 Scraping off the back window - Boxsterboy

>> I also have a neighbour with a Ford and a heated windscreen that he refuses
>> to use. Maybe related in mentality?
>>

I saw a woman scraping the careen of an S-Max this morning. I was tempted to stop and point out which button heated the screen for her, but then thought, "no, let her carry on reinforcing our stereotypes"!
 Scraping off the back window - Dutchie
I use both heated windsceens in the Ford just to put the record straight.Any thick ice I use the scraper.Mentality is fine thank you.
 Scraping off the back window - Bigtee
-4c this morning at 6am at work i scraped rear and rest of windows as condensation in rear screen on inside starts to freeze.

Webasto heater i so wish i had one fitted.
 Scraping off the back window - Dave_
>> I was tempted to stop and point out which button heated the screen

On my 55 plate Mondeo, the front and rear heated 'screens both came on automatically when you started the engine at ambient temperatures of +4°C or less. A standard feature on diesels apparently, just as well as it took so long to bloomin' warm up!
Last edited by: Dave_TDCi on Wed 12 Dec 12 at 19:54
 Scraping off the back window - Runfer D'Hills
It's these cold mornings when I most miss smoking. The whole thing was brutally simple. Make tea, take mug of steaming rosy outside, temporarily place it on the car roof. Start the engine and turn everything heated on full blast. Stand back, lean on house, smoke tab, drink tea. When fag and brew were dealt with I'd just get in the car and drive off.

Now I feel just a bit too lazy with only the tea to occupy me and find myself scraping windows to hurry things along. In fact by the previous method I could actually defrost two cars with minimal effort.

The best technique of course is and indeed always was to get "her" to do it while I'm shaving, but only if she has finished making my sandwiches.

:-)
 Scraping off the back window - DP
>> It's these cold mornings when I most miss smoking. The whole thing was brutally simple.
>> Make tea, take mug of steaming rosy outside, temporarily place it on the car roof.
>> Start the engine and turn everything heated on full blast. Stand back, lean on house,
>> smoke tab, drink tea. When fag and brew were dealt with I'd just get in
>> the car and drive off.

^^ This ^^:-)
 Scraping off the back window - Robin O'Reliant
That's one of the reasons I could never give up smoking.
 Scraping off the back window - Shiny
I usually scrape the rear first so water droplets aren't left clinging to it.
I have webasto, but it flattens the battery by the time it's done it's job, but is good to have on when left idling with all heating, seats, windows, mirrors on and the doors locked and key in the house.
 Scraping off the back window - henry k
I never scrape the windows of my cars.
I might, just prior to moving off use a squeegee on my saloons back window.
( YES YES IMO a rear wiper is the only plus point, to me, on a hatchback :-( )
I always first use a standard de-icing trigger gun then heater on, HRW on and heated screen on and then reverse out then drive off . Non of this pre warming stuff.
The joys of a petrol car, the heater is very soon pumping out lots of hot hot air.
 Scraping off the back window - oilburner
>> The joys of a petrol car, the heater is very soon pumping out lots of
>> hot hot air.
>>

One of the great things of my 2009 Mondeo diesel is that warm air starts to come out of the vents almost immediately. Very impressive it is. There's hot air long before the engine is even half warmed up. I'm guessing there must be a secondary heating system of some sort.

>> I use both heated windsceens in the Ford just to put the record straight.Any thick ice I >> use the scraper.Mentality is fine thank you.

:) But I still don't *understand* why you'd want to scrape a screen that is heated Dutchie? On aforementioned Mondeo the windscreen is completely clear inside and out within 1-3 mins, even when _very_ cold. And, it stays clear too. Why bother scraping?
 Scraping off the back window - Old Navy
>> >> The joys of a petrol car, the heater is very soon pumping out lots
>> of
>> >> hot hot air.
>> >>
>>
>> One of the great things of my 2009 Mondeo diesel is that warm air starts
>> to come out of the vents almost immediately. Very impressive it is. There's hot air
>> long before the engine is even half warmed up. I'm guessing there must be a
>> secondary heating system of some sort.
>>

Like my car I think the Mondeo (and many other) diesels have PTC electric heaters these days.

www.epcos.com/web/generator/Web/Sections/Components/Page,locale=en,r=263282,a=372328.html
 Scraping off the back window - Rudedog
As you've said they are very useful on modern diesels producing hot air very quickly, I have one fitted in the Golf TDi's heating system.
 Scraping off the back window - IJWS14
My Passat has heated windscreen and rear window, I tend to scrape the side windows and part of the back after starting it, by then the wipers will clear the front.

Had it been ordered three months later I could have had a parking heater instead, would have given up the heated screen and heated seats for one of those.
 Scraping off the back window - Boxsterboy

>> On my 55 plate Mondeo, the front and rear heated 'screens both came on automatically
>> when you started the engine at ambient temperatures of +4°C or less. A standard feature
>> on diesels apparently, just as well as it took so long to bloomin' warm up!
>>

On my 10-plate S-Max, the front and rear screens only come on if you switch them on, or if you hit the max de-frost button on the heater. They don't come on their own at low ambient temperatures.
 Scraping off the back window - Alanovich
>> On my 10-plate S-Max, the front and rear screens only come on if you switch
>> them on, or if you hit the max de-frost button on the heater. They don't
>> come on their own at low ambient temperatures.
>>

Same on my 03 reg Galaxy.
 Scraping off the back window - Ted

I feel quite badly done to now...I've only got a heated rear screen.....and I have to switch it on !

I do however have a switch by the gear lever that lights up when you press it.....it's for the heated seat.




Which, sadly, I don't have !

Ted
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