Windscreen demisting ideas needed

[Cahuna]

Fellow Toyspeeders, I need some ideas on how to go about maintaining forward visibility in my FXGT rally car. Currently the car has no fan or heater unit (the donor vehicle did not have one) and fitting the one originally in the current shell will be a bit of a mission. The options I have come up with so far are:

* Use plenty of Fog-off. I haven't had much success with this in the past but it may just work. I'm just concerned about whether the windscreen will stay clear while doing a 38km special stage in the rain.

* Use computer fans. A 15cm computer case fan will fit into the original demister ducting but I don't think it will be capable of pushing sufficient air through the ducts to clear the entire windscreen. (I have also thought of putting one in the top of the instrument cluster blowing straight onto the windscreen in front of the driver to keep the important vision area clear). My main concern with this idea is that it will be blowing cold air, which I believe is not ideal for demisting.

* Find a 12v hairdryer and install that in the demister ducts. Main problems I see with this is mounting and getting sufficient airflow through the ducts (see comments for computer fans), also I don't know whether hairdryers will handle running for long periods of time without overheating.

* Reinstall the original heater/fan. This would undoubtedly give the best result, however the heater/fan unit are from a 1300cc base model whereas the wiring loom is from a FXZS (push-button controls) so I don't know if the two are compatible. Also I neglected to keep the control panels and so would need to find new ones. Finally I would have to reroute the fuel lines (which run through the car). Quite a bit of work.

* Using heated elements (like rear window demisters) aren't really an option as the stick-on ones are apparently not legal for road/motorsport use, only the windscreens with them built in are.

Does anyone have any other ideas which would work better than the above, or alternatively can comment on the effectiveness (or otherwise) of any of the above ideas? At this stage I'm leaning towards a combination of Fog-off and computer fans. Long-term I might try to put the original heater back in anyway but there isn't enough time to sort everything needed to do that before the Far North Rally next weekend.

[RS13]

I'd say run a heater fan remotely mounted, maybe in the glovebox area, and ducted to the factory vents. I see no reason to use the heating radiator, you should just be able to use the fan alone, and regarding the controls, just set it to work at full noise permanently, perhaps hook it up to a switch on the dash.

Easily do-able, just gotta use a little kiwi ingenuity on the mounting, and ducting!

[jondee86]

To effectively demist the inside of a car you need to reduce the
relative humidity until it is below the dewpoint of the glass. In order
of effectiveness, from best to worst :

1. Air conditioner - dehumidifies the incoming air.
2. Fresh Heated air - lowers the RH of the incoming air by heating it.
3. Fresh Cold air - RH higher so doesn't absorb moisture as well as
heated air.
4. Recirculated air - waste of time. This is the same air that is causing
the fogging.

Except for air conditioning, you need to keep windows and vents wide
open to try and prevent your breath and perspiration from raising the
RH inside the cabin. Same reason you should never have your air vent
set to "recirculate" if you are trying to demist the windows in a non-A/C
car.

Cheers.... jondee86

[NZ_AE86]

Stick on demister is the best and who said they were not legal! I have had one one my race car (which is road legal) and never had a problem!
What difference does it make if it is stick on or built in as to being legal??

[matt dunn]

* Reinstall the original heater/fan. This would undoubtedly give the best result, however the heater/fan unit are from a 1300cc base model whereas the wiring loom is from a FXZS (push-button controls) so I don't know if the two are compatible. Also I neglected to keep the control panels and so would need to find new ones. Finally I would have to reroute the fuel lines (which run through the car). Quite a bit of work.

You can just reinstall the fan and duct assembly and just run an on/off switch and a relay to turn it on and off, with none of the original wiring etc required.

Matt

[Cahuna]

Thanks guys, sounds like getting some air coming from outside and forcing it up the demisting ducts sounds like the best (easy) option. I think from memory the original fan unit still fits in around the fuel lines, it is the heater box that gets in the way. The only custom ducting I'll need is the section from the fan to the demister duct as it usually goes through the heater box. Dunno which wires control the fan speed (and which give power) but my boss will be doing the wiring for me and is smart so he can probably figure it out

Stick on demister is the best and who said they were not legal! I have had one one my race car (which is road legal) and never had a problem!
What difference does it make if it is stick on or built in as to being legal??

I was going by a mate from the car club (who is one of the club scrutineers). I think it is something to do with it obscuring the forward vision, in the same way as a crack in the windscreen in your vision zone is a WOF fail. Not sure how ones built into the windscreen are different. It would probably be the easiest option though.

Cheers guys.

[ollieboy]

You can just reinstall the fan and duct assembly and just run an on/off switch and a relay to turn it on and off, with none of the original wiring etc required.

Matt

Doesn't the focus have stick on demister things matt?

[IH8TEC]

where do you get the stick on demisters?

[fangsport]

where do you get the stick on demisters?

Repco etc stock them.

as for their legality, it appears to be a grey area. the WOF regs are along the lines of :nothing (stickers, rollcage tubing etc) is permissable 100mm from the edge of the windscreen. even reg/RUC/Loading cert pockets are able to fall foul of the rules

in the past I have never had an issue with one on the windscreen but the car hasn"t had a WOF for a year or two

to be honest they aren"t much good any way
they don"t create enough heat to keep the screen clear if you encounter a decent outside temperature drop IE valleys

[fj40cruzapete]

apparently shaving foam works quite well i havent tried it yet myself but have had a couple of ppl tell me this

good luck finding a solution

[Loudtoy]

* Use plenty of Fog-off. I haven't had much success with this in the past but it may just work. I'm just concerned about whether the windscreen will stay clear while doing a 38km special stage in the rain.

* Use computer fans. A 15cm computer case fan will fit into the original demister ducting but I don't think it will be capable of pushing sufficient air through the ducts to clear the entire windscreen. (I have also thought of putting one in the top of the instrument cluster blowing straight onto the windscreen in front of the driver to keep the important vision area clear). My main concern with this idea is that it will be blowing cold air, which I believe is not ideal for demisting.

I've used a combination of the two in my datsun, you will find that you will need one on each side of the car however because they only clear 1/4 of the windscreen effectively when there is only 1 but 3/4's when there is two in there. Works well enough though the longest run i've ever done is 7km's in it in the rain. U'm and you'l need to keep the rear windows down very slightly to keep fresh air coming in otherwise you are just recirculating the air in there. Oh and i always leave mine on whenever there is any moisture around as i found that while the fans can keep it clear easily it's a bit of a struggle for them to clear the screen quickly after it's fogged up.
Hope this helps a little

[matt dunn]

You can just reinstall the fan and duct assembly and just run an on/off switch and a relay to turn it on and off, with none of the original wiring etc required.

Matt

Doesn't the focus have stick on demister things matt?

Yup, it does. we use them in all our race cars,
except mine, as I dont think they work properly enough to rely on.

Probably OK if used in conjunction with other methods.
Fog off is Ok too. I thinks that all we used when I run in the rain at the Pukekohe 6hr, although you could see stuff all anyway.

matt

[Cahuna]

Thanks for the advice on the computer fans Loudtoy, I wasn't too sure exactly how well they would work, sounds like they should be an okay (average) solution if I can't get the original fan unit back in.

I had a quick look at how I can get all the existing parts to fit back into the car, after removing the radiator element from the heater box it looks like it will almost fit around the fuel lines, might just need to cut a small area of it out and fill the hole with expanding foam. The plan is to pull the dashboard out tomorrow night and see if I can make the original fit easily, if not then I'll go with plan B (the computer fans).

[Quint]

i paid 8 bux for this bottle of stuff from repco, works like a charm

[panda_dan]

when i ripped out my air con system in my ae85 it left 2 small holes in the firewall. I also ripped out my heating aparatus, leaving myself with the same problem as you have.

Instead of bung-ing the holes i ran 2 small small heatproof pipes through the vacant air con holes to take hot air from the headers to the original windscreen vent ducts in the dash.

de-mists the windscreen perfectly and on a hot day you just wind down the windows

[wde_bdy]

In the back of the Petrolhead magazine there was an add for 12V heaters, commonly used in hot rods. May be worth investigating, it was just in the classifieds section for around $200.

Callum

[suckymotor]

go to wottons and get a rear demister and stick it on the frount have used them on the race car and they seem to work

[Cahuna]

Cheers all.

I took the car to the boss's place last night and we stood there for a while looking at all the parts of the original fan/heater unit. After much umming and ahhing we decided it wasn't actually all that hard to route the fuel lines to another part of the firewall and that we could just put the original parts in. Took around 4 hours from go to woah and I now have a nice working original demister back in. Currently it only blows cold air (I pulled the heater core out and forgot to take it with me ) and it is hard-wired to blow either full bore or not at all but at least it should suffice for the weekend.

[JRCOZY]

Can anyone clarify if the stick on kit is legal or not???
http://www.griffiths.co.nz/shopping/ProductList.asp

Sounds like a very light weight solution.

And the other way is to just blow cold air from the stock fan motor?

Ive hit this problem in my race car too.

[NZ_AE86]

Yes, legal. VIRM states that you can install or repair an electric demister

below is the pasted text-it is better to look at it on the NZTA site.
(look at the bottom of page 5-1-9)

http://www.landtransport.govt.nz/certifiers/virm-in-service-wof-only/general-05-v3.pdf


Fitting of or modification to: Modification always permitted:
Monsoon shields
Electric demisters
Sunroofs (overlays and stickers applied
anywhere on the glazing, radio
antennae, and electric demisters)
Any modification for the purposes of
law enforcement or the provision of
emergency services
• in-service requirements for condition and performance must be met.