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groar 11-24-2008 02:42 PM

Wiper cover test
Searched a little on the site and didn't saw any wiper cover example. As it seams my groar's 2001 Scenic Modding Thread haven't been read a lot (at least it didn't received a lot of reply), I'm promoting my Wiper cover test message as a new thread in the hope others to be inspired, and do better benchmarks ;)


During two weeks I also tested a wiper cover. As it was only a coroplast sheet taped with transparent tape, I had always an eye on it when I was driving with it. While driving it was always very stable, except when a truck was overtaking me then the left part was shacking a bit. I was also inspecting how well it was taped before driving.

I had a "no rain" position (1st and 2nd picture) and a "may rain" position (3rd picture). When driving the coroplast was pushed down and in the "may rain" position it was only at 0.5 cm over the wipers. The vertical sheet in the "may rain" position is simply stuck between the fixed and mobile parts of the hood. It can be put back and removed without untapping the cover.

Not only it removed the wiper from the air flow, but it also smoothed the angle between the hood and the windshield.

My best daily commute consumption since my first message in this thread is 57.3mpg. It has been done with the wiper cover in "no rain" position. The following best daily commute in that tank was 51.4mpg. But this record may have been helped by a very warm 18C (64F) day...

With cover 3/4 of daily commutes were over 47mpg while without cover 1/2 were under 47mpg before (with same temperature range and "full" grill block).

In my daily commute, when I leave the freeway I have to pass over it thanks to a bridge. At the top of the bridge I'm at 60km/h. I coast in neutral to go down. Without the wiper cover I reach 76-77km/h max at the bottom. With the wiper cover I reach 79-80km/h. I tried to follow the same curve, parallel to the right line. I did it 10 times with the cover and 5 without.

A funny thing : when it was raining then the drops fallen on the windshield under the level of the cover were pushed down to the wipers, effect helped by the fact I used an anti-rain product on the windshield.

I think this cover is a success :)

If I put the cover back then I will cut the lower corners so they are not pushed up by the upper sides of the hood. May be that will permit the hood to be opened without removing the cover. I may also cut the cover so it stop just before the wipers, which may help finding a "any rain condition" configuration.


basjoos 11-24-2008 03:48 PM

That's a larger version of the wiper wind deflector installed on my car. With mine, I didn't notice any significant improvement in mileage although it did reduce the wind noise and the amount of ram pressure (no fan) air flow coming through the vents.

Cd 11-24-2008 04:15 PM

I found your results interesting. Thanks for posting.

Have you considered just removing the wipers ?

If there is a chance of rain, both wipers can be reinstalled in less than a minute - just push the wipers back into place and replace the bolt. I did this recently on a trip with no problems.
( Be cautious to have the wipers line up correctly with the teeth of the gear though )

Frank Lee 11-24-2008 07:09 PM

I made one... couldn't tell any differences in mileage or anything. Off it went. I don't think there's really "flow" in that region, at least on my cars.

groar 11-25-2008 07:38 AM


Originally Posted by Cd (Post 74556)
Have you considered just removing the wipers ?

I'm not very comfortable with the idea to have no wiper (even if I know I can put them back in one minute), but I may try it if weather forecast is optimistic. For the next few days they are talking about snow and sub 0C temperatures...

I don't have an idea if the improvement comes from the wipers removed from the air flow, or the angle between the hood and the windshield which is flatter, or both. The no wiper test may help to decide.


i_am_socket 11-25-2008 10:00 AM

A wiper dam is planned for my car since they are most definitely in the airflow, but I'll be shooting for a more subtle "basjoos" style. Spring cannot come soon enough... *grumblestupidcoldweathergrumble*

At least I've got my Guino so I'll be able to see any MPG increase instantly... you know, once its installed and stuff :D

wagonman76 11-25-2008 12:24 PM

Heres mine I did earlier this year. I couldnt tell one way or the other with mpg. But it certainly does not hurt.

Frank Lee 11-25-2008 12:55 PM

How do you know they are most definitely in the airflow?

Mine were very similar to wagonman's- mine went up the windshield a little further and had some more "fillet" to them. Anyway, I made it two piece, left and right. After going through the rain with no wipers and no noticeable fe results I re-installed the driver's wiper and left the passenger side fill panel. On my car I have noticed, fill panel or not, identical behavior of raindrops on the windshield. That is, on about the bottom 1/4 to 1/3 of the windshield, the drops just sit there even at highway speed, whereas on the rest of the windshield they are blown up and to the sides. That whole zone of drops sitting there stationary tells me that flow velocity there is not high at all. So the aerodynamics books I read were right: there is a fairly stagnant high-pressure "bubble" in that region, on cars like mine and wagonman's.

Now, that Renault has such a shallow transition there at the windshield base that I would not want to venture a guess as to whether it has the above described situation.

Christ 11-27-2008 02:52 AM

Frank - My Topaz always "wagged" the windshield wipers at high speeds (post-80mph).. I know you don't drive that fast, and that was the only time I ever saw it happen... but I figured it was interesting enough to post.

When I say "wag", I mean they would waver a little bit.. within the confines of freeplay, and not at a given frequency... I think it had alot more to do with oncoming traffic blasting jets of air, which disrupted my own airflow, but I can't be sure.

Frank Lee 11-27-2008 11:50 AM

Reminds me of when I was airing the tires on the Tempo and forgot I set one of those standard black plastic valve stem caps on the cowl panel. 350 miles later when I got home I discovered it still sitting there! :eek:

Anyone still think there is "flow" there?

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