Fitting Astra GSi bonnet vents

DISCLAIMER: The information on these modifications are a collection from experience (myself or friends), magazine articles, mailing lists, internet web sites etc. So don't take these as 100% correct gospel, hence I don't take any responsibility for any of these guides.

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Difficulty: 2/5 - Just need to be brave

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..and after.
...and after.

This is a step-by-step guide on fitting Astra GSi bonnet vents on to a Nova. But these can easily be fitted to other models in the Vauxhall range. These vents are the original Vauxhall items which are functional, so they are not stuck on, you will need to cut a hole in the bonnet for them to fit.

These vents were intended for the Astra GSi bonnets which have a recess in the bonnet for these items to fit flush. You won't have this option with other models so you will have to fix them on top of the bonnet. If you have the time or the money, you can fill these in so that they appear smooth on the bonnet, which has been done many a time. But with a bit of preparation, these vents will not look out of place when fixed on top of the bonnet. These vents work by the hot air being sucked out of the engine bay when the car is moving, rather than ramming cold air down with other types of bonnet vents.

"So what do I need?" you ask. First you need to buy the two bonnet vents and 6 star clips from your Vauxhall dealer or a scrappy. Those are the major parts, next you will need a jig saw, file, sand paper/wet and dry, rust stopper solution, drill and big diameter drill bit, some paint, primmer, tape measure, masking tape, pencil, sealant and some guts to start cutting your bonnet :) It isn't a very difficult job, it can be done in a weekend including the spraying...if you know what your doing.

Astra GSi vents x2 6 star clips for vents 2x Astra GSi bonnet vents £25
Electric jig saw Hand file 6 star clips for vents (24p ea.) £1.70
Drill and large drill bit Rust stopper solution Rust stopper bottle £4+
Primmer spray paint Spray paint in your car colour Sound Deadening clips (15p ea) A/R
Wet and Dry (400 to 800) Tape measure
  • The part number for the Astra GSi bonnets vents (L & R) are 90426237 and 90426238.
  • Part number for the star clips are 90240551.
  • Part number for the sound deadening clips is 'unknown'.
  • Masking tape Water Sealant
    Stanley knife Pencil/Pen
    Piece of A4 card Sound deadening clips

    Just before you start, make sure you note the following:

    • You'll probably have to order the Astra GSi bonnet vents and star clips from your dealer, you may have to order a bag of 10 clips rather than 6, as that is usually the minimum order. You can buy the vents from a scrappy or get fibreglass copies, but I found that there is very little in money to be saved either way.
    • Before finally putting the Astra GSi bonnet vents on the car, it is ideal to bend the corner on the wide end because this tends to give the impression it sticks up when fitted to the bonnet. In fact the Nova bonnet sweeps down, hence at an angle, and the vent is still straight and flat. You'll have to put something heavy on the corner over a few nights for the vent to hold to the new shape. Either that or use stronger adhesive when fitting the vent.
    • The pencil that was used to mark on the bonnet was off one of those dry wipe boards that you get in the kitchen, seems waxy. This is ideal because you can freely draw on the paintwork, and it will easily wipe off leaving no marks :)
    • Always cut smaller first, as you can always make the hole wider, not the other way round. Always check and check again your measurements before you cut.
    • Always use a rust stopper solution on ANY fresh cuts, before it oxidises too much. Otherwise rust will set in, especially on a bonnet as it is open to the elements.
    • Spraying the air vents. You can get a local paint shop to do this, but as it is a small item, it is very easy to do yourself. To any good spray job, preparation is the key and don't rush. You also need a dry warm day and an area that is free from flowing dust and dirt. First lightly rub the vents over with 400 grit paper and water. Then clean the surface of the vents of grease and dirt etc., I used white sprit, but make sure it evaporates before you start spraying (otherwise the paint begins to 'blister'). Once it is clean, start spraying your first coat of primmer. Use thin layers. Do about 3 or 4 coats. The surface may appear rough, don't worry, just lightly rub it down with 400 grit and water to make it smooth. Once the primmer is done, spray it with your car colour, again using thin layers. Do about 3 or 4 coats. It may again appear to fell rough on the surface, but this time lightly rub it down with 800 or 1000 grit paper with water. That WILL get it nice and smooth (note 100 = rough, 1000 = fine).

    OK, got all the above? Then follow the steps below (remember to click on the pics for a bigger view):

    Step 1 Step 2 Step 3
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    First you need a pair Astra GSi bonnet vents from your local Vauxhall dealer or scrappy. Remember you'll need the 6 star clips as well.

    Make a simple A4 template out of a corn flakes packet, as this will make life simpler when making out the dimensions on the bonnet.

    It's time to open up the bonnet and take off the sound deadening material and clips underneath (if you have one). Then cover up the engine bay with a big dust sheet or take the bonnet off the car, like I did.

    Step 4 Step 5 Step 6
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    With the template, position it where you want to start cutting. Keep in mind that the webbing under the bonnet takes up a lot of room, and your restricted to where you can put the air vent. I found it best to place it 1.5" from the side and 26" down from the top of the bonnet.

    Once your happy with the markings on the bonnet, it's time to be brave and start cutting. I used a tank drill to make big enough holes for the blade of the jig saw to get through. Simply use the jig saw and cut out the vent shape. Once the holes are cut out, offer up the vent and see if any filing is required. Once the vent hole is correct, brush some rust stopper on the fresh cuts (very important).

    Step 7 Step 8 Step 9
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    With both the vent holes cut out, temporally fit the vents to see if they fit square and don't interfere with anything under the engine once the bonnet is closed (my BOSCH unit was very close to the plastic post on the air vent). Easy bit, prepare the bonnet vents to be sprayed, follow what was mentioned above. Do about 3 or 4 coats of primmer and again with the final car colour spray. Once finished, lightly rub it down with 800 or 1000 grit with water to get it smooth. Now that they are sprayed and the vent holes are ready , it's time to fit them on. First cover the outer edges of the inside vent with water sealant, as these don't need to be glued down as such.

    Step 10 Step 11 Step 12
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    Fit and press down on the air vent so that all the sealant squashes out from the vent (as shown). Push fit on the 6 star clips (3 on each vent). These are good enough to hold on the vent to the bonnet. Wipe off any excess sealant and fit the sound deadening material back (you may need to buy new clips). Remember to cut out a suitable hole underneath the vent to allow free movement of hot air. Stand back and admire the work you done. Bonnet vents are usually only done for larger engines as they get really hot under the bonnet.

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