How To Paint Your Plastic Radiator Cowl
This tech article was originally posted at FordF150.net. It is primarily intended for Ford trucks but the processes most likely also apply to other vehicles.
1. Removing the Cowling: The first step is to remove the cowling so that you can work on it. This is done by unscrewing the 8 plastic fasteners and then popping out the compression fittings the screws were in. Here is a picture of the fasteners, sorry it is underexposed:
2. Prepping the Cowling for Paint: Now that you have the cowling removed you can take it over to your nice clean work area.
The first step is to mask off the area you do not want painted. I chose to keep the stickers clean, but you could pull them off if you wanted to go for a cleaner look. Use masking tape and completely cover the sticker. I stayed inside the ridges and used them for a guide. At the end of the box area I ran the tape over the edge. Then, using an Exacto knife I carefully trimmed the ends of the tape back. It helps to use your finger nail before you cut so that is tight against the ridge.
Complete this process for both of the boxes and you are ready to move onto the next step.
3. Sanding the Cowling: This is by far the worst part of this project. When painting surface prep is probably the most important thing. If you start with a good surface it is tough to mess things up. If your surface is not very true then it is easy to get bad results. If I was going to do this over again, I would just clean up the handle and call it good. Whether or not you want to spend the time required to sand it is up to you. Remember, this is different then the tailgate handle. This part goes under the hood, and it doesn't have to match up to the body surrounding it at all. For that reason I suggest you just clean the plastic completely and move on to painting it. If you do choose to sand the surface smooth, give yourself plenty of time and find an pneumatic sander to use. Even with a mechanical sander it will still take quite some time. The problem is the contours in the piece. If you are not careful you will make some big gouges with a mechanical sander. That means that most of the sanding must be done by hand. This is after the first round of sanding with 100:
Here is a close-up of the surface part way through the sanding. This looks good, and will be very smooth after using 600 on it to finish the sanding:
Take your time and make sure you cover the entire surface. Here it is after 220:
The final step in the sanding process is to wet sand the surface. Use a little water on the surface with at least 600 sand paper, and go over the entire surface. Use the water liberally as it will really smooth the surface, and it cleans up a lot of the dust also.
The last step before you spray the primer is to thoroughly clean the surface. Again, the key to good paint is to have good surface prep. I used denatured alcohol to clean the surface. However you use it make sure you use a lint free cloth so you don't add more contamination. From this point on it is important to keep the surface clean. Fingers are especially good at contaminating it because of the oil on our skins. You want the surface to be clean so that the paint has good adhesion.
4. Laying down the primer: Now that you have the surface all prepared you are ready to spray your first coat of primer. As always when painting plastic make sure you use a primer that is specially formulated for this surface. Spray even thin coats. The first coat is often easier if you spray it very thin. I am really stress how important it is to have a solid base, but it really does make huge difference. In the later pictures you will see some flaws in my cowl. The main reason for the imperfections is my haste when preparing the surface. That is why I suggested you leave the cowl as it is and not worry about sanding it. Anyway, here is a pic of the piece after the first coat of primer, as you can see it is very thin:
I sprayed three coats of primer so that I was sure I had completely covered the entire surface. In between coats I lightly scuffed the surface so that the following coat would have some texture. As always read the label on the primer you are using and follow the directions for application.
5. Spraying the base color: From here on out it is very simple. All that work in preparing the surface and keeping it smooth pays off. Basically all you have to do here is lay down smooth even coats of paint. Starting with the first coat, keep it nice and thin. As you lay down more coats the finish should look more and more like the factory paint. The last coat should be completely smooth and look just like the factory paint without the clear coat on. Follow the directions found on the label for best results. Here is the cowl after the first coat of paint:
I sprayed 5 coats of base color, lightly scuffing between the first couple coats. I spent the most effort on the final coat. It looked perfect without clear coat on it. If you make any mistakes let the coat dry and sand it down some, then spray over it.
6. Spraying Clearcoat: This is the step that really makes the paint look good. Refer to the label on the clear you are using for exact directions. Most clears call for one light coat and then one thick "wet" coat that really gives the paint its glossy look. Apply the clear as liberally as you can with out runs or drips. Here is my cowl after the final coat of clear:
Now all that is left do it is remove the tape and make sure everything looks clean. I attempted to paint the plastic pressure fittings, but the paint did not adhere well enough so I left them black. I have some other ideas on how to paint them, so if I figure it out I will update this article.
Finally, install the cowl back in the truck. I would let the paint dry for at least a night before you try to reinstall it. Even though the paint has dried it will still be soft. By waiting as long as possible it will reduce the chances that you mar the surface when you replace the cowl. Just reverse the removal instructions to get it back in.
This project is fairly easy. The painting part really isn't any harder than the tailgate handle, but the prep work is much more involved. Take your time to insure that you have a consistent finish before you start spraying. Look forward to the next how to article.