Hood Vents Installation

Louvers (vents), Drip Pans and Part Numbers The louvers I am using come from a 1994-96 Pontiac Grand Prix GTP. (I haven't checked yet if this vehicle, and the spare parts for it, are available in Oman -- Laurie) These are functional hood louvers and are made out of a high temperature resistant Nylon. In addition to the louvers I also purchased the drip pans, which mount inside the hood, under the louvers. PLEASE NOTE: The drip pans severely restrict airflow out of the louvers. I purchased them to install during the winter weather months when I don’t really want to loose very much of my engine compartment heat. (You can probably do without these in Oman! -- Laurie) Here is a picture of the Louvers (top and bottom, and the drip pans) as they come from the Pontiac dealer.

As you can see the vents come snow-white nylon and have to be painted. I used DupliColor “Bumper Black” as it contains a flex agent that should allow for expansion and contraction without harming the paint. Here is what they looked like after painting.

I did put the nylon louvers in my bead-blasting cabinet for a few minutes to rough them up some prior to painting. I did not use any primer or other flex agent, other then the Bumper Black rattle can stuff. So far the paint is holding up well.

Part Numbers and Costs #10225885 - Left Side Louver - $27.23 US #10230097 - Left Side Drip Pan - $4.56 US #10225886 - Right Side Louver - $27.23 US #10230098 - Right Side Drip Pan - $4.56 US If you are unable to find these parts in Oman, I'm sure other Louvers could be used, but you could obtain the parts from this website: http://www.parts.com - just enter the part numbers you need.

Installation Template Location Once I knew the area I wanted to install the louver at I made a template to match the underside of the louvers so I could mark the holes I needed to cut in the hood of my Jeep. Note: If I can come up with a way to replicate this cardboard template, I will do so and would be happy to send them out to folks if you have an interest. Let me see what I can do with it first. I covered the hood on both sides with masking tape so that I could trace the template out on the hood in the proper location on both side. Here is a picture of the template in place ready to be traced. Please Note, it is the inside edge of the template that gets traced, as well as the holes that mark the drill locations. The outside edge of the template represents the outside edge of the louver when it is installed.

Please take note of the two nickels and the long piece of blue marking tape. The blue tape is exactly 20.75-inches (20 and ¾-inches) from the rear edge of the hood. This is important. This places the front edge of the louvers. If you do this, DO NOT go less then 20 and ¾-inches or you will have a clearance issue inside the hood with the bracing on the rear edge of the hood. The two nickels where used to space the template (and louver) away from the curvature of the hood where it bumps up. Just lay the two nickels down and push them up to the curve while allowing the nickels to remain level and NOT ride up the curve. This will mark one edge of the template (and louvers) for you. Tape the template down and then trace the inner section on the tape. Be sure to trace and mark the eight (8) holes that you will have to drill to mount the louvers through the hood.

Drill and Cut Here is a picture of the template traced on the masking tape and the eight holes (6 are 5/16-inch and two locating holes are 1/8-inch) drilled in my hood. You can also see I marked the section that needs to be cut out with a criss-cross pattern so even if I where having a blonde day it would be difficult for me to screw up!

Piece of advise. Tape and trace the template on both sides of your hood before you do any drilling or cutting. In this project you want to measure 5 times and cut only once for each louver hole.

Prior to making “the big cut” on each side I drilled several pilot holes in the section of my hood that would be cut out. I also protected the hood with some duck tape to keep the vibration on the Air Saw shoe from scratching the paint.

I suppose any number of tools can cut this hole out. I used an Air powered Body Saw which I have had for years. If you don’t have one maybe you can barrow one from a friend. These things cut single thickness sheet metal like a hot knife through butter, leave no distortion in the hood when done. Also, Harbor Freight sells these every day of the week for $39, but every three or four weeks they have them on sale for $20. After cutting the hole on the template line all I had to do was take a file to de-burr the edge and trial fit the louvers. They fit perfectly. I did use touch up paint on the edges that I cut. Sorry don’t have a picture of the hole. I mounted the louvers using 3M-brand Trim tape purchased at Auto Zone. This stuff is incredible. I just laid a 1/8-inch bead of tape all around the underside of the louver and put the louver in place. Tip! DO NOT pull the backing off the 3M trim tape until you have the louver in place on the hood. Once in place you can pull the backing off and press the louver right down. Trust me, it will not move, and you will not get it off again without sliding a knife between the louver and hood to cut the tape. Here is a picture from under the hood at the driver’s side louver. See those little white stand-offs? The drip pan mounts to these stand-offs with screws.

Here is a rather poor picture of the drip pans temporality mounted to the underside of the louvers.

As I said before, the drip pans severely impact the performance of the louvers. I have mine off and they will stay off until winter. Based on the size of each louvers opening I have calculated each is the functional equivalent of cutting a 5-inch square hole on each side of your Jeeps hood. You can see the heat, and distortion cause by the heat from the drivers seat. It is not enough to hinder your vision, but it is quite noticeable. Here are two more pictures of the louvers installed.

End Result: I think the best way to start this off is with the results and a picture of the end result. Given an outside air temperature of 90+ degrees F, I have been able to reduce the under hood air temperatures on my 97 TJ by as much as;   

11 degrees F at Idle. 16 degrees F during Stop and Go 27 degrees F during Highway Travel

Here is what this implementation looks like:

What you are looking at is the hood of my Jeep after installing the Louvers which allow the under hood temperatures to be lowered as I have shared above. Yes I think they look nice, but function is what I was going after in doing this modification. Prior to installing the louvers I did quite a bit of investigating, research and testing. With the help of my friend Kevin, who owns an automotive testing lab capable of measuring temperatures and pressures I set out on this task.

Where to install the louvers? What I was looking for was the most effective location to install the Louvers! 1. Where is the heat the highest under my TJ’s hood? and... 2. Where if any is there a vacuum (low pressure) location on top of the hood? (Yes even a Jeep has aerodynamics, be they poor.) Please note I did give some thought to determining where, if any, a high pressure point would be UNDER the hood, but I did not elect to follow up on this.

Temperature Measurements and Findings: To determine the highest temperature locations under the hood I made more then a few trips to my friend Kevin’s lab. There I borrowed 48 temperature sensors, and the computer/recording device to capture the data I wanted. The 48 sensors where mounted on the underside of my hood, forming a grid that covered the better part of the under hood. (Approximately 1-inch below the hood) My plan was to find those areas that would get the hottest, and then look to see if I could install the louvers in this location. I wasn’t really sure I needed to this as “I was sure I knew” where the greatest heat would be found. Trust me, I was wrong. Here is a simple drawing that reflects the plotted data elements collect from my tests locating the highest under hood air temperatures on my TJ.

The red shaded areas represent the highest temperature areas, under the hood, taken approximately 1-inch below the hood. Everything under the hood gets hot, yet these areas had temperatures of at least 20 Degrees F hotter then all the others. Remember when I said “I already knew” where the heat was located? I was wrong! It wasn’t on top of the engine or even centered on the exhaust manifold as logic would suggest. Why is this? I have no clue, only guesses. I suspect part of this is due to the air movement caused by the fan, and part probably has something to do with heat being trapped between engine compartment components. I am sure there may be other good explanation as well. All I know is that I am confident, at least on my Jeep, this drawing represents the highest under hood AIR temperatures, by geography, in my engine compartment. For the record, the single highest temperature I recorded in this effort was located 4-inches in front of the firewall, and 6-inches off the center toward the driver side. Please note while there are significant differences in high temperatures for each of the three tests that I ran, (Idle, Stop and Go, and Highway) the pattern of High Temp Location never changed significantly. Meaning, the hottest locations remained the hottest locations regardless of what test was performed.

Temperature Testing Methodology In order to capture the temperatures accurately I used a methodology I have used in another cooling system test write-up. It goes like this: The equipment I used this time had 48 temp sensors as explained above. Each was mounted to the underside of the hood about 1-inch off the hood. (I was measuring Air temperatures, not surface temperatures.) These sensors recorded time and temperature data, every 3 seconds, to a small hand-held data collection device. All temperatures are in degrees F and recorded to an accuracy of 1/10 of a degree F. Types of Tests: I performed a set of three different tests throughout this effort (At Idle, Stop and Go, and Highway). Each set was performed no less then 4 times, prior to installing the louvers and after installing the louvers At Idle Test: This test measured and recorded all under hood air temperatures from each of the 48 sensors with the Jeep idling in my driveway for 15 minutes after a 5-minute warm up period. Stop and Go: This test was a 6-mile stop and go, inner city drive, after a 5 minute warm up period. Again measuring and recording all under hood air temperatures from each of the 48 sensors. Obviously each test was not exactly the same as stoplights and traffic most likely did differ to a small degree. But the course was indeed exactly the same each time. Max Speed was 25 MPH.

Highway: This test covered a distance of 18 miles on Interstate 75. Nine miles down the interstate, off the exit, turn around and nine (9) miles back. Highway Speed maintained at 65 MPH. Again measuring and recording all under hood air temperatures from each of the 48 sensors. Test Notes: As I stated, each of these tests was conducted multiple times. The data I am sharing is the data I have for those days when the outside air temperature was the hottest for each setup (with or without louvers.) Also note, the outside air temperatures are different for each of these tests, In every case the outside air temp was lower for the “No Louver” tests, then it was for the “Louvered” tests.

Identifying the Low Pressure / Vacuum Areas on the Hood I wanted to determine where, if any place on the hood a low pressure or vacuum area might be located. However, seeing as I don’t have access to a wind tunnel I had to get creative here. I taped to the hood 48 pieces of yarn (wool), each 3-inches long, in the approximate locations to where the under hood temp sensors where mounted. The yarn was taped to the outside surface of the hood and then I simply drove the Jeep and observed what happened.. You’d be amazed at how and what directions the yarn will flow and point to. Sometime it even sticks straight up! Good Vacuum for a brick! Based on more then a few drives with the yarn on my hood (talk about funny looks from people) and a lot of note taking I determined to my satisfaction the low-pressure area. Here, shaded in the pinkish color are my results.

If you decide to do this little exercise on your own be aware you need to get yourself going at least 25 MPH for this to be effective. I could not discern any significant difference in airflow patterns at any speed over 25 MPH. The shaded areas represent the locations where the yard either shot straight back (To the back of the Jeep) or shot straight UP in the air once up to speed. In some areas, like close to the windshield, the yard pointed toward the front of my Jeep confirming the high-pressure area at the base of the windshield. After I did all this testing and came to my own conclusions about the low-pressure (vacuum) areas I showed my results to Kevin. He looked at them, dropped them on the table, when to a cabinet, and preceded to hand me a testing tool to validate my results. Unfortunately he only had two pressure sensors so I had to do a lot of driving, recording, stopping and moving sensors around. But I did it. For what it is worth I can now tell you this; $1.99 worth of yarn and a bit of duck tape came up with the same answer as a very expensive piece of lab test equipment!

Hood Louver Location I now knew where the highest under hood temperature were located. I also had to a reasonable degree of accuracy, the locations on the outside of the Jeep’s hood where the low pressure / vacuum areas were located. To determine where to mount the louvers all I did was to lay one set of data elements on top of the other and look for commonality of location, or overlap. Here is what it looked like.

See those locations where the High Temp and Low Pressure areas overlay each other?

That’s where my louvers are installed. (Life is Simple! Life is Good!)