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Jeep JK Hood Vent with Test Data

Car Profile


High engine temps lead us to vent our Jeep JK Hood

Can a Jeep JK Hood Vent both improve performance and look decent doing it? After carefully watching how the new 3.6 engine was running, we noticed it gets hot when pushed hard. For example, a drive out to Moab Utah had us impatiently cruising at 85+ MPH over several passes topping 7,000'. As a result, the engine temperature climbed higher than we'd like. During these climbs we had to to slow down and run the heater to prevent engine overheating. 

I'm sure the engineers at Jeep didn't plan for someone building a Jeep JKU up to 7,400 LBS and sending it up grades at that speed and altitude, however, that doesn't mean it shouldn't be able to do it. As a result, we find ourselves tasked with solving the issue. We figured more air flow past the radiator could possibly help shed some of this unwanted heat, fortunately there's a few areas that could be modified to increase air flow.  First will be a hood vent, as this is easy to do quickly. 

Selecting the right Vent or Louver setup

After tons of research, we decided we liked this large vent from RaceLouvers. After that, I made a phone call to ask a few questions, and was pleasantly surprised by a very knowledgeable person that picked up the phone and gave me lots of good information. Most importantly, they put a Jeep Wrangler in a wind tunnel and observed some things that highlight a few of the weaknesses in the JK cooling air flow path. He even recommended a baffle below the radiator because they observed the smoke trails in the wind tunnel passing right under rather than through it. We'll be doing that in the future too, but for now cutting the vent in the hood was simple and we want measurable results as soon as possible. 

Before deciding on the RaceLouvers Vent, we looked into many others including Daystar, Rugged Ridge, Rough Country, Poison Spider, and GenRight. While these are all hood vents, none could compare to the RaceLouvers in sheer open area, or correct positioning on the hood. In fact, I'd bet some of these that have openings near the base of the windshield exist in a high-pressure zone and actually hurt radiator air flow at highway speed more than they help. The only other option that seems to have similar area in the correct spot close behind the radiator is the AEV hood, which is expensive and out of stock everywhere.

Installing the Jeep JK Hood Vent Louvers:

The louvers came packed well enough to protect them from shipping abuse and fairly quickly too. Moreover, they provide a nice template and instructions to make things go smoothly. We followed these directions exactly, and installed them with the supplied rivets:

Testing the hood louvers:

It was now time to test the louvers but we found that highway driving didn't cause the engine temps to climb much beyond thermostat open unless we pushed the Jeep pretty hard. For that reason, we produced the conditions required to see if there was any measurable change. The subsequent tests involved a steady state cruise at 70mph in 8th gear (Remember, we have an 8-speed auto swapped in), and then dropping rapidly to 5th and holding 100% throttle to 100 MPH, shifting back to 8th, and letting the Jeep return to 70 MPH cruise. We did this with the unmodified hood to document temperature rise and fall (Blue line), and then repeated the test with the louver in (Orange line) over the same stretch of road, wind conditions, and temperature (0.4°-0.9°warmer on 2nd run).  

Coolant Temperature Data:

The below chart is corrected for the minor temperature difference between the first run (no louver, blue line) and the 2nd run (with louver, orange line). The ambient temperature was about a degree higher on the 2nd run (0.4°-0.9°F), but even in the uncorrected chart, the temperature peaks later and recovers faster with the louver. The change isn't huge, but it is measurable.

Oil Temperature Data:

The oil temperature showed a more noticeable reduction across the entire range. As a matter of fact, the oil remained a full 3°-4° cooler the entire time. Likewise, we've noticed a lower operating temperature under most driving conditions.


It'll be a while before we have the Jeep climbing grades at high elevation again, however, we look forward to seeing how it performs. We also plan to make those other modifications to radiator shrouding along with relocating the PSC steering cooler and possibly the winch solenoid pack in an effort to improve radiator air flow. Until then, we're happy to see this slightly better control over the skyrocketing engine temperature.

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David is addicted to building things, travel, and photography.

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