Hood Vents - my own personal test: engine bay temperature stats

[PunksJL]

I was considering adding aftermarket hood vents or perhaps modifying my existing hood vents on my 2019 2.0 E-torque JLUR to see if it would help cool things off during towing. After reading lots of posts and looking at YouTube videos no one could state if they actually work to lower under hood or fluid temperatures. Most people said, "Well I can see heat trails coming off the vents so they must work". I really want to see the science/data behind any modification I consider and couldn't find any, so I decided to do my own test.

Using my trusty Multimeter and a good K-type probe clipped to the center of the engine cover I did a couple of test runs. One run with the factory stock hood vents and insulation in place and the second identical run with the hood vents and insulation completely removed. In this test I'm towing my 2-passenger side x side ATV on its utility trailer with a total weight of 2,250 lbs. The run is a 10-mile uphill grade with about 700' of elevation gain. The runs were done back to back to ensure ambient temperature conditions were similar. All temperatures (in F) were recorded under the same conditions/locations (60 mph). I should also mention that my Rubicon is completely stock except for Gladiator grille inserts. Fluid levels (coolant/oil) were checked before the test.

Although the results showed slightly lower under hood temperatures without the vents, this was not always consistent. Also notable was how little effect the hood vents have on coolant, oil, and transmission temperatures. Frankly, I don't see the benefit for towing/normal driving at least. A test like this might reveal more if it were done in a rock crawling environment but I am more concerned with maximizing cooling during towing.

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[Huntnfish85]

I have also been thinking of cutting open the vents to make them functional but after seeing the data looks like it isn’t worth it.

 

[jaymz]

I suspect the only real way to lower under hood temps through the hood without replacing it with some sort of aftermarket piece would be to 3D print something that fits with a scoop facing forward. As you already know, simply venting doesn’t result in a significant change.

 

[Jim1964]

Good work on the test data.

Heat transfer is happening mainly at the radiators in the cooling stack behind the grille. After the heated air exits the radiator, it’s mostly irrelevant whether it goes out a hood vent, or flows out the bottom of the engine compartment.

The engine is bathed in warmed air from the rads. Whether 10% of that warm air exits top wise or not.

 

[Old Dogger]

Excellent data! Thank you for sharing..
The only thing that I do, living in hot as hell Phoenix, is raise my hood in the garage when I get home. But only in the Summer months.

 

[Zandcwhite]

At speed, the vents do nothing. As your post run idle shows, stopped in traffic, low speed crawling, etc is where the vents really help with under hood temps. If that's not your use case, there's no point. The cooling fan doesn't hit high speed as often when crawling in moab or AZ as it did before replacing the fake vents with the valkyrie ones and that's good enough for me.

 

[dcmdon]

Whatever you do, Make sure that the vents are extraction vents and not intake vents.

If you force air into the engine bay, you will decrease the pressure differential between the front and rear of the radiator and actually DECREASE the flow of air through the radiator.

 

[Deleted member 59498]

Wow thanks for sharing.

 

[Reinen]

Interesting data. It does make sense though while the engine is running hard and the fan is operating. What is an extra opening on the hood really going to do in that situation?

I was considering opening up the vents but not for towing. My heat issue is immediately after the engine is turned off. I have a solar panel voltage controller under the hood and it often goes into overtemp protection mode sitting in the engine compartment with the hot (but off) engine and no fan. Rightfully so, the voltage controller gets too hot to touch under the hood. If I open the hood immediately after shutting off the engine it's nowhere near as hot.

 

[rkwfxd]

Hmmm. Also as if the engineers had done this before.

 

[Megawatt]

Can you take temp comparison of Jeep sitting idle when there is no vehicle movement but after the long haul you did?

I would think open vents help letting heat escape at standstill. Should be with measurable lower temps or time to achieve a lower engine bay temp.

Lots of time to sit and wait with AC blowing when I rock crawl with a large group. I like what you tested but you answered the moving question. How about the not using highway speeds air cooling?

 

[Carolina Jeeper]

Isn't it possible that the temperature of the air flow that the probe was exposed to is almost constant from the radiator?

Maybe the results of the open hood vents is an overall cooler engine and not simply a reduced air temperature under the hood.

 

[Tank the Jeep]

Please post some pictures of the open hood vents.

 

[Remorseless]

You're never going to see a drop in outright temps with hood vents with a modern engine, particularly a turbo like the 2.0T. Turbos run hot, and the engine is designed to hit a coolant temp and then open/close the thermostat to keep it from going over that temperature. With turbos running hot and constantly putting heat back into the engine, you're basically just going to sit at that temperature dictated by the thermostat if the cooling system is keeping up. Where the cooling system in the JL fails is if the heat being put into the engine by running and by the turbo is too much for the cooling system to keep up with - and at that point, it just doesn't keep up and the thermostat is wide open trying to get as much coolant through the radiator as possible and coolant temps climb into the 23x and 24x range, eventually resulting in the engine derating to save itself. The best case scenario for the hood vents on the road is that they prevent the engine from derating by assisting the radiator in gaining some additional airflow (your fan doesn't do a ton at 70mph).

Where hood vents shine, and have traditionally shined all the way back to the 4.0 days when EFI was newer in Jeeps, is slow speed heat soak prevention. It used to be a big issue - heat soak caused all kinds of issues with the fuel rails in 4.0 Jeeps, particularly vapor lock. Engine bay would run so hot that, even though coolant temps were fine, the heat transferred to the fuel rail would cause fuel to vaporize prior to injection, thus vapor lock. With the JLs, obviously EFI tech is better insulated and vapor lock is much less likely, but the engine bay still traps heat. This causes the fan to kick in and try and pull air through the radiator because there's just not enough coming through in slower speed crawling.

This is particularly true if you're in low range and geared deeply, as you're running higher RPMs due to the gearing and thus generating more heat, again particularly with a turbo. Heat that is trapped in the engine bay will attempt to soak back into the engine, and thus impart additional heat to the coolant. By allowing this heat to escape upwards, even somewhat, the coolant's job is easier (only fighting heat generated right now, not trapped heat) and the radiator isn't fighting to remove from the coolant the heat imparted by running the engine and the heat stuck in the engine bay. Again, it will not produce a meaningful difference in operating temperature due to how much heat is generated by a turbo and how the thermostat works, but it will mean your radiator isn't dancing on the edge of being able to cool appropriately. It gives you the wiggle room to keep your coolant temps at the temp dictated by the thermostat for, say, that big high RPM hill climb, instead of the radiator failing to keep up during that big high RPM hill climb because there's more heat being put into the coolant than it can handle between it and the fan.

 

[camo4stealth]

PunksJL, if possible you should take temps after parking the jeep with and without open 'vents'. Maybe at 15 minute intervals over say 90 minutes. Sitting with no air flow and engine heat with nowhere to go. I believe, (and I may be completely wrong) that open 'vents' will cool things off much more quickly. IMHO

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