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

[Dr. RGB]

Yes you are reading that correctly. Unfortunately this seemed to have no significant effect on coolant, oil or transmission temperature which is what I was hoping for. Even though temperatures were a bit lower without the vents I felt it was pretty insignificant.

***Warning: Stats Geek Thinking***
So, data are data and can be relatively useless unless we know if the data are statistically significant. I would recommend running a repeated measures t-test to indicate if the temperature differences are statistically significant or not. You can download JASP (free statistical data analysis program), formatting your chart for .CSV and run the analysis. This would give us a better understanding if the changes in temp are truly affected by the vents or if there are other confounding variables (remember extraneous variables become confounding when they influence the variables being measured, here it would be temperature).

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[jeepingib]

Modern vehicle design is sometimes a battle between departments. The bean counters, lawyers, vehicle design, electrical, mechanical, cooling, etc. Often times if an idea isn't shown to be necessary, and someone from another department thinks that it might interfere in some way with something else, it gets axed.

 

[Remorseless]

Modern vehicle design is sometimes a battle between departments. The bean counters, lawyers, vehicle design, electrical, mechanical, cooling, etc. Often times if an idea isn't shown to be necessary, and someone from another department thinks that it might interfere in some way with something else, it gets axed.

Particularly true when it comes to NVH and fuel efficiency, those are definitely weighted more highly than they used to be, even in Jeeps. I honestly wonder what impact functional vents have on those categories in a Wrangler. I suppose they have some form of internal metric they measure the NVH factor against, and MPG seems it would be pretty straightforward to test.

 

[dcmdon]

Correct, I've been to the A2 wind tunnel in NC a number of times. Thus, the reason for adding hood vents is to lower the underhood air pressure and thus lower the amount of drag on the car. On a number of cars, we hook them up with instrumentation and one is, measuring air flow through the radiator. Thus hood vents help increase the air flow through it.

Yup. You can also increase radiator flow by increasing the exiting air flow UNDER the engine compartment out the bottom of the firewall.

This is a big no-no in race cars because it creates lift. But in a Jeep its a non-issue for 2 reasons.
1) we aren't going that fast.
2) there is a huge amount of space between the bottom of the firewall and the road. So its not like the air is exiting into a confined space.

One trick on piston engined aircraft is to actually radius the bottom edge of the firewall to allow air to flow out the bottom more efficiently.

I'm spitballing here. But one crazy idea would be a moveable Venturi that could be lowered on the road, especially when towing, and raised when off road. You could even set it up so that it functioned as a skid plate when it was up.

 

[chwdg10]

I installed the S&B Air Hood Scoops on my JL just last week. Too early to know if they make any difference under the hood, but we off-road in the Southern California desert often so we figured it couldn't hurt. Install was quick and easy and they look really good.

 

[AnnDee4444]

Sone of these "ideas" make me giggle. This is in no way trashing anyone or anything, but don't you think Jeep though about making actual hood vents when they made the fake ones???

I mean it would have 0 cost change to make the rubicon hood vents function if they inded did function, meaning they reduced heat. It's just funny to me that people seem to think that never crossed their mind and you are the first to posit the idea.

Maybe Jeep doesn't want to sell a vehicle that has an open hole above the engine, exposed to rain/snow/sun/UV.

Also in stock form the vents do allow more heat to escape than if the hood was solid metal, so calling them fake isn't exactly true.

 

[AnnDee4444]

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.

Excellent testing. Have you considered modifying/removing the side vents?

 

[Hard Rock Jeep]

Thank you . Data over opinions works for me.

 

[5280]

Thanks for doing the research.

 

[fooldawg]

I haven't read the entire thread and what I'm about to say seems odd to me. I searched around and couldn't find any references...

So we do a lot of beach driving (outter banks, fort fisher, north end, etc). I always keep an eye on all the temps and never run the AC thinking it would make the jeep run hotter. Well the other day the wife wanted some cool air so I fired up the Max AC on our way out of the sand (approximately 5 miles). All the temps that matter decreased (coolant, trans, oil) by at least 10 degrees...

According to "off road pages" running the AC made the jeep run considerable cooler.

Anyone else seen this? Does this make sense?

Would it be the same for towing in OPs scenario?

 

[Dasher320]

Excellent testing. Have you considered modifying/removing the side vents?

I heard the guy who ran the JL program interviewed by Modern Jeepers. The side vents are there to get rid of the hood flutter that JK's had. No mention of cooling.

 

[AnnDee4444]

I heard the guy who ran the JL program interviewed by Modern Jeepers. The side vents are there to get rid of the hood flutter that JK's had. No mention of cooling.

I've read that too. The theory is that the side vents evacuate air and doesn't let the pressure build up under the hood. Evacuating the air quicker could possibly allow more air to flow through the radiators.

https://www.carscoops.com/2017/12/t...8-jeep/#:~:text=the vents where,hood in place.

 

[AnnDee4444]

I haven't read the entire thread and what I'm about to say seems odd to me. I searched around and couldn't find any references...

So we do a lot of beach driving (outter banks, fort fisher, north end, etc). I always keep an eye on all the temps and never run the AC thinking it would make the jeep run hotter. Well the other day the wife wanted some cool air so I fired up the Max AC on our way out of the sand (approximately 5 miles). All the temps that matter decreased (coolant, trans, oil) by at least 10 degrees...

According to "off road pages" running the AC made the jeep run considerable cooler.

Anyone else seen this? Does this make sense?

Would it be the same for towing in OPs scenario?

I've noticed this. I think the fan runs for longer periods of time with the air conditioning on, effectively cooling the other radiators more than if the air conditioning was off.

Something else strange I've noticed is more aggressive throttle response with the air conditioning on. Not sure if this is done with pedal tuning or the motor running a more aggressive tune to compensate for the parasitic losses.

 

[AnnDee4444]

More fun stuff... I have no idea if any of this is accurate or even applies to the JL.


Check out the airflow around where the Rubicon vents would be located:

And the side vents:

 

[jjvincent]

Yup. You can also increase radiator flow by increasing the exiting air flow UNDER the engine compartment out the bottom of the firewall.

That can happen but the dilemma is how do you do that? When you are limited by the design of the vehicle, then you look at how to cheat the system. Thus you have a hood and can vent it. As for the undercarriage, you are pretty much stuck. I've run into this in various series' where you pretty much need to vent the hood as that's the only easy and realistic spot to increase airflow. In addition to increasing that airflow, you decrease drag as you are reducing the underhood pressure.

I will say, the one thing not to do is vent the hood by raising it up in the back. Cowl pressure on a Jeep has to be massive and thus it would reduce the amount of airflow through the radiator as you have air being forced into the back and front of the engine compartment.

As for a Jeep and what people do with it, I doubt that adding vents and whatnot will really make a difference in the overall scheme of things. If anyone wants, send me $12K and I'll rent the A2 tunnel and try whatever you want, then provide the data. It blows at 85 mph, so that's suffice to see what we need.

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