I opened up mine not to cool while running, but after I’m stopped and engine not running and the engine has to dissipate heat by itself…. I didn’t want it sitting with a blanket over it essentially with no escape for th hot air. With my vents open, heat is pouring out the top of the hood, and that means cooler air is replacing it from the bottom.
This. Heat rises. I had no inclination cutting open the stock vents would do diddly for operating temps. I was interested in engine off and dissipating heat once shut off both on the trail and in the garage. There is no adverse effect on the highway by doing this but I have felt the heat "pouring" out the vents when parked. This was especially pronounced in windy conditions on the trail. It has been more pronounced as I have aftermarket inner fenders and aftermarket front bumper and skid. Air enters below very well and hot air escapes from the vents nicely. Living in the desert, I'll take every 1% of heat help I can get.
I have heard of others doing this too, but just curious why it is necessary if the engine is off and you are no longer driving?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.
Thanks for sharing your results.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.
It'd be interesting to see some tests done with these:
.
Excellent analysis and thanks for sharing...love seeing actual numbers!
My idle test temperatures were taken after each pull and after waiting 5 minutes to achieve a normal idle temperature. One would think that without the vents the engine bay would cooler but that was not my observation.
I decided to go with the Gladiator grill inserts due to the posts I researched and the higher tow rating on the Gladiator. Personally I haven’t noticed much difference in my temperatures but I had not towed anything prior to swapping the grille inserts. It’s such an inexpensive modification thought and it definitely can’t hurt anything. Just by looking at the grille inserts you can surmise they are less restrictive than the stock Rubicon grille inserts.
I agree multiple probes would be a good test. I chose the location of my probe as I anticipated that the open vents might allow heat from the radiator to more quickly escape via increased airflow thus lowering the temperature across the probe. I seriously doubt this occurs. My assumption is when moving the air pressure is higher above the hood which probably traps/caps off the under hood hot air from escaping. I’m thinking of the cowl induction principle where a rear facing cowl near the windshield sits in a low pressure zone where outside air could easily enter. That’s why Chevy used cowl induction and Pontiac had their famous shaker hood scoop on the Trans Am. That air was for a cooler intake charge though and not intended to cool off the engine bay. I think the Rubicon vent slots are too far forward to do any good.Thanks for sharing your results.
It'd be interesting to see some tests done with these:
https://www.northridge4x4.com/part/hood-accessories/as-1015-s-b-filters-air-hood-scoops-only-kit
Might be a cool video idea.... Hmmmm.....
Proper probe placement would also be my thought.
Typically engine bays collect heat in the corners at the back of the hood. The fan is pushing air through the radiator, it then hits the engine, some flows around the sides, some drops straight down (which is one reason for splash guards under the radiator, to channel airflow back and help keep it from dropping straight down).
It would be interesting to have a few probes and test air temp in different areas under the hood during the same drive. And to test during some long drives (hour+) to see if there is any heat soak going on.
My entire intent with this test was to maximize engine cooling while towing so I didn’t do any measurement post engine shut down. I understand that heat rises and I’m pretty sure having open hood vents will help cool an engine compartment when the engine is not running. It appears they don’t help much at idle speeds when stationary. Both of my idle temperature tests were done after I had pulled the 10 mile grade and after letting the engine idle for 5 minutes. Although without the vents was only a slight improvement it was not a significant improvement. It would be interesting to see this in a rock crawling/slow four-wheel test.
My reading of your chart is that the ambient engine bay temp with the vents opened up was 11, 17, and 5 degrees cooler than with the vents on, with the exception of the 3rd run being 1 degree warmer. So overall it seems it was cooler with the vents opened, correct?
I do this knowing I'll be wrenching as things cool quicker. For instance, knowing I'm changing the oil when I get home, I open the hood to vent hot air and cool things off quicker. I change the oil with it on the warmer side.
Take a look at my write up: https://www.jlwranglerforums.com/fo...waterproof-rubicon-hood-vents-write-up.82001/
