• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Hood vent design debate

Tankerblade

NAXJA Forum User
Location
Gilbert AZ
So, on my laundry list of stuff to do to my pile, I'm planning on doing some hood vents to dissipate some heat.

So far most vents are louvered and angle back and not all that good looking IMO. So found a pic online of a plasma cut design.

I like the design and idea of it.

However, I question the purpose of the angled back louver. With it angled back does it help force air down around and out the bottom while moving? Or create a venturi affect and help suck hot air out through the top while moving?

How would a set like the picture given do? Obviously anything is better then nothing, just curious as to the design of louvers and its effects on air/heat transfer.

Also, live in AZ. Dont care about rain and water because well what's rain? Lmao
c1326c1da952e94475e93702940187eb.jpg


Sent from my SM-G950U using Tapatalk
 
What I really don't get is:

- Why so many people feel the need for hood vents, when if in proper working order they're not needed
- Why so many people seem hellbent on putting hood vents in that let any precipitation fall right down in/on the engine

Any time I see hood vents (that aren't drain pan'd), hood holes (hole saws) or louvers on the hood itself I just have to laugh.
 
What I really don't get is:

- Why so many people feel the need for hood vents, when if in proper working order they're not needed

Although he doesn't say it here he's running a 2001 XJ -- that means those silly pre-cats under the hood -- He will experience heat soak causing the fuel to vaporize while shut down for short periods -- Happened to me just the other day while filling up with gas -- was 70 degrees out -- Jeep wouldn't start till I opened the hood and gave it 5 minutes to cool down

- Why so many people seem hellbent on putting hood vents in that let any precipitation fall right down in/on the engine

I do agree with this -- doesn't make sense to me either -- the TPS alone is right there up on top exposed to the rain

Any time I see hood vents (that aren't drain pan'd), hood holes (hole saws) or louvers on the hood itself I just have to laugh.

I'm personally thinking of doing some sort of cowl hood -- may build a rain gutter if needed -- in the short term I must get manual control of my electric fan -- It has to run if I'm shutting down for a few minutes to get the heat from the pre-cats out
 
I'm interested in hearing the pros/cons of hood vents/louvers. I've been considering them but haven't pulled the trigger because I haven't had issues running hot...yet.
 
What I really don't get is:

- Why so many people feel the need for hood vents, when if in proper working order they're not needed
- Why so many people seem hellbent on putting hood vents in that let any precipitation fall right down in/on the engine

Any time I see hood vents (that aren't drain pan'd), hood holes (hole saws) or louvers on the hood itself I just have to laugh.

This ^^^ I been here for 53 yrs now and it gets about the hottest in the nation. I've towed my #3500 trailer 1000's of miles and one summer I towed a #12,000 contruction trailer to the dump, yes it was showing +210* but it held!
 
I forgot to say that I'm notorious for crawling w/ my A/C on and never shutting my motor off when I'm on the trail!
 
What I really don't get is:

- Why so many people feel the need for hood vents, when if in proper working order they're not needed
- Why so many people seem hellbent on putting hood vents in that let any precipitation fall right down in/on the engine

Any time I see hood vents (that aren't drain pan'd), hood holes (hole saws) or louvers on the hood itself I just have to laugh.

Mine didn't make a difference in engine coolant temps but made a huge difference in under hood temps at slow speed.
Also, if your engine can't handle a little moisture you have bigger issues than some rain getting on it.
Hardly any water gets through my Lebaron vents.
 
This ^^^ I been here for 53 yrs now and it gets about the hottest in the nation. I've towed my #3500 trailer 1000's of miles and one summer I towed a #12,000 contruction trailer to the dump, yes it was showing +210* but it held!

If I recall correctly none of your XJ's have the cali emission pre-cats under the hood

You must take them into consideration...

When my Xj wouldn't start the other day the temp gauge showed just under 210 -- usually I'm almost a full notch below 210 -- Keep in mind I just started driving this jeep over the winter -- The day that happened was the warmest day I've driven it in and it was only 70-75

I was watching the gauge because I did have the heat soak issue in mind -- and it happened

On the 2000,2001 just turning on the AC does not automatically mean the electric fan runs -- at least not on mine
 
Caveat: I do not have any hood vents.



What I really don't get is:

- Why so many people feel the need for hood vents, when if in proper working order they're not needed
- Why so many people seem hellbent on putting hood vents in that let any precipitation fall right down in/on the engine

Any time I see hood vents (that aren't drain pan'd), hood holes (hole saws) or louvers on the hood itself I just have to laugh.

Biggest problem I have with mine is desert crawling with wind and the AC running. The wind gets high enough to stall the air through the fan (or slow it enough to cause issues). Getting hot air out of the engine bay and giving the reversed airflow somewhere else to go may be helpful.

The moisture on the motor shouldn't be an issue. A little dielectric grease on the connectors under the vents should be more than sufficient to overcome any wear/tear in the factory weatherproofing.

So, on my laundry list of stuff to do to my pile, I'm planning on doing some hood vents to dissipate some heat.

So far most vents are louvered and angle back and not all that good looking IMO. So found a pic online of a plasma cut design.

I like the design and idea of it.

However, I question the purpose of the angled back louver. With it angled back does it help force air down around and out the bottom while moving? Or create a venturi affect and help suck hot air out through the top while moving?

How would a set like the picture given do? Obviously anything is better then nothing, just curious as to the design of louvers and its effects on air/heat transfer.

Also, live in AZ. Dont care about rain and water because well what's rain? Lmao
c1326c1da952e94475e93702940187eb.jpg


Sent from my SM-G950U using Tapatalk

The louvers are for venturi effect. With the slight upward slant of the hood, the flat holes may actually introduce air pressure behind the radiator at speed (bad).

This ^^^ I been here for 53 yrs now and it gets about the hottest in the nation. I've towed my #3500 trailer 1000's of miles and one summer I towed a #12,000 contruction trailer to the dump, yes it was showing +210* but it held!

You towed a 12,000lb trailer with your Jeep? My condolences. :D

Towing/highway speeds aren't where my Jeep has beeped at me from overheating. It's always been on long hill climbs at low speed with the AC on.





That being said: I did notice a significant decrease in coolant temps using the factory recommended 10w30 over 10w40. If you're running heavier oil, try going to factory fill (assuming sufficient oil pressure) and see if it helps. Between that and a ZJ fan clutch, I haven't had any issues with temperatures and the auxiliary fan rarely turns on.
 
As said above, the raised/angled part of the louvers causes a venturi effect to help pull the heat out of the engine compartment. I have the RunCool large high flow louvers. I do not believe they really made much of a difference in water temp but they did make a large difference in under hood temps. You can see the heat rising from them any time you are stopped. I haven't had any water problems from them and my Jeep sits outside in the rain all the time. Would I do them again? Yeah. Did they make a huge difference? Not really.
 
What I really don't get is:

- Why so many people feel the need for hood vents, when if in proper working order they're not needed
- Why so many people seem hellbent on putting hood vents in that let any precipitation fall right down in/on the engine

Any time I see hood vents (that aren't drain pan'd), hood holes (hole saws) or louvers on the hood itself I just have to laugh.
Ha coming from someone who lives in colorado....

I live in az. Temps in the city reach 125ish. Couple that with stop and go traffic on the freeway on a massive black heatsink, the piss ant cooling system can not effectively handle it.

It can not be debated otherwise that 4.0s produce a massive amount of heat and with such a small engine bay, the transfer of heat is not as effective as it should be.

So the fact that you scoff at releasing heat more efficiently baffles me. As well as some notion of needing catch pans. By your comment it seems like engines should never see water, hope you never drive in the rain or wash the engine.

Sent from my SM-G950U using Tapatalk
 
Like others have said, sure it may not have helped water temp, but it certainly helps underhood temps. Which can only help the cooling any other system run cooler and provide a longer life, not to mention the heatsoak issue that plagues these jeeps...oh wait hood vents couldnt help that could they?

Now unless one has a absolutely perfect cooling system,or lives where it snows constantly then props to you.

I appreciate the input rockwood and blubullet. I figured it was for the venturi effect but did not think of the reverse airflow situation.

Honestly, my concern with these vents is not for driving. Its main and sole pupose in my eyes is for underhood temps once the damn thing is shut off. Im tired of a heatsoaked engine bay making my life miserable and its not even 100deg yet.
 
Ha coming from someone who lives in colorado....

I live in az. Temps in the city reach 125ish. Couple that with stop and go traffic on the freeway on a massive black heatsink, the piss ant cooling system can not effectively handle it.

It can not be debated otherwise that 4.0s produce a massive amount of heat and with such a small engine bay, the transfer of heat is not as effective as it should be.

So the fact that you scoff at releasing heat more efficiently baffles me. As well as some notion of needing catch pans. By your comment it seems like engines should never see water, hope you never drive in the rain or wash the engine.

Sent from my SM-G950U using Tapatalk


You have hot temps, that's cute. Try hard incline's going up and down passes. Makes "hot dry temps" seem laughable.

But please, tell all you know about how the engine was designed, tested, and how your fluid dynamics calculations and simulations have worked out.

Sorry, but there are few hood vents out there that are worth a sh*t.

And yeah, I've known plenty of AZ and SoCal folk (lived in SoCal for a brief stint myself) with lifted rigs that don't have issues.

So tell me, the engine should have no problem seeing water on top of it? Now, how does what work when they came from the factory with wheel well liners, a hood, and more to prevent water intrusion? Last time I checked, none of the electrical fittings were water proof. Want to guess how I unfortunately know?

The heatsoak with the precat system can largely be solved with the heat shield that should still be next to the intake manifold and surrounding the injectors (I own a 2001, and know several that do).

But no, by all means, throw holes in your hood...hell take the hood right off!
 
Its main and sole pupose in my eyes is for underhood temps once the damn thing is shut off. Im tired of a heatsoaked engine bay making my life miserable and its not even 100deg yet.

So, why not install an electric fan bypass?

How about a better than OEM pump?

How old is you radiator?

When's the last time you stripped the system down and did a full block flush?

If you're not overheating, then why the **** are you concerned?

It's an engine...it gets hot.
 
You have hot temps, that's cute. Try hard incline's going up and down passes. Makes "hot dry temps" seem laughable.

But please, tell all you know about how the engine was designed, tested, and how your fluid dynamics calculations and simulations have worked out.

Sorry, but there are few hood vents out there that are worth a sh*t.

And yeah, I've known plenty of AZ and SoCal folk (lived in SoCal for a brief stint myself) with lifted rigs that don't have issues.

So tell me, the engine should have no problem seeing water on top of it? Now, how does what work when they came from the factory with wheel well liners, a hood, and more to prevent water intrusion? Last time I checked, none of the electrical fittings were water proof. Want to guess how I unfortunately know?

The heatsoak with the precat system can largely be solved with the heat shield that should still be next to the intake manifold and surrounding the injectors (I own a 2001, and know several that do).

But no, by all means, throw holes in your hood...hell take the hood right off!

Those OEM calculations were with all the splashguards in place, stock tires, etc, etc, etc. In stop and go traffic and yes, some mild offroad. Keep in mind the Cherokee was designed as a ski chalet or "I don't want to drive an Impreza" type vehicle, not a rock crawler. OEM engineers make lots of decisions that involve more than just keeping it cool under all conditions: emissions, cost, packaging, ease of production/servicing (which they didn't do a very good job of :D), etc. Compromises were made.

When I first started wheeling my XJ, my 100% new, flushed and stock cooling system kept up fine with offroading, but my trans cooler and power steering fluid were not at all appreciative. In goes the auxiliary coolers for these items in the only place they would be effective: in front of the radiator. The stock cooling system was no longer happy, so I added a ZJ fan clutch. My temps still creep a little (220* on hot wheeling trips), but at least it's no longer boiling over.

That being said, popping the hood on a hot day requires gloves or a dangerous game of hot potato with the hood prop and the hood due to the crazy high underhood temps, and can't be good for the electronics. Every piece of wire loom, electrical tape, connector and any other piece of plastic is brittle as can be from the heat soak, so I don't think leaving the heat in there is a good thing either.

As for the harness not being weather tight: every connector I've seen under the hood has weather seals on both the connector side and the wire side. I'm sure the weather seals have seen better days (probably from the heatsoaking), so I help them out with dielectric grease and have replaced some of the loom and electrical tape that since cracked off (pretty much everything on top of the intake manifold from the exhaust heat). Keep in mind that all of the connectors on the bottom side of the engine bay (O2 sensors, transmission sensors/connectors, fuel tank related connectors) are all constantly exposed to direct water spray and are reliable as can be expected. These connectors use the same sealing system that the ones on the top of the engine use.

So, why not install an electric fan bypass?

How about a better than OEM pump?

How old is you radiator?

When's the last time you stripped the system down and did a full block flush?

If you're not overheating, then why the **** are you concerned?

It's an engine...it gets hot.

Again: my 100% refreshed cooling system worked fine in SoCal deserts/mountains, but the other hydraulic systems did not. Adding coolers for these items overtaxed the stock coolant system.

Yes, it's an engine. Yes, it gets hot. This is, by far, the hottest under hood engine I've been exposed to, and that includes turbo time attack cars making 5x the power from half the displacement with airflow optimized entirely for downforce, not cooling (more air to the coolers means less downforce). I've never needed gloves just to open the hood on those vehicles. :D

In any case, I think the heat is worse for these 20-ish year old vehicles than occasional water, especially when you consider that most of the places where it's often 100*+ with low humidity (worst case for cooling since hot/dry air has less heat propensity) don't see rain very often.
 
freerider15:

BTW, your XJ is EPIC, but wheeling an open Jeep in Colorado is a lot different than wheeling an enclosed Jeep with the AC cranked to 11 in the SW deserts when it's still well over 90* at 4AM. Overheating Jeep 4.0s are common sights down here. :D
 
Actually, the OEM's do a LOT more testing than most people would think. They don't just run calculations then sit on them. I've had more insight into this, as I have a few friends that have or do work for the big 3 (or others).

One thing they do, is ship the vehicles out to Colorado, in the summer, and run them up and down I-70, among other areas. The hot weather (can be 100* or more), plus the steep inclines going up and down I-70 pushes them a bit harder than they can get outside of a lab within reason.

With discussions from these guys (we're all engineers), more than one of them I came to know through XJ's.

When we've gotten to the subject of cooling, they'll mention that even with larger tires, the vehicles OEM cooling system is plenty adequate as designed. Obviously, things like steering and trans can always benefit from a cooler (and if towing, a trans cooler is always recommended).

That being said, all electrical under the hood, *should* be rated no less than 1.5 times the operating temperature, in many cases, the electrical should be fine upwards of 400* before issues may start. You'll have issues with the PCM long before wiring and such.

Most of the electrical connections are not fully waterproof, but are water resistant, hence why the TPS and IAC can get really irritated when water gets around them (had it happen myself).

There are some waterproof connections (e.g the Weatherpack fitting on the E-Fan), but most aren't, as they didn't need to be.

As to the wheeling in AZ. I've known guys from AZ to Southern FL wheeling full bodied XJ's with anything from 35's to one tons (who still have their AC), and have no cooling issues. I lived in SoCal for a year, driving it to and from CA, and wheeling JV, Calico, etc. without ever a blip on the radar. The only issue I did have, was oil temps wanting to get a little high. I still had AC, full bodied with doors, etc.

People tend to want to take the shot route, instead of putting in the work to make their stuff work (as had been brought up on this site so many times).

A working T-stat (I would verify operation before install), good water pump, a flushed system (and I mean a full flush without the pump of t-stat housing on), a flushed heater core, and good (not clogged, leaking, etc.) radiator tend to be plenty.

The next steps:
- Transmission cooler (this can help engine temps since the trans runs through the radiator)
- ZJ fan clutch - I've seen a few systems where the fan clutch needed replacing, and that helped a bit. People tend to assume because the fan is there, and somewhat rotates it's working as it should
- E- Fan bypass switch - this can really help with just sitting around. Stopping on the trail for lunch? Let the e-fan run. Hell, I think most people just assume their E-Fan runs properly :laugh:
- Exhaust wrap - While it "may" cause a shorter exhaust header life span, it will significantly help direct the heat down and out the exhaust, instead of lingering in the engine bay.
- For the late models, injector heat soak can be an issue. There was a TSB about this, and there should be heat reflector shielding around the injectors and intake. I've got a 2001, and will be replacing it on mine. I could go all out with DEI wrap, but I'll take the easy route for now.
 
The next steps:
- Transmission cooler (this can help engine temps since the trans runs through the radiator)
- ZJ fan clutch - I've seen a few systems where the fan clutch needed replacing, and that helped a bit. People tend to assume because the fan is there, and somewhat rotates it's working as it should
- E- Fan bypass switch - this can really help with just sitting around. Stopping on the trail for lunch? Let the e-fan run. Hell, I think most people just assume their E-Fan runs properly :laugh:
- Exhaust wrap - While it "may" cause a shorter exhaust header life span, it will significantly help direct the heat down and out the exhaust, instead of lingering in the engine bay.
- For the late models, injector heat soak can be an issue. There was a TSB about this, and there should be heat reflector shielding around the injectors and intake. I've got a 2001, and will be replacing it on mine. I could go all out with DEI wrap, but I'll take the easy route for now.


Is there a quality heat shielding "kit" for the late model XJ's -- I need to do this, got rid of everything when I swapped engines -- the whole thing was covered in oil and very sloppy -- If no kit could you point me in the right direction with who makes good stuff
 
Here's the OEM MOPAR heat shield:

https://www.amazon.com/dp/B01EIBMUS...a432-fe6d90b388b5&ie=UTF8&qid=1524240237&sr=1

Here's the full kit from DEI:

https://www.amazon.com/Design-Engineering-010378-Engine-Injecter/dp/B015NOKWQY

You can shop around on both of them and probably find them a little cheaper, or through Advance Auto and use coupon codes.

I haven't ordered mine yet, and I haven't decided if I just want to do the single shield, or the full kit.

EDIT: With a 30% off Advance Auto Coupon code, it comes to $56.03 shipped. So, I'll probably just do the full kit, as it comes with injector covers, manifold heat shield, and a fuel rail cover.
 
Last edited:
Back
Top