Gen 2.5 hood lift

[billygoats]

In reading Kirk's post about his hood scoop for venting engine heat, I don't think I posted about a mod I did to my 2.5 awhile back.

I've seen this mod on other cars, and it makes sense. I got several washers from the hardware store along with 4 longer bolts and spaced the hood away from the hinge. This results in a gap at the rear of the hood and engine heat is surely felt escaping even at idle. With increased airflow from the highway, is imagine even more heat is being purged.

 

[Jay Ayala]

That is super clever.

 

[jeep-N-montero]

Raising the hood(hood risers) can actually stall airflow through the radiator at highway speeds, this is because you actually have air flowing both directions against the windshield, so the air flowing downward pushes against the air trying to come through the engine bay. While it may be a good "trail mod" I wouldn't do it personally, Google it(cowl airflow) and you will find info to support this, I also speak from experience from trying this on my Jeep years ago. Kirk's scoop is far enough forward where it's not as much of an issue.

 

[jlocster]

Not to disparage your mod Brian, but I have to agree with jeep on this one that such a gap is good for for venting heat at trail speeds and idle, but can have a negative cooling effect at highway speeds. Like he said, at speed, a gap at the cowl can actually work to pressurize the engine compartment enough that airflow is slowed through the radiator. If you look at most modern cars, they have rubber seals along the cowl edge of the hood, precisely to avoid this issue. The "cowl induction" hoods of the muscle car era were, like the name implies, for air induction into the carburetor via ducting and not for heat extraction from the engine compartment.

The high pressure area at the base of the windshield extends forward 3-6 inches and tapers off after that. So, ideally any venting for heat extraction should be somewhere towards the center of the hood. This allows heat to escape at idle and trail speeds, while not pressurizing the engine compartment at highway speeds. At speed, air is still able to to flow through the radiator, and low pressure airflow over the top of the hood actually works to pull air out of the engine compartment.

All this said, sometimes theory is not the same as practice, and if you've found this solution to work for your use, well then that's all that counts. In high school I had a 69 Firebird with very built engine. Idle and low speed cooling was always an issue for that car. I had the hood lifted at the cowl with washers and it worked because most of my driving was surface streets and cruising. At speed the increased engine rpm circulated the coolant enough and the engine was powerful enough vs the weight of the car that it wasn't under much load, so I never had a problem with overheating on the highway. Under those conditions the hood lift worked for me.

I personally won't do this on the Montero because the engine works a lot harder to maintain highway speeds, especially when fully loaded with gear...going uphill...in the heat of the Southwest. Because of the combination of vehicle weight and small engine, I want to maintain maximum cooling efficiency through the radiator on the highway.

My 2 cents.

 

[billygoats]

Not to disparage your mod Brian, but I have to agree with jeep on this one that such a gap is good for for venting heat at trail speeds and idle, but can have a negative cooling effect at highway speeds. Like he said, at speed, a gap at the cowl can actually work to pressurize the engine compartment enough that airflow is slowed through the radiator. If you look at most modern cars, they have rubber seals along the cowl edge of the hood, precisely to avoid this issue. The "cowl induction" hoods of the muscle car era were, like the name implies, for air induction into the carburetor via ducting and not for heat extraction from the engine compartment.

The high pressure area at the base of the windshield extends forward 3-6 inches and tapers off after that. So, ideally any venting for heat extraction should be somewhere towards the center of the hood. This allows heat to escape at idle and trail speeds, while not pressurizing the engine compartment at speed. At speed, air is still able to to flow through the radiator, and low pressure airflow over the top of the hood actually works to pull air out of the engine compartment.

All this said, sometimes theory is not the same as practice, and if you've found this solution to work for your use, well then that's all that counts. In high school I had a 69 Firebird with very built engine. Cooling was always an issue for that car. I had the hood lifted at the cowl with washers and it worked because most of my driving was lower speed city driving. At speed the increased engine rpm circulated the coolant enough and the engine was powerful enough vs the weight of the car that it wasn't under much load, so I never had a problem with overheating on the highway. Under those conditions the hood lift worked for me.

I wouldn't do this on the Montero because the engine works a lot harder to maintain highway speeds, especially when fully loaded with gear...uphill...in the heat of the Southwest. Because of the combination of vehicle weight and small engine, I want to maintain maximum cooling efficiency through the radiator on the highway.

My 2 cents.

Wow. Great feedback. I hadn't thought of those new problems I've created. Reality wise, I do know it has helped on the trail, as my ultra guage reads intake temps. As for highway use, I haven't noticed a difference in temps. I guess I'll remove the washers and do a real world highway test to see if it is hindering the intake and cooling temps. I'll report back!

 

[jlocster]

I'd be very interested to see if there were any measurable differences in the Ultragauge readings without the hood lift vs with hood lift...an interesting science experiment. You might make me eat my words.

 

[nnamssorxela]

While this isn't as "scientific" as most people prefer, you can tape some yarn in the questionable areas. This can help show which direction the air is flowing. I know this technique is used to determine the best location for a scoop as it shows areas of positive air pressure. I don't see why it wouldn't work to determine the direction of flow for your lifted hood. ...it's cheap too!

 

[billygoats]

update

Well, I made a trip to Anza Borrego Desert State Park (about 3 hours one-way freeway). The freeway driving made no difference in temps with or without the hood vented. As far as off-road, I don't think I had a before engine water temp, but as slow as trail driving goes, I could definitely feel heat coming out of the rear of the hood. This mod appears to have no ill effects on temp. The only downside I could see is water entry if directly sprayed into the hood gap. Besides that, I think the mod is safe.