Under hood heat

[Phil P.]

   Looking for ways to lower under hood temp. It would seem that eliminating the under hood blanket would help reduce under hood temp by allowing more room for air to circulate. Since I only drive in warm weather, I also plan on closing up the exhaust crossover in the intake manifold. What’s the best way?Currently after about an hour of driving on a hot day, heat build up is great enough to boil gas in the secondary float bowl that then percolates into the air horn. 

[sailingadventure]

While blocking off the exhaust crossover seem like a good solution, it will make your exhaust sound very harsh. I tried it on my car and changed it back because of the sound. I made a heat blanket when I restored my car. I used ironing board material with 1/8" foam sewn between. That material isn`t fireproof, but it will withstand a great deal of heat.

[EnduroDriver]

I wouldn't recommend removing the insulation, part of its job is reducing the impact of heat on the hood and paint. Fiberglass is a terrible choice for a hood for that reason but that's what we have to work with. 

The two things I'd recommend are switch to EFI, the idea being fuel the car more efficiently to simply generate less heat in the first place. And install an electric fan on the radiator. The factory fan is cute and simple but pretty much useless for moving air. Especially at low speed. Install something that can move air and carry that heat away. 

[Phil P.]

Thanks for your response , both of you. Your heat blanket is much more attractive than conventional ones. BTW I already use an electric fan. 

[Gunslinger]

Adding an air deflector under the front end is a big help...it directs air up into the radiator that would otherwise be wasted plus the deflector helps move air around the bottom of the engine bay and bottom of the vehicle where it otherwise cause turbulence and aerodynamic drag.

Of course while sitting still the deflector is of no help but at speed it drops the engine temps at least ten degrees in my experience.  Before Saturn was discontinued by GM they had a deflector that was a very easy install and worked and looked great.  Unfortunately I don't have the part number anymore.  It attached to the underside of the radiator saddle right where it would do the most good.  

[Dunkin]

How thick is your intake gasket to carburetor? 

[wildfelr]

RQB3263/81/305 CHECK OUT MY RECENT POSTS AND PIC  UNDER "HOOD PINS"  DETAILS MY EASY SOLUTION/MODIFICATION TO ACCOMPLISH WHAT YOU ARE TRYING TO DO .....WORKS FOR ME.... BILL IN FLORIDA

[Phil P.]

To Dunkin, gasket is standard 3 ply stapled together. Probably 3/16” or so. Can’t go any thicker as R2 bonnet is already touching the hood. 

[Geoff]

Aside from the notion to direct more air through the radiator (with which I agree), and aside from punching air evacuation holes/louvers in the car (hood and/or fenders), I would include adding Water Wetter to your cooling system.

https://www.redlineoil.com/waterwetter

[Ron Dame]

When my A II starts getting warm, I pop the hood, driving or not, an it allows enough extra air flow to cool it down a bit. It's not a pretty solution, but easy and quick when needed:

[silverstude]

When my A II starts getting warm, I pop the hood, driving.......   That's not a good idea

Edited September 21, 2023 by silverstude

[Footer]

Here’s an article in a recent Avanti Magazine. Mike

https://www.nostalgicmotorcars.net/uploads/1/2/4/8/124888690/nostalgic_cooloff_v2_aoai203__1_.pdf

[billsr2]

Ceramic coat the exhaust manifolds. They do the inside as well as the outside so it will make a huge diff. in heat as well as make them look great!

It will, however make the rest of the exhaust warmer so some exhaust wrap could be in order. You have learned that these cars are stupid hot?

[Leo B]

I agree with Silverstude.
When driving at high speed, there is an external over pressure (downforce) behind the hood that is greater than the pressure in the engine compartment. If a grille or gap is made there, the air will push into the engine room and create more pressure there, causing the air coming through the radiator to meet resistance. This outside air cools the back of the engine and the firewall more and travels downwards. With this method, it is also possible to get a temperature measurement error, because the sensor is in the back part, where this method cools more. The functionality of this theory can be tested by measuring the water temperature on the outlet side after the method and comparing it to the meter reading. I haven't tested it yet, but if this method were good, then air intake (vents) in the rear hood would be common in cars as well. All air should be brought in through the radiator only. The escaping air must be removed from a place where there is a negative pressure. Avanti's problem is that overpressure is created in the engine room, which prevents good flow through the radiator. This can be seen, for example, in the fact that even a small hole inside the firewall blows hot air in. The best way would be to make a grille/vents on the front of the hood where is external negative pressure (lift), but that doesn't fit a historic vehicle. This idea is used in many newer sports cars. Insulating the exhaust manifold is a very good idea and an attempt to get as much air as possible flowing through the radiator and as much out to bottom and to have there a good external negative pressure.
Mr Dan Booth wrote in article (Footer wrote a link): This worked fantastic, as the toilet paper forced the center of the hood up, and crated a very nice gap, so the hot air could leave the engine compartment as we were driving.
This is interesting because all theories state that there is external over pressure at the front bottom of the window, not negative pressure that sucked air from engine compartment. Air flows always from overpressure to negative pressure. I think he lowered the temperature as he turned on the heat and used the heater inside as an additional radiator.

I'm not a professor and I'm happy to read other ideas and theories.

Edited October 17, 2023 by Leo B
Edit not perfect english text and still not perfect :-)

[Ron Dame]

LeoB and Silverstude, all I can say is that it works. and it's not much different than Dan Booth's solution, though I had not considered the bouncing and potential to break the hood, hence his use of the TP and shop rag.

As far as safety, as stated, there is a positive pressure above the hood that keeps it from rising more than a couple of inches, yet it apparently offers enough air to flow out of the engine compartment that it works. For me anyway. I accidentally discovered this when I for got to latch the hood and saw the hood raise a bit on teh highway, but not much. And the engine never got overly warm that hot day.

[Leo B]

59 minutes ago, Ron Dame said:

LeoB and Silverstude, all I can say is that it works. and it's not much different than Dan Booth's solution, though I had not considered the bouncing and potential to break the hood, hence his use of the TP and shop rag.

As far as safety, as stated, there is a positive pressure above the hood that keeps it from rising more than a couple of inches, yet it apparently offers enough air to flow out of the engine compartment that it works. For me anyway. I accidentally discovered this when I for got to latch the hood and saw the hood raise a bit on teh highway, but not much. And the engine never got overly warm that hot day.

It is likely that the air is escaping from the side edges of the hood.

Edited October 19, 2023 by Leo B

[Geoff]

My father would pop the hood on 1025 when daily driving in SF Bay Area congestion in the 1970s. Once the bottleneck cleared he'd stop on the shoulder, slam the hood and go. In his case it definitely worked but the speed we're talking was stop and go. Between the popped hood and the intermittent shift to N with a prod of the accelerator pedal (to spin the engine fan and water pump more) it cooled off the engine bay very well.

My solution is going to be extreme. I love road course racing and both racing Avantis built under Blake. My current project is going to pay visual homage to the Mid-Ohio GT but with some extras. In addition to flared fenders I'll be styling in fender air extractors aft of the front wheel wells. I have a second hood which I will add in a "waterfall" air extracting element and some louvers over the exhaust headers/manifolds.

Edited October 24, 2023 by Geoff
Amended end of first ¶