Under Bonnet/Hood Heat Insulation

[gcarm]

Hi,

I need to insulate the underside of my bonnet/hood from heat coming off the engine. I have some leftover sound deadener that I used under the carpet in the cabin.

Will it work as heat insulation? (its 10mm thick foam rubber but it doesn't have the aluminium foil top layer).

Or should I invest in some proper heat insulation ? If so, any recommendations?

Greg

[stephen low]

Greg

Why would you want to do that?

You want heat to escape, it robs the engine of power, and just impacts other aspects within the engine bay such as elevated brake fluid temps and of course the engine cooling system efficiency.

Would also most like cause greater heat transmission into the cabin too.

I don't recall seeing any cobra bonnets with internal heat shielding

Just my 2cents worth

Cheers Steve

[gcarm]

Hi Steve,

The problem I have is that the bonnet gets rather warm. I'm worried that after some time the heat from the engine will damage the paint.

My Cobra has an LS1 engine which runs at around 105 deg C (which apparently is normal for this engine). By comparasion, a Windsor runs at around 90 deg C. So there is a lot of heat given off by an LS1.

I take your point regarding insulating the bonnet. Installing the bonnet insulation will reduce the areas where heat can escape from the engine bay. However, I'm caught between a rock and a hard place.

Most cars these days have some form of heat insulation under the bonnet. I'm guessing it is for this reason - the heat radiating from the engine heats up the bonnet and can lead to damaged paintwork.

I don't have a lot of space between the top of the engine and the underside of the bonnet. This is probably why the heat radiated from the engine is causing the problem. Maybe if I could direct more airflow over the top of the engine it would mitigate the heating issue to some extent. (at least whilst the car is moving).

Greg

[eschaider]

Greg,

The chances are better than good that the GM calibration engineers chose 105˚C for emissions purposes in the States. Your car is what I call an attitude adjustment vehicle and, as such, does not need to meet Federal emissions targets.

I do recognize that you guys have some sort of regulatory official that you must make happy before you can drive these things on the street among ordinary people. That said, you will probably find that an 82˚C T-Stat, what State-side we call a 180˚F T-Stat, will fix your excessive heat problem with the least amount of effort (and expense) on your part.

[Tommy]

I faced a similar challenge with the nose on my Cheetah. I guessed that the biggest challenge of using an adhesive mounted material would be the combination of weight and high temps overcoming the adhesive. So I selected a relatively lightweight fabric consisting of fiberglass cloth with adhesive on one side and aluminum foil on the other. I've run it for two years in the hot southern USA and see no signs of drooping. And the reflective aluminum seems to be protecting the painted exterior surface.

[Morris]

Why not open the hood about 1”....and let the air out....

[gcarm]

I fitted a 180 deg F thermostat (Mr Gasket MRG-6368) and a high flow water pump (+30% flow). They have helped - maybe reduced the temperature by 5 deg F.

Next step is to put a shroud around the radiator. I had to tilt the radiator to get it to fit (seems to be quite common with Cobras). So I'm concerned the airflow is not properly penetrating the rad but going over the top.

With regard to insulation, I came across a product called 'Lava Shield', made from crushed volcanic rock. Testing shows it can reduce bonnet/hood temperature by around 20% (one test showed a reduction from 121 deg F to 101 deg F). Anyone had experience with this product?

Cheers,
Greg

[Bobcat]

As Morris said , just open the rear of the hood . Did that on my ERA and even in traffic here with temps in the mid to upper 90`s now in SC , I see just under 180* cruising and 190 to 195* in traffic .
I just opened the hood and turned the hood locks like they were closed , slide a piece of rubber tubing on the latch tabs so as to not damage the hood underside paint and "closed" the hood . Since the front of the windshield is a high pressure area , hood doesn`t come up and stays down so far up to 100+.

My thermostat is a 180* unit with bleed holes top and bottom . Bypass between intake and water pump is blocked as per Robert Ponds and stock ERA radiator and shrouding with a rear mounted Spal fan .

Probably doesn`t look as nice as when the hood is completely closed , but my coolant temps are good as is oil at 200 to 210* F.

[gcarm]

I'm not real keen on driving around with my hood open. Thinking that hood vents may be the way to go......

[Tommy]

I later fabricated some hood vents too. Obviously not shaped for a Cobra, but it may provide some ideas. And there are many prefabricated vents of various sizes and shapes on the market.

[MasterAnubis]

I wouldn't use butytl on the inside of the hood. Heaven forbid that turns out to be asphalt.

The underhood insulation is not just for heat but for sound. With the heat under the hood (unless the manufacturer says) I wouldn't use just adhesive to secure that anyway. Manufacturers use mechanical fasteners. They may use adhesive as part of it but they use flanges and the pins with large washers for the most part.

I have seen Ford go with and without underhood insulation depending on the trim levels of a car.

[eschaider]

Originally Posted by gcarm

I fitted a 180 deg F thermostat (Mr Gasket MRG-6368) and a high flow water pump (+30% flow). They have helped - maybe reduced the temperature by 5 deg F.

Next step is to put a shroud around the radiator. I had to tilt the radiator to get it to fit (seems to be quite common with Cobras). So I'm concerned the airflow is not properly penetrating the rad but going over the top.

With regard to insulation, I came across a product called 'Lava Shield', made from crushed volcanic rock. Testing shows it can reduce bonnet/hood temperature by around 20% (one test showed a reduction from 121 deg F to 101 deg F). Anyone had experience with this product?

Cheers,
Greg

Heat energy is an interesting phenomenon.

If I have a glass and pour 200˚F water into the glass, the glass and water temp will measure 200˚F, perhaps a whisker less.

If I stop, empty the glass, and then pour in 180˚F water, the glass and water temp will read 180˚F again, perhaps a whisker less. If I continue to pour 180˚F water into the glass, the temperature will not rise. The phenomenon is not additive.

When you replace your higher temperature T-stat with a 180˚F T-stat your coolant temp will fall to 180˚F. If it does not, you have another problem somewhere else in your cooling system, and that is very likely closely associated with your higher than desired operating temperatures.

If your engine runs at 105˚C as you indicate, which is 221˚F for us Imperial units guys, and you put a 40˚F cooler (earlier opening) T-Stat in but the coolant temp only drops 5˚F Your problems are not t-Stat related they are something much more serious.

[Tommy]

Originally Posted by gcarm

I had to tilt the radiator to get it to fit (seems to be quite common with Cobras). So I'm concerned the airflow is not properly penetrating the rad but going over the top.

Moving air will tend to take the path of least resistance. So if there is path for air that is less restrictive than going through the radiator, some of the air will take that path. There are two basic solutions to this problem. One is to block off ALL the possible paths that air coming in the front can take except the one to the radiator. This should provide plenty of air flow when the car is moving forward. The other solution is, as mentioned before, an electric puller fan with a very good fitting shroud around it. That should help whether or not the car is moving.

[Dominik]

I am not a painter, but I wouldn't worry about heat damage of your paint. Today's insulation is more to keep the noise out. And as above, to keep the operating temperature in a very narrow temp range. I would worry about falling down, whatever you attach. Causing fire.

Get that air out, like Morris said. Find his thread (pun intended) where he used wool threads to evaluate how the wind blows.

[gcarm]

Put a shroud around the radiator and that seems to be stopping the bonnet from heating up.

Still the engine is getting a little too hot for my liking. Not sure how I can cool it down any more?

Greg

[Tommy]

I assume you are speaking of the engine coolant temperature being "too hot for my liking." If so, first know that with the correct coolant mix and system pressure, you should not be too concerned unless the coolant temp exceeds 110C. If mine hit 115C I'd shut it down.

Know that three basic things affect engine coolant temps: 1) the amount of heat transfer provided by air flowing through the radiator; 2) the effective circulation of coolant to move heat from the engine through the radiator; and 3) the amount of heat being generated by the engine. If we assume your coolant system is working properly (e.g., proper water pump and radiator, no collapsed water hoses, etc.) and your recent addition of a shroud is assuring good air flow to the radiator, then the next logical place to look is the engine. Much of the heat generated within an engine goes to propelling the car or is expelled through the exhaust. But an improperly tuned engine can generate heat that merely goes to heating up engine components. The two most common causes are a lean running fuel system and/or incorrect timing. So, I suggest you make sure the engine is properly tuned for all running conditions as your next step.

Note: The standard water pump rotation for a LS1 engine is CCW.

[gcarm]

I had some heat shields on each side of the engine which I have now removed. This seems to have lessened the amount of heat being deflected up under the bonnet. So I think I don't need to do anything further as the bonnet temperature seems more acceptable now.
Regarding the engine temperature, I found the temperature gauge is reading about 10 deg hotter than the temperature reading from the PCM. Not sure at this stage why? Either the gauge is inaccurate or it is due to the position of the sender's. The temp gauge sender is on the rear of the right head whereas the PCM sender is at the front of the left head. Next step is to get another gauge to see where the inaccuracy is coming from.

[DonB]

Call Pat at Koolmat she has some thin foil faced insulation that's self adhesive and is good for up to 1200 degrees F. I used it on my steering column that was close enough to headers the nylon bearing caught fire.

[Tommy]

Temperature variation at different places on the engine can come from having air in the system. If I'm not careful about getting all the air out of my engine's coolant system, it will spike temps at some spots.