Mschneid

do you think the felt pad is holding in extra heat?

ronjenx

In my opinion, when off-roading slowly, and the fan is not running, yes. Enough that removing it will be noticed? Probably not.

GJeep

If you have access to a Jeep with a rear-facing hood vent near the firewall, you can easily test it – just tape a strip of light silk or nylon, and see how it moves when driving. That’s what we did after a friend of mine improvised a rear-facing vent. At speed, the silk strip showed nice air flow out of it.
When moving, in-coming air flow under the hood created more pressure under the hood next to the firewall, than the possible pressure in front the bottom of the windscreen.
Also, if given an exit, hot air would flow up & out.

Hot air concentrates under the hood, at the highest place, from which is has no exit – next to the firewall. The fender liners location is lower, so removing them doesn’t allow that hot air ‘pocket’ to vent out.

Under-hood (engine bay) cooling and engine cooling are two different things.
A more efficient fan reduces the temperature of the water.
The fan air flow doesn’t reach the upper rear corner in the engine bay. Even if it did, it would have forced already hot air, which gets even hotter by flowing over the engine block, into that ‘pocket’, from which the air has no escape.

The same principal you mention regarding the radiator fan, can by applied to cool the engine bay -- use a fan to force the hot air out, from where it is accumulated. Such solutions exist, and are used on vehicles and boats. Some are straight-forward install, some require improvisation.
By sucking air out from the rear of the engine bat, any of these would also increase air flow over the radiator.

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As for the sound insulation under the hood –
Heat insulation materials typically also insulate sound, but not vice versa. Sound insulation does not effectively insulate heat.

That layer under the hood is not – and shouldn’t be – an effective heat insulator.
The hood serves as a large area of steel that absorbs heat from the engine bay and dissipates it.
That’s why I wouldn’t use a fiberglass hood, unless it’s VERY well vented.

Mschneid

1) Hot air concentrates under the hood, at the highest place, from which is has no exit – next to the firewall.


2) Under-hood (engine bay) cooling and engine cooling are two different things.


3) As for the sound insulation under the hood –
Heat insulation materials typically also insulate sound, but not vice versa. Sound insulation does not effectively insulate heat.


Okay, so then:

1) There is a weather strip that runs along the firewall and hood, does it make sense to remove it or at least parts of it (so hood doesn't rattle) in order to let air into the cowl vent area?

2) Correct, thermostat will keep internal engine temp regulated. I'm thinking electronics such as the ECM where heat can damage electronics, ambient air for the intake, as well as helping cool the engine when under load.

3) So you think removing the felt won't help with under hood temps?

GJeep

It seems to me that the area of the open slot would be too small to make a meaningful difference.

The thermostat & fan can keep the coolant temp' only up to a certain ambient temp'.
The higher the ambient temp' is, the lower the radiator efficiency gets.
If the air blown through the radiator it too warm, it doesn't cool it enough.
A more efficient fan, raises the ambient temp' at which it can still cool the water.

Leading ambient temp' air into the engine, while keeping water or dust out, is simple... a snorkel. The low-mount Rugged Ridge snorkel, for instance.

Not really.

jstikel3

Here you go.



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