The ones on the gassers may be fake but the diesel trucks have red screen in them and are for ventilation of the engine compartment.

 

I wonder too with the fan going to be direct drive all the time, will this cut back on the availiable horsepower and fuel mileage of the truck ?

 

I have hot wired a few air fans on big trucks to run all the time, you could feel the power loss (3406b 425 cat) and it sucked fuel.

 

These engines in pure original un-molested stock form will take twelve big Charolais cows up Russell Creek Hill in 4th gear and gain speed all the way to the top; they ain't gonna notice nor care that a little bitty old fan is going along for the ride.


For several years, I have been regularly swapping back and forth on several of these engines/trucks, PINNED direct-drive fan-clutches in the summer and plain old sluggish inoperative un-molested fan-clutches in winter.

I have not been able to detect any difference in fuel-mileage, nor can I detect any difference in power; if anything, the engine seems to "feel better" with the direct-drive fan.


For at least fifty years, there was no such animal as a fan-clutch.

I have two goose-neck hauling trucks in the yard right now, both hooked to trailers as I type this, and neither of them ever had a fan-clutch and either of them will walk off from most newer trucks with the same weight load.


Honestly, from my own experiences, long-hauling HEAVY goose-necks with HEAVY loads, or running around with the naked truck, I can see no benefit whatsoever mileage-wise nor power-wise in a fan-clutch --- pure useless pot-metal junk in my opinion.


If my opinion is not someone else's opinion, I am fine with that; I know what has and has-not worked for me.

 

Jim Lane and Douglas are correct, a cowl hood won't do much to let air out at speed. Here's a thread I remember with a good amount of discussion about it:

http://corner-carvers.com/forums/sho...ight=Hood+vent

Just keep in mind that most of the examples of cowl pressure will be much less extreme than ours, due to them being cars with much better aerodynamics.

Disclaimer: There's quite a bit of reading to that thread and a lot of posts of random mustang hoods, but the good info is in there if you're interested in knowing it.

 

hey-Hey!!!,
Just to put a number on it, the airflow through the radiator at 60 mph is on the order of 5 meter/second. If you can mount an air dam( and lower is better, all the way to direct contact ), you go a long way to reducing pressure under the vehicle. With the dam the only two places air can come from is around the sides, and through the radiator...and the latter is what we're interested in. Skirts also help, and longer is better( contrary the usual aesthetic consideration ).

There is a low pressure area on the hood, and that is up towards the front. Examine a GT40's 'hood' or what ever it is they call that thing on mid-engined cars. Louvers would be cool...
cheers,
Douglas