Increased airflow through grill

[Blazer Eagle]

I have a 1995 K2500 8600 GVWR. It has the 454 and every optional cooler you could get from the factory plus an upgraded transmission cooler. In every respect, it is set up like a diesel truck - minus the engine.......and the nostrils in the bumper

Now, the reason I bring up the nostrils is because my truck likes to get warm if I'm hauling with the A/C on in the summer (think 90+ temps). I have some some cooling mods in mind such as an aluminum radiator, HD fan clutch, larger oil cooler etc. However, I am concerned about how much air is getting to the cooling stack. If you look at any modern heavy duty truck, you'll notice they all have giant grill openings as well as vents in the bumper on many of them.

I imported some pictures of some different GMT400 grills to get a rough idea of the open grill area. While my numbers may not be an exact reflection of the true grill area, they should provide a good basis for comparison between the grills.

Now I have a Chevy, so I started there.
300 square inches

I then measured the GMC grill. I was expecting a fairly large difference since the gmc grill doesn't have the bar across the middle, however, the lights and the bottom of the grill are moved up quite a bit higher.
342 square inches
That is a 14% in frontal area over the Chevy

I then looked at the diesel bumper. and what the nostrils would add.
65 square inches
If I were to run a gmc grill with the diesel bumper, I would have a total of 407 square inches (342+65). A 35.7% increase in frontal area over the Chevy grill.

Then I found that LMC offers a grill that is a combination of the GMC and Chevy grill. It retains the Chevy head light spacing, but without the cross bar. I don't think it is the most attractive grill, but get this - this grill alone has
402 square inches
the combination of the LMC grill and the diesel bumper would net 467 square inches of frontal area, or a 55.7% increase in frontal area!!!

So I ask, is there any reason not to do this? Is there a reason more people aren't doing this?

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[df2x4]

Is there a reason more people aren't doing this?

My guess would be because they don't need to. How warm is "warm?" I find it odd that you're having issues with temperature with all the optional coolers, you're not hauling beyond the limits of what the truck was designed for are you?

 

[Blazer Eagle]

Warm is totally within acceptable limits realistically. I've never pegged the gauge, but then again I back off and kill the A/C whenever I get over 230 or so. My biggest concern is that as soon the coolant temperature starts rising, the transmission temp follows it along. I obviously have some cooling repairs to make, but I feel like a new grill and bumper would give better gains from those modifications.

Honestly, sometimes I feel like the trucks own weight is beyond the limits of what it was designed for. I do tow over my GVWR as the truck weighs 7000 lbs empty and I have a 9' lance camper that is 2000lbs dry. Sometimes I also have an enclosed trailer with me that's about 7k loaded. I have a 4" lift and 35" tires that don't help, though the 4.56 gears take some of the edge off.

I think the real issue is a 7.4l engine that goes 6 miles on a gallon of gas while making a hair over 200 hp. If all that gas isn't going to make power, it's turning into heat....
Honestly, I'm just expecting a more modern experience from a 21 year old truck. I don't want to have to worry about the temperature...

 

[df2x4]

I do tow over my GVWR

Probably the cause of your issues right there. Still curious to know what temp you consider "warm" exactly, though. What's the highest you've seen the dash gauge? Also I'm assuming you have a trans temp gauge installed since you mentioned trans temp, what's the highest you've seen there?

 

[Blazer Eagle]

I do tow over my GVWR, but the manual recommends a maximum towing capacity of 10K lbs. That puts the recommended GCWR at 18.6k lbs, which I do tow under. I have a pretty high profile though, which doesn't help a bit.

The highest I've seen are about 245 on the coolant and 220 on the transmission. So, they're not critical temps, but I don't like them being that high. I really don't like seeing the transmission above 200 degrees, it's already showing its age....

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[df2x4]

My fault, I missed the fact that you said 230 degrees coolant temp in your second post.

Yeah I wouldn't be too happy about those temps either. Looking at the picture though I can definitely see why, you're pretty much driving a barn on wheels towing another barn! Looks like you're absolutely on the upper limit of what that truck is capable of. Hard to tell 100% from that picture but it looks like your rear end is squatted down quite a bit from the load.

 

[Blazer Eagle]

It actually handles real well with all that weight....just don't try to stop and hope you don't hit any hills.....but I say that unloaded too haha. Hydroboost coming soon!

It's a bad picture, the truck is actually fairly level with the camper on it. Unloaded, the truck sits a bit high in the rear. The rear axle has a set of rubber overload springs (they look like solid air bags) that do a great job of holding the weight. Once I'm done overhauling the cooling and braking systems on the truck I'm going to build a flatbed for the camper to take some of the weight off the truck. I'm pretty sure my front end takes a good beating from the camper.

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[brutpwr]

Well I suppose you are probably on the right track looking for better flow by opening up the front but remember most of your air must go past the shroud which defininely blocks flow so you need your fan to work efficiently also. I would defininity look at getting a heavy duty clutch fan as they can help quite a bit with fan pull especially when your hot soaked and pulling up to a red light after having pulled up a long grade. Now it looks like you may have a body lift based on the gap between your nerf bars and your body so usually there will be a gap in the upper and lower parts of your of your fan shroud so you should try and close up that gap and if possible close up the gap at the top of your shroud to so its closer to the top of your fan. There is usually a gap at the bottom of the radiator that can be sealed up as needed. Then to get a place for all the air to go you can remove the rubber splash shields between the fenders and the frame on each side of the truck.

 

[Blazer Eagle]

You bring up a good point. I didn't consider that the air has to have somewhere to go. Possibly the chevy grill already flows as much air as the shroud can accept. I've heard people say that the diesel bumpers are to increase the pressure in front of the cooling stack....

The truck actually doesn't have a body lift, I think its just an awkward angle for the picture. You mention removing the splash shields to create somewhere for the air to go. Do you think a cowl hood that is open in the back would let air flow out of it? Myself and the paint on my hood wouldn't mind if it lowered the temps under the hood as well

 

[Blazer Eagle]

I did a little research. Apparently the area in front of the windshield is an area of high pressure. At highway speeds, air will actually enter through the cowl, instead of exit.
I did find interesting information about about the front air dam under the front bumper. It actually serves to create a low pressure zone under the engine to pull air out from the engine compartment. My truck doesn't have this, but does have a large skid plate that should provide a huge low pressure zone under the engine.

I think I may go with the new grill. My grill is cracked and needs to be replaced anyways.