Baffles in or baffles out?

[US6x4]

I was staring at a picture I took years ago of @quarkz M813 at a car show since his truck is such a big brute and I noticed the recirc baffles on both sides of the radiator were flexed outward toward the headlights. This struck me as odd since I've never seen baffles on the outside like that before.



The baffles indeed have a cut in them that allows the upper half to flex around the angled grill guard flat bar which left me thinking that the intended installation is baffles out. Now I hear Ray Finkle from Ace Ventura yelling "baffles out!" in the back of my head.

My truck came with baffles in and most pics of M809s show baffles in, but the TMs show baffles out:





Is anyone else running baffles out?

Is Finkle really Einhorn?

 

[quarkz]

Thanks for the beautiful picture. You made my overcast, smoke filled, day.
Thinking I may have screwed up the baffles during my repair I went back and looked at the the rig's original pictures.
When I recovered the truck from Ft. Hill I had a bit of a '5 Ton Woe' in Burley, Idaho and had to replace said radiator.
The before pictures show baffles out also.
Do you think it might have something to do with Desert Storm vehicles & sand?
Baffles our might not funnel as much dust into the engine compartment.

 

[US6x4]

Dang, that's a knarly gash! What a mess.

I can fit my fingers between the baffles and headlight sheet metal so baffles out would keep sand out better than baffles in. I'm gonna find my David Doyle AM General book and Tankgrad 809 book to see what the vintage pictures show.

Here's another shot of your 5-ton!

 

[US6x4]

The Tankograd M809 book features US Army and USMC 5-tons stationed in Europe in the '94-'95 time frame and about half of the trucks show baffles out with the other half showing baffles in. AM General corporate photos show baffles out.

I think I'm going to bend my baffles out and paint them to match. I won't see a change in coolant temp but it will keep the rubber away from the fan blades.

 

[US6x4]

I pulled the baffles out in front of the headlight buckets and then that started a snowball effect of repainting everything to match...

 

[msgjd]

An M813 i sold, plus my M818 and an M818 i parted out have/had baffles-in .. My XM818 and M817 are baffles-out .. Motorpool pics i took in '78 or '79 show a mix of both situations. .. I recall a PS-Magazine discussion about changing out the fan bolts on the M809-series trucks but i wonder if there was ever any PS-Mag discussion about the baffles

 

[US6x4]

It would be interesting to know if the magazine covered it. I like the way it looks with the baffles in, but now that mine are out I won't have to worry about the fan blades hitting it as the fan belts stretch.

 

[WillWagner]

You already know what they are for.

From a cooling system engineering point, the baffles flipped around facing forward, or out, or placed anywhere that makes no contact with the headlight panel, will cause a low pressure point between the rubber flap and the headlight panel resulting in the air that the fan moves being directed to the gap/low pressure and being sucked around to the front of the cooling package.

The air that the fan moves is supposed to exit the fan via the tips of the fan and be directed out by the shroud toward the rear of the vehicle, check it out, if you bump the RPM up and go hold a piece of paper, a string, a rag, whatever, in front of the radiator. you will notice that there is almost no suction in the center directly in front of the driven hub, but as the piece of whatever gets moved farther away from the center, in any direction, the whatever will want to suck up against the core . The air passing around, under the vehicle creates a vacuum or low pressure area actually sucking the air out of the engine compartment and venting it away from the power plant. You can do the same test with the rag, string around where the recirculating dams are to see if the air from the fan is coming out of those gaps. Technically, there should be dams on the sides, top and something at the bottom. Bottom is rarely rubber, usually an extension on the shroud, a cross member, a component like a trans cooler or other component that reduces the open area for air to get easily out

Early in my career I got to see how things worked by using a smoke machine while troubleshooting. It is amazing to see a vehicle making full power, fan pulling, a fan in front of the vehicle simulating road speed air and watch the smoke move against the air flow and then move back into the flow and just repeat. Using that tool actually found issues in new model trucks that had overheat issues from day one.

These things don't go down the highway working like a freight hauler works so there probably won't be any issue, but, if you are one of the few that do take your stuff out and move heavy loads long distances, or if the cooling system is restricted internally, the recirculating flaps placed in a way that will allow engine compartment generated air flow out and around the cooling package could give you a slow steady over heat condition.

 

[msgjd]

These things don't go down the highway working like a freight hauler works so there probably won't be any issue, but, if you are one of the few that do take your stuff out and move heavy loads long distances, or if the cooling system is restricted internally, the recirculating flaps placed in a way that will allow engine compartment generated air flow out and around the cooling package could give you a slow steady over heat condition.

amazing ! .. Years ago when i was regularly hauling loaded flatbeds and box trailers 120+ miles continuous with my M818 and the XM818 , the two trucks ran at different temps, especially on the climbs although the hotter one never got beyond 205 degrees .. I always took this to mean one system needed a flush.. I was usually grossing no more than 55k .. One came from the DRMO baffles in, the other came from DRMO baffles out, purchased same day, same location .. Never even thought the baffles may have be the culprit .. This is interesting to learn