Home » Public Forums » GMCnet » [GMCnet] Cooling Shroud Mod
| [GMCnet] Cooling Shroud Mod [message #237411] |
Sat, 25 January 2014 08:32  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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This is more than a little out of season, with the temperature outside
below freezing -- but that leaves me reluctant to go outside, so I generate
obsolete thoughts:
Some of you may remember that back in the spring I modified my Frank
Jenkins fiberglass radiator fan shroud to investigate air stagnation
effects. What I did was cut windows all around the shroud and cover them
with spring-loaded flaps, copying what many modern vehicles have.
The idea was that the rotating fan, when not engaged, obstructs air flow,
creating a high pressure zone behind the radiator and consequently
decreasing cooling. The doors were expected to open under those conditions
and delay fan engagement. I'd thought I might aim a video camera at the
doors to observe their operation, but never did (should have let Dan
install it under his glass hatch). However, there's no question that if
there were pressure there, the doors would open -- they're very lightly
spring-loaded to the closed position.
About half way through my 'round-the-USA summer trip, I decided to try
sealing the doors to observe changes in temperature & fan operation. With
duct tape I closed all but the two small doors unreachable at the top of
the shroud. I never could recognize ANY difference in temperature, fan
operation, nor noise. I've now removed the tape; during only limited
driving, I still observe no change.
Conclusion: Don't bother cutting holes in your radiator shroud.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL
www.gmcwipersetc.com
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Cooling Shroud Mod [message #237414 is a reply to message #237411] |
Sat, 25 January 2014 08:50  |
Jp Benson
Messages: 649
Registered: October 2011
Location: Fla
Karma: 2
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Ken, Thanks for the update on that mod. Most modern vehicles are pretty
crowded in the engine compartment when compared to the GMC motorhome.
On 1/25/2014 9:32 AM, Ken Henderson wrote:
> Some of you may remember that back in the spring I modified my Frank
> Jenkins fiberglass radiator fan shroud to investigate air stagnation
> effects. What I did was cut windows all around the shroud and cover them
> with spring-loaded flaps, copying what many modern vehicles have.
>
> The idea was that the rotating fan, when not engaged, obstructs air flow,
> creating a high pressure zone behind the radiator and consequently
> decreasing cooling. The doors were expected to open under those conditions
> and delay fan engagement. I'd thought I might aim a video camera at the
> doors to observe their operation, but never did (should have let Dan
> install it under his glass hatch). However, there's no question that if
> there were pressure there, the doors would open -- they're very lightly
> spring-loaded to the closed position.
>
> About half way through my 'round-the-USA summer trip, I decided to try
> sealing the doors to observe changes in temperature & fan operation. With
> duct tape I closed all but the two small doors unreachable at the top of
> the shroud. I never could recognize ANY difference in temperature, fan
> operation, nor noise. I've now removed the tape; during only limited
> driving, I still observe no change.
>
> Conclusion: Don't bother cutting holes in your radiator shroud.
>
> Ken H.
> Americus, GA
> '76 X-Birchaven w/Cad500/Howell EFI & EBL
> www.gmcwipersetc.com
> _______________________________________________
> GMCnet mailing list
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| Re: [GMCnet] Cooling Shroud Mod [message #237425 is a reply to message #237411] |
Sat, 25 January 2014 09:48 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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My "guess" is more like air is getting under the coach going down the road and creating a slight positive pressure in the engine compartment. Hence the flaps will stay closed. We need a full size wind tunnel with a front roller dyno and a smoke gennerator and video system. Anyone want to book that? Short of that, the hard fibreglas chin spoiler under the core support from Jim K made a huge difference at road speed on my coach preventing temp rise creep. I don't have the fender boat vents as to me they just don't flow enough CFM to warrent the chop job, though they might help a bit with hot soak at shut off. I know ftom experience the GM 76 C3 (a bottom feeder with no 'grill' ) would creep in temp on the highway on a hot day til the clutch fan came on for a 30 second cool down every few minuites over and over. Clearly a starved natural air flow situation. So we share more than just Corvette FRP!
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Cooling Shroud Mod [message #237465 is a reply to message #237425] |
Sat, 25 January 2014 16:52 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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John,
Without the video, or your more thorough data collection, I can't be sure,
but I'm pretty confident that there's always positive pressure inside my
radiator shroud unless it's defeated by the fan. All this duct work makes
sure 'most all the air impinging on the front of the radiator actually
passes through it:
http://www.gmcmhphotos.com/photos/g5632-under-bumper-air-scoop-amp-rock-guard.html
http://www.gmcmhphotos.com/photos/g6117-grille-to-radiator-duct.html
I don't have even a hint of an overheating problem, so this is all pretty
academic to me.
Ken H.
On Sat, Jan 25, 2014 at 10:48 AM, John R. Lebetski <gransport@aol.com>wrote:
>
>
> My "guess" is more like air is getting under the coach going down the road
> and creating a slight positive pressure in the engine compartment. Hence
> the flaps will stay closed. We need a full size wind tunnel with a front
> roller dyno and a smoke gennerator and video system. Anyone want to book
> that? Short of that, the hard fibreglas chin spoiler under the core support
> from Jim K made a huge difference at road speed on my coach preventing temp
> rise creep. I don't have the fender boat vents as to me they just don't
> flow enough CFM to warrent the chop job, though they might help a bit with
> hot soak at shut off. I know ftom experience the GM 76 C3 (a bottom feeder
> with no 'grill' ) would creep in temp on the highway on a hot day til the
> clutch fan came on for a 30 second cool down every few minuites over and
> over. Clearly a starved natural air flow situation. So we share more than
> just Corvette FRP!
> --
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Cooling Shroud Mod [message #237469 is a reply to message #237411] |
Sat, 25 January 2014 17:31 |
 |
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Ken,
For the record:
1) What kind of radiator do you have in your coach?
2) What thermostat are you running?
3) What's the final drive ratio?
Regards,
Rob M.
Sydney, Australia
-----Original Message-----
From: Ken Henderson
This is more than a little out of season, with the temperature outside
below freezing -- but that leaves me reluctant to go outside, so I generate
obsolete thoughts:
Some of you may remember that back in the spring I modified my Frank
Jenkins fiberglass radiator fan shroud to investigate air stagnation
effects. What I did was cut windows all around the shroud and cover them
with spring-loaded flaps, copying what many modern vehicles have.
The idea was that the rotating fan, when not engaged, obstructs air flow,
creating a high pressure zone behind the radiator and consequently
decreasing cooling. The doors were expected to open under those conditions
and delay fan engagement. I'd thought I might aim a video camera at the
doors to observe their operation, but never did (should have let Dan
install it under his glass hatch). However, there's no question that if
there were pressure there, the doors would open -- they're very lightly
spring-loaded to the closed position.
About half way through my 'round-the-USA summer trip, I decided to try
sealing the doors to observe changes in temperature & fan operation. With
duct tape I closed all but the two small doors unreachable at the top of
the shroud. I never could recognize ANY difference in temperature, fan
operation, nor noise. I've now removed the tape; during only limited
driving, I still observe no change.
Conclusion: Don't bother cutting holes in your radiator shroud.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL
www.gmcwipersetc.com
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Cooling Shroud Mod [message #237476 is a reply to message #237469] |
Sat, 25 January 2014 18:15 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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On Sat, Jan 25, 2014 at 6:31 PM, Robert Mueller wrote:
> Ken,
>
> For the record:
>
> 1) What kind of radiator do you have in your coach?
Aluminum
>
>
2) What thermostat are you running?
>
195*F
>
> 3) What's the final drive ratio?
3.55:1
4) Engine?
Cad 500
Regards,
> Rob M.
> Sydney, Australia
>
> -----Original Message-----
> From: Ken Henderson
> ...
> Conclusion: Don't bother cutting holes in your radiator shroud.
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Cooling Shroud Mod [message #237543 is a reply to message #237522] |
Sun, 26 January 2014 15:28 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Terry,
The photos to which I posted the links show grille-to-radiator ducting --
side and top shields. I did not put a bottom shield in because the scoop
below the bumper, shown in the other album, serves the same purpose,
I have not tried a scoop to deflect air into the engine compartment behind
the radiator rather than through it -- the concept makes no sense to me, as
compared to making sure as much air as possible passes through the radiator.
Ken H.
On Sun, Jan 26, 2014 at 2:11 PM, terry skinner <gmcnut@msn.com> wrote:
>
>
> Ken
> Have you installed the flaps on each side of the radiator to direct the
> air thru the radiator rather than around??
>
> Have you messed with an air dam to draw hot air out of the engine
> compartment??
>
> Just curious........Terry
>
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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