Home » Public Forums » GMCnet » [GMCnet] Hot or What?
| [GMCnet] Hot or What? [message #165038] |
Mon, 02 April 2012 13:33  |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Coming back from Newna yeasterday I ran into a problem. I was cruising up I 85 at ~~65 per on cruise control, Junkerac running perfectly, and the roof A/C plus the chassis A/C keeping it bearable in the coach. I then had to get off in Atlanta and do city streets in traffic for about 15 minutes. Six lanes on 85 - 75 closed in the center of town for an accident.
Anyhow, watched the temp, no rise. Genset kept on chugging. Back on I 85, and another 45 minutes up to my get-off. And when I turned off the freeway ramp, I got a flat spot on the throttle, which quickly went away and we proceeded. 55MPH on a country highway, with ups and downs. Sometime in this 6 mile segment, the Junkerac quit. I didn't notice exactly when, I just looked in the mirror a mile from the house at a light and the RUN light was out, roof A/C stopped. That close to home, not a propblem. But, coming off the light, it wanted to die and then picked up again. Drove it to the house - a mile - without problems, all about 45 per on country roads. When I got home, showing half full on the main guage, so it would have been a quarter off full when I left to head home (down and back starting full). I cracked the fuel filler, incredible presure in the tanks. So, did I get the tanks hot in town? Is there a vent which opens at
half full? Would hot fuel screw up the genset running? Genset has a 'block' pump feeding it, and I believe an MGM instrall - at any rate it's installed properly with a nice fan in the door which pressurizes the generator bay. Sitting still, cooling has never been a problem.
Assuming I'm boiling what passes for gas around here ('summer blend") what's the heal? Never slow down? More shielding? I dunno what's under there, haven't looked closely. But I weill be looking in the next couple of days, and insulating/rerouting as necessaery. If it packs it in on the freeway, I have a problem. I've a coated dog in there. Most sumaritans aren't interested in giving a lift to the guy with the curly white behemopth on the lead.
--johnny
'76 23; transmide norris
'76 palm beach
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Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] Hot or What? [message #165065 is a reply to message #165038] |
Mon, 02 April 2012 17:22  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Johnny,
As early and cool (for us) as it is, you apparently had vapor lock, and
perhaps boiling in the tanks (pressurizing them). First thing you need to
do is check the liquid-vapor separator in the front of the left rear wheel
well. It's a little black box hidden behind a sheet metal cover. The box
is a float bowl with an inlet and an outlet. The inlet is fed from the top
of each tank to a tee just below the separator. It dumps into the float
bowl with a little "ping pong ball" float. Normally, only vapor reaches
that point. If, for any reason, liquid gets into the bowl, the ball
floats, closing a needle valve to the outlet. The outlet, which is
connected to the carbon canister below the passenger's feet is thus
prevented from allowing liquid gasoline to reach the canister (and pour out
on the ground). But, that also allows the tanks to become pressurized.
The gas cap is supposed to have a 1 psi vent, but not all do, and even 1
psi in 50 gallon tanks amounts to a lot of vapor coming out of the filler
neck when you open it.
It's not unusual for the black box to become deformed, preventing the ball
from moving so that the thing is never closed or always closed. I've been
cutting mine open and resealing it every few years since 1999. New ones
are available from our vendors, or, I've heard, as Corvette replacement
parts.
For the vapor lock problem, you know the answer: a pusher electric pump
back by the tanks. Most choose to use just one, downstream of the selector
valve. Many allow it to pump through the mechanical pump. I especially
dislike that option because of the potential oil pollution problem with a
leaking mechanical diaphragm, so when I ran one pump, I tee'd the
electrical and mechanical pump outputs. Even that bit me: I used a check
valve to prevent flow back through the electric pump, but depended on the
output valve of the mechanical pump to protect it. In the east side of
Yellowstone NP, I developed a leak ABOVE the mechanical check valve!
Poured gasoline all over our protected environment! Fortunately, I had a
plug to isolate the mechanical pump so we continued with just the
electrical pump.
After that trip, I replaced the mechanical pump and the selector valve with
a second electric pump, using the tank selector wiring to choose between
the Main and Aux electric pumps, whose outputs are check valve'd together.
That combination suits me better than any other. I've never, AFAIK,
experienced vapor lock on the GMC (and never driven it without an electric
pump since I brought it home the first time).
The Generac may have just overheated; or, may, if it takes its fuel from
the engine fuel line like a Coachmen installation, have injested some to
the bubbles created by the engine pump suction; or, may have been flooded
by the excess pressure in the fuel tanks -- awful hard to guess --
especially when you hate Generac's as much as I do. :-)
Ken H.
On Mon, Apr 2, 2012 at 2:33 PM, Johnny Bridges wrote:
> ...
> Assuming I'm boiling what passes for gas around here ('summer blend")
> what's the heal? Never slow down? More shielding? I dunno what's under
> there, haven't looked closely. But I weill be looking in the next couple
> of days, and insulating/rerouting as necessaery. If it packs it in on the
> freeway, I have a problem. I've a coated dog in there. Most sumaritans
> aren't interested in giving a lift to the guy with the curly white
> behemopth on the lead.
>
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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] Hot or What? [message #165078 is a reply to message #165038] |
Mon, 02 April 2012 19:01 |
captjack
Messages: 271
Registered: February 2010
Location: Sebastopol, California
Karma: 1
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Senior Member |
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I've had a similar problem in the past. I would get vapor lock in the generator just before I got vapor lock in the GMC engine. Final solution ended up being fuel pumps mounted in the tanks. It doesn't solve the generator problem since I decided not to plumb the generator into the engine fuel lines, but Oh well, at least I not stuck by the side of the road with no engine AC or coach AC.
Jack Christensen - K6ROW,
'76 Glenbrook/Clasco - "The Silver Bullet",
Sebastopol, CA
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| Re: [GMCnet] Hot or What? [message #165138 is a reply to message #165065] |
Tue, 03 April 2012 06:36 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Thanks, I'll pull the seperator out and see what's with it. I probably heated everything up going through the city with very little aiurflow under teh coach, and once heated it doesn't cool bck down. My problem is, I got to run up to Charlotte Friday afternoon. I duno if I have time to play with the thing before then.
--johnny
From: Ken Henderson <hend4800@bellsouth.net>
To: gmclist@temp.gmcnet.org
Sent: Monday, April 2, 2012 6:22 PM
Subject: Re: [GMCnet] Hot or What?
Johnny,
As early and cool (for us) as it is, you apparently had vapor lock, and
perhaps boiling in the tanks (pressurizing them). First thing you need to
do is check the liquid-vapor separator in the front of the left rear wheel
well. It's a little black box hidden behind a sheet metal cover. The box
is a float bowl with an inlet and an outlet. The inlet is fed from the top
of each tank to a tee just below the separator. It dumps into the float
bowl with a little "ping pong ball" float. Normally, only vapor reaches
that point. If, for any reason, liquid gets into the bowl, the ball
floats, closing a needle valve to the outlet. The outlet, which is
connected to the carbon canister below the passenger's feet is thus
prevented from allowing liquid gasoline to reach the canister (and pour out
on the ground). But, that also allows the tanks to become pressurized.
The gas cap is supposed to have a 1 psi vent, but not all do, and even 1
psi in 50 gallon tanks amounts to a lot of vapor coming out of the filler
neck when you open it.
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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