Heat, pumps, and the gas tanks.

[Bob Dunahugh]

Heating of the gas is an issue that seems to come up a lot. So when I ins=
talled the Howell system. I thought of in tank pumps. So that the fuel is =
under pressure from inside the tanks. To the TB. This concept has true meri=
t. But I've had too many pumps from China that failed. I wanted both tank =
pumps simple/quick to get too. So I put the two pumps for my EFI on the out=
side of the main steel frame. Plus. In an attempt to get away from engine h=
eat that's more prevalent inboard of that steel frame. Plus back to the sim=
plicity of the service concept. That did prove out way sooner then I ever e=
xpected. As one of the EFI pumps failed after only 6 blocks into my first t=
est run of the EFI. The aux tank pump got me back home. Pump change took a=
bout 15 minutes. Now back to the heat. Most of the heat is coming from the =
engine. The extreme heat goes out the back by way of the tail pipe. Heade=
r displace a lot of the heat into the engine bay. That originally went out=
the tail pipe, back from the gas tanks. Thus headers acerbating the heatin=
g of the gas tanks. There are vents that can be put in the body, above the =
front wheels. These vents are about straight out board of the headers. This=
header heat leaves the engine bay by way of under the gas tanks. Our GMC d=
oesn't have headers. Does still have the GM gas tank exhaust pipe heat shie=
lds. ( Did make mine taller. No surprise that I'd do that kind of thing.)=
Last year I was monitoring tank temps. I was very surprised as to how hig=
h tank temps got. Gas temps at the outboard pumps was at the tank temps. =
So no gas temp rise to the pumps. Has anyone put gas tank heat shi=
elds bellow their gas tanks. Then a cool air duct to the outside of the tan=
ks? Bob Dunahugh ________________________________ From: gmcmh-ef=
i on behalf of Randy Van Wink=
le Sent: Sunday, May 20, 201:58 AM To: gmcmh-efi=
ooglegroups.com Subject: Re: [GMCMH-EFI] Fuel Pump Questions Seems l=
ike more complication than necessary. I would wait until you were ready to =
install the efi system (sounds like you are close to doing that anyway) the=
n remove the sometimes troublesome fuel selector switch and intall two high=
pressure pumps as close to the tanks as possible or in the tanks if you ar=
e up to the extra work. To me the low pressure oump is just added complicat=
ion. If you need the low pressure electric for the carb to prevent vap=
or lock until you do the efi then install an inexpensive pump to feed the m=
echanical. Remove it when you go to efi. The goal is to keep fuel under pre=
ssure from tanks to engine. Randy (liking simplicity) '77 Eleganza I=
I "403" On Sat, May 19, 2018, 8:51 PM Ty Hardiman wrote: Thanks all. I've gotten some=
useful information to think about. I realize there are many ways to lay ou=
t the fuel supply system. But my takeaway is this: Q: What are the opi=
nions about using a low-pressure external pump to feed the high-pressure ex=
ternal pump. A. It's a hedge against vapor lock. And if you installed a b=
ypass loop with a check valve on the low-pressure pump, the high-pressure p=
ump would work with or without the low pressure pump operating. On =
Saturday, May 19, 2018 at 7:17:39 PM UTC-5, Larry Davick wrote: Unless yo=
u have an urgent need to replace the mechanical fuel pump, I would wait. I=
don=E2=80=99t see a good reason to put an electric pump in place when it=
=E2=80=99s really not needed. I did this and regretted it. My tired old c=
arb was not happy with the pump and despite some fiddling I was not ever ha=
ppy I=E2=80=99d replaced the pump. It finally worked perfectly, but it did=
not improve the stock set-up in any way for me. Larry Davick A Myst=
ery Machine 1976(ish) Palm Beach Fremont, CA Howell EFI + EBL + Elect=
ronic Distributor On May 18, 2018, at 8:01 PM, Ty Hardiman wrote: Fair enough. Let me expand my question: I would =
like to install electric fuel pumps on my coach, with my q-jet. Upgrading l=
ater to a Rochester TBI. I can put in a pair of 4070s now, but would that b=
e wasted money if I'm just going to go to an Airtex + EFI in a few months? =
Or would it be beneficial to feed the dual 4070's into an Airtex? On F=
riday, May 18, 2018 at 9:41:49 PM UTC-5, Ty Hardiman wrote: Hello all, fi=
rst post. What a great resource this forum is! I have spent a lot of time o=
ver the past month reading the forum posts and the related resources, worki=
ng on understanding EFI for the GMCMH. I'm in the "learning, thinking,=
& planning" phase and I'll try to ask concise and specific questions. I'm =
doing some fuel pump planning right now. Q: What are opinions on using=
a Carter 4070 to supply an Airtex 8094 - is this required, not required bu=
t beneficial, or completely unnecessary? Thanks in advance, Ty =
-- You received this message because you are subscribed to the Google Gro=
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t https://groups.google.com/group/gmcmh-efi. For more options, visit http=
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com/d/optout. -- You received this message because you are subscribe=
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o this group, send email to gmcmh-efi. Visit this group at https://groups.google.com/group/gmcmh=
-efi. For more options, visit https://groups.google.com/d/optout.

 

[robert mueller]

G'day,

I have seen photos of fuel tanks "covered" with diamond plate attached to the main frame with short spacers unfortunately I can't
seem to remember where I saw the photos.

On a hot sunny summers day the amount of heat radiated from the road surface would not provide any "cool" air. It might be a bit
cooler than what flows down from the engine compartment but it's not going to solve the issue. I don't know how you'd duct it from
outside the frame rails without reducing the road clearance of the frame. Sooner or later the gas tank will reach the OAT plus what
heat it picks up radiated from the road surface.

Having said that I'm going to put plates on the Kingsley in the USA and the Avion in Australia, the cost is negligible and its not
much work so what the hell.

Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808

-----Original Message-----
From: Gmclist [mailto:gmclist-bounces] On Behalf Of Bob Dunahugh
Sent: Sunday, May 20, 2018 1:45 PM
To: gmclist
Subject: [GMCnet] Heat, pumps, and the gas tanks.

Heating of the gas is an issue that seems to come up a lot. So when I installed the Howell system. I thought of in tank pumps. So
that the fuel is under pressure from inside the tanks. To the TB. This concept has true merit. But I've had too many pumps from
China that failed. I wanted both tank pumps simple/quick to get too. So I put the two pumps for my EFI on the outside of the main
steel frame. Plus. In an attempt to get away from engine heat that's more prevalent inboard of that steel frame. Plus back to the
simplicity of the service concept. That did prove out way sooner then I ever expected. As one of the EFI pumps failed after only 6
blocks into my first test run of the EFI. The aux tank pump got me back home. Pump change took about 15 minutes. Now back to the
heat. Most of the heat is coming from the engine. The extreme heat goes out the back by way of the tail pipe. Header displace a
lot of the heat into the engine bay. That originally went out the tail pipe, back from the gas tanks. Thus headers acerbating the
heating of the gas tanks. There are vents that can be put in the body, above the front wheels. These vents are about straight out
board of the headers. This header heat leaves the engine bay by way of under the gas tanks. Our GMC doesn't have headers. Does still
have the GM gas tank exhaust pipe heat shields. ( Did make mine taller. No surprise that I'd do that kind of thing.) Last year I
was monitoring tank temps. I was very surprised as to how high tank temps got. Gas temps at the outboard pumps was at the tank
temps. So no gas temp rise to the pumps.

Has anyone put gas tank heat shields bellow their gas tanks. Then a cool air duct to the outside of the tanks? Bob Dunahugh

 

[billvv]

I'm considering the installation of a fuel cooler in the EFI return line. Shell and tube heat exchanger, about 8" long with AC evap discharge in the
tube and fuel in the shell. Got one from a Mercedes on Ebay. The more fuel that bypasses, the cooler the fuel in the tank. Good for stop/go traffic
and oversized fuel pumps. Location is an issue - route the AC to the fuel line or vice versa or somewhere in between?

Reducing heat gain in the tanks makes sense in that arrangement.

At least I'll get some benefit from that '76 dash air system.
--
Bill Van Vlack
'76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath, Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o mid
November 2015.

 

[john r. lebetski]

Bob what about ducts sourced from the rear flooding the tanks. Sourced just below the tail lights where body curves and air wraps around. This should
give a more ambiant source away from the road heat. Or just above the bumper or using the bumper itself that "scoops" air as you drive anyway. Or get
stylish with a NACA or Testarosa styled inlet. I'm sure with your racing experience you have lots of ideas. You would have to use some oval or flat
duct to bring it forward but if you boxed in the tanks you could then have an area pressurized with only this cooler source. Maybe.
--
John Lebetski
Woodstock, IL
77 Eleganza II

 

[Jim Hupy]

I have one of those Mercedes fuel coolers, and it looks like a fairly
effective way to cool the fuel. Just have some A/C hoses the right length,
ditto fuel lines, and it should do the trick. Mercedes has been using them
for about 30 years, so it is proven technology. I just got mine this
weekend, so I haven't done anything with it yet, but, I will.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

On Mon, May 21, 2018, 7:42 AM Bill Van Vlack
wrote:

> I'm considering the installation of a fuel cooler in the EFI return line.
> Shell and tube heat exchanger, about 8" long with AC evap discharge in the
> tube and fuel in the shell. Got one from a Mercedes on Ebay. The more fuel
> that bypasses, the cooler the fuel in the tank. Good for stop/go traffic
> and oversized fuel pumps. Location is an issue - route the AC to the fuel
> line or vice versa or somewhere in between?
>
> Reducing heat gain in the tanks makes sense in that arrangement.
>
> At least I'll get some benefit from that '76 dash air system.
> --
> Bill Van Vlack
> '76 Royale; Guemes Island, Washington; Twin bed, full (DS) side bath,
> Brazilian Redwood counter and settee tops,455, 6KW generator; new owner a/o
> mid
> November 2015.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[michael1]

When I bought my GMC, it had steel plates welded to the frame covering each tank.
There was no ducting or scoops added, just giant steel plates.
I still vapor locked when driving through NM and AZ in the middle of August every afternoon.
At that point in ownership, I still had a mechanical fuel pump and an inline electric fuel pump.

I do not think these plates help, I may use a thermal paint on them this year.
I would love to remove them, but that is not a priority at this point.

--
1973 GMC 26' Glacier - Unknown Mileage - Has a new switch pitch transmission with Powerdrive

 

[lw8000]

I was really close to installing the aluminum panels under the tanks as well. I'm not a fan of the high amount of pressure that builds up in the
tanks on hot days. This write-up was one that I found very interesting:

http://minniebiz.com/gmcmotorhome/2017/02/25/insulating-the-fuel-tanks/

I'm particularly interested in it due to the fact it seemed to help with the tank pressure issue that we see often.

I too have seen pics of the diamond plate aluminum, similar fashion to above, but cannot find it.

I researched reflective coatings, but did not find anything that seemed promising or proven to actually work. I found that some had tried to coat the
tanks with thermal coatings (including Jim B) but the conclusions seem to indicate it did not help.

I also tinkered with the idea of installing a deflector to direct the hot engine air down below the tanks but so far have not revisited. That would
be much easier to install but would probably not help the issue with road heat. We did install the side air vents from JimK to vent the engine box,
and so far I'm convinced those are well worth it. I figure getting any hot air out of that area can only help.
--
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan

 

[johnny]

Bob -

My coach has shields on the front tank, made of aluminum checkerplate. Vertical from the floor down to the horizontal one which runs horizontal the
length and width of the tank. And exhaust pipe shields. Tank seems to stay cool, at least n o pressure when opened at a gas stop on a hot day.
I'll get you a picture or two when we reconnect, I had the coach towed to Chuck's place - closest around - because yet again it looks as if I've
lunched yet another transmission. If I'm lucky, it lost a governor gear. I don't think that's the case but that's first check Wednesday when I get
back up there to figure out the problem.

--johnny
--
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" - ol Andy, paraphrased

 

[richard h staples]

Just a couple of thoughts here. A couple of pounds pressure in the fuel tanks is a GOOD thing on a hot day. It raises the boiling point of the gas
and helps prevent vapor lock. Almost any modern car will exhibit a slight whoosh when the gas cap is removed (when hot) as this how they are
designed. (OTOH, if you perceive any suction when opening the gas cap, there's a problem.) The difficulty is making almost a seventy feet of pipes,
tubes, hoses and fittings tight enough to sustain a little pressure. I'm still trying, with some success.

For what it's worth, here's my anti-vapor-lock saga on a limited budget '75 GMC with stock carburetor at 5500'+ altitude:

1 - Insulated the steel fuel lines where they run alongside of the engine near the left exhaust manifold and near the radiator by encasing them in
several layers of rubber fuel and heater hose. Seemed to help.
2 - Added homemade heat shields to the exhaust pipe where it passes the fuel tanks. Made from surplus stove pipe, mine cover both the side and top of
the pipe. Seems to help.
3 - Added an auxiliary (Carter) electric fuel pump just in front of the tanks. Mine is plumbed into the auxiliary tank line, and comes on when
"Auxiliary" fuel is selected. Also has a momentary switch to allow priming the carburetor. Helps a lot.
4 - Replaced the stock fuel pump with an Oldsmobile "A/C" pump with a vapor return fitting to circulate some fuel, and hopefully vapor bubbles, back
to the tanks. Helps less than I hoped.
5 - Replaced every darned piece of hose in the fuel system with steel tubing or SAE30R9 fuel injection grade hose. Replaced tank pickup O'rings.
Don't know how much it helps, but at least I can build a little pressure (see above) and not belch fuel on the ground when filling the tanks.

JWID, HTH
Rick Staples

--
Rick Staples, '75 Eleganza, Johnstown, CO

"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien

 

[emerystora]

Hi Rick

Its not the slight pressure that is the problem. At times the tanks get so hot that when one removes the fuel cap there is a geyser of gasoline which can shoot up a foot or so. Then the gasoline boils for a while and copious amounts fo fuel continue to come out of the fill spout. This happened to me a couple of times in the past. I had to wait about 10 minutes before I could put any fuel into the tank.

Emery Stora
77 Kingsley
Frederick, CO

>
> Just a couple of thoughts here. A couple of pounds pressure in the fuel tanks is a GOOD thing on a hot day. It raises the boiling point of the gas
> and helps prevent vapor lock. Almost any modern car will exhibit a slight whoosh when the gas cap is removed (when hot) as this how they are
> designed. (OTOH, if you perceive any suction when opening the gas cap, there's a problem.) The difficulty is making almost a seventy feet of pipes,
> tubes, hoses and fittings tight enough to sustain a little pressure. I'm still trying, with some success.
>
> For what it's worth, here's my anti-vapor-lock saga on a limited budget '75 GMC with stock carburetor at 5500'+ altitude:
>
> 1 - Insulated the steel fuel lines where they run alongside of the engine near the left exhaust manifold and near the radiator by encasing them in
> several layers of rubber fuel and heater hose. Seemed to help.
> 2 - Added homemade heat shields to the exhaust pipe where it passes the fuel tanks. Made from surplus stove pipe, mine cover both the side and top of
> the pipe. Seems to help.
> 3 - Added an auxiliary (Carter) electric fuel pump just in front of the tanks. Mine is plumbed into the auxiliary tank line, and comes on when
> "Auxiliary" fuel is selected. Also has a momentary switch to allow priming the carburetor. Helps a lot.
> 4 - Replaced the stock fuel pump with an Oldsmobile "A/C" pump with a vapor return fitting to circulate some fuel, and hopefully vapor bubbles, back
> to the tanks. Helps less than I hoped.
> 5 - Replaced every darned piece of hose in the fuel system with steel tubing or SAE30R9 fuel injection grade hose. Replaced tank pickup O'rings.
> Don't know how much it helps, but at least I can build a little pressure (see above) and not belch fuel on the ground when filling the tanks.
>
> JWID, HTH
> Rick Staples
>
> --
> Rick Staples, '75 Eleganza, Johnstown, CO
>
> "Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

 

[jack christensen1]

Armand Minnie Insulated his tanks not long before he sold his beautiful unit using ceramic insulating blankets and metal roofing panels. Here's a
link to his presentation.
http://minniebiz.com/gmcmotorhome/2017/02/25/insulating-the-fuel-tank

--
Jack Christensen - K6ROW,
'76 Glenbrook/Clasco - "The Silver Bullet",
Sebastopol, CA

 

[Jim Hupy]

The problem is not the tanks, lines, or pumps. It is the Reformulated
Gasoline. First of all, the viscosity is correct for engines that have high
pressure supply systems and fuel injectors. Not carbs.
So consider using more fuel pressure between the tank and the carb
inlet. But not in the carb itself. The float inlet valve will not handle
much more than 4 psi. If you continue to use a carb, expect vapor lock.
Drive as much as possible in the cool part of the day, fuel up in the early
morning, make sure there are no leaks in the supply lines. A low pressure
fuel pump, like the Carter 4070 helps a great deal in the supply line as
well. Fuel injection helps too. But, don't blame the coach, blame the
gasoline. And the folks that insist that alcohol is good for blending into
it. Just how it is.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

Armand Minnie Insulated his tanks not long before he sold his beautiful
unit using ceramic insulating blankets and metal roofing panels. Here's a
link to his presentation.
http://minniebiz.com/gmcmotorhome/2017/02/25/insulating-the-fuel-tank

--
Jack Christensen - K6ROW,
'76 Glenbrook/Clasco - "The Silver Bullet",
Sebastopol, CA

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Unsubscribe or Change List Options:
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[jerry work]

With our two coaches I found re-plumbing the fuel tanks helped a lot. By r=
emoving the tank selector valve and mounting two electric pumps outboard of=
the frame rails, one for each tank, you can plumb the gas lines to remain =
outboard the frame and around the front of the coach where it is relatively=
cooler before entering the carb, mechanical fuel pump, EFI surge tank or d=
irectly to the EFI fuel rail depending on the pressure of the pumps. You c=
an use the the dash tank selector switch to flip a relay from the normally =
closed to the normally open posts on a five pin relay to select which elect=
ric pump you want to run. The fuel gage will still register the tanks indi=
vidually. I always filled the tanks, ran 200 to 250 miles and filled again=
so was always pulling off of one tank. You can access around 40 to 42 gal=
lons this way without switching tanks so the second fuel pump is just a bac=
kup. The fuel in the tanks will still get hot from radiated road heat but =
you can easily baffle between the exhaust pipe and the tanks to reduce that=
heat load. No need to cover or coat the tanks. I tried that and could se=
e no difference. The EFI guys will seldom have any vapor lock issues d=
oing this and really none if they use a front mounted surge tank or they pu=
t the pumps inside the tanks. The carb guys are going to continue to have =
issues, although at a slower rate, simply due to the fact that the gas toda=
y is formulated to atomize when pressure fed through a fuel injector instea=
d of drawn into the air stream via venturi effect inside the carb. Jer=
ry Jerry Work The Dovetail Joint Fine furniture designed and hand cra=
fted in the 1907 former Masonic Temple building in historic Kerby, OR =
glwork http://jerrywork.com =
Message: 1 Date: Mon, 21 May 2018 10:05:17 -0600 From: Chri=
s S. To: gmclist Subject: Re: [=
GMCnet] Heat, pumps, and the gas tanks. Message-ID: Content-Type: text/plain; charset "utf-8" I was =
really close to installing the aluminum panels under the tanks as well. I'=
m not a fan of the high amount of pressure that builds up in the tanks on=
hot days. This write-up was one that I found very interesting: http:=
//minniebiz.com/gmcmotorhome/2017/02/25/insulating-the-fuel-tanks/ I'm=
particularly interested in it due to the fact it seemed to help with the t=
ank pressure issue that we see often. I too have seen pics of the diam=
ond plate aluminum, similar fashion to above, but cannot find it. I r=
esearched reflective coatings, but did not find anything that seemed promis=
ing or proven to actually work. I found that some had tried to coat the =
tanks with thermal coatings (including Jim B) but the conclusions seem to i=
ndicate it did not help. I also tinkered with the idea of installing a=
deflector to direct the hot engine air down below the tanks but so far hav=
e not revisited. That would be much easier to install but would probably=
not help the issue with road heat. We did install the side air vents from=
JimK to vent the engine box, and so far I'm convinced those are well wor=
th it. I figure getting any hot air out of that area can only help. -- =
Chris S. - 77 Kingsley, 3.70 FD, mostly OEM - S.E. Michigan =

 

[johnny]

I drove all over the southeast in july and august after putting the electric pumps in the 23' without any vapor lock problems. On just the mechanical
punmp, don't slow down. I ran it on no alcohol gas, especially in the summertime. Alcohol laced gas is going to lock it up when it's hot and
carbureted.

--johnny
--
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" - ol Andy, paraphrased

 

[lw8000]

[SNIP]

> 3 - Added an auxiliary (Carter) electric fuel pump just in front of the tanks. Mine is plumbed into the auxiliary tank line, and comes on when
> "Auxiliary" fuel is selected. Also has a momentary switch to allow priming the carburetor. Helps a lot.

[SNIP]

I second this workaround. I too have done many things to the coach to try and work around vapor lock, and this is the only one I know for sure works,
and it's simple to install. I talked to JimB (@ Co-Op) extensively about vapor lock in June 2016 while we were in Florida as we had severe vapor lock
while down there; his guys installed that low pressure pump to the aux line/switch in under an hour, and our vapor lock problems were instantly
resolved. Jim's instructions were: When the engine starts to sputter after sitting or taking off in hot weather, just flip the switch to aux and let
everything return to normal (usually takes 10-20 seconds). At that point, flip the switch back to main and use the mechanical pump which will keep
you going. It's not perfect, but it works every time.

And, the additional benefit is it really does help to prime the carb after sitting for an extended period of time. Flip the switch, start the engine
(usually goes after 1 - 2 tries), and flip it back once it's started up.
--
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan