Home » Public Forums » GMCnet » Matron Voyage
| Matron Voyage [message #224770] |
Mon, 07 October 2013 10:09  |
xplorid
Messages: 213
Registered: February 2012
Location: Boise
Karma: 0
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Senior Member |
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My coach is no virgin, so I can't call it a maiden voyage - but, this past weekend took my wife, the two dogs and me to the Oregon coast and back, our first real travel and living in it. It was great, everything worked, and those of you in Coos Bay know the weather was pretty spectacular. I did have some surging idle weirdness when the engine warmed that needs some follow-up.
BUT, on the way back, after running perfectly for hours even going up that long grade east out of Pendleton, I had vapor lock issues and had the fan clutch cycling with the engine coolant temp at 185. It was not more than 70 degrees out, the tanks were 75 degrees when I shot them with the IR.
If the gas was vaporizing, it was doing close to the carb with ambient heat, I guess. So hot intake manifold + un-baffled grill to radiator (poor air flow)? Any other speculation is welcome, but time to pull the intake, check for cracks, and reassemble with block-off plates and get the baffle kit from Jim K?
Looking thru PO docs, previous problems of running hot, carb rebuild and carb replacement. I have an Al radiator, hot weather driving runs at 185 this past summer and never above 200.
Jeff
1974/94 GMCII by Explorer
Manny 6.5 TD Al radiator
1 ton front 4 bags back
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| Re: [GMCnet] Matron Voyage [message #224784 is a reply to message #224770] |
Mon, 07 October 2013 11:43  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Jeff,
Your mention of "un-baffled grill to radiator" prompts me to comment: I've
been concerned for years about that "deficiency" and finally did something
about it a year or so ago. I'd already installed side baffles, made from
truck mud flaps. I also have long had a below-the-bumper aluminum scoop
that prevents all air flow around the lower radiator. For the latest
iteration, I installed a thick plastic top on the side baffles so that
there's no way for any significant amount of the air impinging on the plane
of the grill to bypass the radiator.
To my surprise, during the initial testing in the Spring, there seemed to
be no benefit from the baffling. If anything, the water temperature seemed
to be slightly less steady. The 10,000+ mile western trip I just finished
reinforced that analysis: I had no water temperature problem, but did have
what appeared to perhaps be vapor lock (despite booster pumps and EFI). At
one time, I speculated that the absence of air flow over the top of the
radiator might be increasing the engine compartment temperature (and maybe
that's why GMC for '77 & '78 did not add a top). Removing the top of the
baffle made no obvious difference. I may have had no vapor lock (the HEI
coil MAY have been the problem), but if I did, the cooling system probably
did not contribute to it.
My conclusion from all this is that baffling, while theoretically
satisfying, and providing a convenient storage shelf, is of little cooling
benefit.
JMHO,
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL
www.gmcwipersetc.com
On Mon, Oct 7, 2013 at 11:09 AM, jeff sugheir <jeff.sugheir@gmail.com>wrote:
>
>
> My coach is no virgin, so I can't call it a maiden voyage - but, this past
> weekend took my wife, the two dogs and me to the Oregon coast and back, our
> first real travel and living in it. It was great, everything worked, and
> those of you in Coos Bay know the weather was pretty spectacular. I did
> have some surging idle weirdness when the engine warmed that needs some
> follow-up.
>
> BUT, on the way back, after running perfectly for hours even going up that
> long grade east out of Pendleton, I had vapor lock issues and had the fan
> clutch cycling with the engine coolant temp at 185. It was not more than
> 70 degrees out, the tanks were 75 degrees when I shot them with the IR.
>
> If the gas was vaporizing, it was doing close to the carb with ambient
> heat, I guess. So hot intake manifold + un-baffled grill to radiator (poor
> air flow)? Any other speculation is welcome, but time to pull the intake,
> check for cracks, and reassemble with block-off plates and get the baffle
> kit from Jim K?
>
> Looking thru PO docs, previous problems of running hot, carb rebuild and
> carb replacement. I have an Al radiator, hot weather driving runs at 185
> this past summer and never above 200.
>
> Jeff
> --
> 1973/94 GMCII in Boise 76 455 with headers & Paterson distributor,1 ton
> front, 4 bags back, Precision Steering Gearbox
>
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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] Matron Voyage [message #224789 is a reply to message #224784] |
Mon, 07 October 2013 13:11 |
xplorid
Messages: 213
Registered: February 2012
Location: Boise
Karma: 0
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Senior Member |
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Hey thanks for the responses. Tom - I found a disconnected fuel pump under the coach after I drove it from Orlando to Toledo to Boise a year ago. That would explain why hitting the fuel pump switch on the dash did nothing for the vapor lock then. Dan - That climb is about as relentless as it gets, and yes, when I finally got to the top (still going 55-60mph) I had that confidence that I could drive this pretty much anywhere. And Ken - your experience is quite revealing, and reinforces my guess that this is heat generated on top of the engine that is feeding both the vapor lock and maybe the fan clutch. I suppose cracks in the intake, opening wider as the engine gets hot might explain the surging idle problem as well.
OBTW - I got this far with help from many of you here on the forum, with thanks as well to Jim K, Jim B, Jeff Sirum, Cliff Golby, Manny, Gene Dotson, Dick Paterson, Bill Hubler (esp Bill Hubler)and a few others. What an experience this has been so far, and even though I am 1.5 years of spare time into this, and a little over $30,000 (yup), I am still thrilled.
1974/94 GMCII by Explorer
Manny 6.5 TD Al radiator
1 ton front 4 bags back
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| Re: [GMCnet] Matron Voyage [message #224816 is a reply to message #224770] |
Mon, 07 October 2013 18:51 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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I'd shoot the carb with the IR, and the manifold center.
--johnny
'76 23' transmode niorris
--------------------------------------------
On Mon, 10/7/13, jeff sugheir <jeff.sugheir@gmail.com> wrote:
Subject: [GMCnet] Matron Voyage
To: gmclist@temp.gmcnet.org
Date: Monday, October 7, 2013, 3:09 PM
My coach is no virgin, so I can't call it a maiden voyage -
but, this past weekend took my wife, the two dogs and me to
the Oregon coast and back, our first real travel and living
in it. It was great, everything worked, and those of
you in Coos Bay know the weather was pretty
spectacular. I did have some surging idle weirdness
when the engine warmed that needs some follow-up.
BUT, on the way back, after running perfectly for hours even
going up that long grade east out of Pendleton, I had vapor
lock issues and had the fan clutch cycling with the engine
coolant temp at 185. It was not more than 70 degrees
out, the tanks were 75 degrees when I shot them with the
IR.
If the gas was vaporizing, it was doing close to the carb
with ambient heat, I guess. So hot intake manifold +
un-baffled grill to radiator (poor air flow)? Any
other speculation is welcome, but time to pull the intake,
check for cracks, and reassemble with block-off plates and
get the baffle kit from Jim K?
Looking thru PO docs, previous problems of running hot, carb
rebuild and carb replacement. I have an Al radiator, hot
weather driving runs at 185 this past summer and never above
200.
Jeff
--
1973/94 GMCII in Boise 76 455 with headers & Paterson
distributor,1 ton front, 4 bags back, Precision Steering
Gearbox
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
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_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
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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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