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03-15-2018, 12:06 PM
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#1
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79 Airstream Excella
1979 28' Airstream Excella 28
Norfolk
, Virginia
Join Date: Apr 2005
Posts: 18
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Exhaust - Vac Valve -OverHeating
Hi this is Jerry
I have a 1979 Chev 454 Excella on a C3 truck frame with approx. 68,000 miles. The exhaust system has (not sure proper term) what appears to be a vaccum operated (warm up) valve on the right Exhaust pipe. Which (should be) opens and closes with the exhaust temperature. Causing the truck to overheat after it has been running for a while and put on the street for few miles. Can’t find any true maintenance prints showing this component and how to troubleshoot or replace it. Hoping some of you may have some suggestions.
Thanks Jerry
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03-15-2018, 12:42 PM
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#2
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Site Team
2007 30' Classic S/O
Somewhere
, South Carolina
Join Date: Apr 2010
Posts: 6,436
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Try search for Chevy 454 HEAT RISER. Good luck.
__________________
S/OS #001 2005 Dodge Ram 2500 5.9L 6 Speed
16" Michelins, Hi Spec Wheels, Max Brake, Dexter 4 Piston Disc Brakes, Carslile Actuator, Equal-I-Zer, Dill TPMS. Campfire cook. BMV-712. DEMCO 21K Lb Cast Iron coupler
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03-15-2018, 01:59 PM
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#3
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Rivet Master
1974 20' Argosy 20
Richmond
, Kentucky
Join Date: Jan 2003
Posts: 9,116
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Jerry, your 79 Excella is actually on a P30 (P32) chassis.
I wish I could help you on the heat riser but I swapped out my cast iron manifolds for Thorley headers.
Brad
__________________
Air forums # 1674
1974 20' Argosy Motor Home
1975 24' Argosy Motor Home
1974 31' Excella trailer (parting out, as of 4/1/2015 I have wheels & windows left to sell)
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03-15-2018, 08:41 PM
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#4
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Rivet Master
1984 31' Airstream310
Honokaa
, Hawaii
Join Date: Jun 2010
Posts: 993
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in the "Classic Motorhome" section there is a "Classic Motorhome Sticky Thread". Post #93 on that thread has links to a bunch of service manuals, including a 1979 light truck manual. Here's a link to that one:
http://www.73-87chevytrucks.com/tech...ice_Manual.pdf
From what I can tell, the valve you are worried about is part of the "early fuel evaporative" system described in section E-3 of the manual.
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03-16-2018, 12:53 PM
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#5
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2 Rivet Member
Currently Looking...
Griffin
, Georgia
Join Date: Sep 2015
Posts: 34
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Exhaust - Vac Valve -OverHeating
Hi Jerry,
The exhaust manifold heat riser can malfunction due to either vacuum leak, bad sensor not supplying signal, bad vacuum motor at valve, etc. It is not likely to cause much of an engine overheating as it just supplies warm air to the intake system for environmental pollution control. On the other hand, weakened and collapsing under low pressure radiator hoses, bad thermostats, loose fan belts, worn out fan clutches, internally clogged radiators or externally clogged radiators and/or air conditioning condensers will all cause the over heat conditions - as well as defective temperature gauges or senders cause signals of overheating when there is, in fact, none.
If you disconnect the heat riser valve you are worried about and be sure to wedge the valve in the open condition, then drive the unit as you have and it does not overheat, track the valve problem and replace what is broken. If it does overheat, look at the list above and start with the easy stuff. Radiators clog internally over the years. Road dirt and bugs clog radiators but can be cleaned out. Fan clutches wear out and belts should be kept in good shape and tight. You can find guidelines on line for belt adjustment, checking radiators for flow and hot spots. If you want better fuel mileage and more power to the wheels, consider a high performance electric radiator fan with built in shrouds. Should be worth 5 to 12 HP and between 1/2 to 1.5 MPG at cruise.
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03-16-2018, 01:20 PM
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#6
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79 Airstream Excella
1979 28' Airstream Excella 28
Norfolk
, Virginia
Join Date: Apr 2005
Posts: 18
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More info if possible.
Quote:
Originally Posted by Travel Pro
Hi Jerry,
The exhaust manifold heat riser can malfunction due to either vacuum leak, bad sensor not supplying signal, bad vacuum motor at valve, etc. It is not likely to cause much of an engine overheating as it just supplies warm air to the intake system for environmental pollution control. On the other hand, weakened and collapsing under low pressure radiator hoses, bad thermostats, loose fan belts, worn out fan clutches, internally clogged radiators or externally clogged radiators and/or air conditioning condensers will all cause the over heat conditions - as well as defective temperature gauges or senders cause signals of overheating when there is, in fact, none.
If you disconnect the heat riser valve you are worried about and be sure to wedge the valve in the open condition, then drive the unit as you have and it does not overheat, track the valve problem and replace what is broken. If it does overheat, look at the list above and start with the easy stuff. Radiators clog internally over the years. Road dirt and bugs clog radiators but can be cleaned out. Fan clutches wear out and belts should be kept in good shape and tight. You can find guidelines on line for belt adjustment, checking radiators for flow and hot spots. If you want better fuel mileage and more power to the wheels, consider a high performance electric radiator fan with built in shrouds. Should be worth 5 to 12 HP and between 1/2 to 1.5 MPG at cruise.
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Plan on putting some money into it this summer. what brand elec fan did you use? Been thrugh the brakes & diverter valve. bearings redone. Need a/c worked on. and need to find some p[arts for the windshield wipers and drive window - can not see rear view glass has smoked up needs replacing. Comments suggestion all appreciated. Jerry
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03-16-2018, 01:23 PM
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#7
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79 Airstream Excella
1979 28' Airstream Excella 28
Norfolk
, Virginia
Join Date: Apr 2005
Posts: 18
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Learning site - again
Quote:
Originally Posted by TR6RMC
Hi this is Jerry
I have a 1979 Chev 454 Excella on a C3 truck frame with approx. 68,000 miles. The exhaust system has (not sure proper term) what appears to be a vaccum operated (warm up) valve on the right Exhaust pipe. Which (should be) opens and closes with the exhaust temperature. Causing the truck to overheat after it has been running for a while and put on the street for few miles. Can’t find any true maintenance prints showing this component and how to troubleshoot or replace it. Hoping some of you may have some suggestions.
Thanks Jerry
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Been awhile since i have been active. sorry if all my response are not showing up correctly - replying the wrong way. User Error.
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03-16-2018, 01:26 PM
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#8
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79 Airstream Excella
1979 28' Airstream Excella 28
Norfolk
, Virginia
Join Date: Apr 2005
Posts: 18
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Open position.
Quote:
Originally Posted by TR6RMC
Plan on putting some money into it this summer. what brand elec fan did you use? Been thrugh the brakes & diverter valve. bearings redone. Need a/c worked on. and need to find some p[arts for the windshield wipers and drive window - can not see rear view glass has smoked up needs replacing. Comments suggestion all appreciated. Jerry
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And not sure which is the open position. In Alabama, I am in Norfolk. Headed that way in a month or so. trying to get all my eggs in one basket before I leave THANKS>
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03-22-2018, 12:02 PM
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#9
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Rivet Master
1984 34.5' Airstream 345
Foothill Ranch
, California
Join Date: Mar 2010
Posts: 4,695
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The heat riser or EFE(Early Fuel Evaporation) valve is a butterfly style valve exhaust flow restrictor on the drivers side designed to respond to a vacuum signal from the Thermostatic valve(TVS) in the thermostat housing...
When cold, the thermostatic valve allows vacuum to flow to the bellows on the butterfly and shuts it. This forces hot exhaust gasses into a special port on the head and heat the intake manifold and therefore speeds warm-up and gets the choke off quicker, therefore reducing emissions. When the engine warms, the Thermo valve shuts off vacuum to the heat riser, and it should return the butterfly to the open position via its spring.
I believe this system was replaced with the EGR system on later models, which has proven to be more reliable.
In reality, the EFE Valve cokes up, rusts, or the spring breaks, or the TVS valve fails.
Results...
Info here...
http://tech.oldsgmail.com/emis_EFE.php
These valves are unobtainium now... the was a place in Canada making and selling them, but I cannot find them at this moment, and they are $300 ish!
You might get luck and find a NOS unit... but I bet it would be $$$.
You have a couple of options...
1/ Spray the EFE valve down with WD-40 or the like until it frees up, replace the spring, so it goes to the open position. You could then block the vacuum actuator vacuum so it stays there and become non fuctional.
2/ Remove it. be warned, that the valve is about 1/2" thick, so you will either need to put a spacer in, or adjust the exhaust pipe to relocate it.
__________________
My name is Steve.... and I am an Alumaholic!
Working in my Garage is like playing TETRIS with Tools!
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03-22-2018, 12:13 PM
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#10
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Rivet Master
1984 34.5' Airstream 345
Foothill Ranch
, California
Join Date: Mar 2010
Posts: 4,695
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This is a pic of the 81up EFE valve...
Note the position of the actuator arm in the open position as shown...
So, arm pointing down the exhaust is open, and arm 90deg to exhaust is closed...
__________________
My name is Steve.... and I am an Alumaholic!
Working in my Garage is like playing TETRIS with Tools!
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