Exhaust - Vac Valve -OverHeating

[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

[GCinSC2]

Try search for Chevy 454 HEAT RISER. Good luck.

[bkahler]

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

[Waipio Rim]

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.

[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.

[TR6RMC]

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.

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

[TR6RMC]

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

Been awhile since i have been active. sorry if all my response are not showing up correctly - replying the wrong way. User Error.

[TR6RMC]

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

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>

[Keyair]

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.

[Keyair]

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...