heat riser valve on 1978 corvette
Thread Starter
5th Gear
Joined: Aug 2015
Posts: 5
Likes: 0
From: Findlay Ohio
heat riser valve on 1978 corvette
I have a pretty much stock 1978 corvette and I have noticed that there is a device on the passenger side exhaust (that I believe is called a heat riser valve) keeps kicking off the linkage to the vacuum operator. The Vacuum operator seems to be working, but the connection to the exhaust valve comes off. I have tried on several occasions to get it reconnected and to get it to stay connected without success.
first of all, is this device necessary? What is it's purpose, and can I "lock it open" and not do any damage?
first of all, is this device necessary? What is it's purpose, and can I "lock it open" and not do any damage?
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,851
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
The function is to help warm the car up during cold engine startup.
The efe or Early Fuel Evaporation valve is part of the emissions system on your car. It is not available in reproduction at this time and is becoming harder and harder to find.
Can you do without it.. yes, you can wire it open and some people will remove it, cut the center out of it and re-install it too.
You might look into fixing the existing rod.
Willcox
The efe or Early Fuel Evaporation valve is part of the emissions system on your car. It is not available in reproduction at this time and is becoming harder and harder to find.
Can you do without it.. yes, you can wire it open and some people will remove it, cut the center out of it and re-install it too.
You might look into fixing the existing rod.
Willcox
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
Yeah but a double pumper will take care of that. Double pumpers will fix anything and I hear there are now bumper stickers that say "I've Got A Double Pumper Under My Hood" and double pumper fan clubs have sprung up in the deep south.
Burning Brakes
Joined: Oct 2008
Posts: 1,037
Likes: 14
From: Mobile Alabama
If I remember correctly, I think the 78 has a vacuum actuated valve and is normally open until the engine is running and closes it. So if it is disconnected, it should be fine. You may want to wire it open because it could make a rattling noise if left loose.
Cruising
Joined: May 2015
Posts: 13
Likes: 0
Heat riser
The function is to help warm the car up during cold engine startup.
The efe or Early Fuel Evaporation valve is part of the emissions system on your car. It is not available in reproduction at this time and is becoming harder and harder to find.
Can you do without it.. yes, you can wire it open and some people will remove it, cut the center out of it and re-install it too.
You might look into fixing the existing rod.
Willcox
The efe or Early Fuel Evaporation valve is part of the emissions system on your car. It is not available in reproduction at this time and is becoming harder and harder to find.
Can you do without it.. yes, you can wire it open and some people will remove it, cut the center out of it and re-install it too.
You might look into fixing the existing rod.
Willcox
To be open? I think mine is getting vapor lock. After driving clear filter
Bubbles gas out of filter. Edelbrock 600. Makes for hard starting.78/l82
Motor. Thanks!!
Melting Slicks
Joined: Jan 2014
Posts: 2,478
Likes: 254
From: Downers Grove Illinois
how can I tell if it's open.I wired mine to what I thought was open. The rod should be? Up or down
To be open? I think mine is getting vapor lock. After driving clear filter
Bubbles gas out of filter. Edelbrock 600. Makes for hard starting.78/l82
Motor. Thanks!!
To be open? I think mine is getting vapor lock. After driving clear filter
Bubbles gas out of filter. Edelbrock 600. Makes for hard starting.78/l82
Motor. Thanks!!
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Le Mans Master
Joined: Dec 2006
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Burning Brakes
Joined: Oct 2008
Posts: 1,037
Likes: 14
From: Mobile Alabama
how can I tell if it's open.I wired mine to what I thought was open. The rod should be? Up or down
To be open? I think mine is getting vapor lock. After driving clear filter
Bubbles gas out of filter. Edelbrock 600. Makes for hard starting.78/l82
Motor. Thanks!!
To be open? I think mine is getting vapor lock. After driving clear filter
Bubbles gas out of filter. Edelbrock 600. Makes for hard starting.78/l82
Motor. Thanks!!
Cruising
Joined: May 2015
Posts: 13
Likes: 0
The exhaust going through the bottom of the intake would more likely heat the carburetor, and cause fuel to boil in the float bowl. Overheating in your fuel line/filter (bubbles coming up from pump) is more likely from exhaust or engine compartment heat. This would be better helped by a return line, and/or insulation/re-routing the fuel line.
Use to wrap the fuel line from pump
To carb.
Burning Brakes
Joined: Oct 2008
Posts: 1,037
Likes: 14
From: Mobile Alabama
You can buy heat shield sleeves that you could slide over the tubing -from a number of vendors. I am guessing your line is not completely stock because you are running an Edelbrock. You would also not want it too close to hot parts. Years ago I had a car with that problem, and wrapped rags around the fuel line and doused it with water – it worked until I could get home. It could be the line feeding the pump is the problem as you have exhaust heat down there. Also a functioning return line off of the pump or (better) the carb can keep the fuel circulating. Without a return, the fuel sits in the line gaining heat. If you have access to an infrared heat gun, you could shoot the line and look for hot spots. Good Luck
Cruising
Joined: May 2015
Posts: 13
Likes: 0
Heat riser seems open
You can buy heat shield sleeves that you could slide over the tubing -from a number of vendors. I am guessing your line is not completely stock because you are running an Edelbrock. You would also not want it too close to hot parts. Years ago I had a car with that problem, and wrapped rags around the fuel line and doused it with water – it worked until I could get home. It could be the line feeding the pump is the problem as you have exhaust heat down there. Also a functioning return line off of the pump or (better) the carb can keep the fuel circulating. Without a return, the fuel sits in the line gaining heat. If you have access to an infrared heat gun, you could shoot the line and look for hot spots. Good Luck
Crank motor,good to go.fuel lines run
On top of frame rail. Line up to carb I
Saw today does touch hose to water pump at one point. Put rag between
Filter&intake, no diff. Car at idle, return
Line has solid stream to tank.will hit
Line to carb w/ temp gauge. Been a problem. Thanks for reply!!!
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
I have had a heat riser valve stick "closed". For normal city driving, you will not notice anything. But, on the highway, you will notice reduced power. And, if you push any real power out of the engine, you can do some major damage, if that valve is closed.
On my car, the right side exhaust manifold got so hot that the metal actually "balooned" outward. It didn't blow thru, but almost. It did get so hot that the head gasket between cylinders #4 and #6 blew out. It was only when I went to repair the blown head gasket that I realized what happened. Naturally, I cut the riser valve off its center shaft to guarantee that it wouldn't happen again. I don't really need the car in very cold periods that might require the heat riser, anyway.
On my car, the right side exhaust manifold got so hot that the metal actually "balooned" outward. It didn't blow thru, but almost. It did get so hot that the head gasket between cylinders #4 and #6 blew out. It was only when I went to repair the blown head gasket that I realized what happened. Naturally, I cut the riser valve off its center shaft to guarantee that it wouldn't happen again. I don't really need the car in very cold periods that might require the heat riser, anyway.
Drifting
Joined: Apr 2004
Posts: 1,414
Likes: 126
From: Mequon WI
The connecting rod on mine keeps coming off too. Correct me if I'm wrong. When cold this valve holds the damper in the closed position. As the engine heats up the vacuum actuator opens the damper. When the rod is disconnected the exhaust flow will open this damper. Result is the purpose of this valve on a cold engine is gone. On a hot engine the weight of the damper will add some exhaust restriction and some power loss.
Drifting
Joined: Jul 2002
Posts: 1,995
Likes: 110
From: Garland Texas
The connecting rod on mine keeps coming off too. Correct me if I'm wrong. When cold this valve holds the damper in the closed position. As the engine heats up the vacuum actuator opens the damper. When the rod is disconnected the exhaust flow will open this damper. Result is the purpose of this valve on a cold engine is gone. On a hot engine the weight of the damper will add some exhaust restriction and some power loss.
The vacuum actuator is spring loaded. With the engine off, hot or cold, the heat riser is held open by the rod and the spring in the actuator. When a cold engine is started the TVS in the thermostat housing allows vacuum to the actuator and closes the riser. When the coolant at the TVS reaches a certain temp it closes and blocks vacuum to the actuator. The spring in the actuator then holds the riser open.
Mike
Cruising
Joined: May 2015
Posts: 13
Likes: 0
You're close.
The vacuum actuator is spring loaded. With the engine off, hot or cold, the heat riser is held open by the rod and the spring in the actuator. When a cold engine is started the TVS in the thermostat housing allows vacuum to the actuator and closes the riser. When the coolant at the TVS reaches a certain temp it closes and blocks vacuum to the actuator. The spring in the actuator then holds the riser open.
Mike
The vacuum actuator is spring loaded. With the engine off, hot or cold, the heat riser is held open by the rod and the spring in the actuator. When a cold engine is started the TVS in the thermostat housing allows vacuum to the actuator and closes the riser. When the coolant at the TVS reaches a certain temp it closes and blocks vacuum to the actuator. The spring in the actuator then holds the riser open.
Mike
Closest to the ground. I thought this was in the open position. About ready
To pull the crossover down and see if
It's open or closed. Thanks!!
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
un wire it. start engine and move actuator. you will feel exhaust pressure push on it. that will tell you which way it is obstructing exhaust flow. BTW, do this with engine cold or wear gloves...this is all emissions stuff designed to make car idle hotter. most of us don't have that worry anymore...
Cruising
Joined: May 2015
Posts: 13
Likes: 0
un wire it. start engine and move actuator. you will feel exhaust pressure push on it. that will tell you which way it is obstructing exhaust flow. BTW, do this with engine cold or wear gloves...this is all emissions stuff designed to make car idle hotter. most of us don't have that worry anymore...
Way than removing crossover. Always
Glad to get other advice. This forum is
Great for that.
Thread Starter
5th Gear
Joined: Aug 2015
Posts: 5
Likes: 0
From: Findlay Ohio
Heat riser valve on 1978 corvette
I orginally posted on this back some time ago... my final fix was to replace the clip that held the rod into the actuator with a small hose clamp with one of the "threads" filed away so that it held the ball end of the actuator in place. Has been on for about a year now and the connection has held up nicely.