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In this case you are risking damaging the assembly by trying to keep this outdated terrible system intact….it had only ONE useful reason and that was to appease an emission standard in 1975…..it was there only for quicker warm up only. Disable it like I said with a cut off screw plugging the hose and no one will be any wiser…..
This terrible heat riser system was responsible for thousands of engine failures in the salt belt where I grew up…..
Keeping a car original is one thing…..keeping something working that will destroy your engine is not sound thinking….
There are many useless and terrible systems on a 75’ Corvette and this is one of them….
Jebby
thanks Jebby .. if I decide to plug the hose at the actuator do I have to do anything else , does that effect the yellow strip hose on the top port of the TVS switch leading to the carburetor .. Also where does the vacuum go that is trapped in the hose thanks
thanks Jebby .. if I decide to plug the hose at the actuator do I have to do anything else , does that effect the yellow strip hose on the top port of the TVS switch leading to the carburetor .. Also where does the vacuum go that is trapped in the hose thanks
If you pull and plug the hose at actuator you won't have any trapped vacuum to be concerned about.
The TVS switch will still function normally ONLY exhausting what vacuum that was in the hose, you've created a dead end plugging it.
Instead of a pissssssst heard at the TVS switch when actuator and hose exhausted you MAY just hear a pist...
With the actuator rod still connected the heat riser valve door it will remain open, but unless you physically wire the heat riser valve open there is a chance the actuator might FAIL closing heat riser door, you don't want that to happen.
I have just gotten into the habit to open the hood, do a visual, check fluids, cold start watch for heat riser door to open, fast idle drops off then go for a ride...
If you pull and plug the hose at actuator you won't have any trapped vacuum to be concerned about.
The TVS switch will still function normally ONLY exhausting what vacuum that was in the hose, you've created a dead end plugging it.
Instead of a pissssssst heard at the TVS switch when actuator and hose exhausted you MAY just hear a pist...
With the actuator rod still connected the heat riser valve door it will remain open, but unless you physically wire the heat riser valve open there is a chance the actuator might FAIL closing heat riser door, you don't want that to happen.
I have just gotten into the habit to open the hood, do a visual, check fluids, cold start watch for heat riser door to open, fast idle drops off then go for a ride...
ok thank you I am going to change thermostat to 195 , but for now I will do that
In this case you are risking damaging the assembly by trying to keep this outdated terrible system intact….it had only ONE useful reason and that was to appease an emission standard in 1975…..it was there only for quicker warm up only. Disable it like I said with a cut off screw plugging the hose and no one will be any wiser…..
This terrible heat riser system was responsible for thousands of engine failures in the salt belt where I grew up…..
Keeping a car original is one thing…..keeping something working that will destroy your engine is not sound thinking….
There are many useless and terrible systems on a 75’ Corvette and this is one of them….
Jebby
thanks jebby, I will go to a 195 thermostat when i get to change it , for now I will take your advice and pull the hose off 👍
thanks jebby, I will go to a 195 thermostat when i get to change it , for now I will take your advice and pull the hose off 👍
ok guys after spending $175 on parts I didn’t need(lesson learned) I changed to a 195 thermostat and EFE system is working again .. I would never have thought it was the 195 thermostat especially because the original TVS switch said 180 .. however I i’m going to take your advice and plug up the hose at the actuator… thank u all so much for ur professional advice it was absolutely appreciated.. I order some manuals to help me with all of that pollution stuff I don’t know about..
Happy your EFE TVS switch is now functioning as designed...
Something to put in the vault if you ever have a question on the EGR TVS switch.
As you can see the EGR TVS switch is set to change state at even a lower temperature...
Happy your EFE TVS switch is now functioning as designed...
Something to put in the vault if you ever have a question on the EGR TVS switch.
As you can see the EGR TVS switch is set to change state at even a lower temperature...
wow wonder why .. I thought the EFE TVS would open at 180 taking to account it came out of the factory with 180 and it didn’t!! Beats me 🤷♂️
wow wonder why .. I thought the EFE TVS would open at 180 taking to account it came out of the factory with 180 and it didn’t!! Beats me 🤷♂️
grady white -- My '75 came with a 195 deg F thermostat. I am the original owner. I know you said earlier that you read in your Owners Manual the thermostat is a 180 deg F. thermostat. Those manuals are printed months in advance of the model year production, and are often revised during the production run. 180 deg F was a carry over value from the 1974 manual.
As an engineer who works in the petroleum and petrochemical industries, I can tell you that even though the TVS switch is designed to open at 180 deg F, it may open at 180 deg F, +/- 5 deg F. Same with the thermostat. It may be off +/- 5 deg F. The manufacture of these devises wasn't that precise. In order to keep the cost down, some precision was sacrificed With a 195 deg F thermostat installed, the engineer could insure the TVS would be open at 180 deg F +/- . and account for the variance in the TVS switch.
Glad to hear you sorted this situation out. Please continue to post pictures of your car. Great color combo by the way.
Last edited by '73and'75; Mar 24, 2022 at 04:01 PM.
grady white -- My '75 came with a 195 deg F thermostat. I am the original owner. I know you said earlier that you read in your Owners Manual the thermostat is a 180 deg F. thermostat. Those manuals are printed months in advance of the model year production, and are often revised during the production run. 180 deg F was a carry over value from the 1974 manual.
As an engineer who works in the petroleum and petrochemical industries, I can tell you that even though the TVS switch is designed to open at 180 deg F, it may open at 180 deg F, +/- 5 deg F. Same with the thermostat. It may be off +/- 5 deg F. The manufacture of these devises wasn't that precise. In order to keep the cost down, some precision was sacrificed With a 195 deg F thermostat installed, the engineer could insure the TVS would be open at 180 deg F +/- . and account for the variance in the TVS switch.
Glad to hear you sorted this situation out. Please continue to post pictures of your car. Great color combo by the way.
thank you for that info well appreciated.. I replaced thermostat (180)-12.00, TVS switch -35.00 heat riser 100 and actuator 150 over 300 bucks in parts.🤦♂️. Fixing the problem priceless .. Only to find out it was the thermostat all along .. I truly appreciate all the help from all of you !! Great people Great forum. 👍
Grady, you now have a few spare parts...
Little Back Story of my parts quest for my 77.
I purchased my 77 in the spring of 1983 (I think?).
One of my neighbors at the time was the Parts Manager for a Local Chevrolet Dealership.
He stopped me one day and told me stop by the dealership if I needed any parts, so one day I did.
He told me about all the 1 year only parts for the 1977 and others that would soon be discontinued.
I asked him when he had time make me a list and would purchase what I could afford at the time.
So from then on when I find a part for a reasonable price I purchase it.
These 14 containers are large 68qt size...If you notice #11 is missing it is near with a set of ready to rebuild calipers in it...lol
Grady, you now have a few spare parts...
Little Back Story of my parts quest for my 77.
I purchased my 77 in the spring of 1983 (I think?).
One of my neighbors at the time was the Parts Manager for a Local Chevrolet Dealership.
He stopped me one day and told me stop by the dealership if I needed any parts, so one day I did.
He told me about all the 1 year only parts for the 1977 and others that would soon be discontinued.
I asked him when he had time make me a list and would purchase what I could afford at the time.
So from then on when I find a part for a reasonable price I purchase it.
These 14 containers are large 68qt size...If you notice #11 is missing it is near with a set of ready to rebuild calipers in it...lol
wow 😮 very impressive spare parts collection .. wish they were 75 NOS parts . You know me 😂
Glad I found this thread. It is relevant to me as am in the process of putting my 78 Pace Car back to stock condition and will be dealing with where all the vacuum hoses go and what they control.
Hi , Does anyone know how to disconnect and reinstall the rod coming off the vacuum actuator leading to the heat riser on my 75 ?? I changed the TVS switch and thermostat, however when she warms up it still does not open..I hear sounds coming from the actuator so I am thinking that is the final part that is not working .. If I pull off the rubber hose on the actuator then the heat riser opens. As always
thank you
Perhaps a newbie question, but in your photo # 3, is the valve open or closed as shown? Also, anyway to check if it operates? Thanks
