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I have a 1979 L48 and there are three thermal switches on the front top of the motor. Two in the thermostat housing and one more to the left on the manifold. Are these all the same type of thermal switch? Does anyone have the part # for each and know where I can get them. Thanks
I have a 1979 L48 and there are three thermal switches on the front top of the motor. Two in the thermostat housing and one more to the left on the manifold. Are these all the same type of thermal switch? Does anyone have the part # for each and know where I can get them. Thanks
While they all function off vacuum (thermal vacuum switch - TVS), they have a different purpose and "measure" differently.
My 78 L48 has only two TVS switches, the EGR (your #3) and the EFE (#2). So your #1 had limited L48 applications and one I have not seen before. If you look at Dr. Rebuild Schematics (link below). It could be this is the California or high-altitude emission control option.
What is the code on your emission control label up by the brake booster?
Here is the Wilcox 1979 emission hose/switch schematic: Note the #3 TVS is not shown? I have not seen this configuration before so it makes me curious. Also, smithandwestern is also in search of the same #3 TVS but you both use the same image.
As you'll see with the Dr. Rebuild schematics, TVS switches are color-coded. It looks like your #2 and #3 are both yellow topped. So replace #3 with same as #2 and it should give you the same functionality...once you get the hoses hooked up. Looks like the upper hose is coming off the check valve.
Last edited by hunt4cleanair; 11-30-2016 at 04:50 AM.
Reason: add emission hose link
While they all function off vacuum (thermal vacuum switch - TVS), they have a different purpose and "measure" differently.
My 78 L48 has only two TVS switches, the EGR (your #3) and the EFE (#2). So your #1 had limited L48 applications and one I have not seen before. If you look at Dr. Rebuild Schematics (link below). It could be this is the California or high-altitude emission control option.
What is the code on your emission control label up by the brake booster?
Here is the Wilcox 1979 emission hose/switch schematic: Note the #3 TVS is not shown? I have not seen this configuration before so it makes me curious. Also, smithandwestern is also in search of the same #3 TVS but you both use the same image.
As you'll see with the Dr. Rebuild schematics, TVS switches are color-coded. It looks like your #2 and #3 are both yellow topped. So replace #3 with same as #2 and it should give you the same functionality...once you get the hoses hooked up. Looks like the upper hose is coming off the check valve.
That picture is not from my car, but from another forum user. It looks much like mine. Mine has purple, yellow and green from left to right in the picture. I really appreciate all of the info you provided. I bought my car in 1988 in CA, but the guy I bought it from told me he bought it from the original owner, it was originally purchased in Boston.
That picture is not from my car, but from another forum user. It looks much like mine. Mine has purple, yellow and green from left to right in the picture. I really appreciate all of the info you provided. I bought my car in 1988 in CA, but the guy I bought it from told me he bought it from the original owner, it was originally purchased in Boston.
Just to clarify the purple is going directly into the intake manifold. The yellow and green go into the thermostat housing.
You have to be really careful in which design of TVS you get. They come in two different designs. Normally Open ( allowing vacuum to flow when it is cold...but closes when it gets hot.) and Normally Closed...which means it will not allow vacuum to flow when cold and when it gets hot....the switch opens so the vacuum can flow.
SO do not assume anything.
I need to see a photo of yore heat riser/EFE so I can see which heat riser you have...just in case it has been swapped out over the years.
You have to be really careful in which design of TVS you get. They come in two different designs. Normally Open ( allowing vacuum to flow when it is cold...but closes when it gets hot.) and Normally Closed...which means it will not allow vacuum to flow when cold and when it gets hot....the switch opens so the vacuum can flow.
SO do not assume anything.
I need to see a photo of yore heat riser/EFE so I can see which heat riser you have...just in case it has been swapped out over the years.
DUB
Thanks Dub, I think the heat riser/EFE is the EFE that attaches to the exhaust manifold. I have it off the engine now. Couple of pictures attached.
If they came assembled on the engine, the AIM will not reference them. They should be shown in the Chevrolet Service Manual for that year.
Of course the 1979 was the first year Chevrolet published a dedicated shop manual for Corvette and its nice. I use it for my 78. The troubleshooting is much more detailed and specific than previous shop manuals. However, it does not list part numbers.
I would think the 1979 AIM would provide the part numbers for those temp/vacuum switches. Anyone have a '79 AIM?
The AIM tags the TVS with its function but the part number is not listed. But #1 is shown as the Transmission Spark TVS and apparently used for federal emission L48s. I would trust the color code markings on the original, get the replacements while also getting a copy of the 79 AIM as a reference guide.
Either the TVS switches were assembled at the factory, most likely, or were a component in the emission hose assembly. The AIM schematic shows three 1979 configurations.
Last edited by hunt4cleanair; 12-01-2016 at 04:37 PM.
Thanks Dub, I think the heat riser/EFE is the EFE that attaches to the exhaust manifold. I have it off the engine now. Couple of pictures attached.
MAJOR THANKS on the photos.
I can 'say' this. This hear riser design....when you get it installed back on the engine...you will notice that when it is all hooked up. That the heat riser flap will be OPEN. SO..knowing that your exhaust will flow freely with NO vacuum going to the vacuum pod for the EFE....because the OPEN mode is the 'default setting' GM chose when they designed it.....and thus.....the TVS for this EFE then would be OPEN when it is cold.. Because the TVS is OPEN and allowing vacuum to go to the vacuum pod and thus CLOSE the heat riser. This is begin done when the engine is cold to aid in heating up the rest of the choke components.
SO...when the coolant temp gets hot....this TVS will then CLOSE....thus stopping the vacuum...and thus allowing the heat riser to open and allow the exhaust to flow....because it is now hot enough and no need in suppressing the exhaust any further.
Did that make sense??????????
Your EGR TVS will more than likely be opposite of the TVS for your EFE. When the engine is COLD..NO vacuum will make it to the EGR until it gets hot enough to allow the EGR to work. SO..the TVS for your EGR is CLOSED.
The term that is often used is NORMALLY OPEN (NO)....or NORMALLY CLOSED (NC)...and this can often times be applied to hot water shut off valves and electric relays and so on that 'switch' positions.
I can 'say' this. This hear riser design....when you get it installed back on the engine...you will notice that when it is all hooked up. That the heat riser flap will be OPEN. SO..knowing that your exhaust will flow freely with NO vacuum going to the vacuum pod for the EFE....because the OPEN mode is the 'default setting' GM chose when they designed it.....and thus.....the TVS for this EFE then would be OPEN when it is cold.. Because the TVS is OPEN and allowing vacuum to go to the vacuum pod and thus CLOSE the heat riser. This is begin done when the engine is cold to aid in heating up teh rest of teh choke components.
SO...when the coolant temp gets hot....this TVS will then CLOSE....thus stopping the vacuum...and thus allowing the heat riser to open and allow the exhaust to flow....because it is now hot enough and no need in suppressing the exhaust any further.
Did that make sense??????????
Your EGR TVS will more than likely be opposite of the TVS for your EFE. When the engine is COLD..NO vacuum will make it to the EGR until it gets hot enough to allow the EGR to work. SO..the TVS for your EGR is CLOSED.
The term that is often used is NORMALLY OPEN (NO)....or NORMALLY CLOSED (NC)...and this can often times be applied to hot water shut off valves and electric relays and so on that 'switch' positions.
Did have a question where can I get all three TVS, green, yellow and purple. I checked doc rebuild and he had yellow only, the purple was out of stock and I did not see the green. thanks again for the help.
Did have a question where can I get all three TVS, green, yellow and purple. I checked doc rebuild and he had yellow only, the purple was out of stock and I did not see the green. thanks again for the help.
Is there a reason you want all three???
I do not know of any company who is reproducing these.
I bought about 20 of them when GM still offered them many years ago....but what I have is not for sale at this time.
Unless they are broken..I would wait and test them when you get the car started.
I do not know of any company who is reproducing these.
I bought about 20 of them when GM still offered them many years ago....but what I have is not for sale at this time.
Unless they are broken..I would wait and test them when you get the car started.
DUB
DUB, you are an asset to this forum and all of us trying keep these cars on the road. Your support helped me learn how my '81 carb and emissions worked to the point everything operates correctly. Otherwise I would have gutted it and taken what seemed like the easy route. Now I just have to get the HVAC system working correctly. BTW, I hope you're enjoying the mini C2 dash I sent you.
I do not know of any company who is reproducing these.
I bought about 20 of them when GM still offered them many years ago....but what I have is not for sale at this time.
Unless they are broken..I would wait and test them when you get the car started.
DUB
Thanks Dub the purple one broke off at the head, so I have to try to get that one. The other two are locked into the old housing and have a bunch of build up around them inside the thermostat housing, I can trying cleaning them up and see if I can reuse them. I appreciate the guidance. Thanks again for all your help.
Thanks Dub the purple one broke off at the head, so I have to try to get that one.
That happened to mine but I had the nipple and glued it back on...still works! These can be found at swap meets such as Carlisle...but that is August unless you have a close one by.
The other two are locked into the old housing and have a bunch of build up around them inside the thermostat housing, I can trying cleaning them up and see if I can reuse them.
A plumber's trick but try soaking in CLR...Calcium-Lime-Rust solution. it is used to loosen deposits from shower/faucet heads. And it works. Get it at Home Depot.
Last edited by hunt4cleanair; 12-03-2016 at 04:13 AM.
That happened to mine but I had the nipple and glued it back on...still works! These can be found at swap meets such as Carlisle...but that is August unless you have a close one by.
A plumber's trick but try soaking in CLR...Calcium-Lime-Rust solution. it is used to loosen deposits from shower/faucet heads. And it works. Get it at Home Depot.
Thank you all for helping me with this, figured I show you my project. Bought it in 1988 right after I got out of college, wanted a stick an this was the only one I could afford at the time. Since then I become married with children, and my car has sat in the garage the last 15+ years. So now it is time to fix her up. DUB was nice enough to guide me step by step in fixing fiberglass crack on left front fender, was able to fix it. I finished installing new body cushions. thanks again, I am sure I will be asking more questions.
11-29-2016, 06:28 PM
Question on Thermal Switches
