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So am replacing some vacuum lines and doing some basic stuff under the hood and I don’t know what this does or what hooks into it. Any help and/or guidance would be appreciated!! Thanks in advance.
Vacuum controlled heat riser valve. Connected to a TVS that allows vacuum to flow to open the valve as the engine warms up. TVS is thermal vacuum switch controlled by engine coolant temp. Has manifold vac on one side of switch ( "inlet side") Can have 1, 2, 3, 4 ports on "outlet side". Switch is normally screwed into water passage in intake manifold or thermostat housing.
I've removed most of the rubber hoses shown in my 80 4-speed.
The heat riser is not needed unless you are driving in the snow. If it is closed, it forces all of the passenger side exhaust through the intake and out the driver side exhaust. Good for warming up the engine quickly, but bad for peformance and vapor-lock. Below is a photo of how it should look with no vacuum to compare to the position of your lever (yours appears to be open). If you apply a vacuum to that port, the valve closes. It's easy to check the function with a vacuum pump, but you want it open!
The flapper(s) in the cold air intake are driven by that thermo-vacuum switch. Again, they should fail open (check). I've removed the flappers entirely by driving out the large pins in the dual-snorkel air filter housing. When operating correctly, they will balance "cold" air from above the radiator with warm air from the heat stove around the exhaust manifold. In practice, and assuming you don't drive in snow, when would you ever want anything but the coldest air possible going into your engine?
The same goes for any TVSs in your waterneck. I've replaced mine with a simple waterneck with no threaded holes (GM Part 10108470), since I don't need the temperature-sensitive vacuum lines to go anywhere.
Have you done the Lars-style tune, and ensured that you are getting (full-time) manifold vacuum to your distributor's vacuum advance?
Last edited by Bikespace; Jun 25, 2020 at 12:26 AM.
Thank to both of you. That makes sense to me and I will make they it is open when I go back out there to work on it again today.
I will also take tour advice on the distributor vacuum advance and work on it tonight.
I was searching for a broken vacuum line, because my blower only blows out in the floor, and that lead me to about a million other little things!!
If you figure out the vacuum leak causing the blower to only blow out the floor, let me know. I have an '80 4-speed and have the same issue, but haven't chased it down yet.
Still replacing vacuum hoses but I am told I probably need this. I ordered it and plan to replace it once I have enough excuses to take apart the center console
Still replacing vacuum hoses but I am told I probably need this. I ordered it and plan to replace it once I have enough excuses to take apart the center console
i would not buy..rebuild the old one..too many threads on replacement actuators no good. It is the control selector most times..search c3 corvette blowing floor only etc..many threads..
If you figure out the vacuum leak causing the blower to only blow out the floor, let me know. I have an '80 4-speed and have the same issue, but haven't chased it down yet.
Wanna be mechanic needing help
