Thermal Vacuum Switch

[The_Eagles’_Nest]

So cleaning up the engine compartment on my Dad’s 73 Fury I found a thermal vacuum switch screwed into the radiator. One end is connected to the vacuum amplifier and the other end is not connected to anything. Where is the end without a hose supposed to go. The service manual does not mention it, that I can find. Engine is a 360.

 

[CBODY67]

Should be a vacuum line map on the top of the core support. Thinking of the items which were coolant heat sensitive, meaning they worked when the coolant got up to operating temperature, that would be the EGR valve, except that without an EGR valve, there probably are "floor jets" in the intake manifold plenum, right under the carb. SO . . . it could be that it was between the vac amp and the vac advance can? How is the vac advance line currently run?

Look on page 7-9 of the 1973 Dodge FSM. See if that might not be what you have? This situation was started with a TSB for the 1972 models. In that TSB, it termed it a "Thermal Ignition Valve" which past a certain coolant temp, would switch the vac advance to manifold vac rather than ported vac, with the intent that the added advance would increase the engine speed enough to keep the engine cooler and the a/c lines from blowing off from too much compressor head pressure. That '72 TSB also included some die-cut masticated rubber panels to seal off the air coming into the radiator/ac condenser so that all of the air came in through the grille, rather than being recycled hot engine air from underneath being recycled. When the engine cooled off, back to less than 225 degrees F, then the vac source to the vac advance returned to ported vacuum.

In the FSM, there is a different name for the TVS, but it operates as the '72 TSB indicates. Except it is hooked to the cowl-mounted OSAC item between it and the vac advance.

CBODY67

 

[The_Eagles’_Nest]

Should be a vacuum line map on the top of the core support. Thinking of the items which were coolant heat sensitive, meaning they worked when the coolant got up to operating temperature, that would be the EGR valve, except that without an EGR valve, there probably are "floor jets" in the intake manifold plenum, right under the carb. SO . . . it could be that it was between the vac amp and the vac advance can? How is the vac advance line currently?

There isn’t any vacuum diagram. Doesn’t look like there ever was.

The vacuum lines run from the carburetor to the OSAC valve then from the OSAC valve to the bypass valve. From the bypass valve one hose goes to the vacuum amplifier and the other to the distributor. This is correct as far as I can tell.

 

[rags]

I’m sick of the crap of modern cars. The needlessly over complicated procedures, Federally mandated equipment that causes more harm than good,

for me, a '73 is a modern car and that switch and everything associated with it is just the type of federally mandated equipment that caused more harm than good. we couldn't wait to rip that stuff off and throw it right in the trash where it belongs.

 

[The_Eagles’_Nest]

for me, a '73 is a modern car and that switch and everything associated with it is just the type of federally mandated equipment that caused more harm than good. we couldn't wait to rip that stuff off and throw it right in the trash where it belongs.

50 years is ancient as far as cars go. The car runs perfectly with ECS, OSAC, EGR and everything just the way it was when new, now that the deferred maintenance has been completed. I’m leaving it all in place because it is not bad equipment, ECS and EGR are better for the environment and actually benefit the car. Not to mention you have nothing to truly contribute with your post to answer my question.

 

[thethee]

This is the diagram I followed for my 1975 440. Might not be correct for your application but hope it helps

 

[The_Eagles’_Nest]

View attachment 614177

This is the diagram I followed for my 1975 440. Might not be correct for your application but hope it helps

It does somewhat, I see the other end on yours goes to the EGR. Mine is on the molded hose that come off the vacuum amplifier, but I will check it out again.

 

[thethee]

It corresponds to this page in my FSM so I'm 90% sure this way is correct.

 

[The_Eagles’_Nest]

Mine is a 360 but it should be the same. My manual does not show those diagrams. Odd.

 

[thethee]

Well in that case:

 

[Big_John]

From the '73 FSM

 

[CBODY67]

IIRC, genuine EGR valves were not on everything until the 1974 model year. Prior to that, it was "floor jets" in the bottom of the intake manifold plenum. The "bypass valve" item is on page 7-9 of the 1973 Dodge FSM (only 1973 manual at www.mymopar.com). By observation, LA motors did not have the same exact emission control items on them as B/RB motors. AND it could vary model year to model year.

In trying to figure out what a particular TVS operates, one must first determine what devices on the engine would be temperature sensitive. As in what is there that should not be operating until the coolant reaches a certain temperature. Usually, that means: EGR valves, vac-operated heat riser valves, or the TIC (thermostatic ignition control) on the '72 TSB I mentioned, which was probably regular production for 1973.

My recommendation of hooking the vac advance to ported vacuum on the base of the carb directly still stands. (The air cleaner "trap door" gets full manifold vac from the other vac port on the carb base, for the smaller vac hose size.) Then increase the initial timing a slight bit from stock. Hot base idle should usually be about 650-700rpm, or what the tune up specs sticker indicates. Set the hot base idle speed after adjusting the timing and adjusting the idle mixture screws, using the "20rpm drop method", for "lean best idle", using a dwell tach.

What other vac lines are hooked to the vac amp item?

Enjoy!
CBODY67

 

[The_Eagles’_Nest]

This is the page I have been using. This shows the set up on the car is correct the way it is.

 

[Big_John]

This is the page I have been using. This shows the set up on the car is correct the way it is.

View attachment 614224

Look in section 7, cooling, for specific info.

 

[rags]

Not to mention you have nothing to truly contribute with your post to answer my question.

i did answer the question. you wanted to know where the hose goes. so far as i'm concerned it goes right in the trash along with the rest of that junk!

 

[The_Eagles’_Nest]

i did answer the question. you wanted to know where the hose goes. so far as i'm concerned it goes right in the trash along with the rest of that junk!

Don’t be a jackass.

 

[rags]

Don’t be a jackass.

way off topic. please be respectful. also, i'm right.

 

[The_Eagles’_Nest]

way off topic. please be respectful. also, i'm right.

You have been nothing but disrespectful to me, my car and this thread. You are one to talk, sir…