thermo vacuum switch

[Tim Potter]

On my 1980 345 there are two thermo vacuum switches screwed into the water passages of the intake maifold. The one one the left side is brown in color and the one on the right side is white in color.

I haven't been able to find any information specifically about these switches anywhere. The question I have is: are these two switches identical in operation or are they are different? In other words do they open at the same water temp. Or at different temps?

 

[RobertC]

Yes, they are different and they will have different IH part numbers --- based on my 73 CA smog 392 (t/a).

It has 3 thermo / vacuum switches -- each a different color (and different colors from your 1980 switches).

A different IH part number goes with each switch (blue, bronze and red).

Also, the vacuum line page in the service manual lists the color of the switch at each spot where a switch is positioned.

 

[ihpartsjeff]

We stock the blue ones and bronze ones. Cost is $15.95 and $16.95 respectively.

 

[ihpartsjeff]

I breifly researched the different tvs(thermal vacuum switch) that IH used in the light line models. All in all there was 8 different ones used according to the parts book. Some are high temp, some are low temp and are different depending on whether its being used for the vacuum advance or the egr system. According to my parts book for Scout II's the colors/parts numbers were:

red - 384716c92 - high temp
white - 700390c1 - ?
Blue - 428050c91 - low temp
bronze - 441120c1 - low temp
violet - 448683c1 - ?
Yellow - 480827c1 - ?
Brown - 496028c1 - ?
Green - 496029c1 - ?

Now depending on your emissions package and year determined which color tvs you used. The only ones available from Scout line line are the blue and bronze which are both three port switchs and both considered low temperature. To determine which switch's your Scout use's refer back to the factory service manual and match your appropriate year and carb configuration with the diagram near the back of the fuel system chapter.

 

[RobertC]

Great info, Jeff. Thanks for taking the time to post.

Looking at my 72 - 73 t/a, p/u parts book, the red, blue and bronze part numbers match the switches on my 73 t/a CA smog 392.

 

[Tim Potter]

I checked in the bible and it appears that for 1980 the brown tvs that controls vacuum to the egr valve is a low temp. Switch that should open at temps above 82* f. In 1978 the same switch (probably different color/ part #) wouldn't open until the water temp. Reached 115* (go figure)

also the white tvs on the right side that controls vacuum advance is a high temp. Switch. Don't know the operating temp of this switch but mine is now "always open" which answers a question I've had for a while. I actually noted that change in vacuum supply when I was first tuning the oregon engine. I eventually bypassed the switch going straight to ported vac. Didn't seem to make any difference in cold performance.

The intended purpose of the switch is to lower emissions by delaying vacuum advance until the engine warms up to a certain point. It occurs to me that this engine was originally equipped with a prestolite distributor and now has a dui with it's hotter spark. I'm wondering whether the white thermo switch would serve any purpose even if it was operating correctly. Maybe straight ported vacuum is what I want. What say you?

 

[Michael Mayben]

As Jeff posted, the various switches and combinations of switches were specific to each engine spec in each platform, and dependent upon whether the oem vehicle was 49 state, cali, or export.

Most all of the definitive emissions data was published in service letters specific to each platform combo, by emissions class. This is a far more complex "subject" than simply speculating "why" and "what for".

Because the Scout II service manual "set" had to be considerably updated for m/y '77 and later, much of the emissions data for those vehicles is present in the manual but it's not the be-all/end-all. It is the best we can do at this point unless one has access to the individual service letter specific to a given market engine/platform combo. I do have service letters for m/y '73 stuff and m/y '74 stuff, but nothing beyond. 1973 was the big year for emissions/drivability problems for all manufacturers, that continued through m/y '75 and was always a problem for many GM vehicles until they ceased to be. M/y '77 was another benchmark year as the feds tighten the smogbelt even more.

Many of these tiny details really made no difference in actual emissions under an idle-only test program. But did make a tiny bit of difference (if all items were functioning perfectly) in the numbers in dynamic test mode used in some markets back in the day.

These temp switches all function in exactly the same manner and simply open or close a vacuum port to direct vacuum (or not direct vacuum) to a specified location at a specified engine coolant temp, the color code simply denotes the setpoint of the various switches.

Don't know about this information regarding a dui having a "hotter" spark than a prestolite electronic or any other electronic system of that era! The voltage required to fire any plug on any single compression stroke varies tremendously every time an ignition event occurs! The voltage required to ionize the plug gap each time is based upon many factors in the combustion chamber at that point but rarely exceeds 8>12kv. A dui system is nothing more than a simple inductive ignition unit. On paper...it's capable of providing a "voltage available" factor of around 40kv...but so is a prestolite with a high turn ratio coil...no difference! Likewise for a Holley gold box system.

A spark is a spark when we're talking inductive systems.

 

[Robert Kenney]

I checked in the bible and it appears that for 1980 the brown tvs that controls vacuum to the egr valve is a low temp. Switch that should open at temps above 82* f. In 1978 the same switch (probably different color/ part #) wouldn't open until the water temp. Reached 115* (go figure)

Either vacuum switching valve will work fine. The later emissions engines were tuned leaner and needed a bit more time to warm up before egr activity came on. This prevented low temp low power drivability issues. You are nolonger setup that lean so it is a non issue. It is however very important that your egr system be working because it will lessen the potential for detonation. We/I know the egr valve is nonop as of the last time I saw it and with your increased compression and more agressive cam timing.

Also the white tvs on the right side that controls vacuum advance is a high temp. Switch. Don't know the operating temp of this switch but mine is now "always open" which answers a question I've had for a while. I actually noted that change in vacuum supply when I was first tuning the oregon engine. I eventually bypassed the switch going straight to ported vac. Didn't seem to make any difference in cold performance.

Other that passing visual inspections in kali. You can run ported or not as long as your tvs is opening.

The intended purpose of the switch is to lower emissions by delaying vacuum advance until the engine warms up to a certain point. It occurs to me that this engine was originally equipped with a prestolite distributor and now has a dui with it's hotter spark. I'm wondering whether the white thermo switch would serve any purpose even if it was operating correctly. Maybe straight ported vacuum is what I want. What say you?

2nd wat mm said. Ignition spark intensity won't change how you setup the vacuum advance. I'd leave it on the tvs.

 

[mbergthold]

Based on a visual inspection and fig 56 on pg 36 of the fuel system section, my '77 345 calif motor w/ac has a 2-port low temp switch on the drivers side, and a 3-port high temp on the pax side, neither of which are avail thru light line. Since the motor hasn't run since 2006, I would like to replace both (even tho the hi-temp May be always open). Does anyone know of a source for these 2 switches?

 

[bvscout]

I had to do a bit of research to track these down for myself, but here's what I found:

the 'high temperature' 3 port switch on the passenger side (us) is interchangeable with a "pvs14 or tomco 13312", which is pretty common. Bascially this is to help prevent the engine from over heating while the engine is at idle (say stop and go traffic) it basically switches from 'ported' vacuum to manifold vacuum at around 220-225 degrees, which bumps up the timing advance, and causes the engine idle to go up a couple hundred rpm, which causes the fan to pull more air over the radiator, which in turn cools down the engine
ironically, I see a lot of folks in this forum remove this:-( why? It really doesn't hurt anything, and it helps keep the engine from over heating!

The 2-port pvs on the drivers side, prevents the egr from operating until the engine is up to operating temperature. This make the engine easier to start, and warm up.
This can be replace with just about any 2-port pvs that opens between 100-165 degrees. (stock one opens around 100)
here are a few that should work:
tomco 13301, 13240 (pvs7,pvs31) - the pvs7 appears to be closest to original.

The other thing on these is to be they are 3/8" thread and not 1/2.

There can both be easily found on-line from the usual supects

 

[mbiver]

Kind of new to the forums and Scout maintenance, so trying to learn as much as I can. Both the driver side and passenger side thermal vacuum switches on my 345 have no hoses attached to them. Should I just cap them for now? Haven’t got my service manuals just yet, so not sure exactly what they’re supposed to plug into. ALso, i’ve attached some photos of my carburetor and distributor and would appreciate any help in a definitive identification. Based on some of the threads I’ve read it would seem like a prestolite dizzy and a Holley 2210, but wanted to be sure. Thanks!

 

[1975IH200]

The TVS with no vacuum hoses attached do not need to be capped.

You have a Prestolite distributor.
It does not use a remote ignition module or "box".
The electronic ignition module is inside the distributor body.

Your Scout II, if still stock, should have Dana 44 axles front and rear.
Disk brakes front and drum brakes rear.
They should be power brakes as a standard build item for 1975 and later model years.

Is your transmission manual or automatic?
If auto, it is a Chrysler torque-flite A727 3-speed auto.
If manual, is it a 3-speed or a 4-speed?

The carb is a POS and not worth me typing any more about it.

Does your Scout II run and drive, or just run, or nothing?

Pictures of the vehicle, engine, etc. are always welcome and useful.

 

[mbiver]

Thanks for the reply. I did cap the TVS, but will just pull off the caps if they're not supposed to be there. The Scout does run and drive but currently fighting an issue where it starts missing after warming up. All of a sudden it will lose power and get real sluggish. Having trouble keeping it idling as well. It has sat for some years and I do still need to go through the carb. So far, I've replaced the coil, plugs, wires, distributor cap and rotor. I've attached a couple more pictures and will get some more taken/uploaded tonight.

 

[mbiver]

Here were the additional pictures. Any help identifying further appreciated. Thanks.

 

[1975IH200]

Thank you for posting the photos. Very helpful.

Your Scout II looks to be unmodified and stock.
Equipped as I speculated in my previous post.
Dana 44 Axle's, Dana 20 T-Case, Power Steering, Power Brakes (Disc/Drum), no A/C.
You have a manual trans, Borg Warner 3-speed w/floor shift.
I suggest you install a radiator fan should when you can.

As for the TVS: no need to cap them as there is nothing going thru them when they are not connected to any vacuum hose/source.
You can cap them if you wish, but that serves no purpose but also causes no harm.

The Ignition coil has three (3) wires connected to the positive (+) terminal and two (2) wires connected to the negative (-) terminal.
I wonder why all the extra wiring there? One wire could be for a tachometer. Do you have a tachometer installed?
Stock, it only has one on each terminal.

Which new distributor cap did you put on? The Prestolite?
Can you pull off a plug wire or two and take a photo of the cap terminals?

The box on the firewall is an emissions unit and no cause for concern right now.

Vehicles sitting for long periods, tend to have fuel issues.
Fuel/Gasoline has a limited shelf life and deteriorates or tries to return to its original state after several months, especially after years.
That causes fuel issues with "bad fuel", sticky gummed up carbs that don't function properly, clogged fuel lines and filter, it even damages the mechanical fuel pump over time.

This needs to be addressed in a complete fashion, not a hit-and-miss effort. It's all or nothing. Starting at pulling the fuel tank and cleaning it out, flushing the fuel lines, new fuel pump, new fuel filter, new rubber hoses where installed, and fresh carb (either rebuilt or new).

I recommend the Holley p/n 0-7448 carb (with manual choke) or the Holley p/n 0-80350 (with electric choke) as a replacement for your original Holley p/n 2245 carb.
The Holley 0-80350 would be my preference.

 

[mbiver]

Thanks again. Thought I'd be smart and take your advice. Pulled the tank and hoses. Got a poly tank and related odds and ends on order from you now. Fuel neck filler looks decent but did have rust inside the bottom of the neck so took it to a local guy who cleans them out and coats them with fuel tank liner. I'd like to try and rebuild the carb, for now. Both as a learning experience and to try and keep it stock. But I'm not married to the thing or to keeping it totally stock, so if I can't get it just right, I'll definitely take your advice on the new carb as well. Since I have the tank off, thought I'd fix the wiring a little. Some of the wires to the taillights were literally falling apart and exposed. Others just cut from rubbing on the body. I'll start a new thread for that in the electrical section.

 

[mbiver]

Got my 2245 carb all cleaned up and rebuilt. Does anyone know how many pounds of torque to use when mounting it back on the engine? I didn’t see it in the service manual. Thanks!

 

[Scoutboy74]

Not many. I would be thinking more in terms of inches rather than pounds. Use an "educated elbow" method. Snug, but not too tight. You don't want to warp it or break it.

 

[mbiver]

Thanks, @Scoutboy74. I just hand tightened and tried to be careful. Fired her up and no leaks at the base...Was a leak at the fuel inlet where I put an elbow adapter. Just had to tighten it, though. She runs A LOT better. Still not 100% but at least it will sit and idle without dying. The power valve piston was frozen...couldn't even turn it with a pliers (I was being very careful and also used a rag so I didn't scratch it). I dunked it in a can of carburetor cleaner for about a half hour and sprayed some more gumout down the vacuum port leading to it and then very very gently tapped straight down on the piston with the plastic end of my screwdriver...totally freed up. Power Valve had thick gunk underneath it as well...very messy. Anyway, thanks again!