My 3rd thermostat gasket is leaking, I'm beginning to think the waterneck is warped or bent. I was looking at chrome waternecks, but I am wondering what the hole in the housing is for. Right now it's plugged, but what went in it?

Thanks

I would REALLY like to see a picture of this engine (68 390) in stock condition, in the truck, so I could figure some of this out for myself....

 

The hole is for a thermal vacuum switch (TVS). I can't remember if yours uses one or not (stupid memory)! It's not important anyway, basically it connects manifold vacuum to the dizzy when the motor gets above 230 degrees. This speeds up the idle rpms to help cool things down.

If it's leaking at the flange it could be warped or corroded on the gasket surface. Check it with a straight edge. If it's just warped you can take a file and flatten it out. Check the manifold too.

BTW the chrome ones like to warp.

Barry

 

Thanks Barry.

Was that switch used as part of factory air? When I look at the parts stores, some show these as being for factory air? I don't have air, btw, factory or otherwise.

 

Yes that’s usually the case, the a/c raises temperatures in the engine compartment but I’ve also seen them used on engines without a/c. I'll have to dig up some vacuum diagrams to know for sure.

Barry

 

Barry, I thought those were called ported vacuum switches. They project into the water flow and when the wax pellet inside heats up, it pushes a rod that closes off the vacuum ports. What I've seen labelled a TVS (mounted on the top left rear of the manifold) was in connection with the dist. vacuum control on the early seventies trucks. These worked in conjunction with a thermostat mounted below the driver's side interior light switch on the door frame. I've seen these used with or without air.

 

You are absolutely correct mk, it's the ported vacuum switch. If you really want to get technical, Ford Tech Ops calls it the Distributor Vacuum Control Valve or DVCV. I was just getting lazy with the lingo and went with the generic name.

The system you described was called a couple of things depending on the year. I think there was Disc-O-Vac, Transmission Regulated Spark (TRS), and others, would have to dig that up too. It used a speed sensor on the speedo cable or a switch in the trans to control when the distributor gets vacuum.

If I'm reading this right, it says that all IMCO engines would have a PVS system. It says it's needed because these engines will run hotter due to the lean calibration. Makes sense, Thermactor engines run richer to help with the afterburn.

Barry

 

Use a cast iron housing, not aluminum or crome. I put white grease on the gasket. It will come apart a lot easier.

 

>You are absolutely correct mk, it's the ported vacuum
>switch. If you really want to get technical, Ford Tech Ops
>calls it the Distributor Vacuum Control Valve or DVCV. I
>was just getting lazy with the lingo and went with the
>generic name.
>
>The system you described was called a couple of things
>depending on the year. I think there was Disc-O-Vac,
>Transmission Regulated Spark (TRS), and others, would have
>to dig that up too. It used a speed sensor on the speedo
>cable or a switch in the trans to control when the
>distributor gets vacuum.
>
>If I'm reading this right, it says that all IMCO engines
>would have a PVS system. It says it's needed because these
>engines will run hotter due to the lean calibration. Makes
>sense, Thermactor engines run richer to help with the
>afterburn.
>
>Barry


Ok guys, I'm reading in my shop manual about something called a Distributor Vacuum Advance Control Valve. Unfortunatley there are no pics of it. Here is what the manual says,
"On some engines, a distributor vacuum advance control valve (deceleration valve) is incorporated in the distributor vacuum system to provide additional control of the ignition timing. This device is used in conjunction with the dual-diaphragm vacuum advance unit. Normally, the outer (advanvce) diaphragm is connected to a vacuum port on the carburetor. During deceleration periods when intake manifold rises above a specific value, the deceleration valve closes off the the carburetor vacuum and provides direct intake manifold vacuum to the distributor outer diaphragm. This permits maximum ignition timing advance to prevent afterburning or popping in the engine exhaust system. When the vehicle slows down, and the engine is operated at idle, the deceleration valve shuts off the intake manifold vacuum and opens the carburetor vacuum to the distributor."

Is this what we are taking about? How does this integrate with the water temp? I have an IMCO engine with the dual diaphragm advance system, the outer diaphragm is indeed connected to the carburetor advance, and the inner diaphragm is connected to the intake manifold vacuum, but there is no switch between them. Or are we talking about two different things here? (PVS and DVCV) Ok, if all IMCO engines need the PVS system, how do I tell if I have it or if the PO removed it? I have a Pertronix Ignitor module on the way and I want this engine to run smooth as glass. I wonder if I need to get the PVS set back up if it's missing?

Confused....

 

The Distributor Vacuum Advance Control Valve or deceleration valve is a totally different smog device. It looks like a round thing with three hose nipples and a spring on the end (boy that was a good description). Believe me you don't want one of those, you let off the gas and it feels like it's still going. This system would have tied into the PVS system. They sure liked to jack around with the vacuum advance to pass smog.

I really don't think you need the PVS system either. Does it ever overheat while idling? I'd just run it the way you have it, nice and simple. Richen the idle a little and advance the initial timing and IMCO is practically gone.

Barry

 

I don't think it overheats at idle, I haven't driven it that much since I bought it. It needs suspension work, a new exhaust system, and tuned up before it will be any fun at all to drive. It sure is nice to be able to ask questions and get intelligent answers.

When I replaced the thermostat (it was 180 degree) with the 195 degree. I noticed that the heat gauge needle settled at about 3/4 of the way to hot, which kind of concerned me. But then again, I put 5w30 in when I changed the oil, I'm probably going to go with 10w40 to try and keep it just a tad cooler.

Thanks

 

Please let us know if changing to 10-40 oil lowers the temperature gauge reading.

 

Use a razor blade and acetone to clean the intake, use sandpaper on a flat surface and clean the mating surface on the housing. Then use a new gasket and Permatex non hardening sealer. I stick the thermostat in the housing using a couple of small dabs of silicone. This will keep it from sliding down and causing a leak. Use new bolts and lock washers and just tighten it with a short grip on the wrench. In other words just tighten it snug. If it leaks snug it up a bit more. A 190 degree thermostat is good. Don't worry about the gauge it sounds about right and they are not totally accurate anyway.
William in Atlanta

 

>Use a razor blade and acetone to clean the intake, use
>sandpaper on a flat surface and clean the mating surface on
>the housing. Then use a new gasket and Permatex non
>hardening sealer. I stick the thermostat in the housing
>using a couple of small dabs of silicone. This will keep it
>from sliding down and causing a leak. Use new bolts and
>lock washers and just tighten it with a short grip on the
>wrench. In other words just tighten it snug. If it leaks
>snug it up a bit more. A 190 degree thermostat is good.
>Don't worry about the gauge it sounds about right and they
>are not totally accurate anyway.
>William in Atlanta

Hi William,

I did put a thin coat of permatex on this gasket, I will put a couple dabs on the thermostat housing to stick down the thermostat. I will be tightening to spec with my torque wrench this time instead of just winging it. I may have over-tightened....

Thanks

 

More than likely the housing is cracked. You can get a new housing from autozone for about 10 bucks. If you look real hard you may se it. I installed mine about 3 times before discovering mine was cracked.