i have a 160 t stat in my 350 vortec that has about 150k on it.
the heat barely works in the freezing cold days.i like it to run cool in the summer so I just bear with the low heat in the winter.
I had problems with the temp being erratic when I tried to put a 185 in.lately ive had to add coolant about every 2 weeks.when the rad is down the coolant looks kinda foamy.there is nothing in the oil and I don't see or smell any antifreeze from the exhaust.i bought one of those rad testers with the blue fluid in it and just ran out to check it.the rad was way down but it was foamy so I thought it would definitely register the exhaust gas even if the rad was way low.it came out negative.the fluid never changed color at all.
now im at a total loss as to whrere the coolant is going.any ideas?there are no visable leaks but I did have to put a ball valve this winter where the vac heater control valve is because it was dripping under pressure once the car warmed up.i bought a new one and it did the same thing.somehow I guess it building too much pressure in the system but I put a hand pump checker on the rad and it was leaking at about 5 lbs under what it was rated.

Head gasket is leaking.

Vortecs are known for cracking between the center 2 exhaust seats. When its hot that crack is opening up and using coolant.

I THOUGHT thats what was going on with my truck until I pressurized the system and water literally poured out the weep hole of the water pump it never leaked out in the driveway at all.

wouldn't the rad test with the blue fluid show the headgasket leak?

Not if its leaking into the cylinder.

is there someway I could make sure that's where the leak is before tearing it down?
thanks guys!

pressure test

I had a coolant leak recently and could never find the antifreeze under the car in my garage. Turns out it was my radiator cap so check that. Especially if it's the original "MADE IN ENGLAND" one.

If it's leaking in to the cylinder don't leave it sit for more than a day or two without running or it might hydrolock the next time it turns over. Did that on an old express van at work and blew the gasket the rest of the way.

Sounds like you have several problems as a 160 T stant is pretty cold and causes extra engine wear. A healthy SBC should be able to run a 195 with no overheating problems. Try cracking the oil drain plug and let a little out, if there is a internal antifreeze leak, it will come out of the oil drain plug first.

Should you really have pressure problems with a pressure relief radiator cap that releases the excess into the expansion tank?

buick is right 195ish is best. don't be afraid to go hot. The pressure gets you 20ish degrees over boiling and the anti freeze is another 20ish.
Basically you can be around 250 with 50/50 antifreeze/water before it blows up.

And when a cylinder fills with coolant it's possible to hydrolock, which may bend a connecting rod when the engine is cranked. If enough coolant is in the cylinder that is coming up on it's compression stroke the engine may lock, stop turning. This shock may bend a rod.

If you pull all the plugs compare then to each other. If one looks nice and clean that is your cyl which has a leak. If you have a bore scope inspection the tops of the pistons will show which cyl is leaking.

Common SBC leaks, water pump seal, water pump gaskets, heater core, rad core, hose clamps area, intake gaskets at the front and rear, check all these areas before condemning the head gaskets. As mentioned some heads are prone to cracking, may cause leaks.

The Vortec 4.3 in my Astro I've done head gaskets twice, same place #5 back and lower corner, that would be #7 on a V8. The first time between the coolant passage and cyl, the second time a head bolt and cyl. New head bolts went in both times. The engine now has 255K on it, and going strong.
Bob

The foaming alludes to head gasket but just for grins check the carpet on the passenger side front and back. Could just be a heater core leak...

heater core is just a year old.i did the test with the blue fluid and it came up neg.
doesn't this say that the foaming is definitely not from the head gasket or exhaust gasses?

If the head or the head gasket has a small (say 1/4 inch) crack or tear the coolant loss is going to be exactly as you described in your opening post. The fact that you state that coolant is foamy is a clear indication of this.

Now if you have a borescope you could simply run the car until it comes up to temp, shut it off and let it cool down for several hours. Then pull the spark plug on the suspected cylinder or cylinders and pop the borescope in and examine the cylinder. Even a tiny leak from a cracked head or the beginnings of a blown head gasket will leave tell tale signs of fresh coolant on top of the piston or pooling up along the cylinder wall.

If you have a laptop you can get a USB borescope pretty cheap these days.

The coolant gas test is OK when you have a big coolant loss, but they're not so reliable with the small amount of coolant loss as you describe.

Id say check for intake gasket leaks.....

First generation SBC intake gaskets leaking will surely show up in the oil.

Not always, we had a mystery coolant loss on our old suburban that was a split in the gasket between the coolant passage and an intake runner. Small enough that we didn't smell it, but enough to repeatedly need to refill every week or so. No signs in the oil, no drips. Didn't have a borescope, but finally checked the plugs and one was MUCH cleaner than the others.

3 degrees of temperature rise for every pound of pressure above atmospheric!