the thermostat flange (bolts on top of the thermostat) is rusty on the inside. should I use a rust reformer? or should I forget about it because they never rust through? The water pump housing is thick *** cast iron so it should take another geologic era to rust through, but the flange neck is thin.

 

The one on my old GSL-SE rusted through and I didn't know until I took it off. It worked fine because it was inside the hose that was clamped. I would get another one.

 

Fairly common on Sa,FBs,even when 8-10 years old. Back then i attributed it to lack of cooling system maintenance,judging by condition of drained coolant. Seen several cars in last couple years that although not rusted through,had lots of chunks of rust growing inside t stat housing.

 

So they do rust from the inside out

I got a spare flange. Should I por-15 the insides? primer it, and paint it? and then replace it?

 

It sounds like a good idea,i would have concerns about paint coming off and traveling in cooling system being exposed to coolant and heating and cooling cycles. FWIW i've had my current car almost 30 years. @6 years ago i replaced water pump,fan clutch,thermostat. I'm pretty good about changing coolant every 2 years or so. My t-stat housing had some small rust chunks forming on inside,i scraped them off followed by a small wire brush to inspect housing. It's still on my car,i believe i'll be long gone before it rusts out.
If you have a decent used one,put it on,change coolant every 2-3 years,it'll be fine.

 

I powder coat mine. The powder is baked at 400 degrees so it won't come off.

 

What's your powdercoating setup?

 

You will want to remove as much of the rust as possible by sandblasting the housing. This is a very effective method but if the metal is too thin, you will turn it into swiss cheese. If the inside of the neck is not rusty and full of scale, you can surface the flange and then use a wire wheel on the outside of the housing to clean it to bare metal and prep it and paint it. If it's too nasty then it should be replaced.

 

Last I checked you can get a replacement from Atkins Rotary.

 

Unfortunately, I believe you can't buy a thermostat housing for a GSLSE just the 12a one you buy new...

 

I was thinking of wire brushing the inside, and using naval jelly. It is supposed to form an iron phosphate impenetrable to water barrier. And do the good guy stuff to the outside with remove all the rust, then primer and paint.

and not paint the inside.........or maybe use high temp paint?

 

VHT engine paint is supposed to be good to 550 degrees. Brake caliper paint another option,good to over@1500 degrees. Either of these you could use to paint inside and outside.

 

Nothing fancy. I have a couple of Eastwood dual-voltage guns. I like to keep one gun for just clear and the other for color changes. A spray booth with a dust collector, and an old oven. I blast everything in a cheap Harbor Freight blaster and use Black Beauty (coal slag from Tractor Supply). I did upgrade the blaster with a foot pedal and use a Clemco gun with carbon insert. I did build an oven extension. It just sits on the open door to extend the oven when doing big parts. I need to build a better oven.

 

You could always use POR15 to paint the housing and seal any remaining areas of question. You wont be able to get all the rust so this would be a good option.