Technical flathead pressure cap and thermostat

If you are concerned about rust and issues with using aluminum heads, I recommend the following products.

First, if running water and not antifreeze, use purified water that was purified by reverse osmosis. This type of water is even more impurity free than distilled. If you poke around the tech data on this sight, they explain why to use purified water over distilled. Look here: https://www.norosion.com/tech_coolant.htm

Use these two products by No-Rosion.

Once a year or every other year, flush the system out with this. Cleans it out and leaves an anti-rust coating behind.
https://www.norosion.com/norosionflush.htm

Use this when running water or antifreeze.
https://www.norosion.com/norosioncoolant.htm

I've been using only water for about 4 years now and the water remains clear and without rust, so I know it is working.

 

You dont need any thermostat. I have used all my flathead engines Alum. washers in upper hoses. If original pumps ( for 2 v-belt) washer hole can be bigger for example 11/16". If new speedway etc. waterpumps, those are too efficient. Water is flow too fast, makes easily pressure.... 9/16 or 5/8" holes in alum.washers are OK.

use 4psi - 7psi cap. You dont need higher. Originally no pressure at all (1932, maybe 1934 too).
Enought advance in engine, it keep engine cooler. Now a days gasoline is enough good and mostly flatheads are lowcompression engines.

New engine, every time when start up when engine is cold --> remove spark plugs and start engine. You can see if it push water out. Thats good control that there is not "water compression" in cylinder. Easily long thin rod is flattened if there is liquid in cylinder....

Of course retighten headbolts/nuts, intakebolts....

Aulis