Here it goes, I'm building a heat exchanger for my 460 in a jetboat. I'm building a flat plat heat exchanger so I've kinda run into a design flaw when it comes to pressurizing the system. I could completely eliminate this problem by just using a vented recovery tank with no radiator cap. This would in effect drop the pressure down to almost zero psi in the cooling system outside of the engine. The engine will still develope some sort of psi as the water pump pushes against the T-stat restriction. So if I'm thinking right I'll still have some kind of pressure inside the engine, but the rest of the system will approach zero psi.

It's my understanding that there are two reasons why cooling systems are pressurized. First to raise the boiling point of the coolant. Second to contact the coolant better to the hottest areas of the motor (push out small air and steam pockets I suppose). Am I missing something?

There is no way for me to know how effective my heat exchanger will be until I actually run the SOB, but I'm pretty confident that it will have no problem cooling the beast down. But there will be several instances where if I were to run a pressurized cooling system I'll risk damaging the heat exchanger because the raw water side will be at zero psi when the engine is off.

If anyone can add some insite I'd greatly appreciate it, because for some dumb reason I think I'm missing something.

Thanks, Nick

 

By having the cooling system pressurized you're also helping provide sufficient suction pressure for the water pump. If you run your coolant system vented to atmosphere I would think it would cause the water pump to cavitate, meaning it's just churning the coolant now, not pumping anymore. I would find a way to make it work pressurized. I also agree with the 2 other reasons you stated for having the cooling system prassurized.

 

When using Evans coolant it is recommended to drill a 1/8 inch hole in the radiator cap to eliminate pressurizing the system and to allow any water in the system to bleed off as it boils. If the system is full of coolant and circulating, the coolant will reach all areas of the engine. You don't need a pressurized system for the water pump to operate, it creates its own suction for intaking coolant. Pressurizing will raise the boiling point of coolant but that is the only reason for presurizing. As a matter of fact if you can get away from pressurizing hoses, water pump, all cooling system parts will last longer.

 

Thank you for the tip, this is just what I was hoping for. It's gonna be a bit on the expensive side for coolant, but well worth it. I just read all the stuff on the Evans website and I think my problem is solved! I really do appreciate the input jtmerritt. To be honest, I didn't even think of a different type of coolant. Oh well, at least I'm not too proud to ask right?! Thanks again, I'll keep you guys posted on my progress.

Nick