drain block and manifold after each use?

[sabastianunf]

I just put a new exhaust manifold, riser and seals in my 120hp sterndrive mercruiser last year. Pretty pricey parts for my wallet. Since then I have flushed the motor and drained the block and manifold after each use. I was wondering if draining all the water out was neccessary and if I should add anything to the system after draining to prevent my new parts from rusting? Also I have been doing this while the motor is still slightly warm - not hot - thinking any water left inside would evaporate is this a good thought?

 

[Haut Medoc]

Re: drain block and manifold after each use?

I would think that leaving water in it would slow the corrosion.....
Especially the manifold & riser becaus they are not the same steel as the block....
Provided said water was fresh water.....
I'm curious to see what others think about this.....

 

[ziggy]

Re: drain block and manifold after each use?

i think it takes air + the wet metal to make the rust. if it's covered with water. it wont rust as fast. to me it's kinda like winterizen with antifreeze or air. the air promotes the rust inside the block. while anitreeze has rust inhibitors in it. water would be somewhere inbetween i'd think, the point being that it doesn't allow the air to get to the wet inside surface of the block....that's my guess......

 

[sabastianunf]

Re: drain block and manifold after each use?

Ever leave a steel frying pan submerged in water? it still rusts that's why I have been draining it. Still wondering what everyone thinks and if there are any manufacturer reccomendations on this?

 

[f_inscreenname]

Re: drain block and manifold after each use?

I think it is flush only or it would be easier to drain a block from the factory but I winterize by draining only. So what do I know?

 

[sabastianunf]

Re: drain block and manifold after each use?

my block is actually very easy to drain - it has a petcock valve easily accessible. It is actually harder to drain the manifold - I actually have to remove a small brass bolt but have been considering putting a petcock on it as well.

 

[I/O WALDO]

Re: drain block and manifold after each use?

"anitreeze has rust inhibitors in it " Pink,"RV" antifreeze has no corrosion inhibitors in it!

 

[WillyBWright]

Re: drain block and manifold after each use?

Oxygen is the enemy. Damp iron exposed to air rusts much faster than submerged iron. Water contains some dissolved oxygen, but not nearly much as the same amount of air. Draining it would accelerate the rusting process tremendously. You can see this on steel-posted piers. The worst rusting is at and a bit above water level where it is contstantly wet/dry/wet/dry...

True about RV antifreeze containing no rust inhibitors. Many are toxic. Pink RV IS a rust inhibitor. It doesn't contain oxygen and prevents oxygen from contacting the metal it covers. So for full rust protection, you'd have to completely fill the block and manifolds with pink RV.

But even just puddling some into the block and manifolds goes a long way to slowing the process. It'll absorb condensation and prevent that moisture from contributing to the rusting. For those that drain-only for storage, leave everything open till recommissiioning. That too will reduce the moisture in the block and manifolds.

 

[whywhyzed]

Re: drain block and manifold after each use?

the cast iron kettle that sits on my wood stove will rust inside the most right where the waterline is, where the air is hitting it. Huge globs of rust actually.
Whereas under the water it only gets a slimy film of rust.
Based on this, I would not drain it.
I just sold a new Merc 120 manifold on eBay for $110...yeesh, where were you and your fat wallet? haha