Why is this rusty?

[huntndakota]

I got this boat last year but have not had it on the water and only ran it for 1-2 minutes on muffs last year. I was going to do a compression test to check for a head gasket leak as i saw a little white smoke in the exhaust. Decided before i did test to check out cooling system (manifold, resivoir, flapper, and elbow). I was wondering why i had a little surface rust inside the the holes (i guess ehaust ports) beside the spark plugs? The boat sat for the last 2 yrs. and the majority of its life it only has 150 hrs on the motor. Motor is an 88' mercruiser140, 165hp

 

[Bondo]

Re: Why is this rusty?

Ayuh,... Your picture is too small to see,..
But,..
Rust comes from exposure to Water...

 

[huntndakota]

Re: Why is this rusty?

I know it comes from water. I looked at the manifold and it looked okay going to test it with acetone tonight . Reservior looks okay anyway to test it? Could one of the cause a little smoke? Closed cooling system coolant and water could mix and get into valves cause smoke and rust in side? Manifold isn't rusty inside. Could i test coolant leak by putting clear tube between reservior and holding bottle? A buddy said make tube a u shape with a couple inches of coolant in the middle if air bubbless contiune after warm up i have a leak. He says its the most sensitive way to test it.

 

[robert graham]

Re: Why is this rusty?

Cast iron cylinder head, no problem, that's what they do.

 

[Don S]

Re: Why is this rusty?

Motor is an 88' mercruiser140, 165hp

Hate to be the one to tell you, but you do not have a 3.0L aka 140. The 165 is a renamed 470 3.7L engine Made by Mercruiser.
The exhaust manifold is cooled by antifreeze. The only things that see raw water is the heat exchanger, the voltage regulator, and the elbow coming off the top of the manifold.
I would say you are getting water from a leaky hatch cover. and from the looks of it, you are around salt water.