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Old 14-02-2020, 06:21   #1
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Painting surface rust on marine diesel

I have some surface rust on my universal m25 marine diesel as well as large sections of peeling paint. My question is, what is the best paint to stop the rust, AND can I paint the motor without removing it from the engine compartment?? The engine is in a Catalina 30 so its kind of tight quarters in the engine compartment... see attached pics. Thanks!
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Old 14-02-2020, 06:54   #2
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Re: Painting surface rust on marine diesel

Corroseal or similar rust converters (all acids; Corroseal leaves a varnish-like surface) will handle the rust. Yes, you can spray with high-temperature paint. It's readily available in spray cans.

Good luck with the project> I hope it becomes beautiful rather than an eye sore.
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Old 14-02-2020, 06:59   #3
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Re: Painting surface rust on marine diesel

Here's Corroseal.

https://www.amazon.com/Corroseal-Wat...1688613&sr=8-4

Here's high temp paint in the silver that your M-25 once was:

https://www.amazon.com/Rust-Oleum-27...s%2C211&sr=8-4
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Old 14-02-2020, 07:26   #4
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Re: Painting surface rust on marine diesel

Quote:
Originally Posted by tkeithlu View Post
Here's Corroseal.

https://www.amazon.com/Corroseal-Wat...1688613&sr=8-4

Here's high temp paint in the silver that your M-25 once was:

https://www.amazon.com/Rust-Oleum-27...s%2C211&sr=8-4
One of the Customer Q&A's on Amazon for Corroseal says:

Quote:
Q: Can this be used on an engine block? i've got some rust on the outside of my mercruiser 4.3l v6
A: The product is not heat resistant.
Am I misunderstanding something?
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Old 14-02-2020, 09:02   #5
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Re: Painting surface rust on marine diesel

Ospho 605 followed by engine primer and enamel.
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Old 14-02-2020, 09:08   #6
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Re: Painting surface rust on marine diesel

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Originally Posted by Scubaseas View Post
Ospho 605 followed by engine primer and enamel.
Ospho (Phosphoric acid) is what we use on ships for all rust. look around and you will find it cheap.

M
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Old 14-02-2020, 09:10   #7
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Re: Painting surface rust on marine diesel

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Originally Posted by CaptTom View Post
One of the Customer Q&A's on Amazon for Corroseal says:



Am I misunderstanding something?
Yes I would not put it on an engine block, go to your nearest car accesories shop or google is your friend plenty of paints sold their for high temp applications, Engine blocksand brake disks .

As advised paint on the rust converter and then either spray or brush, on the paint afterwards , it does not need to be show quality just a good clean up and rust protected, have done my Perkins last season , and used a brush no problems
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Old 14-02-2020, 09:19   #8
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Re: Painting surface rust on marine diesel

Quote:
Originally Posted by Dpmmvc View Post
I have some surface rust on my universal m25 marine diesel as well as large sections of peeling paint. My question is, what is the best paint to stop the rust, AND can I paint the motor without removing it from the engine compartment?? The engine is in a Catalina 30 so it’s kind of tight quarters in the engine compartment... see attached pics. Thanks!
If you can a scaling gun will help a lot.
The biggest issue I see here, and correct me folks if I'm incorrect.
I'm VERY concerned about what you'll not be able to get to.
The picture with the black hose that is routed under your oil pan/sump shows an abundence of rust.
The pan on those diesels, are not as robust as say a Perkins or Atomic 4(gas)and will pinhole soon.
This potentially can seize that engine if not noticed soon enough.
It's really not that difficult to remove that engine and do it correctly.
Those will sit right in the salon or right on the bay of the engine and Are simple to remove.
You'll benefit from a good look at area and be able to probe it abit to inspect its condition.
If you think it solid enough, coat it with a converter and paint several coats, remember it's not coming out again for awhile.
It's a PITA for sure, and I respect your interest in taking care of that rust.
You may find a few Gremlins in there with all that rusty stuff but it's going to be well worth the work you'll be doing.
Whatever you decide, know that if you do this removal and inspect and clean ,repair and repaint, it's going to be to your advantage.
Professional opinion!
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Old 14-02-2020, 09:20   #9
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Re: Painting surface rust on marine diesel

I have used POR 15 very successfully on my Westerbeke Diesel.
POR15.com
After applying, followup with a good heat resistant primer and engine enamel.
JMHO
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Old 14-02-2020, 09:24   #10
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Re: Painting surface rust on marine diesel

Going to try this on my 30 year old but never used engine that has suffered rain damage. Hope I can find it here and that Ospho 605 comes with adequate instructions. Thanks guys!
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Old 14-02-2020, 09:32   #11
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Re: Painting surface rust on marine diesel

Another vote for POR-15, it loves to stick to rust. I have painted many engine blocks with it and it holds up fine and is way more durable than a standard engine enamel.

It's not UV resistant, so if you are going to using it other things that will get sunlight, you need a top coat of normal paint. I normally use the Rustoleum "professional" enamel from home depot.
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Old 14-02-2020, 10:11   #12
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Re: Painting surface rust on marine diesel

Another fan of POR15. Actually sticks best to lightly rusted surfaces. Prep is wire brush to knock off loose rust, clean the surface with degreaser, spray with POR rust prep, and paint. Paint surface is extremely hard and not a good base for 2nd coat without sanding when cured so apply 2nd coat or UV resistant topcoat before the paint is completely dry.

Painted the block on a Series Landrover rebuild with POR engine paint. Painted the head with Rustoleum. After 5 years the block was still shiny and paint intact. The head Rustoleum paint had turned chalky and was flaking off in places.
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Old 14-02-2020, 10:18   #13
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Re: Painting surface rust on marine diesel

Another por 15 fan. (the name is "Paint over Rust"!

I did mine and used their paint and Yanmar topcoat and it has been 4 years and it looks great!
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Old 14-02-2020, 14:29   #14
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Re: Painting surface rust on marine diesel

Quote:
Originally Posted by EqPierre View Post
Going to try this on my 30 year old but never used engine that has suffered rain damage. Hope I can find it here and that Ospho 605 comes with adequate instructions. Thanks guys!
I'm guessing you are in NZ with a Ganley so you will be able to find a rust converter with phosphoric acid in it at any of the big chain hardware places if you cant find Ospho.
Your engine with only rainwater damage should be easy enough to clean up & paint. I just used ordinary spray on zinc galv & clear lacquer top coat on our Yanmar but it's raw water cooled so doesnt get above 60oC
You may need engine enamel on a coolant engine, plenty of choice at car accessories chain store.
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Old 14-02-2020, 14:48   #15
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Re: Painting surface rust on marine diesel

Dp make sure you put some paper down around the engine so you catch all the drips and over spray. Nothing worse than seeing a bilge that has paint splashes in it?
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