To Primer or Not to Primer?

[BigEasy]

Google NAPA know-how on how to paint an engine. Sorry, can't seem to figure out how to copy and paste the link using my phone.

No primer is the bottom line. You want as thin of a coat of paint as possible according to that source.
dj

Is that guidance for automotive engines? Marine application is quite different, especially in a salt water atmosphere/environment. When I was in the Navy, corrosion control was a big deal. Everyone associated with aircraft maintenance had to have corrosion control training. We used primer on everything aircraft related, engines included. I have been a firm believer in primers since that time. If I had to repaint my Yanmar, I would use primer regardless of what the factory does. Those engines are used in tractors, pumps, and other non marine applications; if they don’t use primers, it could be due to cost saving opportunities.

 

[dLj]

The statement was because of temperature. Temperature is a major consideration when painting engines.

As they say, it's your boat, do what you want.

dj

 

[dlochner]

The statement was because of temperature. Temperature is a major consideration when painting engines.

As they say, it's your boat, do what you want.

dj

Except for the ares immediately adjacent to the exhaust manifold, the exterior of the engine should never have a higher temperature than the cooling water, typically 160 to 180°

 

[dLj]

So I'm now at a computer - here's the link to the NAPA how-to:

How To Paint an Engine » NAPA Know How Blog

So you think you know how to paint an engine? Sure you can just spray bomb it, but with a few extra steps you can have a great finish that really lasts.

knowhow.napaonline.com

The main points they seem to be making are; you have to have excellent surface preparation (we certainly all agree with that), the coating must be complete, i.e no holes or incomplete coverage (in painting language that means no holidays, we also all agree with this), and the coating must be as thin as possible.

This last point seems to be in disagreement but not for thickness; rather adhesion, corrosion resistance and coating system longevity. Tell me if that's incorrect.

Reading between the lines a bit of the NAPA page, I see they are likely using epoxy paints or some other two part paint, all of which have a very low permeability. That means the coating does not allow water to go through them. A thin layer of epoxy paint will have better corrosion resistance that a somewhat thicker layer of a different type of paint. The modern paints can be formulated to have excellent adhesion, corrosion resistance and, if applied correctly, excellent longevity.

So for the OP - if the paint being used is meant to be applied without primer, use it without primer. While the use of primers and thicker paint systems may well have been needed with some of the older paint systems, I feel the modern paints are going to greatly out-perform those older paints systems if used correctly. As I know nothing of what the paint is the OP is using, I can't comment on that paint, only that you need good surface preparation and follow the instructions.

dj

 

[sailnoproblem]

If you clean the engine properly and it is degreased just use the paint in thin multiple coats. When I painted mine, the engine was sand blasted and degreased. It still looks good after 8 years.
Universal high temp engine paint is what I used on my Atomic 4. I did not use primer.