Painting radiator & coolant pipes

[motorazr]

Besides the goofy pumpkin turn signals, the other thing about my 2015 FZ-07 that has always bugged me is the unfinished-looking silver radiator. Black radiators look better to me but anodizing costs extra (US$100-150 if you get it done) and the FZ07/MT07 has always been a budget bike. I finally undertook to change my coolant and so used the opportunity to paint my radiator black.

Taking the extra step of removing the coolant pipes, I found a fair bit of corrosion under the hoses and some rusting inside both pipes (partly scrubbed out with a bottle brush). I wanted to primer and paint the pipes black too and found that just touching them with sandpaper instantly scratches through the green oxide coating over the mild steel. Another budget part which owners have complained about for years.

Tips; 1) The day-old paint is pretty soft so you’ll need to be extremely careful and have a black sharpie ready to cover any dings. 2) Mount the top left radiator hose to the radiator BEFORE it gets near the bike (the other end easily attaches with a screw-type hose clamp). 3) If your reservoir tank is stained, soak it overnight in an Oyxclean solution (sodium percarbonate). 4) Make certain that no wires or hoses are touching the exhaust headers before starting the engine (seems obvious but, doh!, it’s not).

[motorazr]

BTW; Painting a radiator core isn’t great for cooling. I primered and painted AROUND the core (plus stripped and repainted the aftermarket radiator guard). 

[Triple Jim]

21 minutes ago, motorazr said:

BTW; Painting a radiator core isn’t great for cooling. I primered and painted AROUND the core (plus stripped and repainted the aftermarket radiator guard). 

Many years ago NASA proved that if the paint is thin it can actually help cooling by making a smoother surface to promote laminar flow.  Figure 4 on the 5th page of the .pdf file (page 655) is a graph of cooling vs. paint thickness as measured in their test.

http://lakeserv.net/kaw/files/nasa_paint_test_p5.pdf

Edited September 12, 2021 by Triple Jim

[motorazr]

Thanks for sharing. That’s an interesting pre-WWII study but it relates to finned cylinders in air-cooled radial engines (sand cast aluminum or iron).
 

Applying insulating paint to razor-thin and very smooth aluminum ribbons within a radiator core is always going to negatively impact cooling efficiency (convective heat transfer rather than heat radiation). On the other hand, a light application of spray paint from an angle on the front side of a radiator may not make a noticeable difference in overall cooling.

Edited September 12, 2021 by motorazr

[Triple Jim]

Yes, I suppose the fins are already pretty smooth.  The graph of paint thickness vs. heat transfer does show that as long as the paint is down in the range of a couple thousandths of an inch thick it really doesn't have much effect.  I'm sure that the radiator guard I put on my MT reduces available cooling a lot more than that.

[klx678]

Probably temp differences are irrelevant.  Black vs alumimum is more about rider preference.  To each their own.

The coolant line are another story.  I wonder what it would cost to get a new set (edit  $100! ouch) and have them ceramic coated.  They would be impervious to rust and chipping inside and out.  The coating could be painted or have a color coat layer of ceramic over the silver...  may gave to look into that.   

Edited September 12, 2021 by klx678

[Pursuvant]

6 hours ago, motorazr said:

Painting a radiator core isn’t great for cooling

My experience was

On fins, 2 mist coats of high-temp-primer + 3 mist coats of hi-temp black during the off season last year.

No noticable change in cooling behavior, Houston, TX. I expected some change, but the bike just eats it and spits out this generalization. YMMV