Painting engine block?

I was considering painting my engine black, using engine paint (1500 temp) but a friend had made a comment to me about the motor possibly not getting cooled enough if I do this??? I can see peeled black paint on the lower half of my block (must have been black at one point) but not the upper half. Will painting the block really hurt the cooling?? I saw a article some where that sounded awesome and would like to try, about painting the block, then running a drimmel with a fine sander wheel over the edge of the fines to have the "silver" edges shine thru giving a great accent to the engine, but now I am hesitant to try after hearing the cooling issue, any helpful comments would be appreciated.
(82 XJ 750 Maxim by the way)

 

Actually, I'm pretty sure that black paint on an engine block will HELP the cooling. It's not the same as absorption of heat, where white reflects and black absorbs heat. In the radiation of heat from a hot source to the atmosphere, black should accelerate the dispersal of heat. Or something like that...

 

True about the color black, but the paint itself might actually insulate the engine block, thus slowing heat transfer. I might be way off, but it's something to consider.

 

I dont think it should create too much of a problem, providing you apply a light coat, however I still wouldnt do it too my bike...

 

The Midnight Maxim's all had black engines from the factory, so it can't be that huge of a difference. I know a lot of air-cooled VW guys that won't paint their blocks, there's probably some truth to it, but for a street driven bike that will probably only see occasional abuse, I wouldn't worry about it.

 

Painting the surface (even with a flat finish) will diminish the cooling capacity of the surface area as Jason mentioned. This loss of surface area can be off-set with the addition of an auxilary oil cooler (not too expensive and worth the investment if you ask me) if you are worried about it. With air/oil cooled engines, any cooling you can pick up is usually a very good idea (Antarctica being an obvious exception). I blasted and painted my engine this past year and have added the cooler. I haven't got the engine back in the bike but I will be installing an oil temperature gauge to be able to follow what is going on inside and will report back to you all. I would do it but add the cooler, it looks nice.

 

thanks all, once again good advise, the paint coating the engine was my concern. I did notice a couple engine blocks that where painted last night at a get together, most where liquid cooled, but did see a few that were air cooled, no one said they had issues but still would like to hear more thoughts, or any other options to enhance the look.

 

The minute thickness of the paint will not affect the cooling of the engine. I painted mine with flat high heat paint and it didn't make one bit of difference. There is some change in emissivity, which affects radiation heat transfer, but if anything, it is probably better for flat black paint than oxidized aluminum.

 

Agree with your point on emissivness, well taken. A painted surface is infinitely more useful for heat emission than corrosion. The effect of heat transmission of the paint is there, however small it may be, but it is there. One might say it is neglegible rather than non-existant. Point of view I guess. Besides, the painted surface will last longer and is easier to clean. Both benefits worth concidering.

 

aluminum has an emissivity of about 0.25, paint is usually around 0.9
that's a big difference and means a painted bike will run a lot cooler (provided the paint isn't stupidly thick to stop heat transfer)

 

I painted mine with a thin coat of black high-temp ceramic engine block paint. I have used an infrared thermometer on it several times before and after and notice no change whatsoever. As mentioned in previous posts, keep the coat of paint as thin as possible.


Robert, out of curiosity, where can I get information of the auxiliary air cooler? My neighbor has problems with his Suzuki running a tad hot.

 

I swiped mine off of ebay from a donor 83 turbo and a Brit 750. I looked up the physical dimentions of oil filter spin on plates in the JC Whitney catalog as they have a metric spin on adaptor that will work. I have no idea what to suggest for your buddies Suzuki but you are in luck. As I recall, most Suzuki's have spin on oil filters already so the adaptor plate for a cooler will be easy to score and install. Hook up with some appropriate size AN fittings and stainless lines and your golden (might cost a bit though, about $120 by my reckoning including the cost of the smallest air cooler, which if your lucky can be sourced at the wreckers). Oh yeah, the power steering cooler off of a more modern Ford would work nicely. TN ought to have scads of these and I'm sure you will find just what your looking for in a short time Bozo. Good luck on that one! Mike, your paint plug is just the kind if detail that makes these discussions worthwhile, keep it up!! Good thread all!

 

Thanks Robert. I'll get with him and see what we can come up with.

 

curious about the infrared thermometer, did you change the emissivity settings for the bare metal and then for the paint?
just wondering because most them use as a default something between 0.9 and 1 but aluminum is far from a black body
if you didn't change the emissivity settings for the metal it would give you a really off reading

 

LOL, being that I didn't even know there was a word called emissivity until today I would say not. However, if it has been off since I first took the readings, and I never changed anything on the thermometer, wouldn’t it have been consistently off? I mean, if it were always off say 20 degrees, would it matter if it were the same after I painted it as it was before? It may not be a true indicator of the specific temperature of aluminum, but it would be the same indicator of heat.

I really don't know much about metallurgy but the head was painted from the factory, I just removed the old paint and added new. So, in the case of the thermometer, I have always been aiming at a painted surface.

 

paint has an emissivity usually around 0.9 so if the surface was actually 100 degrees the radiative temp would be 90 degrees (if you had the emissivity on the thermometer set to 1)
aluminum has an emissivity of around 0.25 so if it was 100 degrees (and again you had the emissivity on the thermometer set to 1) then it would read as 25 degrees
so you'd get a reading of almost 4 times higher with the painted surface than the bare aluminum if you didn't properly adjust the emissivity on the instrument, most cheaper ones don't have an adjustment anyway and just have a default around 0.9 or 0.95
see all the stupid stuff you learn when you get a degree in geography? (and this isn't even getting into specific band emissivity or that the angle at which you hold the thermometer to the surface will affect the reading as it'll be looking at a different size area)

 

I was going to powder coat mine.

Decided against it due to cooling issues.

 

Wow, I'm glad I stuck with Marketing....

 

Okay can I or can I not paint the engine? And if it's safe to paint how many coats do I use? And thanks to Robert about the oil cooling.

 

Is there a way to clean the engine up so it looks new without painting it?