Diesel exhaust gas pipe temperature

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Jun 14, 2011
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Denmark, Europe
Hi, I want to paint my entire exhaust gas system from the manifold to the rear/end/tail pipe. I have bought the POR15 heat resistant paint for this job, however this product needs to be baked in an oven or just experience the heat from a running engine. My problem is, that for naturally aspirated diesel engines, I believe the tail pipe never gets really hot and thus the baking process will never complete. Thus in this area it would be better to use a normal paint which does not require the baking process. I have bought an infrared thermometer to determine the temperatures all the way from the manifold to the tail pipe ... however it seems that the thermometer has trouble showing the correct temperature ... I really dont know why. Anyhow, could anyone elaborate on the diesel temperatures along the pipe system? Thanks, Lucas
 
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Oct 1, 2010
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I don't know what the metal temperature on the exhaust pipes would be on a naturally aspirated diesel. I agree with Charlie1935 that exhaust temperature at max power will be in the range of 1250F, but the manifold and piping metal temperatures will not be the same. Also, the further down the exhaust system you go, the lower the metal temperatures will be. I think that the muffler would be a major dividing point as far as temperature is concerned. Hotter before the muffler, colder after. I guess that the manifold and piping before the muffler would be in the range of 450-900F. After the muffler, 200-300F.
 
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Dec 11, 2013
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I painted the manifold and downpipe in VHT, partly for aesthetics and partly to stop rust forming. The manifold is cast iron and the downpipe is mild steel. At first I panicked when I smelled the solvents coming out of the paint, thought I'd set the car on fire! The downpipe looks just as good as it did when I painted and fitted it, but the paint on the manifold (literally) couldn't take the heat. The label on the can said it would withstand prolonged contact with surfaces upto 300c which I thought would be enough, but either the paint is faulty or my exhaust runs TOO DARNED HOT!
 
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Not too sure of the relevance of this comment, but; As EGT drops, so does gas flow velocity. I don't know enough about your particular setup to comment on scavenging but ideally you'd want to keep the temp as high as possible as long as possible.
 
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Aug 12, 2002
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Originally Posted By: LucasDK
Hi, I have bought an infrared thermometer to determine the temperatures all the way from the manifold to the tail pipe ... however it seems that the thermometer has trouble showing the correct temperature ... I really dont know why.
it's because your ir thermometer needs a surface with high emissivity in order to get a relatively accurate reading. you're pointing the laser at either stainless or aluminum coated steel, which has a very low emissivity thus you are measuring a reflected temperature. you need to paint an area that you want to measure with some black paint or black primer, which will have a high E. or get a multimeter with a J or K thermocouple and measure it conductively.
 
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Jan 5, 2008
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Central Iowa
Originally Posted By: Olas
Not too sure of the relevance of this comment, but; As EGT drops, so does gas flow velocity. I don't know enough about your particular setup to comment on scavenging but ideally you'd want to keep the temp as high as possible as long as possible.
Yepper. That is why I have a ported, polished, ceramic coated manifold on my Detroit Series 60 12.7L, with a Borg Warner 171702 turbo that has a blanket on it, and about 3 feet of heat wrap on the flange pipe off the turbo. With final exit thru a Walker Megaflow muffler. While keeping exhaust temps up along the flow will keep things moving better, it also has an effect of actually keeping EGTs at a more moderate level coming out of the manifold because the exhaust flow is not being restricted. Nonetheless, my Detroit is a solid performer that walks hills under loads right along with larger Cats and Cummins engines, and get fuel economy numbers that makes my bank account very happy.
 
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OP, Regardless of your EGT temps, for the rear most portion of the exhaust system I would use a heat gun to bake the paint onto the system. Use cardboard wrapped in aluminum foil, or some other heat shielding, to protect any lines or rubber suspension bushings that are in close proximity to the piping while your baking.
 
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