iam going to pressure test my headers in the spring,,,i want to know where iam at with this cmi headers (525 mercury marine headers),,,,will this pipe plug work,,,looking for inside diamater of headers at the collector,,,http://www.grainger.com/Grainger/CHE...ipe-Plug-1VNF7

You do not close off the end of the pipe to test them. You pressurize the water part of the headers with air and check for leaks.

i just checked mine last week,i did it with my water hose,35 psi of water,there should not be more than that in them.i hooked the water hose to the pipe on the bottom(water hose fits inside the 1 inch hose,attach with hose clamp)plug off other ends of bottom pipe.then i put a short piece of hose on the top of the header(were the u shaped hose dumps into the tail pipes)and installed a 3/4 water spicket in the end of the hose.then i stood the header uprite opened the upper spicket,turned on the water,let it run until all the air was pushed out the top,then shut the top spicket and let it build pressure.then checked inside for leaks.

that is the way to do it....

ok,, if the water empties into the tailpipe after the collector,,,this will make what iam trying to do easier,,,i want to just use air ,,like it do on a car radiator ,,,pump it up to a certain pressure and watch the gage for leaks,,,talked to cmi tech,,they thought it should work,,,,i am trying to do this with the headers on the boat,,,ifs there something i am missing,,, or could this work,,,now it the air test shows a leak then off they come,,,im doing this as a precaution only,,,did not have any isues last season

take them off to test,,what if their is a leak and theirs still water in the header tubes? then it will get water in the cylinder..their is also a visual inspection before pressure testing..

some headers will seep after they get hot so the visual inspection is also a good idea,,look for white spots in the inner tubes and rust build up in the cylinder heads..