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Making HP ain’t free. . .
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4,318 Posts
If it’s pushing coolant it’s more than likely a HG. I don’t think it’s a compression issue. I know I’ve mentioned this numerous times, but I’m at 13.4:1, and I run 91 octane. And I’ve been to some very tight, technical, rocky trails in Missouri and northern Minnesota, and I’ve been to the dunes on the west coast on hot summer days many times and I’ve never had a problem, granted, sometimes I sneak some race gas in the 501 just because I had it on hand for my 542.

I remember one of my 501s I built I was pushing coolant on one of the first rides after the build. I finished the ride, pulled the head, and I could see where it was leaking. I cleaned it up, threw a new gasket on it and ran it for a few years without another single HG issue.

I would say stick with the setup you have, make sure you clean up the surfaces really well, use a new gasket, and torque it in several steps to 40 or just a touch over.

I personally have never seen the need for a different rad. I’ve ran my 542 with 14.2:1 in the dunes on some crazy hot days, riding for hours straight and I’ve never seen my light come on, and that’s with a stock rad, hoses, and impeller, and I’m just running Honda HP coolant.
 

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Truck Yea
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5,511 Posts
Discussion Starter #42 (Edited)
Im going to go down to 12:1, its only a little bit and then I wont have to worry. we are going to check the head and replace the head gasket and of course check the head for warping

Theres an old school trick I used to use as a tech, take the rad cap off and take a plastic bag and put it on the neck where the cap goes. then rubberband it tightly on there. if it pushes out you know you have exhaust gasses being vented out. did that and a leak down test same way and nothing.

I truly think its a very minor leak if anything, but it tends to get very hot. The 04-05 I had ran much cooler, maybe the oil cooler helps. Ill slap on the water pump and rad and see where it all takes me to with the new piston. Friend of mine had the same setup and same issue awhile back-we swapped to a cut down piston no more problems. Its not a huge deal, i expect things like this to happen sometimes. I will say, there are days I miss the old 400EX..tractor like power down low and unkillable. 450R can be fickle.
 
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