Unable to fix overheating problem with 2005 Polaris 700 RMK, 151 track with ice scratchers, 1900 miles, and always ran Polaris Gold oil. Compression is 105 and 107 when warmed up and measured with WOT. Problem began after snow flap was bent inward and blocked snow to rear heat exchanger. Sled overheated on 45F day and blew coolant at 5 miles from trailer. Let it cool, rode until in limp mode, let it cool, repeated cycle several times until got it back to trailer. Big mistake, learned, and now trying to fix it! Sled had never overheated before; not even on warm spring days. Fixed flap. Removed head and cylinders. O-rings and gaskets appeared to be perfect. Pistons, rings and cylinders were also in good condition. No coolant wash on top of pistons. Heated cylinders in 400F oven and checked for cracks - none. Capped cylinder ends, pressurized, checked for cracks with soap/water solution - none. Checked water pump belt - good. Checked case, cylinder ends, and head for flatness. Base and cylinders good, head is bowed approx. 0.005" in middle measured across length (I read they are designed this way to seat properly on cylinders). Removed T-stat. Reassembled with light coat of high temp grease on o-rings. Torqued head bolts in three increments, then cylinder base nuts in three increments. Swapped thermistor and radiator cap with good sister sled parts - no change. Purged air from system by pouring 50/50 Prestone antifreeze into T-stat housing, and pouring into T-stat housing hose until ran out top of motor. Also opened T-Stat housing bleed screw until coolant flow was steady (no air). Coolant flow appears to be good into bottom and out top of motor - all hoses warm or hot and coolant in bottle is churning. Pressure tested cooling system - held 13 psi but leaked 1 psi every 4 minutes. Cold started motor and shut off after 2 minutes - no cooling system pressure. No bubbles rising in coolant bottle when running. Cooling system is pressurized when motor is warmed up. Checked cylinders and head with temp gun - appears to be fairly uniform with highest temp near T-stat housing. Temp on head plate reaches 195F after idling approx. 10 minutes on 45F day. At approx. 180F, idle increase significantly. Replaced all gaskets and o-rings a second time - no change. Sled is not using or leaking coolant. When compared to an identical sled, the motor on the overheating sled appears to simply develop more heat than the cooling system can handle. It also smokes more than other sled - blue/grey color. I haven't yet inspected the impeller, but I've heard they rarely fail (nut backs off) and I believe my coolant flow is good. I sure would appreciate any advice. Thank you!
2005 Polaris 700 RMK Overheating
