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2005 Polaris 700 RMK Overheating

6K views 5 replies 2 participants last post by  BC_Dan 
#1 · (Edited)
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!
 
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#2 ·
Did you feel the rear heat exchanger to see if there is heat? You could have an air bubble. You may have to get the front of the sled higher than the rear heat exchanger to clear any bubble. When I had Edge sleds, I would put the sled on my tilt trailer and then idle with the cap off. That usually purged any air in the system.
 
#4 ·
You have covered all the other main issues with overheating, I would check the nut on the impeller. I had a similar issue with overheating on a big block 700 and after seizing it three times and going through 3 cylinders and 6 pistons, finally checked the impeller. On a NEW engine, the nut wasn't tight and had fallen off. At idle, no issues, the impeller would turn enough to circulate coolant. At speed, the coolant acted as a hydraulic lock and the shaft was spinning inside the impeller. No flow at speed. It was pretty frustrating (and expensive!) to find.
 
#5 ·
I found the issue - water pump impeller was spinning on shaft. Ran the problem sled next a known good identical sled at idle for 20 minutes while measuring temperature of both motors and left/right running board coolant tubes with temperature gun. Neither sled overheated and temperature measurements were identical. Took both sleds for a ride in 45 F weather, stopping occasionally to check the motor and running board temps on the problem sled. Seemed to be okay at slow speed with left and right running boards moderately warm. Opened her up for about 3 minutes at 50 mph and then stopped to check temps. Right running board was hot and left running board was very cold. Heat exchanger was packed with snow. Returned to my open trailer and loaded the problem sled on the right side so I could best get to the water pump. Fortunately, I had soaked the two screws for the coolant tube clamps with penetrating oil a few days before. Put a small socked on the screws and was able to break them free. Did not need to removed the Y-pipe. Removed the cooling tube and then the five hex bolts attaching the water pump housing (needed 10 mm open/closed end wrench, short 10 mm socket with 1/4" universal joint and 3" extension, and a long 10 mm socket). Popped the water pump housing cover off and the problem was obvious! The end of the locknut holding the impeller on was flush with the end of the shaft. I could practically take it off with my fingers. The nut was being held in place by it's nylon locking material only. The nut did not make contact with the inside of the housing. When in the nut is at the end of the shaft, the plastic impeller's double-D hole is only partially engaging the shaft. The impeller will turn with the shaft at low rpm because the load on the impeller's fins from the water being moved is small. But at high RPM, the load from the water being moved is higher, causing the impeller to spin on the shaft. I am positive my sled left the factory with the nut in this loose condition. There is no way for the nut to loosen with time. After 1800 miles with only a small part of the shaft engaging the impeller's double-D hole, the plastic impeller started to give way. Thanks again for your guidance, BC Dan!
 
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