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Discussion Starter #1
Hello all!

First time posting on this forum. I recently fixed up a 1999 Sportsman 500. I took it to torture test for the first time over the past weekend (trail riding and a few mud puddles) and the overheating light went on after about 20 minutes. I realized about a third of the coolant was missing after so I packed up and went home. One thing to note is while I was riding I could swear felt hot coolant on my leg squirting out by the fuel cock for a brief second before I visually saw smoke coming through the front by the cap. I bought some UV dye and after riding around the neighborhood for 10 minutes and idling and additional 5, there was only a little coming out by the cap which I've read is normal. I idled it another 10 and saw no more at the cap.

UV test wise could not find any other coolant anywhere. Checked underneath, the radiator, and the pump housing. Next I suspected the head gasket was bad, so I drained some oil and let it sit. Didn't see any water and oil separate. Also boiled some in a frying pan and noticed very minor crackling for maybe a few seconds then it stopped. Is that an indicator if there were a few quick little crackings? Also did not see any oil in the coolant while topping it off and refilling the reservoir.

Is it possible there was just air bubbles when I flushed the radiator before and it not all settled? Or does it sound like I've got coolant leaking into the engine? Is there another test to identify what could be the problem? I'm stumped.

Thanks,

Pierce
 

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It sounds like compression is leaking into the water jacket vaporizing coolant - head gasket on the 500 is notorious for the phenomena - leaks compression, but does not leak coolant.
 

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Discussion Starter #3
OEM head gasket on the way. I do not have a torque wrench. How critical is this while reinstalling the 12 point 14mm bolts?
 

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Torque is very critical on the 500 and other engines - get a good torque wrench and use the sequence in the service manual - those are 10 mm bolts with 14 mm heads
 

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No - a leaking head gasket does not normally leak coolant into the oil - a leaking water pump seal is the common way to get coolant into the oil.
 

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Discussion Starter #7
Great - will follow up after the weekend with the answer if this was the problem (I trust you are right about the HG).
 

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You will know if there is coolant in the oil after you run it a bit. If there is any foam / white stuff on dipstick.
 

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2001 Sportsman 500 HO DUSE, 2017 Sportsman 450 HO EFI EPS
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Hello Pierce. Ironically I was logging on to post the same issue on 2001 Sportsman 500 HO. I don't want to hijack your thread, but thought we could compare notes.

My coolant was disappearing but without a noticeable leak and never appeared discolored. I had bubbling out of the overflow with coolant hitting my left leg. Small amount of smoke off the front end now and then, never persistent. Oil looked good, wasn't cloudy, but did notice a couple small bubbles on the dipstick. Never did a pressure test nor UV test. I pulled the water pump and it appeared good. The spark plug looked good and wasn't white, but after a lot of research on the forum and talking with the Polaris dealer, figured it had to be the head gasket. I tried a new radiator cap, which seemed to help a small amount, but still had the issue. So I tore down the top end to see how deep the issue went before ordering parts and that's when I became confused. I expected to see a distinctive leak area on the head gasket, but I just don't see it. The head gasket does have a small amount of separation at the top, on the water jacket side, but it appears solid on the cylinder side. The piston and head do have a small "whitening" area at the top, where the head gasket showed signs of separating, but not sure if this is an indication of coolant evaporation or not. Especially at the rate coolant was disappearing. Straight edging the head and cylinder doesn't appear to show any warping (rudimentary but still). Curious if you or anyone else has any thoughts on this. Thanks in advance!

Here are pics, in order (top of pic corresponds with the top of the engine): Cylinder, head, head gasket (3 pics - head side, cylinder side and third showing separation), and water pump.
 

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Discussion Starter #10
Xcitbl,

Sounds like an completely identical set of symptoms you are having. The other guys replying on this thread are the experts, but if I could take a guess, the whiting part of the piston is where coolant was leaking through and vaporizing. I do know that sometimes even if certain areas of a gasket look okay, it does not indicate that there was a proper seal. If there was any separation at all I would doubt the integrity of the gasket as a whole.

Based on all the research I've done plus some earlier comments on this thread, it seems that the highest probability of issue is the head gasket on these engines. I will have the new one on Fri-Sat of this week and will try to get out Sunday to test and see if this was the issue and I'll report back. Thanks for the photos!

Pierce
 

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2001 Sportsman 500 HO DUSE, 2017 Sportsman 450 HO EFI EPS
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Thanks Pierce. My piston seems to have little to no play in the cylinder, the valves have no slop in them and the cam doesn't look worn, so I'm going to leave the bottom end and valve train alone. So if I can pickup the new gaskets this week, I'l also be putting mine back together this weekend. Curious to hear what your head gasket looks like. Good luck.
 

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Discussion Starter #12
Alright everyone, I replaced the head gasket back on Thursday. While having the old gasket out, there weren't really any signs of leakage, plus when you take off the head it kinda rips the old one apart to where it is hard to tell.

Regardless, today's torture test on the trails concluded that yes, the head gasket was the issue. I didn't lose any coolant whatsoever in hot Florida weather all day. So Xcitbl, go ahead and swap it out, looks like even without much evidence it is indeed the head gasket.

Thanks everyone for the help, I'm so glad this solved the issue.
 
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