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Discussion Starter #1
New to me 2008 Ranger 500 EFI 4x4. Guy I bought it from says it overheats. He replaced the thermostat. His mechanic told him if that didn't fix it, then the water pump impeller is probably bad. Is that correct? I can see the pump housing. I'm guessing no big deal to pull and inspect/replace stuff?

I drained the radiator and filled with 1/2 bottle of Prestone flush and water. Ran it 15 minutes through a field, mostly idling. After getting warm, fan kicks on and runs all the time. It begins squirting fluid out the auxiliary tank lid.

I've read something about bleeding air out of the system?
 

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yaeh j, get the front end up as high as possible to get the radiator fill hole above the engine and with the cap off and idling, keep the radiator full while it cycles about five times. The reservoir should be 1/2 full when cold. If you stare down the hole long enough you can see if the coolant is circulating which would eliminate the impeller guess. Air in these systems is the biggest problem with over heating .
 

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Discussion Starter #4
Fascinating. Filled radiator to the top. Reservoir empty. Jacked up the front. Left radiator cap off. Started engine

Runs a long time at idle. I see the coolant letting off fumes. Bubbles. Overflow reservoir fills up. Coolant bouncing up and down slightly, overflowing a little. Fan kicks on. Within
60 seconds coolant drains. Within 60 seconds I can see coolant returning in top hose.

I guess the water pump and impeller are working.

When fan shuts off, I refill to top. More bubbles. I repeated this for three cycles.

Temp light never came on like before. No time to test drive now. Got honey-do errands. I may run through a couple of more cycles since I've still got jacked up.
 

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J, squeeze the hoses going on back to push the air out of them. They will be warm so use some gloves...... ALWAYS keep an eye on the overflow bottle in the future so it doesn't go empty and start sucking in air........It should be half full .............right now !
 

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Discussion Starter #6
Okay I've burped it a couple of times and I filled it with coolant a couple of times and it still overheats. It wants to squirt all the fluid out the overflow reservoir leaving nothing in the radiator system itself. When I run it with the radiator cap off I can see it go through the cycles moving coolant around. So it appears the water pump and the impeller work. Do I still have air in the line?
 

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Others on here are more experienced than me, but if you are seeing bubbles, would seem you may have a head gasket leaking compression into coolant. Also causes steam and adds to overheating.
 

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Okay I've burped it a couple of times and I filled it with coolant a couple of times and it still overheats. It wants to squirt all the fluid out the overflow reservoir leaving nothing in the radiator system itself. When I run it with the radiator cap off I can see it go through the cycles moving coolant around. So it appears the water pump and the impeller work. Do I still have air in the line?
" Do I still have air in the line?"............................................Yes. ............. Did you jack the front up as high as possible ? Squeeze the hoses to move the air out of them. ? Have your mom read this stuff and direct you on the correct procedure. These UTV's cuts NO ONE any slack. Take the time to bleed the air properly and you will be alright. :)
 

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What works for me is to get the radiator completely full then find a funnel that will fit tightly in the radiator cap hole. Fill up the funnel and then loosen the bleed screw on the thermostat housing until coolant with no air flows out.
 

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Once you have followed the well advised advice noted above, if your overheating problem persists and you continue to see bubbles, consider the possibility of a head gasket leak or even a crack in the head. A tool like this one:
Amazon.com: Block Tester BT-500 Combustion Leak Test Kit - Made in USA: Automotive
will detect the presence of exhaust gasses in the in cooling system.

I've had good luck filling the cooling system of my Ranger 570 XP by using a vacuum radiator filler kit like this one:
https://www.amazon.com/OEMTOOLS-24444-Cooling-System-Refiller/dp/B01BW39HJS/ref=sr_1_5?crid=1K66102F004LE&keywords=radiator+fill+kit&qid=1582943545&sprefix=radiator+fill,aps,205&sr=8-5
It left no air pockets when I refilled my system after installing a Firestorm heater.
 

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Discussion Starter #12
Aaaarrrrrggggg! I tried again, twice. Very careful both times. Used the bleeder on the thermostat housing and the bleeder on the water pump housing. No overheating while idling, front end jacked way up, radiator cap off. Whenever I put the radiator cap back on, the overheat light comes on very soon. Still idling. The guy who sold it to me says he replaced the headgasket and I don't see any bubbles in the coolant as I look into the radiator.

Confession: I maintain the coolant level during this process not full. I let it go below the return hose so I can make sure the coolant is cycling, etc. If I fill all the way to the top, it will overflow, so I've not been doing that. Is that my mistake? Is this letting air back in the system? I don't see how it could since the coolant drains out the bottom hose to circulate into the engine. Should I keep the radiator 100% full at all times?
 

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The guy who sold it to me says he replaced the headgasket
That is suspect to me. Changing a head gasket is not rocket science but it does take knowledge and HAS to be done correctly, head bolt torque, etc. Also, if the head was damaged or warped a new head gasket is useless. Go with pyro and get the block tester even though you don't see bubbles.

I just finished with a Mule that was overheating. No bubbles but couldn't get air out of the system. Ten minutes worth of work and the block tester fluid turned from blue to yellow in seconds. Combustion gas getting by the head gasket due to one improperly torqued bolt from the factory.

I get so many recently purchased machines in here where the new owner says the seller told him all it needs is xyz. That xyz turns into xyzxyzxyzxyzxyz and $$$$.
 

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Did battle with my 500 overheating after replacing piston because oil line to reservoir was pulled off by a stick. Head shave and oem gasket fixed it. Block tester was my definitive answer to my problem.
 

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Discussion Starter #15
I feel sure I've bled the system properly. Front jacked way up. Filled up the radiator. Used a tight fitting funnel so that when the engine heats up the excess coolant would not spill onto my garage floor. This seemed to be a good move since the coolant rose in the funnel without spilling. Ran it for a long time this way. Beat on the hoses, massaged the hoses. Got a large bubble every few seconds the entire time it ran. No small fizzy bubbles.

Turned off. Let cool down.

Filled up the system, cap on. Ran at idle for a long time with no fan or no overheating. This was an improvement since last attempt. After a bit, some coolant squirts out of the reservoir. Eventually the fan comes on. In a few minutes the overheating light comes on. Aaaarrrggg! I thought I had it whipped. Here's what I've got left:
1. Still air in the system.
2. Bad radiator cap or need higher pressure cap
3. Worn impeller/water pump which won't circulate well under pressure.
4. Bad head gasket.
 

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Get the block tester and you will know for sure. Careful not to suck up antifreeze during test. Dropped the level in the radiator about 2 inches at cold because of mixing with test fluid..
 

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You should not need a higher pressure cap it the one you have is the specified pressure by Polaris. If the one you have is original, it's 12 years old now. Caps are cheap, replace it and be done with wondering.

Given the steps you've taken to purge air I doubt air in the system is a problem.

Not seeing small fizzy bubbles is not an indicator that the head gasket seal is good. Bubbles may accumulate on a pocket somewhere and eventually come out as one large one.
The block tester will, without question, allow you to determine whether exhaust is making it into the cooling system or not. The test is simple to perform, the tool is not expensive and the liquid that comes with the tool can be reused if it's aerated with fresh air, it will return to it's normal color.

I agree with BPS, if the head gasket has been replaced previously it is suspect. The work done may have been improper or the head may be warped so that a gasket alone won't seal. Since the head gasket was replaced previously, I would also suspect a previous overheat, and there's no way of knowing how hot it got at some point. That means the plastic impeller on the water pump may also be bad, or the opposite may have happened - the impeller may have failed and caused an overheat which warped the head and blew the original head gasket.

Something else to consider (maybe I missed it in a previous post) is that the thermostat is bad. Many times when an engine overheats severely the wax pellet in the thermostat goes away, sometimes partially, and the thermostat no longer functions properly. I have more than one thermostat on vehicles require replacement after an overheat.

If it were mine, at this point, I would replace the radiator cap, test the thermostat on my kitchen stove with a known good thermometer (send the kitchen policeman out shopping), get the block check and check for exhaust in the cooling system and go from there.

If all those check out OK the water pump is suspect.

Thermostat test:
Pan large enough to completely submerge the thermostat filled with water on stove. Thermostat hung from a piece of wire and held so it does not touch any part of the pan, preferably in the center of the pan and completely submerged. End of thermometer next to but not touching the thermostat. Begin heating water. Note temperature when thermostat begins to open. Test over.
Note: It's important that the thermostat nor thermometer contact the pan adn that both are submerged and cloes to each other during the test. This assures that heat is not conducted directly from the pan to the thermostat or thermometer and that the temperature is the same for the reading as well as at the thermostat pellet. All water in the pan may not be at the same temperature as the heat rises.
Every thermostat I've ever seen has it's rated temperature stamped into the thermostat that is the opening point. If it opens at a higer than rated temperature or doesn't open at all, it's bad.
 

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Errrrrrrr, if the cap is 12 years old, it is bad and you can purge all day & night and reinstall a bad cap and you will be right back where you started with a closed system full of air and overheating....... Not only will it suck air from around the cap but you LOSE 3 degrees per pound of bad cap boiling prootection.
 

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Discussion Starter #19
I really appreciate the extensive help. I really wanted to hide my head in the sand and think "bad head gaskets can't happen to me." As I said, I'm not a mechanic, so the only way I knew to test/check was to remove the head. So thank you very much @pyromedic for suggesting various tests. I did order a replacement cap. But I also went to Harbor Freight and got a Combustion leak test kit. And...

Yellow! Even worse than I thought. Can I do a head-gasket replacement myself? I have a good bit of patience and can follow instructions.
 

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Check out this video. Yours is half a hard because it's one cyl. lol. I would take jug and head to a machine shop and replace the piston and rings of course. Used Namura on mine and running great. I got bit because I didn't have the head shaved the first time. Without my mishaps probably woult have cost me 300 bucks.


Download a 10.00 PDF service manual if you don't already have one, for your procedure and specs.
 
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