overflow reservour building pressure - Polaris ATV Forum
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post #1 of 13 (permalink) Old 03-26-2019, 05:51 PM Thread Starter
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overflow reservour building pressure

I have a 95 explorer 400 (2 stroke) with new top end building pressure and squirting out coolant from overflow bottle after it warms up but only when revved up had it apart twice and its definitely not a head gasket and it doesn't matter if I replace radiator cap i have a new one and 2 used ones I'm guessing something is wrong with the radiator neck where it seals to the cap everything else functions like it should doesn't over heat fan comes on and everything has anyone seen this happen? thanks
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post #2 of 13 (permalink) Old 03-27-2019, 06:50 AM
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The coolant bottle is supposed to be vented - perhaps you need a new cap, gasket and what Polaris call a plug. The plug is a domed plastic bladder with a small hole in it.

How much coolant do you have in the bottle before you start the engine and where is to coolant coming out of?

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post #3 of 13 (permalink) Old 03-27-2019, 08:11 AM Thread Starter
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I forgot to mention i replaced the little thimble and the cap on overflow and its coming out of the cap still and the bottle doesn't matter how full it is it still comes out once it warms up unless there is a crack in a exhaust transfer port that can't be seen I'm thinking it's the radiator isn't sealing correctly
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post #4 of 13 (permalink) Old 03-27-2019, 08:20 AM
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If you run the engine with the radiator cap off, are there bubbles in the coolant at the radiator neck? I have never seen a cracked head or cylinder, but that doesn't mean it can't happen - I've just never seen it. The problem usually comes down to a head or cylinder that is not flat due to over torquing or being assembled with used gaskets.

The only way to pressurize the cooling system is from combustion pressure or expansion and expansion does not generate a great deal of pressure. It has to be leaking combustion pressure or boiling the coolant

Good luck.

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post #5 of 13 (permalink) Old 03-27-2019, 08:54 AM Thread Starter
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there is no bubbles but it flows so hard that you can't leave the cap off it has all new gaskets and I even swapped the head and the cylinder was bored out and the shop had the cylinder twice and didn't find anything wrong with it what if the radiator was quite flowing like it should it was pretty gunked up it did even want to drain out of the petcock before I flushed it maybe I didn't get it flushed well enough
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post #6 of 13 (permalink) Old 03-27-2019, 09:38 AM
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There are only two things that cause pressure in the cooling system - expansion and cylinder compression - the water pump is only an impeller to move the coolant - if the radiator is clogged, the coolant will not move and the engine will overheat - the water pump is only an impeller - unlike an oil pump with tight tolerances, the impeller does not generate high pressure - 4 to 8 psi is about it and the radiator pressure cap is about 8 psi, so the water pump could not create enough pressure to push past the cap.

There is a remote possibility that crankcase pressure could pressurize the counter balance chamber and push past the water pump seal to pressurize the cooling system, but if it were doing that, there should be iol in the coolant

See if you can get someone to pressure test the crankcase - should hold 7 lbs and no more than 15 - above 15 psi, the seals can be pushed out of engine case

I believe the problem will come down to a compression leak into the cooling system

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post #7 of 13 (permalink) Old 03-27-2019, 10:00 AM Thread Starter
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I also replaced all the seals for the water pump seals/bearings and crank seal on the balance shaft side and there is no antifreeze in the case/balance shaft oil lol that has been apart twice as well. when you run it without the cap on it doesn't pour or squirt its just very turbulent and just kinda spits or splashes and it doesn't matter even if I put on a 30lb cap it still leaks past like I said before everything seems to be working as it should the machine is actually at a shop right now cuz I can't figure it out and they have confirmed everything is working properly as well cooling fan comes on as needed like I mentioned before it's almost like the radiator neck isn't sealing properly to the cap
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post #8 of 13 (permalink) Old 03-27-2019, 10:41 AM Thread Starter
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well I just got confirmation from shop they pressurized the cylinder and at close to TDC at 100 psi it started pushing out antifreeze and this is while cold even so I'm picking up today and going to tear back apart for inspection but it has to be the cylinder it's the only thing that hasn't been replaced and during each inspection before everything appeared to be ok and the gaskets weren't leaking as well....
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post #9 of 13 (permalink) Old 05-10-2019, 08:12 AM Thread Starter
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So I replaced the top end with a complete good used top end and it's still doing the same thing so I'm thinking it's time to pull the entire motor and pull the top end and try to pressurize the cooling ports on the bottom end and see if I can locate a leak because everything else has been checked out it has to be a fluke gasket leak or a crack somewhere in the case causing this... has anyone ever encountered this before?
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post #10 of 13 (permalink) Old 05-10-2019, 08:26 AM
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Nope - you are the first - let us know what the cause and solution are.

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