Ok its a 95 sportsman 400 4x4 2 stroke thats pushing coolant out the over flow tank.i checked all the fluids made sure they were full then drove it 5 mins when this happened.took off rad cap to look and water pump is circulating great.seems like alot of small bubbles but had to tell with 2 stroke as they shake so much.also have no coolant in any of my oils and no white smoke from exhaust to indicate a bad head gasket.BUT pulled my spark plug and did a compression test and think my tester is broke lol.I have no compression reading maybe 5 lbs.bike starts and runs great idles fine and has all kinds of power.GO FIGURE.sometimes it can be stubborn to start but when it does its good.no coolant leaks anywhere but out the little hole in the over flow tank cap.any ideas?could it be just a top head gasket gone?causing all this and how hard is it to change?PS im going to buy a new rad cap to eliminate that first.I just dont want to blow it up without fixing it right first.thanks.PS compression test done with electric start only as recoil is broke and only rolls 1-3 times before starter kicks out each time so very hard to get a good constant roll.

 

Bleed the 10mm screw on top of the head to eliminate any trapped air pockets that can cause a 400 to over heat very quickly.Plus you never mentioned about the fan kicking on and off.If the fan doesn't kick on and the battery is ok,a coolant sensor may be faulty on the radiator.You can jump the two wires on the sensor and see if the fan works ok. It could be as simple as a faulty radiator cap,but I'd either buy or rent(at most auto stores) a coolant pressure tester plus might want to get a cheap compression tester to replace your broken one if it's bad.

 

thx for the reply.yes new battery and yes fan works as well.i even hooked it up direct so it comes on with key all the time thought it was sensor as well.just bought a new cap will test it tomorrow and bleed the coolant in the head screw as you mentioned and see if it works.next a pressure test.thx again.

 

new rad cap, opened bleed screw,filled rad but when running im getting air bubbles in my rad all the time.let it run for about 3-4 mins brought up rpms a few times as well and still bubbles.Is this a head gasket issue?would it be just the top head gasket or base cyl gasket?also have only 5 psi with new tester.but cant believe it runs so good with only 5 psi compression.maybe this will help to narrow down issue.Anyone with an opinion befor i buy just uper gasket?

 

Bleed the head with the engine off until all air bubbles are removed from the system and only coolant runs out of the head.Run the engine it until the fan kicks on. If you have a new radiator cap and the hot light comes on or it starts to spew coolant out of the bottle before the fan kicks on,then just kill it and do a radiator pressure test. Must hold around 10psi without any drop or you could have some seepage from the base gasket or a head gasket problem.

 

well heres the update .i tore down my 400 today to be amazed what i saw.OMG piston was busted shrapnal all in the head and cylinder scored (but not that bad) the piston and head took the worst.so much for me hoping it was a head gasket gone lol.anyway i still cant believe the bike ran so good and never smoked.gues its just luck after 3 diff tests done on the compression can anyone tell me how this bike ran so good with only 5 lbs of compression and wasnt even that hard to start?anyway now its a waiting game for all the parts.will keep you posted.time for a coffee now shop door is closed with all the bad news inside it.

 

Seen them run with broken piston skirts for while also. Main thing is to check for any up and down play on the rod and rough feeling crank bearings as you roll the rod around. If the bottom end needs work just doing a top end may not last.

 

no all looks wel no play and very smooth.fingures crossed.

 

Clean the cases out with kerosene or naphtha,etc,oil the bottom end and cross fingers on both hands. If the top end is trashed,a lot of the finer shavings hits the bottom end. Hard to get all this crap out. If the lower rod bearing starts to spit out parts up into the cylinder it can take out a fresh top end and just cost more money to do it right and rebuild from the cases up. Just a warning on doing just top ends as I've seen this happen too many times.