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Joe Breaux

2017 Massimo MSU500 Thermostat Malfunction

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Got a 2017 Massimo MSU500 UTV with thermostat malfunction.. hot light comes on in 4-5 minutes but radiator is ice cold... where exactly is it?  The hose neck on the head has nothing in it.  I was told it was down by oil drain plug.. only thing I see is water pump.. Is in inside pump housing?  Cant find any exploded diagrams that show it.. how to I remove it? any help would be appreciated

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There’s not one. There is air in the system. 

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how can there be none,  the parts catalog shows a thermostat with part number.....just no location .. I have tried calling Massimo but they never call me back 

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Massimo Tech finally called me back just now .. There IS  a Thermostat. underneath the engine..... I asked about air pocket being the cause , they advised to jack up machine in front , remove caps on Radiator and recovery bottle and run it . watch for burping . I ll try that first .. 

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found no air in system.. water is not circulating.. will remove thermostat today. 

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20200514_181113.thumb.jpg.305df5917de05fc37b9ba159dccaedf8.jpgHey Joe I had the exact same problem with my 750.  Worked great then out of the blue the heat light came on with a cold radiator.  After alot of research and troubleshooting I found their is a bleeder screw on the housing on the driver side of engine on the hose housing and a second one down at the waterpump at the back of engine.  I bleed the top one and 0 water.  I went to the lower one(which is a nightmare to see and bled it and then went back to the top one and bam it now works great.  As you are doing it you have to keep radiator full.  My reserve was full the whole time but the trapped air didnt allow it to move.  I included a pic I took with my cell as that was the only was to see it.  The bleeder is the bottom right of flange.

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thanks   a lot .. I will do that after T-Stat is done..   how does air enter a closed system, I wonder ..  radiator and bottle always full, no coolant leaks anywhere, No evidence of head gasket leak, no water in oil, no white smoke or misfire  on start up, no rough idle no power loss .. The machine runs perfectly all the time.. just no water circulating.   This is the first issue its had in 3 years 

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20200514_181113.thumb.jpg.305df5917de05fc37b9ba159dccaedf8.jpgHey Joe I had the exact same problem with my 750.  Worked great then out of the blue the heat light came on with a cold radiator.  After alot of research and troubleshooting I found their is a bleeder screw on the housing on the driver side of engine on the hose housing and a second one down at the waterpump at the back of engine.  I bleed the top one and 0 water.  I went to the lower one(which is a nightmare to see and bled it and then went back to the top one and bam it now works great.  As you are doing it you have to keep radiator full.  My reserve was full the whole time but the trapped air didnt allow it to move.  I included a pic I took with my cell as that was the only was to see it.  The bleeder is the bottom right of flange.

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I had exactly same question.  I bought mine used and had no issues.  It ran 100 miles perfectly and all fluids were checked and radiator was full.  What I found was it does not take much for it to become air bound.  I once smelled antifreeze so went thru and tightened all clamps and checked for leaks with none found but I did find one clamp that I tightened a few turns so could have been sucking air.  Good luck as I think the thermost is on the bottom and a bear to get to.  You may want to try the bleeder first and see if it helps.   

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I bought mine new in 2017.. it has always run perfectly.. It goes thru anything in 4 WD Lock... You are right the T-Stat is on the bottom of engine .. a real pita to get at .. Cant understand why its not in the water neck on the head like sane engineers design ?   Thanks for the info.. I ll run it on the trails next weekend.. I hope its cured.. 

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Good luck.  I fixed mine 2 days ago and have run it hard up and down road and seemed good but have not hit trails yet which will be the real test.

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sorry to hear that. ...Is water circulating? Any misfire or white smoke on start up? That's a dead giveaway,  air bubbles in radiator while idling ? /  check oil for signs of water dilution 

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Its starts and runs fine.  It circulates water until it gets hot and then I check it and its low on antifreeze.  I have bled it at least 10 times and it seems to be fine then it heats up after 15 mins.  No smoke and no water coming out exhaust.  I pulled the plug and its brown as it should be.  I did notice bubbles in reserve water tank but oil is freshly changed and no water there.  Based on the bubbles and continuous loss of water I fear its a gasket.  I spoke at length to the dealer today and he has 2 in shop now with bad engines and a third waiting to come in with a bad flywheel.  They stopped selling them because of bad engine issues.  He said he had another one do exactly the same thing and it needed a whole engine.  I am praying Im wrong or its just a gasket.  😔

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well so far no joy on overheating.. got water circulating at idle for an hour and a half .. radiator warm, no hot light.. run it down the trail half throttle, 10-15 minutes , HOT LIGHT ON... radiator cold again.. someone please tell me what the hell is going on... no water in oil, no misfire on start, no white smoke at start or running down the road..  driving me nutz

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Welcome to my world.  When you fill and bleed it check for bubbles coming up in reserve tank.  Mine is doing same exact thing.  99% sure its head gasket.  I spoke to dealer and he has 3 in shop now with overheat issues and the motors are bad.  If I am lucky and its only a gasket im selling it while Im ahead and will get a Canam.

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I took it to the local Massimo authorized shop, he kept it 3 days . Said it was just air lock.. brought it home, first 2 hours or so was fine.. then light came on and radiator was ice  cold again.. This thing only has less than 400 miles on it . it runs perfectly otherwise... I guess it must be the gasket allowing gas into cooling system, but it shows no evidence  of leak in the exhaust or oil.. it must be a very tiny leak.    I will bring it back to him tomorrow .. I found out, Hes the only one in the area that will work on them...  I wish I had bought the Honda instead. We have 4 Honda machines. thousands of miles on them, never any issues on any of them..

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Its possible he didnt get all the air out.  My dealer first said it takes 2 or 3 times to purge it sometimes.  Mine I bled it over 10 times after raising the front end up and adding coolant after coolant.  The only symptom I could find is air bubbles in coolant tank.  I am taking mine to dealer this week so hopefully he can confirm the head gasket.   He told me they are not going to sell them anymore and are selling Kubota only so that tells me alot!!

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