2006 Kodiak 450 - Overheating/rapid idle/hard to shift - HELP - new owner!

[AndoverHorseMom]

Hoping for some help for a newbie's wife. Bought a used 06 Kodiak 450 with 550 miles and just over 100 hours on it. Had been used primarily for plowing snow. The unit ran well, started with no issues in zero weather, and ran very smoothly when it was tested (two different occasions). Not convinced it was cared for like my husband would, we brought it to our local auto guy whose young son can fix or service anything recreational (specialty is quads and snowmobiles). We had him change all the fluids, spark plug, new tires, and give it a general look-see to make sure all was good. There were no noted leaks, but the son said the rear differential was basically dry...two drops came out when it was drained. No evidence of any leak, but he said it had to have gone somewhere. The shop did the work, but said to watch it carefully in case a leak developed. Well, we've put only about 6 miles on it just puttering around the house and suddenly it started revving fast, and it was difficult to get into park or neutral. The hubby parked it, but cooling fan continued to run for several minutes, then shut off. The first time this happened, we called our guy and he asked how much gas was in it. Well, it was in the red zone. He said to fill it because the lack of fuel could have caused the engine to starve and suck from areas in the carb (hope I'm remembering the verbiage). Basically, the quad was empty. Our bad. Hubby filled it up last night, started it up and rode it around the yard again and we thought that was the problem. Then the same issue happened. I'm having a severe stomach ache thinking that we have purchased a really expensive problem. Before we take it back to our shop (who we have used and trusted for dozens of years), is there any obvious thing we can try? We do not have a service manual--only an owner's manual. Or is the dry differential issue that the son discovered possibly a heinous culprit? Hubby wants this for this fall's hunting season, so we have time to fix the issue...I'm just curious if it is something stupidly simple. I apologize in advance for not really knowing much, and the hubby has no idea I'm posting this! HELP PLEASE!

[oxidized_black]

the rear diff might be from a bad seal or crack in the housing. is there any visible spots you can see it dripping? there would be only 4 spots it could go, thru both axles, driveshaft or fill/empty plug. idle problems might be rectified with some "sea foam" (brand name) additive to the fuel tank, double the dose on the first shot, then run specified amount thereafter ... overheating might be either from too hot of a plug (some guys run a hotter plug thru the winter as you stated it was used for plowing), or remove the muffler and start it and use it without, could be a plugged muffler (dirt/mud) ... i think this is liquid cooled? could be a worn out/bad sensor keeping your fan running too. did anyone check the valves to see if they are in spec?

i think i have a service manual for this beast, will check and post a link here ...

[AndoverHorseMom]

Thanks for the info. I looked at the maintenance sheet they gave me and it says a NGK 7162 spark plug was installed (is that a hot one?), along with 80w/90 gear lube, 10x/30 semi synthetic oil and a 1358 oil filter. There were no signs of differential fluid leaks anywhere (they looked and we looked). Yes, this is liquid cooled. That's the only thing that wasn't changed since it was up to spec and checked out. My hubby called the shop today and we'll be bringing it in later this week. I will print out your comments and have them look into it. Like I mentioned, they are experienced with these machines, and even have their own plus a few on site for use around the shop (Grizzly 660's). It just seems odd that we literally have put under 10 miles on it and now are having issues. Thanks much for looking to see if you have a service manual too.

[oxidized_black]

that is the standard plug ... here is a manual from 2005 ...

2005 Yamaha Kodiak YFM 450 Service Manual.pdf