I just purchased a 2001 Sportsman 400 for primarily hunting purposes. It was not in perfect condition but was in the right price range and the obvious problems did not concern me. There were some serious electrical issues which were caused by an apparent lack of use and a mouse infestation. I have gone through the whole bike and do have all systems functioning again. This is when I started on all the lubrication points. I noticed that the engine oil was way overfull in the reservoir and the coolant overflow bottle was about half low. I didn’t put two and two together until I drained the oil. It was not milky but very obvious that it was mixed with coolant. After much reading on similar threads throughout this forum I started troubleshooting. First of all the weep hole at the water pump is not clogged and very dry. So I assume no mechanical or oil seal issue. I topped off and burped coolant and flushed and changed the oil to be sure this hadn’t happened over a long period of time. After just ten minutes of running and a full cool down the overflow reservoir is a half inch low, and after slowly pulling sump drain plug I was visually able to watch water drain first before oil so definitely a serious leak. So I have seen people mention head gasket and possibly base gasket as well. Worst case scenario obviously some sort of cracked jug or block.
So very long winded I apologize and ill get to the question. With the above mentioned troubleshooting where would you guys start? Head gasket? And if I go through that trouble should i do the base gasket as well to rule it out since I am in there? I have a strong small engine and aircraft engine repair background but am new to ATVS. The process does not concern me but I do want to avoid unnecessary parts and extensive labor if it is not needed. Does it seem plausible that the leak is occurring there since I believe I have ruled out the pump shaft seals? Also the machine starts and runs great idles fine, does not lag on throttle and as far as i can tell no smoke or sweet smell in exhaust but I have nothing to compare to. So I was hesitant with the head gasket. Is it possible to fail in such a way to allow coolant in oil but not combustion chamber?
Any insight or recommendations would greatly be appreciated. The hunting season is approaching and I wasn’t looking for a project ( I have enough of those!) LOL. I’m really hoping to get her up and running reliably soon.
Thanks for any advice!!
