I have a 2002 DS 650 BAJA and i have done some minor modifications (exhaust, pro com cdi, polished intake, jets, and k&n filter) but nothing major. Now i can not get it to stop overheating. I have tried and checked everything. It is pumping oil, and its pumping coolant, but i have not put a gauge on either one to check for correct pressure) it has the correct spark plug heat range. I took the thermostat out and now it does not overheat but it is borderline causer the fan kicks on and off. And it overheats within approx. 20min of easy riding. Any tips, suggestions, or checks i can try woulds be greatly appreciated.

 

How old is your coolant? May be time to drain the system, fill with white vinegar, make sure it cycles for a few minutes, drain and flush several times, refill with new coolant mixture. Cured my overheating problems. About every other season I do this with no issues.

 

what is your indication that it is overheating - coolant coming from expansion tank overflow, or do you have a temp gauge installed?

if the red light is the only thing flagging you, be aware that it warns of either a high temp, OR a lack of oil pressure. the oil pressure sensors can and do go bad, and I've replaced mine 3 times in 7 years. if you are uncertain which sensor is making the red light come on, simply unplug the oil sensor (right behind the oil filter cover, top of trany, right side) and see if light goes out - if it does then that is your problem, and they are cheap to replace.

but if are indeed overheating, thermostat removal is not the answer - with total removal the coolant does not spend as much time in the radiator due to increased flow, and can sometimes actually make a motor run even warmer. which by the way, you might wanna check and make sure radiator fins are not overly dirty or clogged.

here is anther thread talking about coolant system a bit too:
http://forums.atvconnection.co...atid/6/threadid/529622

 

The coolant is new 50/50 ratio I drained, flushed with water and refilled. I have never heard the white vinegar bit but sounds worth a try.
My indication of overheating first was the fan kicking on then shortly after that the red light, so i did what you said and unplugged the temp sensor wire and the light went off. Plus coolant is going into the over flow. But i still might replace the oil pressure sensor anyways if you have had that many problems with yours. And the odd thing about the thermostat removal was that it made it run cooler. So i checked the thermostat in boiling water and it functions properly. Also I can put a light behind the radiator and i can see all the way through. I'm about to pull my hair out...
By the way thanks for the fast reply. Got anything else I can try.

 

I can not for the life of me remember if there is supposed to be oil in the right side case were the magneto is, anybody else know.

 

Yes there will be a little oil on the magneto side.

 

Stop by a smog station amd have them put a sniffer over the open radiator and see if you are getting exhaust in the system. The Rotax's are known to have a few head gasket problems.

 

How about the jetting, i know you said you changed them but what are you running. It soulds like you might be lean. What attitude are you at and what size of main jet do you have installed ? How does it run now (before it overheats) ?

Check the rad as Hightower said and make sure you can see threw all the fine (remember no pressure washers either).

 

well it ran good but then the intake valves got out of tolerance so i put new valves in and while it was down i had the intake ported and polished and ever since i put it back together it overheats. It runs great up to the point it overheats (which is about 20 min.) then it misses and bogs down. I tore it back down to the cylinder today to see if i missed something, and nothing looks out of the ordinary. I don't know what could be?

 

<div class="FTQUOTE"><begin quote>Originally posted by: Cardiac

Stop by a smog station amd have them put a sniffer over the open radiator and see if you are getting exhaust in the system. The Rotax's are known to have a few head gasket problems.</end quote></div>

I have not heard of any head gasket problems with the stock bore, please elaborate.