I know this is mostly a racer/street bike deal but I don't belong to any dirt bike forums and figure there is enough of us that cross over between dirt and street someone might head me in the right direction. 2019 Honda CRF250rx, just bought the bike rode it around for about 5 minutes (20 degrees outside) before loading it on the truck and heading home. Get home (45 degrees) bomb around the field for about 15 minutes and park it. About 5 minutes later I notice a good size pool of coolant under the overflow tube. Supposedly the bike has less than 20 hours on it. 1. Tusk radiator hoses with 2-3 hours of ride time since they were switched with stock. 2. Power seems normal 3. Oil doesn't seem discolored but maybe a little "runnier" than normal. The oil was pretty dark, but normal fill level. 4. Compression is almost 60psi, slightly warmed up which seems about right from what I could research on the interenet. However, this number seems to be a little difficult to pin down on the internet. 5. Some sort of aftermarket radiator cap with built-in temp gauge (possible weak link) 6. With the radiator cap off it occasionally will get a few little air bubbles if I blip the throttle. 7. Starts hard when cold but fires right up and idles when warmed up after about 5 minutes. Wondering if I popped the head gasket or it was already bad I just didn't ride it long enough to make it overflow when I test rode it.
If you have tools pressure check cooling system and do cylinder leak down to see if you push out coolant. If not put an oem radiator cap on at least. Those tusk ones with temp gage I have seen leak when newish. Try that.
Yep, just read they have built-in decompression so a traditional compression check is probably pointless. I am on the hunt for a stock cap and hopefully will have one by Tuesday. I, unfortunately, do not have a leak-down test kit but might be a good excuse to add a tool to the inventory!
dirt bikes do not have an overflow catch, they use empty space in the rad for expansion, they will all puke fluid if filled to the top. I zip tied a baby bottle to the rad to catch and recirculate it.
Those temp reading caps are known leakers, but I agree with racepro, likely just overfilled and finding it's level. Took me forever to figure that out with my first KTM, 'full' when cold was just to the top of the cores in the radiator. Any more and it'd push some out when ridden. I must have panicked seeing steam 15 and topping off 15 times before putting two and two together.
look at the tabs on the cap... seen 2 of them that did not lock like a standard cap. Lil duckbill manipulation and problem solved.
Been raining like hell here so I haven't ridden it. I did let it idle for about 15 minutes in the barn with no overflow. Checked the cap, hoses and changed the oil. Once it dries up I will have to run it around the house a bit to see if the problem continues. Thanks for all the feedback.
I agree with the cap. Bought a new one for my FS450 so I could see the temp and it leaked immediately.