Hi,
I have a 5th gen vfr800 that after a coolant change was overheating in standstill. this lead to me going through the coolant system, I replaced the thermostat with OEM, I pressure tested the system and fixed any leaks and it holds at 16psi. I replaced the radiator cap because it wasn’t holding pressure with a stant 10223 as recommended by someone on a forum. I am sure the water pump works as if the bikes hot and sitting off, when I turn the bike on (pump starts moving) the temp drops as if it’s getting recirculated. The fan turns on at exactly 219F so I am sure it’s not a fan issue either. When the bike reads hot it feels hot so I don’t think it’s a poor temp sensor either. At this point I have no ideas, the bike runs fine gets to topspeed no issue but it runs hot.
By hot I mean 206-209F on highway in 6th gear cruising at 80. I rarely see less than 200 now which was not an issue before my very initial coolant change. I am using standard green coolant. Please help I have no idea what to check now.
My 99 runs at a right around 180F on the freeway which is the thermostat opening point, which tells me there is excess radiator cooling capacity at that point. I would be rechecking your thermostat as it sounds like it may be jammed. My easy thermostat test (no disassembly needed!) is to start the cold engine and let it warm at a standstill and keep a hand on the radiator. If the thermostat is working the radiator stays cold until you reach 176-odd which is when it should start to open and dump hot coolant out to the radiator, which you feel as a sudden jump in temperature. If the radiator slowly heats up from when you start the bike, the thermostat is jammed open. If the radiator doesn't get hot around 176 then it may be jammed closed.
If you see *continuous* temps higher than 220ºF or below 180ºF then
trouble shooting is in order:
Continuous engine temps above 220ºF or 104ºC is a problem and the proper
order of items to trouble shoot are:
1)Faulty radiator cap... system should hold 1.1 pressure ratio...
2)Insufficient coolant...
3)Passages blocked in the radiator, hose or water jacket...
4)Air in the system...
5)Thermostat stuck closed...
6)Faulty temp meter or thermo sensor...
7)Faulty fan...
8)Faulty fan switch...
Engine temps below 180ºF or 82ºC is also a problem... it means that the
moisture produced during combustion is not getting hot enough to
evaporate out the pipe as steam... instead that moisture will migrate
to the oil and produce a milky white contamination...
Note normal by products of combustion is water... . Every gallon of gas
creates roughly 8 pounds of water vapor... we all have witnessed water
escaping out of tail pipes on cold mornings...
The sequence of events to trouble shoot are:
1)Faulty temp meter...
2)Thermostat stuck open...
3)Faulty fan switch... (stuck on)
Great advice from Terry and BLS as usual.
If your temps were fine before the coolant change, and you didn't mention there was a problem before, it might simply be a case that you haven't burped the system properly (BLS point 4)
Remember to burp you cooling system by blipping the throttle hard a couple times and massaging the hoses. Cranking the bike over sideways also helps get air bubbles out. This could also lead you back to BLS point 2.
Edited May 19 by Presson
Correction
New to the forum. I have a 2015 VFR800. I stopped to help a guy on a Goldwing who had tipped over, I jumped off my bike and left it running while helping get his upright and pushed back up onto the shoulder, by the time we got his up on the shoulder and was checking it out, I noticed mine had overheated and boiled over. I shut it off, helped him get started then rode home with the temperature light on, about three miles. I let it cool down and filled the reserve reservoir to the Full mark. The next day I rode it about 12 miles and when I got back in the garage it was pouring coolant out again but no light was on, so I let it sit overnight. This morning when I checked the level, it was not even to the Low line. I only added less that 16 ozs of coolant from it overheating the first time. I see Presson said to burp it. I didn't open the radiator cap, when blipping the throttle and messaging the hoses is the bike up to temp when doing this? Does the radiator cap need to be off, or the reserve cap open?
Found the manual on here, will try to burp the system.
More than likely, you need a new radiator cap. If it can't hold pressure, you get localised boiling in the engine causing steam and that will cough coolant right out of the reservoir. When the engine cools it will suck back and drain the coolant reservoir.
HONDA OEM CAP, RADIATOR | 19045-GBF-700 $48.59 at Partzilla.
Terry is probably spot on. The burping is used when you drain and refill the system to remove localised air pockets that could restrict circulation of the coolant. If you haven't recently changed your coolant and the problem is new, it's likely to be a problem with retaining pressure as Terry observed.