5th Gen Thermostat

Last Spring the bike randomly started to have cooling issues. Inconveniently I was 350 miles from home. I went through western Maine to avoid Mass Traffic and ended up stuck in traffic because of construction on 84, when I noticed my temp was reading 229-231f. There was no breakdown lane, so I nursed the bike along for 30 min or so until I could pull over.

I confirmed I had coolant in the reservoir and the fan was running hard, constantly. I Let the bike cool down for a while and decided to keep going as I was still 300 miles from my hotel. It was around 95F ambient temp, so quite a bit more on the tarmac, but it started raining fairly hard so I figured that might help. Long story short I pulled in a bit after 9pm into Wilkes Barre and parked up. The bike sat at 219-226 f for the rest of the day. I had skipped a gas stop and ran the bike to 210 miles on the trip Odometer in case I ended up having to have a go at the thermostat, I had all my tools with me if I did.

6am the next day I lifted the tank and started to remove the airbox, when I decided to just start the bike and see what happened. In the cool of the morning it would get to about 185f then drop. It did this for 5 or six cycles so I ran the engine up to 219f (it took a while) fan came on, temp dropped.

I hate it when things fix themselves. I loaded up and did 2,100 miles after with no issues.

4 days after getting home, I headed out with 2 buddies for 1,700 up to Cape Breton and Nova Scotia, no issues.

Parked the bike up for June and July.

Mid August headed to the White Mountains to meet some other friends, ride Mt. Washington, etc. it was 95f here in Maine at noon, never have seen it that hot. Bike ran up to 226-230f until early evening when the ambient temp dropped, then the bike was fine.

Sept. took a 2,800 ride to western PA for a Fall meet, returned via the Adirondacks and Quebec. no  issues.

Oct. took a 1,300 mile ill advised ride up to the St. Lawrence in Quebec., never saw above 46f ambient, obviously no issues.

So, a new Thermostat is in order, I'm sure its original as the PO admitted to never working on the bike. I have read Mello Dudes and others excellent write ups on this, so I know whats involved. I have also pulled and installed pretty much all the carbs on my earlier V4's, some multiple times, so not to worried about the TB's. Well maybe the Vacuum hoses😁

BTW, got sticker shock when I went looking for a Thermostat, $52-$75, yikes

Thinking a Radiator flush would be a good idea also.

Lastly, it appears that even when the cooling system is working as it should, it struggles when the ambient temp starts to hit 90f and it cant shed heat quickly enough. I'm looking at installing a lower temp sending unit 210f to help get ahead of that. Thoughts or experience on this would be welcome.

Lastly, when looking at my wiring diagram, I notice the sending unit has constant postive power to it like my earlier V4's, but the ground is routed through the ECU. Why would they do that?

If your thinking this is a long, long post, you are correct, It started snowing here 2 weeks before Thanksgiving and the plow trucks have been by my house 5 times today, Cabin fever has set in.⛄☃️😶‍🌫️

Thanks

Michael

i think the larger culprit is that the stock fan is just not fit for purpose. my suzuki was having similar problems; when the summer would hit here in tejas, the fan would come on and the temp would just continue to climb regardless, even with a fresh coolant flush and new tstat. swapping in a nice beefy 5" spal unit fixed the problem, though i had to wire it to a switch and relay because the original fan circuit just couldn't handle it. admittedly my vfr isn't quite yet in a running state, but i did put power to it and feel the airflow from the fan just to see if i'd be potentially dealing with the same issues, and a typhoon it sure ain't. even though the spal is a good bit smaller, it flows a whole lot more air.

of course the problem we run into is finding one that'll fit, considering the distinct lack of space between either radiator and the engine. this mishimoto unit appears like it'll fit the bill; i ordered one and have it on my shelf ready to go in, but up until just recently i've just been too busy with life things to turn any wrenches. fitment results will be forthcoming.

My gut tells me your thermostat is probably opening.  Wheel the bike outside and have an IR thermostat gun in hand.  Pull one of the side plastics, maybe the right so you can get a good shot at the radiator.  Start the bike and watch the radiator's temp with your temp gun and the indicated temp on the dash.  During initial warm up as the bike temp climbs you should see a slight slow rise in the radiator, but nothing drastic or hurried.  Watch the VFR approach indicated 180 on the dash.  Around this time you should observe a rapid rise in radiator temperature as the thermostat begins to open.  If this occurs, congratulations your thermostat is probably fine.

If you're still not convinced this way, pull the current thermostat and dunk it in hot water as per the service manual.

Thanks Burger, it had occurred to me also that maybe the fan wasn't up to the job at really high ambient temp, as this issue only occurred at those times. That fan you linked to looks pretty nifty!

vfrgiving: I do in fact have an IR thermometer and should have thought of that. Thanks for shaking the cobwebs out of the old noggin. Only issue at the moment is the bike is on an unheated garage. Temps last night went to -15f, I don’t think I could get the bike anywhere near operating temp at the moment. 😁

I have had similar overheating symptoms develop twice on my 2001.  The culprit has been the OEM thermostat only opening 1/3 to 1/2 even at the high temps.   I have tested both the thermostats I have removed and the new replacements on the stove while watching the water come up to 210 F.  The difference in how far they open is very obvious.  The old thermostats have had no corrosion or deposits; in fact they look identical to the new ones, yet they have failed to operate correctly.    Somewhat disappointing for a $50+ part that should have been perfected decades ago.

I have had the bike since new so I know the temperatures it normally runs in weather from 30 degrees to 110 degrees, and in various traffic conditions.   The cooling system struggles a bit in very hot weather when stuck in traffic, however the thermostat problem creates a rather obvious departure from those normal temps and causes the temperature to rise very quickly in warm weather.   

Regarding all the vacuum hoses, if you still have the stock hoses, Honda has done us a favor and labeled each of the 15 hoses to match the diagrams in the factory Service Manual (page 5-66).   I still mark each one with different colored tape to ensure I get it back onto the correct fitting, but it's not as daunting as it might be due to the unique hose numbering.