1999 VFR800: Engine gets hot, but radiators and hoses stay cold after coolant flush. Thermostat??

Discussion in 'Mechanics Garage' started by ONE PUNCH, May 4, 2020.

  1. ONE PUNCH

    ONE PUNCH New Member

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    Hi everyone! I hope you all are doing well. I was wondering if I may hear your thoughts on what might be wrong.
    My VFR was running well, but as the second owner of a 21-year-old bike with over 57K miles, I decided to give it a coolant flush. The old coolant that came out was still pretty clean, bright, and green. I also drained the engine block. I ran the bike with distilled water and after opening the water pump drain again the water came out clear. Nice, it appears the previous owner looked after the coolant. I then added fresh coolant.
    When I started the bike this time, I noticed the coolant temp. inching up and the engine getting hotter, but the radiators and hoses stayed COOL. At 220 F, the radiator fan did not kick on like it usually did. At 227 F, I immediately turned the bike off. The engine hot; both radiators and hoses still cold. I tried squeezing the hoses and snapping the throttle thinking it might be air trapped in the system, but nothing changed.

    I'm thinking maybe my thermostat is stuck CLOSED, which is preventing hot coolant in the block from reaching the radiators, which in turn is keeping the radiators cool, which in turn is preventing the radiator fan from turning on. That's just my guess. I believe the thermostat is original & has never been replaced! What does everyone think?? Sorry for the long post, and thank you all in advance for any advice.
     
    Last edited: May 4, 2020
  2. NorcalBoy

    NorcalBoy Member

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    Air in the system. Follow the bleed procedure in the service manual.
     
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  3. Terry Smith

    Terry Smith Member

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    NCB could well be right, and it is what you should address first. Did you fire the bike up with the radiator cap off, on the sidestand, and blip the throttle a few times? That would enable you to judge whether the radiators are properly filled and flowing.

    You are correct that if the radiators don't get hot, the fan won't come on.
     
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  4. ONE PUNCH

    ONE PUNCH New Member

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    Thanks. I did start the bike with the radiator cap off but I was sitting on the bike keeping it centered. I squeezed the radiator hoses gently and then snapped the throttle a few times, but the coolant would keep rising & spilling out of the radiator filler neck, & the engine would continue to get hotter but the radiators stay cool. I'll try to bleed out the air while it's on the side stand and report back.
     
    Last edited: May 4, 2020
  5. Terry Smith

    Terry Smith Member

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    upload_2020-5-5_15-33-51.png
    The manual doesn't state that the bike should be on the sidestand for this but given the radiator filler is on the right side, I think it is the right thing to do. The manual for my VTR1000F (same side mount radiator layout) is quite specific about that.
     
  6. ONE PUNCH

    ONE PUNCH New Member

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    I tried it again by letting it run on its side stand for 2-3 minuets, and snapping the throttle 3-4 times. It was at that time the coolant level started rising in the radiator filler neck and began spilling out onto a rag I had wrapped around the filler neck. The coolant temp. continued to rise up to 222 F/105 C but both radiators were cool to the touch and the radiator fan did not turn on; I then turned the engine off. Could it be the thermostat calling it quits, or maybe something else?
     
  7. Terry Smith

    Terry Smith Member

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    Well that could be correct but it seems like a coincidence that it happened at the same time as the coolant change. If it were me I'd give the bike a short sharp run around the block and see if it won't clear any air blockage. As long as you don' get excessive engine temperatures this should do no harm.
    Be prepared for some deep diving to pull the thermostat out, you will need to pull the tank, airbox and throttle bodies to get at it. It is however easy to do a function check on the thermostat by dipping it in a pot of boiling water.
    upload_2020-5-5_16-36-5.png
    The picture below is of a working thermostat
     
  8. GreginDenver

    GreginDenver New Member

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    When you're doing these warmup test runs is the Radiator Bypass Tube heating up? The Radiator Bypass Tube is the tube that runs from the top of the thermostat housing around and down to the top of the water pump. This is the coolant line that stays open to circulate coolant directly back to the water pump until the thermostat opens.
     
  9. ONE PUNCH

    ONE PUNCH New Member

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    ***UPDATE: PROBLEM SOLVED!***
    So, to be on the safe side and because I had a little bit of coin stored away, I decided to have my local small town motorcycle mechanic have a look.
    The verdict: According to the mechanic, I waited too long to put the radiator cap back on after running the bike, which wasn't allowing the cooling system to build pressure on time, which prevented the coolant from circulating properly. NorCalBoy and Terry Smith - you gentlemen are correct; silly me didn't bleed the cooling system correctly, but now my VFR runs great, the radiators get HOT (my legs are cookin'!), the coolant temp is at 177 F-185 F (80 C-85 C), and the original thermostat is still working.
    I learned a lesson here: Follow the service manual EXACTLY! D'OH!:homer:
    Thank you all once again for your advice & time! :) Now I'm going to put the fairings back on and give it a nice wash.
     
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  10. Diving Pete

    Diving Pete Member

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    great news, thanks for the update & enjoy your VFR.
     
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  11. Terry Smith

    Terry Smith Member

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    I am very pleased that worked out for you. I've been working on my 600cc Silverwing scooter today, drained the coolant, then re-filled it with fresh. I got exactly the same problem as you; the radiator was apparently full, and the level rose in the neck as the engine was running/being blipped, but there was a massive airlock in the engine. The airlock was obvious for me as I had re-filled the system from a 750mL water bottle (due to the godawful position of the filler, this was the easiest way to try to do a no-spill fill) and I knew I was well short of the approx 2L that had come out. The coolant in the neck/radiator was still cold by the time steam started coming out, and the engine temp was high, and about a half cup had overflowed and spilt on the floor. Then there was a big gurgle and the level dropped suddenly and I could complete the fill.
     
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  12. NorcalBoy

    NorcalBoy Member

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    I figured out (after getting nasty red Motul coolant all over everything)) that pouring in the coolant slowly, pour, wait a few seconds, pour some more, until there was about an inch left below the bottom of the filler neck was key. Then going around and squeezing all the hoses while they were cold, topping back up to within an inch of the bottom of the filler neck, then starting the bike. Once all was good and it got up to temp, a quick visual inspection that it was circulating and not bouncing up and down in the radiator, shut it off, then top it up and fill the overflow to the correct level. This allows you to blip the throttle as much as you think you need to get the air out, without having it burp the coolant out of the filler neck and all over your pristine moto.
     
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  13. Terry Smith

    Terry Smith Member

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    Thanks for the tips, NCB, I will remember that for next time. I didn't think I had filled too fast, as I was squeezing the liquid in from a water bottle, but there was no way the air was coming out until (I think) the thermostat decided to open. It was certainly "bouncing up and down" as you describe when the air was in there.

    It could be that the thermostat needs to be oriented a specific way in this scooter to bleed air? I didn't dive in that deep as thermostat was functioning normally, but in some compensation for the stupid location of the radiator filler, the thermostat is easily accessed on the side of the motor so that won't be a big deal to check one day.
     
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