'02 overheating. T-stat questions

Discussion in '6th Generation 2002-2013' started by kevlar750, Sep 5, 2020.

  1. kevlar750

    kevlar750 New Member

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    Red Sonja comes to "normal" temperature, about 175°F in a few minutes. OK.
    While splitting lanes on my ride home from work in SF Bay Area traffic it will jump to 200°F-210°F. OK.
    Once I get up to 75-80mph the temp. won't drop below 190°F. Recently would not fall below 210°F. Since I bought the bike about 18 months ago, this is a new problem. I checked coolant level and all is perfect and the fan comes on at about 215°F.
    Might the t-stat be frozen just barely open, not allowing proper flow? If so, what's the procedure for t-stat replacement. I don't have a manual to refer to since the place of purchase didn't have one to give me.

    Any assistance or recommendations would be greatly appreciated.
     
  2. jstehman

    jstehman New Member

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    How long are you traveling at 80mph?

    Are you in 5th or 6th gear?



    Sent from my SM-N950U using Tapatalk
     
  3. squirrelman

    squirrelman Member

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    try replacing the radiator cap as they can and do go bad after a few years. if it won't hold pressure, overheating is likely.
     
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  4. Terry Smith

    Terry Smith Member

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    You can download a manual from the "other" VFR site:
    https://www.vfrdiscussion.com/index...h-gen-2002-vtec-with-bookmarks-new-cover-ocr/

    Thermostat replacement is no fun; the airbox and throttle bodies have to be removed to get to it, tedious but not too complicated as long as you have patience and a really long philips head screwdriver.

    A simple function test would be to start the bike from cold and keep your hand on the radiator. That should stay cold until then engine reaches around 175F, then you should feel a sudden rise in temperature until its too hot to touch, which is normal thermostat operation. If instead the radiator slowly rises in temperature from the time the engine is started, it is stuck open and should be replaced.

    Take squirrel's advice, replace the radiator cap first, it is cheap and much easier to do.
     
  5. kevlar750

    kevlar750 New Member

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    80+ mph usually for about 20 miles. 15 minutes or so and I cruise in 6th gear at about 5000rpm.
     
  6. kevlar750

    kevlar750 New Member

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    I will definitely give this a lk.
    If it won't hold pressure, wouldn't there be a leak noticeable at some point?
    I have absolutely ØØØ leaks anywhere on this bike.

    Thanx for responding.
     
  7. kevlar750

    kevlar750 New Member

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    Thanks Terry for the link. I downloaded it and looked at the process. Just what I wanted to do!!!
    Pretty much functions just like a car except when cars 'overheat' they tend to spray coolant all over eventually. I have no leaking of any kind anywhere.
    I will do the cap swap as recommended and keep my fingers crossed.

    Thanx for responding.
     
  8. Terry Smith

    Terry Smith Member

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    The purpose of the cap is to hold pressure in the cooling system; more pressure means the fluid won't boil until at a much higher temperature, higher than the engine's safe upper limit. Without holding pressure, the fluid can boil at a lower temperature and the cooling is much less effective. There won't normally be any visible leak as the expanding fluid is pushed across to the reservoir, and pulled back when the system cools down. You can sometimes have an ejection of coolant from the reservoir overflow if steam is formed in the engine (when it gets really hot) and blows through the line to the reservoir.

    From my own experience with my 5th gen, you can rag on the engine as hard as you like as long as you are moving steadily, and it won't heat up at all, usually sitting right around 180F. Heating only occurs when stop/start in traffic at very low speed. Check out the video of a VFR at Nurburgring, running near redline and sitting steady at 82C/180F.

     
  9. kevlar750

    kevlar750 New Member

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    I watched this video several times a few months ago and have it saved on YouTube. Quite impressive.
    Obviously I don't ride like THAT on my commute but I understand the point you are making. The only concern I have is that this is a new issue
    and my riding style and environment hasn't changed at all. Ambient temperature has risen for the summer months but this issue never appeared
    during the same conditions last year around this time.
    I will replace the cap and do the radiator touch test and see what happens.

    Thanx again for your input. It's greatly appreciated.
     
  10. skimad4x4

    skimad4x4 "Official" VFRWorld Greeter

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    This may or may not be relevant...

    When servicing bikes with side mounted radiators it is quite easy to end up with an airlock somewhere in the cooling system. It has happened to my 6th Gen after almost every major service when they replace the coolant. (Its been done several times now as the bike is over 200k).

    Even though levels in the overflow reservoir looked perfect when I got the bike home, there was air trapped somewhere in the pipework meaning the engine was running hotter than usual and on one occasion one radiator was cooler that the other. When the bike runs hot I now know to check, and thankfully it is easy to fix. Just put bike on main stand and remove filler cap and then run bike until it gets warm. Once warm round up a strong assistant and tilt the bike swiftly side to side. You may need to repeat several times until eventually a big slurp of air bubbles out from wherever it was trapped. Top up, fit cap and go ride...
     
  11. GreginDenver

    GreginDenver New Member

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    This forum thread is interesting to me.

    In my 5 years of VFR800 (5th Gen) ownership I've seen exactly the results this thread is pointing to: The bike maintains a normal temp range when you're riding, but it ends up right at the edge of acceptable temp at low speeds or in stop-and-go traffic.

    I believe this is due to an engineering compromise the Honda design engineers had to make when they chose to configure the bike with side-mounted radiators. The crux of the problem is the need to cross-connect the two radiators. This cross-connection has to be done at both the bottom and the top of each radiator which resulted in a large water hose having to pass very close to the exhaust headers for the forward cylinders.

    I've wondered if there's anything that could be done to cut down some of the radiant heating that transfers from the exhaust headers to the lower coolant crossover tube.

    I've been considering the idea of trying to install a heat barrier that would fit into the gap between the exhaust headers and the lower coolant crossover tube. Something like this item: https://www.designengineering.com/titanium-pipe-shield-12-x-4/

    So far this summer I haven't had the time to look into this issue, but I think about it every time I ride my 5th Gen.

    (The last time I brought this up on a VFR800 forum I was shouted down by a guy who couldn't understand the difference between radiant heating and convective heating).
     
    Last edited: Sep 8, 2020
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  12. kevlar750

    kevlar750 New Member

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    A co-worker of mine said it sounds to him like an air pocket.
    I'm going to replace the radiator cap, then drain, if not flush, the coolant.
    After refill I will surely be "burping" the air out.
    Thanks for your input.
     
  13. raYzerman

    raYzerman Insider

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    I'd put the bike on the side stand before filling or topping up, so right rad is highest point. Pour the coolant in slowly so not to trap air, underfill it a bit and run the bike until the thermostat starts to open... circulating coolant can be seen and air should purge. At this point you can blip the throttle a couple of times if you like. Once warm, ignition off and top up the rad, put the cap on. Top up the reservoir to max or a little more and mark the level. Run the bike again until the thermostat opens then shut it down overnight. You should see a slight drop in the reservoir level, open the cap again and top up the rad if necessary. Put the cap back on and warm the bike up again and you should be done. Top up the reservoir to max again as you always want max fluid available.
    Another thing you can do while filling (almost full) is squeeze the hoses to burp out any potential air.
     
  14. kevlar750

    kevlar750 New Member

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    I drained the coolant and replaced the rad cap (new). Added coolant the way most of you recommended and seemingly got all the air out. I rode to work a few days later and noticed pretty much the exact same problem. But the temperature was reading a few degrees higher this time! WTF!!!!
    Did I not clear all the air from the system? I'll try burping it again. The temp doesn't get above 220℉ but still won't drop below 195℉ on my way home in the afternoon. This is after lane splitting for about 40 minutes. Same riding conditions as last year, as I mentioned previously. Don't know if I have the patience to replace the t-stat, if it were to come to that. Don't really want to spend too much either. But who does?
    Thanx for any input and suggestions. I greatly appreciate it.
     
  15. raYzerman

    raYzerman Insider

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    I always re-check rad level after a couple of hot/cold cycles. There may be enough air to not allow full suction from the reservoir, so always good to check it anyway. Just top it up this time and another hot/cold cycle should do it.
    Hard to tell what is normal... lane splitting implies you're not getting enough air flow through the rads, perhaps try a longer highway run. If it doesn't behave better, then, yep, you are looking at a thermostat replacement, o-rings, etc.
     
  16. OOTV

    OOTV Member

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    I can definitely say that a bad radiator cap is a good place to start. I had overflow issues, where the reservoir would fill up and start pouring fluid out the overflow tube. I knew it wasn’t the thermostat as the bikes temperatures were operating normally. Replaced rad cap and all was good. That being said, if you’re going to test the thermostat, you might as well just replace it. Going through all the trouble to get to it, remove it and then test it, might as well just drop in a new one and be good with it.

    Also, if going through the trouble of draining the system and pulling everything out to get to the thermostat, maybe consider replacing the hoses with new silicone hoses., particularly if the bike is an earlier model 6 Gem i.e. 18 years old. Of course that’s just this riders opinion.
     
  17. kevlar750

    kevlar750 New Member

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    40-45 minutes of lane splitting. Then about 25 or 30 minutes of 6th gear, 5000rpm, 80mph until my freeway exit. Temperature reads no lower than 195℉ that entire time.
    Probably going to 're-burp' the system sometime this weekend. I'm not too optimistic on those results but I can hope for the best.
    Thanks again for the input from all.
     
  18. GreginDenver

    GreginDenver New Member

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    How clean are your bike's radiators?

    When I purchased my '99 in the Fall of 2016 it was clean and shiny on the outside, nicely waxed and detailed on the surfaces you could easily reach for a wash-n-wax session.

    Underneath the fairings it was a very dirty machine. And the radiators were also very dirty. During my extensive after-purchase maintenance and refurbishment efforts I cleaned the layer of dried-on crud off of the radiators.

    It seems to me that the radiators will work better if they're clean. Yes, it's true that my '99 will heat up in traffic and stop-and-go riding, just like your '98. When I get out from behind cars, riding in free air running at highway speeds, the bike cools off pretty quickly (to VFR-normal temperatures).

    But I have to admit that there are hot summer days in Denver when nothing seems to help after the bike reaches 220 in traffic (or at least it takes way longer than you'd expect for the bike to cool off on an open highway).
     
    Last edited: Oct 17, 2020
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