Symptoms of Overheating?

Discussion in 'Road Warriors' started by signal9, Aug 4, 2009.

  1. signal9

    signal9 Road Pirate

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    I'm riding a Honda CM400C, which is an air-cooled bike. It's been pretty hot of late and I'm noticing, particularly riding in the city, that the bike runs a little rougher when it warms up. The spark plugs read fine, best I can tell, but it's clear that the character of the ride changes.

    What are the symptoms of overheating on an air-cooled engine? What strategies would one pursue to manage heat?
    #1
  2. 1200B

    1200B Ride everywhere...

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    idk but when my ducati monster 750 got really really hot once it wouldn't shift and when my bandit 1200 got really hot and ran a lil rough then poured out black smoke when i finally got to open up the throttle all the way, then ran perfect...
    #2
  3. markk53

    markk53 jack of all trades...

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    The engine will start to sieze and forcibly slow up. Don't worry about it your 400 can handle any temps you're going to run into. Those engines were tough as nails. You have to believe Honda knows a little bit about how to build a four stroke engine for a motorcycle that will run from 0 degrees to well over 100 degrees... they were at it for a little while before they made your CM400 and in the years I sold Hondas from 1983 thru 2006 I can't remember ever seeing an air cooled Honda road bike come in seized due to heat. Maybe due to lack of oil but never heat.

    I would bet your running "a little rougher" is more psychological than physiological. I remember thinking the center cylinder on my 400 triple was seizing, when I first got it. All in my imagination. My bet is it is you, not the bike... Been there thought that. :D
    #3
  4. dyna mo

    dyna mo Guest

    you can smell things start to cook when the motor gets hotter than norm.

    i also notice the inside of my leg can feel the heat when it's above normal.

    to manage the heat on my harley, i've installed an oil cooler and switched to synthetic oil.
    #4
  5. kraven

    kraven Hegelian Scum

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    I agree with Mark K. I ride a little CB450SC right now and even in summer heat here in the south it doesn't overheat.
    I think that what happens to most bikes is that the carbs are tailored for a cooler engine temp and when it heats up the change you notice is in the mixture being too rich for a nice and hot engine.

    I've been riding air cooled hondas and kawi's for years. Never overheated one, including my CB900SS (4 cylinders).
    #5
  6. dtysdalx2

    dtysdalx2 PITA but useful

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    My XT did this on Sunday. Riding in 1st gear trails in the woods. It started to die wouldn't run. I assume the fuel was too hot/boiling and I loosened the gas cap, but it didn't help.

    You could get one of those oil temp gauges/dipsticks. I assume temps over 250 for oil is pretty high.
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  7. markjenn

    markjenn Long timer

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    Whether an air-cooled engine "overheats" or not is mostly a question of semantics. They may not overheat enough to cause immediate damage or seize, but they can overheat enough to shorten engine life and run more poorly over time. Frequent oil changes and synthetic oil helps.

    My experience is that air-cooled engines do tend to run a bit more roughly as they get very hot. It's probably due to having to use more throttle and revs to get the same power as warmer air is less dense and the barrel distortion that occurs in hotter weather results in more cylinder blowby. Its just something you live with and carry on, but it does help to take what measures you can to better cool an air-cooled engine in very hot weather - avoid idling, shut down at long lights, don't blip the throttle, use more revs and less throttle, etc.

    It hot climates and stop-and-go traffic, a liquid-cooled engine is a huge plus.

    - Mark
    #7
  8. Claim Jumper

    Claim Jumper will work for knobbies

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    My BMW seems to idle a little higher than normal when it gets really hot. My old '82 GS1100E suzuki once got so hot in uphill stop and go traffic that it started to diesel (or so I thought, I was really hot at the time). My Buell gets hot, the fan comes on, and my right ankle roasts, but it doesn't seem to run any different.
    #8
  9. 2slow

    2slow Road toad

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    Add an oil temperature gauge and you'll know if it is too hot. You want it around 200-210 degrees. Anything over 240 can shorten oil life, cooler than 180 will keep it from working properly and allow moisture buildup. Synthetic oils can stand higher temps. Stop and go traffic is tough on any air-cooled engine, though most of them can stand it better than you can.

    Overheating will cook your oil, turning it black, then lead to detonation which can wreck pistons, rings, heads. If you have seriously overheated an engine you will know but it will be too late.
    #9
  10. markk53

    markk53 jack of all trades...

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    Just remember though, one of the best desert bikes from back in the 1980s and 90s was the XR500-600-650R air cooled. And this CM is far far from the Equator so real heat is not much of an issue. The manufacturers do a fair amount of testing in conditions of higher heat than this CM is likely to be in.
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  11. markk53

    markk53 jack of all trades...

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    Interesting, how about my truck, with a 195 thermostat (possibly some bikes have them that high too)? I'd bet my truck's oil is at least 210 plus. At one time Kawasaki's Ninja 600 was having gages reading to the hot side. The fix was to add a resistor to bring the gage down. They felt there was no problem with oil temps as high as 280... under warranty.
    #11
  12. signal9

    signal9 Road Pirate

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    I've heard this said a couple times before, but I don't really know what it means. Should I wind out a bit more before shifting? Shift earlier?
    #12
  13. concours

    concours WFO for 44 years

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    use a lower gear, higher RPM (free revving) and don't lug the engine
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  14. signal9

    signal9 Road Pirate

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    Turns out I have been shifting pretty early, so I took this advice and started letting the engine wind out a bit more before shifting. Also I'm cruising town in lower gears, revs between 4k and 5k. Too soon to tell, but I think the bike is running a bit better?
    #14
  15. McB

    McB Joe 40 ouncer

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    It's a 30 year old motorcycle. Could be anything. Fuel, air, electric. Valves, rings, carbs........
    Or it could be nothing.

    Have you looked at the carb boots to make sure they're not cracked or worn, and are sealing tightly on the carbs and airbox? For that matter, have you checked the air filter recently?
    #15
  16. signal9

    signal9 Road Pirate

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    I checked the air filter right away, and it's brand new, perfectly clean.

    I suspect I do need to get into the carb, but I'm a bit intimidated at the thought. I've got the Clymer manual for the bike, so I think I could follow directions. What's the level of difficulty to remove and clean carburetors?
    #16