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Tech Tips Index > Suzuki King Quad 450/700/750 Sign up or Logon

Cooling System - Overheating - 450/700/750

by Glenlivet, 2008-09-18


The King Quad is a big relatively high compression single, with a cooling system roughly equal to the Suzuki 500 Vinson, in fact the Vinson is equipped with a full shroud and fan on a radiator of the same capacity as the King Quad, which uses a contained circumference fan of much smaller swept area! Add to this the fact that the King Quad radiator has small and closely spaced finning that is readily plugged by mud, and difficult to detect this is so. Overheating is a distinct possibility, and this can lead to early wear and failure of top end parts, requiring an expensive rebuild.

For a liquid cooled motor vehicle the King Quad tends to run relatively hot, by design. Trying to make the engine run below its designed operating temperature would serve no good purpose and in fact would be counter to a goal of getting the best service life out of the motor, but if the motor seems to be running overly hot or the fan is heard to be operating a great deal of the time then something might be wrong. (1)
  • The thermostat opens at 177* - 182*(degrees).
  • The electric cooling fan kicks in at 199* and off at 189*) and,
  • The King Quad has a fairly high pressure rad cap (15.6 - 19.9 pounds!)

    The classic sign of an untended liquid cooled motor overheating is 'boiling over'. The coolant reaches a temperature such that it begins to boil and the resulting pressure spike overcomes the pressure cap, and the coolant escapes (in the King Quad's case, into the overflow reservoir)
    This is an undesirable thing. (Normal expansion of the coolant as it reaches operating temperature also causes some of it to go into the reservoir, that's a different thing)

    Now straight water boils at 212* (at sea level) and at 15 pounds additional pressure in a cooling system, boils at 256*. If you are running standard 50% water/antifreeze then that mixture's additional density moves the boiling point up by about 13-14*, so in order for coolant to have escaped the rad cap into the overflow reservoir,(assuming the cap is working properly) it has to have exceeded a cracking 280 degrees! That's hot. And dangerous, not only to people but to the engine.

    There are a number of temperature gauges available designed for use on a liquid cooled motorcycle or ATV, and easily found through an internet search engine using a prompt like 'ATV Temperature Gauge'. One of these can be a valuable asset for people wanting to keep a keen eye on their engine's operating status.

    The gauge needn't be a source of worry, so that the rider is constantly looking at it and seeking to lower the reading, after all if it weren't for the gauge you wouldn't know that a King Quad normally runs a bit 'warm'. The dash 'overheat' light isn't on.

    Some gauges do not have a numerical display or graduation but rather the needle sweeps through a colour bar.
    The colour schemes on the un-graduated gauge are a good guideline for telling you when you might want to stop operating the quad and let it cool (the red zone), or find out why it isn't doing so.
    If you have that gauge and are concerned about actual readout, you could get yourself a candy thermometer (they are quite accurate large glass thermometers, like a great big version of the kind moms used to stick in a sick kid's mouth) and leave the rad cap off and stick the thermometer into the coolant, read what the real temperature is for the corresponding indication on the gauge, and remember it for future reference.

    The protocol for a King Quad rider who has a temperature gauge might go like this:
    When doing something IE. mud running or hill climbing, that might create lots of heat...

    - If the overheat dash light comes on then stop doing what's causing the overheating, but leave the quad running (2) (as long as the fan is working), and watch the gauge.
    - If it goes up more, shut the ATV off and let it cool down. Then find out what's going on, clogged rad, bad pump, stopped fan, lost coolant...
    - If it goes down, then let it cool off some (and clean out that rad ).

    And while doing things that might cause overheating, keep an eye on the gauge from time to time because the overheat light in the King Quad and the sensor that runs that light, have been known to fail.

    (1) What can go wrong to cause overheating? In (I hope) descending order of likelihood:

  • The most frequent cause of a King Quad running too hot is a plugged radiator. The fins are tightly spaced and mud or dust accumulates fairly easily. Many King Quad owners have thought their rad was clean but have been proven wrong when flushing loosens a flow of mud from the vanes.
  • The fan/motor can fail. The fan is either physically stopped from spinning or the motor is damaged or the fuse blown from the fan being stopped from turning by mud, water, whatever.
  • Coolant lost. A damaged rad or hoses allows the coolant to escape and the reduced volume of coolant is less effective at dissipating heat.
  • The coolant pump can fail. This is sometimes accompanied by leakage of coolant from the hole below the pump body on the left front of the engine.
  • Blown head gasket. Some of the combustion gases blow straight into the water jacket, heating and over-pressurizing the coolant. This is usually accompanied by antifreeze smelling steam from the exhaust and contaminated engine oil.
  • The thermostat can stick, inhibiting the circulation of the coolant. In automotive theory at least. Haven't seen a report of this in a King Quad yet.

    (2) The overheat light is set to come on at around 230 degrees though the exact temperature is not provided in the service manual. In any event it will come on well before the coolant boils in a properly pressurized system, so running the motor for a bit following the light coming on will still be far below the temperature at which a King Quad boils over.
    One should be plenty safe to run the motor for a short time while watching the gauge in order to see if things are going to be under control.



    Making sure the Air is out of the system. If not you will experience overheating issues. In this Thread it explains possible overheating issues.
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