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Old 07-21-2005, 03:08 PM   #1
Ian640 OP
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Question LC4 Overheating

My 2002 640 LC4-E is overheating at low speeds on the trails and around town. Sometimes the fan switches on at the same time, sometimes it doesn't. The overheating warning lamp has switched on once. The overheating is evident as jets of very hot water coming out of the overflow pipe. The flow stops when the engine is switched off. Here's the full story:

From new the bike had a very tiny leak of liquid from the joint between the cyclinder head and the cylinder, around the rear of the cylinder to the right of the inlet. Sometimes the leak wasn't even evident. I first discovered it in the Sahara so I wasn't in a position to return to the dealer I bought it from.

I finally got around to fixing it about a year ago, assuming the head gasket was faulty. When the head and gasket was removed, there was a scratch on the surface of the cylinder barrel (the surface that the head gasket rests on) between the water jacket and the outside world. The surface was 'rough' presumably to aid sealing.

I took the cylinder barrel to a reputable machine shop and had it machined to remove the scratch. I don't recall how much the machinist took off, but do recall that it was between 0.1 and 0.2mm i.e. it wouldn't raise the compression ratio anymore than fitting a 0.5mm base gasket (I believe the stock base gasket is 0.7mm). The surface was now smooth due to the machining.

The whole show was carefully reassembled. On the first slow going on a trail on a hot day, about 1000 miles after the fix, the problem became evident. I've replaced the thermostat, fan thermoswitch and radiator cap. There's no evidence of coolant leaks. There's no evidence of conatmination of the oil with coolant and no evidence of contamination of the coolant with oil. Yet the problem persists. Anyone any pointers?

Thanks in advance.
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Old 07-21-2005, 07:59 PM   #2
lvdukerider
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The only input I can offer is make sure the radiator isnt overfilled, The manual for my 00 Duke II says the coolant should not be filled all the way to the top, to allow for expantion I suppose. I ride my Duke II here in Las Vegas where it has been teribly hot lately,117 F. the other day and the fan runs but it does not over heat even in traffic.
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Old 07-21-2005, 08:17 PM   #3
dagwood
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another thought.
higher compression might need to be fattened up abit. could be its running on the lean side now and in turn will run hotter. that and high test petrol 92+ might help.
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Old 07-21-2005, 08:28 PM   #4
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Longshot, but did you ever take a look at the water pump to see what the impeller looked like? And maybe the thermal switch for the fan has gone wonky.

Also, not that it would have anything to do with the problem at hand, but your cam timing is going to be a slight tad off from machining the barrel.

What jetting are you running, and are there any other mods to the exhaust or intake?

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Old 07-21-2005, 08:49 PM   #5
DC950
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this is just an opinion so take it for what it cost you. I don't think your current problem has anything to do with the old one. Your first two sentences are the key:

My 2002 640 LC4-E is overheating at low speeds on the trails and around town. Sometimes the fan switches on at the same time, sometimes it doesn't.

From that, I'm assuming there are times the fan is not on before the engine overheats. The fan should ALWAYS come on before the engine overheats. Stating the obvious, its there to provide additional cooling airflow before coolant starts spewing. For some reason, 1) your fan isn't being told to come on when it should; or 2) it wants to come on but can't; or 3) something is wrong with the fan motor itself.

This should be easy to diagnose with a multi meter and the specs for the various parts. Where you get those specs, I don't know. I have no idea what tests you did before you replaced parts, but in the words of a very, very good mechanic I used to know "replacing parts is an expensive way to diagnose electrical problems".

Always start simple and go from there. Jetting, timing, octane, etc are all long shots that are way down the lists of possible problems to check out.

And definitely check the level like LVDuke says - its the simplest answer! If I fill mine too much, it leaks when hot till it reaches its equilibrium level (then it leaks more when I crash but that's another story)

I wouldn't be surprised if its a ground (earth) problem. Good luck!
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Old 07-21-2005, 09:45 PM   #6
markjenn
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DC950 is right on with his advice. If the bike is overheating with the fan off, then you've found your problem - the fan. These things will always overheat in traffic without the fan.

- Mark
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Old 07-22-2005, 11:10 AM   #7
Ian640 OP
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Thanks for the replies. Further investigation required. I have tested the fan by shorting out the thermoswitch terminals and it's switched on every time, but this doesn't eliminate the possibility of an intermittant fault e.g. a poor connection. I suppose a better test would be to borrow a fan from another LC4 and check if the problem persists.

I'm loosing a lot of coolant, like half a litre.

I can't think how the pump could fail other than the bearing but I'll strip it down to check the condition.

Jets are as recommended by Sommer for my pipe/airbox setup.

I almost always use '98' fuel.

My thinking was and still is that the coolant is boiling at a lower temperature than it ought to, implying an inability to build up sufficient pressure implying a leak.

Cheers.
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Old 07-22-2005, 12:42 PM   #8
Mack
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check the seal on the rad cap valve very closely for debris/tears, and the radiator sealing surface for the deformities. if symptoms persist i'd change the cap.

[caps/shift key inop.]

for lc4's in hot climates, i strongly suggest a manual override switch for the fan and mixing h2o to anti-freeze at 75/25 or even 80/20.
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Old 07-22-2005, 12:53 PM   #9
markjenn
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An override switch would be an easy way to confirm that it is the lack of fan that is the problem.

Shorting the fan thermoswitch doesn't tell you if the switch is malfunctioning. I wonder if the thermoswitch is coming on late putting you right on the edge where, depending on heat distribution and specific conditions, sometimes the fan activates (late), and sometimes not at all before it has boiled over.

New pressure caps are cheap.

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Old 07-22-2005, 12:55 PM   #10
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Quote:
Originally Posted by Ian640
I have tested the fan by shorting out the thermoswitch terminals and it's switched on every time, but this doesn't eliminate the possibility of an intermittant fault e.g. a poor connection.
I'd be more interested in what temp the switch trips and if its consistanly less than 1 ohm when it does. Somewhere around 90-100C is the switch continuity point isn't it?
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Old 07-22-2005, 01:31 PM   #11
Ian640 OP
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Thumb

Thanks.

I doubt if either the new thermoswitch nor the new radiator cap I bought (see original post) are faulty, but at this time I don't know. The cap, seal and area where the cap fits are all clean.

I think the temperature at which the thermoswitch operates is around 90-100 degrees C.

Checking the resistance of the fan circuit (i.e. consistently very low) with the switch closed is something else to add to the check list.

Cheers.
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Old 07-22-2005, 01:48 PM   #12
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Quote:
Originally Posted by Ian640
Thanks.

I doubt if either the new thermoswitch nor the new radiator cap I bought (see original post) are faulty, but at this time I don't know. The cap, seal and area where the cap fits are all clean.

I think the temperature at which the thermoswitch operates is around 90-100 degrees C.

Checking the resistance of the fan circuit (i.e. consistently very low) with the switch closed is something else to add to the check list.

Cheers.
Gota remember Ian, with any electrical component, even brand new... there is always a percentage that fail right out of the box.
If they can have a faulty ground on the space shuttle... imagine what the QC is on a $5 switch for a dirt bike.
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Old 07-22-2005, 02:10 PM   #13
Ian640 OP
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Fair enough. Surely the resistance test will give an indication. Again borrowing a known working one is another approach.
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Old 07-22-2005, 02:43 PM   #14
meat popsicle
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I just bought a second fan off a guy in the UK (eBay). Sorry but I think it's already en route here or I would ask it to go to you first.

But if the fan comes on then it ain't broke eh? wiring sure, but that would suck.
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Old 07-22-2005, 02:49 PM   #15
Ian640 OP
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Thanks for the thought.

FWIW I had a second fan on my LC4 for a desert trip. I recall the plastic case of the fan had to be cut a little to make it fit, due to the shape of the fuel tank. The tank was from a 2002 640 Adventure.
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