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how to check is cooling fan works

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Ideally without baking the engine... 

I know 2strokes don't overheat as quickly as 4bangers but when I rode my TXT 250 (2004) the other day in the woods it seemed to be kicking out a fair amount of heat, but without a temp gauge and not managing to find anything in the manual from GasGas I have no idea if my fan works or not.

Is there way to test polarity/resistance with a multimeter?   

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You could try holding a thermometer against the cylinder head as this in theory will be the hottest part save for the exhaust port area. You can buy for about £14 a multi-meter with thermo probe attachment which is very useful. Alternatively you could temporarily remove fan connector and power the fan up or remove temp sensor connector and bridge both terminals in the wire connector, this should run fan. Before you do all of this make sure the fan is free to turn and not trapped by a dislodged cover etc.

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Don’t hold a thermometer to anything - it will explode.

If I’m right the Gas Gas txt pro 250 has an in-line t-block that has the sensor in it. Will have two wires - probably going to a relay.  With the bike running - connect those terminals together. The relay should switch , and the fan should run. If this happens , then the thermo-switch or wiring is faulty.  

 For a simple continuity-test , set the digital-multimeter to the Omega/ohms setting , in the higher range.  Open probes will read 1 , or infinity. Touch the probes together , and they should show zero or 0 on the meter. On an old analogue meter -  Closed terminals it rises to zero.  (i think! It’s been so long). Use crocodile clips and join the probes to the wires.

If I have ascertained that my fan and relay are both fully working - then I would perform the thermo-switch test with the thing removed from the bike , using a pan of water on the stove - instead of risking over-heating the bike.

If jury-rigging the relay isn’t successful. Then try and apply voltage to the fan to check that. Once you know the fan is ok - then it is more than likely the relay (or wiring) at fault.

You don’t have to do these tests in any particular order , but the fan and relay checks are the least-messy if you have an external power-supply or battery.

Edited by Nebulous
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6 hours ago, Broadburner said:

Ideally without baking the engine... 

I know 2strokes don't overheat as quickly as 4bangers but when I rode my TXT 250 (2004) the other day in the woods it seemed to be kicking out a fair amount of heat, but without a temp gauge and not managing to find anything in the manual from GasGas I have no idea if my fan works or not.

Is there way to test polarity/resistance with a multimeter?   

if the fan is working it will come on and you will be able to hear it spinning and  feel the air being pushed near the cylinder .....you can also see that the blades are spinning...if its does not work you will know very quickly with the resulting steam and blowing coolant pipe etc

Edited by oni nou

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22 minutes ago, oni nou said:

if the fan is working it will come on and you will be able to hear and feel the air and see that the blades are spinning...if its does not work you will know very quickly with the resulting steam and blowing coolant pipe etc

Since Oni Nou is hanging about - I’ve a related question (no , not about my cousin!) - since most trials riding is at relatively low-speeds , and the air-flow through the radiator isn’t perhaps paramount. How important is it , that the fins of the rad are straight - and unbent to allow air to pass through the elements?  Exuberant power-washing tends to flatten the fins down. Is this going to really cause problems on a trials bike - especially the 4RT with it’s over-specced rad?

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I would suspect that your fan is a 12V DC unit. It may state that on a label if present. If you can isolate the connections to the fan motor (i.e., break the power and ground connections) you should be able to power it from a external source (say a 12VDC automotive-type battery).

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2 hours ago, Nebulous said:

Since Oni Nou is hanging about - I’ve a related question (no , not about my cousin!) - since most trials riding is at relatively low-speeds , and the air-flow through the radiator isn’t perhaps paramount. How important is it , that the fins of the rad are straight - and unbent to allow air to pass through the elements?  Exuberant power-washing tends to flatten the fins down. Is this going to really cause problems on a trials bike - especially the 4RT with it’s over-specced rad?

Hello Nebulous yes it is important that your rad fins are not all mashed up ....the best way to get any dirt out from between the fins is to release the radiator and remove the fan with its cowling then blow compressed air through in the reverse flow of the air.....you can straighten mashed fins a little by carefully moving them with a fine flat ended jewellers screw driver or similar to open them up for the free passage of air.Good morning to you.

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11 hours ago, oni nou said:

Hello Nebulous yes it is important that your rad fins are not all mashed up

I avoid this by jet washing from a distance so the full power of the water stream isn't bending my fins. 

My 600 has an ally rad and the find are super easy to bend. 

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1 hour ago, Broadburner said:

I avoid this by jet washing from a distance so the full power of the water stream isn't bending my fins. 

Indeed.  Unfortunately , out of my control when taking delivery of a 2009 bike that’s seen plenty of mud.  When I built refrigeration units for the printing-trade - we PDI’d the units , and one operation was to comb the fins and spray them with matt black if needed. We used a plastic comb so as not to scratch-off the coating - otherwise rust could form. Alloy rads probably don’t have that problem. But the 4RT rad uses oval fins - which can’t be combed with any efficiency. Looks like a long night with a flat-blade.

I just wondered , how much leeway have I got before it becomes an issue? A new rad being just over a hundred squids.  When a bike is idling and stationery  - does it matter that airflow is restricted?       I agree with Oni , that removing the cover , getting it wet with soapy-water - and using an airline from the back , is the best method for blowing mud out.  Mostly all cleaning operations on a trials-bike can be done with hot soapy water and a soft brush. A hose with your thumb over the end is about the strongest you need to go. The same goes for most domestic modes of transport.  The prevalence of high-pressure powerwashes outside of industrial deep-cleaning , high-volume car-valeting ,sewer-work or patio freshening - is just overkill , and just the sort of male-posturing that got this world into the mess it’s currently in!

Edited by Nebulous

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2 hours ago, Nebulous said:

I just wondered , how much leeway have I got before it becomes an issue? A new rad being just over a hundred squids.  When a bike is idling and stationery  - does it matter that airflow is restricted?      

Well as you pointed out there isn't a lot of air flow over the rad fins when stationary - unless you aim it upwind - however the main idea of a rad is increased surface area to facilitate cooling by heat transfer, so long as the ambient temp is less than the rad temp via the magic of thermodynamics, specifically heat transfer rates, the flow of the coolant around the engine and through the rad will still aid in cooling your motor. Your pump is circulating coolant through the rad all the time it's running.

Air flow over the rad simply makes this transfer more efficient. 

The level of impediment posed by a few few bent fins would be so insignificant that it would be beyond regular measurement.  If the rad is very damaged however, ~60% of the fins surface area is damaged - then you would see a decrease in thermal transfer which could lead to overheating. 

2 hours ago, Nebulous said:

The prevalence of high-pressure powerwashes outside of industrial deep-cleaning , high-volume car-valeting ,sewer-work or patio freshening - is just overkill , and just the sort of male-posturing that got this world into the mess it’s currently in!

I wouldn't necessarily disagree with that, I use powerwashers sparingly on bikes as it's quite easy to blow water past things like carb seals, brake caliper pistons. and electrics and cause damage.  

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