GPX250 Fan operation - how to check?

aubeasty · Post by **aubeasty** » Sun Aug 20, 2006 10:20 pm

Hey all,

In my ongoing battle with my mates '88 GPX, I need to know how I can test/check that the fan (and I guess the entire cooling system) is actually working?

Any solution on or off bike would be fine

FrogZ · Post by **FrogZ** » Mon Aug 21, 2006 6:48 am

...stick your finger in the blades, you can BET the sucker will kick in then.

Better off describing the symptoms, it might not be what you think..

aubeasty · Post by **aubeasty** » Mon Aug 21, 2006 11:48 am

frogzx12r wrote:...stick your finger in the blades, you can BET the sucker will kick in then.
Better off describing the symptoms, it might not be what you think..

I like your thinking, but we already worked out that you can idle the bike for about 15 mins on about 100ml of petrol + vapour....Don't like my luck

Symptoms are odd - bike runs fine, then once it has been running for some time, the temp goes above half, then dies. My mate says he had to hold the throttle to about 2k rpm to prevent the engine from dying, and on a copuple of occasions it died for a few mins....seems to be temperature related. Anyways, in our tests over the weekend, once the temp got high, the bike started to die - we never noticed the fan actually working, hence the reason for my qn.

Things we've worked out:
1) It's not the fuel tap from the tank
2) It's not the carbies (we rigged up a direct-carbie-injection system to prove the bike can run with direct fuel into the carbies)
3) It seems to have had an 'aftermarket' inline filter placed between the bottom of the fuel tap and the entry point into the carbs...I believe this was 'starving' fuel, but we never had a chance to replace it with a straight-through fuel line...

In essence we're trying to work out if there's a kinky combination of high temp + fuelling issues that's starving the engine of fuel....

mike-s · Post by **mike-s** » Mon Aug 21, 2006 1:56 pm

have you checked that the water pump isn't shot?

that'd be one of the first things i'd try.

Duane · Post by **Duane** » Mon Aug 21, 2006 2:00 pm

Make sure the airbox is sealed correctly, if it's getting too much air at idle it can die (was happening with a zzr250) quick fix

aubeasty · Post by **aubeasty** » Mon Aug 21, 2006 3:59 pm

mike-s wrote:have you checked that the water pump isn't shot?

Ta - I think once we've isolated it to the cooling system, the whole thing will be investigated....pump, hoses, thermostat, fan, etc. Any idea on exactly how to check the water pump? I have noticed a swirling vortex thingy inside the radiator when the bike is running. I am assuming this means something is sucking the water through, and again am assuming this is the water pump at work...)

Duane wrote:Make sure the airbox is sealed correctly, if it's getting too much air at idle it can die (was happening with a zzr250) quick fix

Yep - we checked the air filter and ensured the airbox is sealed all around (short of removing it to see if maybe there was a hole somewhere we could not see....)

Thanks for your help so far, tis appreciated

Duane · Post by **Duane** » Mon Aug 21, 2006 4:43 pm

Check your coolant for milk

aubeasty · Post by **aubeasty** » Tue Aug 22, 2006 8:28 pm

Duane wrote:Check your coolant for milk

Well, so far no milk...what came out of the bike was a copper-brown, and currently it's still showing the greenish tinge from when we flushed it out and refilled it......

mike-s · Post by **mike-s** » Tue Aug 22, 2006 11:11 pm

if its brownish, remove the radiator tube, point a hose at it, turn it the hell up and flush all of that shit out of every part of the cooling system. once that's done, run some (correctly diluted) alkaline coolant flush through it for about 40 mins, then flush it again, replace it with coolant.

but re the cutting out, i'd check the thermostat on there too.

photomike666 · Post by **photomike666** » Wed Aug 23, 2006 12:06 am

I'd probably start by replacing the plugs - all sorts of things affect them and is often the problem.

Steve_TLS · Post by **Steve_TLS** » Wed Aug 23, 2006 9:43 pm

Could be ignition / electrical, coil(s) failing when hot etc. I've had a coil that would only work when cold before.

1/2 gauge isn't all that hot. In the red is hot. Not 100% familiar with the GPX, havn't touched one since about 92, but there's probably a bimetallic temperature switch mounted in the side of the radiator, pull the plug off and use a paper clip or something and bridge the two wires, the fan should come on.

(I'm 99% sure the temperature sender for the gauge is mounted in the thermostat housing - you don't want that one for the test.)