Fan kicks in extremely late!

[desewer]

Hi all

My fan kicks in extremely late and I'm wondering where to start troubleshooting. I've changed the thermo sensor thrice in the past 6 months to no avail. Right now I'm riding with a direct current to the fan, so it's permanently running.

Fyi I'm riding in tropical Singapore and a couple nights ago I was caught in a traffic snarl the fan didn't run when it should, the coolant reservoir cap just blew out and some boiling coolant scalded my right thigh. The problem doesn't seem to recur once I had the fan permanently on.

Almost everything else is new. I just had the engine overhauled and the main wire harness changed last October. Even my fan relay is brand new. I'm also running Christian's multi gauge but the water temp reading is just missing (shows a dash or hyphen).

Any ideas? Is it possible the thermo sensor wire needs replacement? Could the fan possibly be waiting for a Fahrenheit reading (high!) from a Celsius sensor?

Thanks in advance!

[desewer]

Some photos of my bike at overhaul. There was a bloody leaf in the intake valves I got done pretty bad by the previous owner

[Red Ceri]

I can't remember where in relation to the thermostat hot side the Temperature sensor is but it sounds like that either the Thermostat is not opening or there is a massive air lock in the system preventing hot coolant getting to the temperature sensor and thus the reason the fan is not kicking in is it is relying on surrounding parts getting hot and not the flow of hot coolant over it.


Worst case scenario is water pump failure, thus not pumping hot coolant around the system and  past the temperature sensor.

[PieEater]

I don't know if this is relevant but I had something similar inasmuch as coolant being forced out of the bike all over my leg with a RD350 YPVS this apparently was due to a cylinder head gasket failure,  I assume somehow this had pressurised the cooling system. I know that you have had a major rebuild but was the head checked to make sure it wasn't warped at all before it went back together?

[desewer]

I can't remember where in relation to the thermostat hot side the Temperature sensor is but it sounds like that either the Thermostat is not opening or there is a massive air lock in the system preventing hot coolant getting to the temperature sensor and thus the reason the fan is not kicking in is it is relying on surrounding parts getting hot and not the flow of hot coolant over it.

Worst case scenario is water pump failure, thus not pumping hot coolant around the system and  past the temperature sensor.

thermostat is new too, but i think your explanation about the fan waiting for surrounding heat transfer makes sense

[desewer]

I don't know if this is relevant but I had something similar inasmuch as coolant being forced out of the bike all over my leg with a RD350 YPVS this apparently was due to a cylinder head gasket failure,  I assume somehow this had pressurised the cooling system. I know that you have had a major rebuild but was the head checked to make sure it wasn't warped at all before it went back together?

this could very well be what's causing the problem. we tried idling with the radiator cap off, and every once in a while we saw a few air bubbles making their way up. mechanic said he'll remove and check the head for warping.


still doesnt address why my water temp isnt showing on the multi gauge though

[PieEater]

I'm not a mechanic but hypothetically you may have a warped head which is causing air to get into the cooling system. This air is finding it's way to the top of the system and sooner or later getting into  the thermostat housing. With some air going through or remaining in the housing the thermostat will take longer to get up to temperature and activate the cooling system which would explain the delay in the fan spinning up. If the thermostat housing completely fills with air the thermostat may not get to temperature to open the cooling system at all causing the local coolant to boil and pressurise leading to it being forced out of the system, which would explain your scalded leg.

You're right though that this doesn't explain why the multiguage isn't picking up the temperature reading as it should. I would contact Christian and see if he is able to make any suggestions, he was active on these forums a while ago and is very helpful. I assume you bought the multiguage direct from Christian so can lay your hands on his contact details.

[ram]

could you take out the temp sensor and put it in boiling water (may have to add some wire to reach) to see if gauge works then?
also can your garage do a sniff test on the rad while bubbles are coming up? - that will show if head gasket is leaking.
also, i had a car once that used to leak water and when it was below temp sensor the gauge would read cold so it could be air pocket around sensor as stated above?