Fan Control Switch

[lragan]

While idling in a long queue at the north entrance of the White Sands Missile Range, the engine on my '96 got hot, as indicated by the idiot light, and from the emitted odor.  The fan would come on for a short while, but did not stay on long enough to cool the engine.  Air temperature was around 40 degrees at the time.  Of course, as soon as we cleared the inspectors and moved up to speed, it cooled.

I concluded that the fan switch was faulty, and purchased and installed a new one.  In an attempt to confirm my diagnosis, I clipped onto the old switch and immersed it in boiling water.  It did not close.

I perused the Magna manual and the shop manual, and could find no information regarding the on or off temperature for the fan switch, or, for that matter, the thermostat temperature characteristics.

If you have this information, please post it.  Thanks in advance.

[LateStart]

I can't help you on the specs but I'm in Texas and my 98 magna will not overheat in 100+ degree summer jacked traffic.  On the other hand my v65 would overheat first in line at a light waiting for the green.  The problem was tracked down to a plugged core in the radiator.  I can now sit on the v65 in traffic during the summer and it doesn't overheat either.  The fanstat may have been a problem but at 40 degrees ambient, I would suspect a severely restricted flow through the radiator.  At that temp the bike should have been able to idle for hours without overheating. 

[hootmon]

I now keep a piece of wire in my saddle bag.. If worse comes to worse, I can short the wire that goes to the thermister in the radiator to ground and the fan will run continuously.. Or the wire is long enough that I can run it up and short it at a light or stopped traffic if I don't want it to run all the time.

[SkyRide]

Lawrence,

I don't know about newer bikes, but I found this in Haynes for older ones.  Maybe yours is in the same ballpark.

Year     Turnss on  Goes off
83-84  191-197    182-188
85-88  208-215    208

Rick Frankenberger

[TLRam1]

Maybe the fan itself or the thermostat is faulty also.

[lragan]

Thanks all, for the info. 

It seems unlikely the radiator is plugged.  The anti-freeze/water mixture shows no contaminants at all. 

I have never idled the bike this long -- anywhere, at any time, and I suspect that others haven't ether.  We were idling for 40 minutes, minimum.  It did not show hot until about 30 minutes in.  When the light first came on, the fan ran long enough to turn it off, but as time went on, the idiot light remained lit.  The fan never ran more than 15 seconds at a time.  By itself, the fan will run just fine.

Like most of you, even on the hottest days, stopped at a light, at low speeds through traffic, the fan never activates.

The pressure did not build to the point where water or steam escaped the radiator cap relief tube.

I have not checked the thermostat, but suspect that the coolant would have overheated much quicker than it did.

Given Skyride's input, I am going to proceed on the assumption that the fan control switch was the only problem.  We shall see...

[hootmon]

I don't think it needs to be said, but my fan has run longer than 30 seconds...
Also (probably doesn't need to be said) the switch only supplies a path to ground, so, IF you have a wire, you can force the fan to run longer IF the switch goes bad..

[lragan]

Good point, Hoot!

I will add a clip lead to the inventory of items I carry in a saddle bag.

[hootmon]

Good point, Hoot!

I will add a clip lead to the inventory of items I carry in a saddle bag.

Seems like a good item to carry for LOTS of reasons anyways.. Can be used for many electrical issues
Could be used to tie a loose part if needed
Good McGeiver supply!!! LOL

[MagnaMan]

Lawrence,

Awhile back I had to replace my fan thermoswitch in the radiator and it behaved similarly. I believe I found the operating range for it buried somewhere in the specifications table at the front of the Magna manual. The actual testing of it was covered in the Honda Common Service manual, I believe.

[doscoras]

magnaman i have this link it might help im not sure. its old but it works

http://www.cantonmg.com/stewsplace/ShopManualVF750C.html

[lragan]

Update -- I replaced the fan switch, and then tested the old one in water -- up to boiling, still did not close.

Have not experienced the problem since, but haven't idled for 40 minutes, either..

[rrodscott]

Replaced my defective fan switch with one from a 84 civic. Rewired the circuit so the switch activated a relay that then runs the fan. Also installed LED that lights when fan is running and put in bypass switch if the radiator switch fails. I feel much better now idling in the summer.