Coolant all over the place

[laxin20]

Well I am a new owner of 78 GL1000 that my wife purchased for me for a wedding present (clearly she is a keeper). This is the first bike I have owned. Last night my neighbor and I were putting in some fuel/carb cleaner in the gas tank and letting the bike run a little to work the cleaner through. In doing so I turned off the fan (the previous owner had hard wired a switch for it) by accident, I didn't know what the switch was for. About 5 mins later... coolant is all over the ground. I turned off the engine and then could hear coolant boiling.

Couple questions....
1. Where did the coolant come from?
2. How bad did I screw up my bike?

Thanks!

[WingAdmin]

You overheated the bike. Same thing as when you see a car overheating with steam coming out of the hood.

What happened is the bike's engine got too hot, the coolant boiled, and the superheated steam, now under tremendous pressure, forced the coolant past the radiator cap.

With any luck you haven't done any damage. Once it's cool, check the coolant reservoir tank and make sure it's full up to the line. Check the radiator and make sure the coolant is up to the fill neck. You will very likely have to add coolant to replace what was lost - make sure you use the correct kind (non-silicate) - you can't go wrong with using Honda coolant.

If you run the bike overheated like this for any length of time, you can warp heads and cause head gasket failures, but the fact that it was just idling in the driveway, and that you shut it off right away, hopefully means you've avoided any of this.

I'd recommend replacing the thermostat switch and getting rid of that manual switch. That will switch the fan on and off as the bike's engine requires it, as it was originally designed. This will prevent this from happening again.

[laxin20]

Well that defiantly makes me feel better! Where is the thermostat located?

[WingAdmin]

Have a look at this diagram of the coolant tubes (located on the top of the engine):

GL1000 Thermostats

The temperature sending unit is what actuates your temperature gauge. It varies resistance based on temperature.

The thermostat is a valve that opens and closes to allow coolant to flow when the engine heats up.

The thermostatic switch is a switch that closes when the engine heats up, actuating the radiator fan.

[laxin20]

Alright when I get home from work I will take a gander at this.

Thanks for the advice!

[scotterichmond]

I would add ; replace with OEM honda

[laxin20]

Alright I started everything up, let it run in the garage (with the fan on) for a few minutes and evrything seems to be looking good.


Why would I change the thermostat?

[WingAdmin]

I'm assuming the reason for the switch is due to the failure of the thermostat switch - instead of replacing it, just add a switch to actuate it manually. It's a fairly common "non-fix".

Occasionally people will add a switch in parallel with the thermostat switch so that they can FORCE the fan to come on even if the thermostat switch isn't calling for it. But you really should have the thermostat switch connected and working as a fail-safe to guard against human error - as you have learned.

[sfruechte]

Just to clarify, Wingadmin is saying change the thermostat 'SWITCH', not the thermostat. Two different things.

[tom84std]

On my '84 (which had previously belonged to my brother) I found he had installed the aforementioned added toggle switch. After I got it from him, I diagnosed the circuit as I wanted to restore the function of the bike's thermo switch for exactly that reason. I found the problem to be in the circuit, not the thermo switch.
With the key ON, the fan motor has +12V always connected. The fan motor gets it's ground (-Voltage) through the thermo switch. I found that the problem with the circuit was that the fan motor was not receiving the +12V. The problem was a blown glass AGC fuse located under the seat that he didn't know about. I replaced the fuse and the function was restored so I removed the added switch. Now it works fine. One way to test the circuit is to locate the rubber plug on the thermo switch, unplug it and jump across the two conductors of the rubber plug with a short piece of wire. Turn the keyswitch ON and the fan motor should run. If it does, the problem indeed lies in the thermo switch. If it doesen't, the problem lies in the bike's wiring somewhere. Perform this test with the added switch in it's OFF position or removed. You can easily test the circuit with a simple test lamp, the alligator connector hooked to a good ground such as the -BATT terminal. Verify the fan motor's connector has +voltage present with the keyswitch turned ON. With the wire jumper still installed into the rubber plug, move the test lamp's alligator connector to the +BAT terminal and probe the other side of the fan's connector to insure it's still grounded. You need to get a good schematic diagram. I've found the factory manual's schematic to be a bit crowded and difficult to read and prefer the Haynes myself. I'm sure there are differences between my '84 and your '78. It would be easier to help you with yours if I had the proper schematic but alas I gave mine to the new owner when I sold my '79.

[glhier]

I recently had the cooling system "opened up" on my '84 Aspencade, to replace hoses, etc. While I was there, I removed and tested the thermostatic switch, and the thermostat, using a pot of hot water, a thermometer, and a test meter. The thermostat checked out fine, opening as expected and closing again when cooled. The thermo switch, however, behaved differently. An Ohmmeter was connected to it and read infinity as it should, and when the water temperature was increased (roughly 190 to 200 degrees F), the thermo switch operated, but displayed significant resistance across the contacts (fluctuating between 10 and 30 ohms). Of course, it should have read 0 ohms. This elevated resistance limited the full +12V to some value less than that, which prevented my cooling fan from operating at full speed. The fan was observed to be running when it was on the bike, but it was running very slow and not providing the necessary cooling. Needless to say, I replaced the thermo switch at a cost of just over $100 from my local Honda dealer (ya, it was expensive). But, the cooling system now functions as designed.