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Bike overheated today...

2K views 19 replies 10 participants last post by  bigdyno 
#1 ·
So I'd been riding around in town doing a few errands when I see the temp gauge is entering the danger zone so I decide to limp it home (~10 minutes away).

The last few stoplights, there was steam coming out of the coolant overflow hose, and the coolant was boiling in the overflow reservoir - wtf?

Could I have caused damage to the engine? Warped head maybe?

I've got manuals so am starting the trouble-shooting, but advice is welcome!

A couple questions:

[1] the fan was not running (so maybe the motor or the switch is faulty), but with 10 degree temperatures today, is that even relevant?

[2] because the coolant was boiling (BTW - what temp does it do that?) does that mean there's air in the coolant passages, and I'll need to flush the whole system?
 
#2 ·
specifics on the bike might help but there is a possibility that you damaged the engine although not a foregone conclusion at this point. have you done any work lately to the cooling system ie:thermostat, flush, etc... If the coolant was boiling then yes there was air in your system but you shouldn't have to do a flush to get it out unless the water lever has dropped to a point where air pockets can form.

things to check are thermostat, thermoswitch, radiator for flow, and waterpump
 
#3 ·
[1] yes even in cool temps the engine puts out enough heat to require the fan
[2] water boils at 212 F (coolant is slightly higher) add in your ~13psi pressurized cooling system (water under pressure boils at a higher point 1.5 deg. for each psi) you're looking at a boiling point of at least 232 deg. F (again, a little bit higher for coolant)
 
#4 · (Edited)
Thanks. I'll check the fan motor/switch first.

Bike is an '89 Honda CB-1 (aka NC27 aka CB400F). No recent work on the cooling system whatsoever.

FWIW, on Wednesday I was out to RMR in Abbottsford and back and didn't have any issues, so hopefully that rules out a few possibilities.

PS Woo - BCSB.com 1000-post milestone :)
 
#9 · (Edited)
Thanks Wrenchette - fuse is OK. Delving...

Greg - oil looks clear. If coolant had gotten in I'd be pretty obvious, right?

pherthyl - I topped up the coolant in the reservoir, and it is stable when revving the engine.
 
#10 ·
Fan motor runs when jumpering the connector to ground so could be the switch.

Is there a way to test this? The Honda Common Service Manual shows how to test the thermostat and thermo sensor by putting it in heated water, but they don't show this test for a thermo switch - weird.
 
#11 ·
The Honda Common Service Manual shows how to test the thermostat and thermo sensor by putting it in heated water, but they don't show this test for a thermo switch - weird.
Test the themo switch the same way ..use a continuity setting on your mulitmeter. Sometimes there is a temp. in centigrade, stamped on the side of the thermoswitch also check the cap for cracks ,missing gasket and hoses for leaks.
 
#14 ·
Yup - on this system anyway, no relay.



Ok - thanks. I couldn't find a temp. spec in the Service Manual so hopefully it's stamped on the switch. (I think I'll pull the thermostat and test it at the same time).

Quick question: the Manual says to use "sealant" when reinstalling the switch but doesn't say what kind. I don't suppose plumbing teflon tape is what they have in mind. What should I use?
 
#15 ·
either at the end or start a of the manual it will give you a list of all consumables you might require for ... everything

at least the one for my old gixxer did.
it also had a hard wired switch to turn on the fan... from previous previous owner. I brought the bike in for a post storage check and had a shop unfuck all that was fucked up. IIRC on the bill there was something to do with the switch assembly. Yours could have went. Roughly same vintage bikes.
 
#16 ·
either at the end or start a of the manual it will give you a list of all consumables you might require for ... everything
at least the one for my old gixxer did.
Sadly, both the bike-specific Service Manual and the Honda Common SM just say "Apply Sealant" in the description...

Suzuki Service Manuals FTW! ;)

it also had a hard wired switch to turn on the fan... from previous previous owner. I brought the bike in for a post storage check and had a shop unfuck all that was fucked up. IIRC on the bill there was something to do with the switch assembly. Yours could have went. Roughly same vintage bikes.
Yeah, I've already written down the part number to see if Honda Centre has it in stock.

Ironically, I was on my way there to pick up some front caliper rebuild parts & pads when the overheating happened and I headed for home.
 
#17 ·
Quick question: the Manual says to use "sealant" when reinstalling the switch but doesn't say what kind. I don't suppose plumbing teflon tape is what they have in mind. What should I use?
Don't use teflon tape,its not designed to seal it is for higher torque on pipe threads. Use Threebond liguid gasket1194 (Mspeed,Modern has it)
 
#20 ·
You said you had the fan going by jumping power to it, but another thing to watch for is rocks preventing the fan from turning. When I went to Cali I picked up a rock in the fan and it blew a fuse and threw the engine light but no code. Easy enough fix, remove rock, replace fuse, ride like hell.
 
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