Overheating

[PmodelinUS]

I had noticed that the bike had been running in the upper half of the temp gauge this fall. Kind of odd for a cooler time. I have also noticed that once in a while it ses the fan didn't engage. Well today my procrastinating bite me in the butt. I was about 60 miles from home sitting at a stop light when I looked down and saw the gauge moving past the red with no fan on. I quickly bailed onto the shoulder and made a right turn, praying the temp would come back down. After a few mins the temp was back to a more normal range. I managed to nurse it home having similar encounters at the stop lights. Fan never came on. Managed to get going before it got to hot.

My first thoughts are the thermostat and relay for the fan both died all at once. I .however looking for other thoughts. Don't say water pump. Lol

 

[kiltman]

You can ground the fan switch to see if the fan is actually working.
I would also check the main ground in the loom. It is attached either to the folding grab handle or the left mounting bolt to the pannier rail.
You can also check the thermostat sending unit by connecting an ohm meter. ( this requires removing some Tupperware.). With the motor running measure the ohms, as the motor heats up you will get less resistance. I don’t have my manual with me but the fan usually will kick on when it’s between 12 and 15 ohms.
These things cost next to no coin and will aid in the diagnosis before replacing parts that you may not need.

 

[Larry Fine]

First suspect is the infamous overflow-bottle hose at the fill neck, slowly allowing air to be drawn in as it cools.

The coolant level might be too low to activate the fan.

 

[Bush]

If the overflow bottle is over full and the rad is low on coolant, you will find the hose to the overflow has a split in it where it connects to the rad cap, as Larry alludes too. Cut off about one inch of hose to eliminate the split, re-attach and fill the rad and overflow coolant levels back to normal. Also a good idea to blow through that hose from the rad end to clear any crud which may have settled inside it.

 

[PmodelinUS]

I love you guys!! So I managed to sneak in time to dismantle way too much body work in between baking cookies for our troop. Anyways, it seemed to be air in the system. The overflow was just at full so I sucked some out. Then started the bike with the radiator cap off. At first all the looked good then suddenly a mass of air bubbles so big came up, it was as like foam. This quickly went away then ran clear after that. I put the cap back on and waited to see if it would work. Well after an eternity it finally got hot and the fan came on and to he temp dropped. Thanks once again oh great collect of ST owners. This site is kinda like the Borg.

 

[kiltman]

Glad your issue is resolved. Bush and Larry mentioned the most common issue for overheating and I can kick myself for not mentioning it right off the bat. Inspect that hose carefully where it joins the fill cap. It doesn’t take much crud to block it and could explain why your overflow was too full.

 

[Larry Fine]

. . . It . . . could explain why your overflow was too full.

And the engine not full enough. Be sure to replace the air bubbles with coolant.

 

[Bush]

This site is kinda like the Borg.

You have been assimilated.

 

[PmodelinUS]

Couldn't find any noticable cracks in the hose but replaced anyways since I was there. Topped it off this morning. Putting all the plastic back on tonight after trick or treating. Get 3 days in the upper 60s to start off Nov. Taking Wednesday off to take the oldest to get his driving permit then off for a mid week to ride.

 

[Al st1100]

The nipple at the filler neck gets clogged. Hoses under the carbs get corroded at the ends and seep ever so slightly. I would check those and the O rings on the outlets.

 

[PmodelinUS]

Did the carbs, elbows and hoses under there all this last spring so good there.