Water temp slowly going up and back down.

CompressorStall

CompressorStall

Self appointed wizard of light bulb moments.
Joined
Aug 6, 2018
Messages
24
Bike
'96 ST1100
I searched around on the forum but didn't find exactly what my bike has been doing for a thousand miles or so. I will be cruising on the highway and seemingly randomly, I'll notice more heat on my legs and feet from the engine. A look at the engine temp gauge shows me at about the 1 oclock position. Then after a few seconds, the gauge will start dropping and I can feel the temp of the engine going back down to normal.

During highway riding in 80 degree temps, my gauge usually stays just above the lower mark. My guess is a thermostat issue, or water in the cooling system since this temp change takes time to work its way up and then back down again.

Thoughts?

Also, has anyone had the privilege to change the thermostat? I read about it in the manual and it doesn't look enjoyable.

Thanks!
 
I would check the coolant level first. That's the level in the radiator and expansion tank.
I presume your fan is working because the temperature comes back down.
The hose from the radiator to expansion crumbles to dust and may be allowing coolant to leak from the sealed loop.
Hope it helps.
Upt'North.
 
Upt' North said:
I would check the coolant level first. That's the level in the radiator and expansion tank.
I presume your fan is working because the temperature comes back down.
The hose from the radiator to the expansion crumbles to dust and may be allowing coolant to leak from the sealed loop.
Hope it helps.
Upt'North.
Click to expand...
 
The fan comes on about the 12:30-1 position, maybe you're feeling the warm air from the fan. Clean vs dirty air makes a difference too, i.e. riding behind a group of cars or a truck. Air in your system is another possible culprit. Thermostat replacement is not too bad, just need to remove some plastic.
 
Likely not the thermostat. If it was stuck open, your bike would run colder than normal. If stuck closed it would overheat pretty damn quick and not cool off. As Up't said, check the hose at the rad cap for a split or small tear which allows air into the system and your overflow tank to overfill. If it is split, cut off about an inch and re-attach, then check the overflow bottle and the coolant level in the rad - when cold.

Confirm that the fan comes on too. Actually, from your description, the system appears to be working normally, but generally, if doing highway speeds the fan is not likely to come on, as the airflow through the rad is sufficient to keep the temp gauge below that point, unless the ambient temp is really high possibly.

Check the easy things first and, failing to find a tear in that hose, run the bike in your garage to see what is happening with the gauge and fan, then report back.

Pulling off of plastic is required for this, probably the hardest part of doing the job.

Also, I hope you have coolant in the system and NOT 'water'.
 
Mine did the normal- hot guage dance a year ago. Flushed it a couple of times and changed fan switch and thermostat. guage is reading normal at one quarter on the highway with no guage deflection. Still notices it gets a little warmer by my feet and legs.
 
Bush said:
Likely not the thermostat. If it was stuck open, your bike would run colder than normal. If stuck closed it would overheat pretty damn quick and not cool off. As Up't said, check the hose at the rad cap for a split or small tear which allows air into the system and your overflow tank to overfill. If it is split, cut off about an inch and re-attach, then check the overflow bottle and the coolant level in the rad - when cold.

Confirm that the fan comes on too. Actually, from your description, the system appears to be working normally, but generally, if doing highway speeds the fan is not likely to come on, as the airflow through the rad is sufficient to keep the temp gauge below that point, unless the ambient temp is really high possibly.

Check the easy things first and, failing to find a tear in that hose, run the bike in your garage to see what is happening with the gauge and fan, then report back.

Pulling off of plastic is required for this, probably the hardest part of doing the job.

Also, I hope you have coolant in the system and NOT 'water'.
Click to expand...
Like Bush says at about 80 f you shouldn't be getting spikes at normal speeds, the only time I found the system working harder than normal was well into three figures and even then I don't think the fan cut in on the highway.
Upt'North.
 
Two things:

1. check the level of the coolant in the radiator, not just the reservoir. If the reservoir looks normal yet the radiator is low you have a bad overflow hose.
2. If all of that checks out, you may have a "sticky" thermostat. I've had it happen on cars where the temp would get almost to the red then suddenly plunge back down to normal repeatedly. A small amount of gauge oscillation is normal though.
 
I had a funky thermostat that was acting similarly. I replaced it and things were back to normal after replacement. But check for a cracked small hose at the thermostat housing first.
 
What is the value of the space or distance from normal 1/4 to 3/4 but not red on our indicators? I have had some quick rise and return to normal. Generally 90ish or above, very slow, in traffic but not while above 20mph or so. Who knows what temp we are running at normal and the rate of rise in the space between normal and red, is it 20 deg. or 50 deg. ? Has anyone swapped in an actual quality temp gauge on an ST 11 or 13 with your idiot bars you are no better off ? Would be nice to have true reading of Temps.
 
Thanks for all the replies folks. I'll have some time to tear into it on Friday before heading to eastern Ohio for some riding. I'll report back my findings if I find any!
 
Bush said:
Likely not the thermostat. If it was stuck open, your bike would run colder than normal. If stuck closed it would overheat pretty damn quick and not cool off. As Up't said, check the hose at the rad cap for a split or small tear which allows air into the system and your overflow tank to overfill. If it is split, cut off about an inch and re-attach, then check the overflow bottle and the coolant level in the rad - when cold.

Confirm that the fan comes on too. Actually, from your description, the system appears to be working normally, but generally, if doing highway speeds the fan is not likely to come on, as the airflow through the rad is sufficient to keep the temp gauge below that point, unless the ambient temp is really high possibly.

Check the easy things first and, failing to find a tear in that hose, run the bike in your garage to see what is happening with the gauge and fan, then report back.

Pulling off of plastic is required for this, probably the hardest part of doing the job.

Also, I hope you have coolant in the system and NOT 'water'.
Click to expand...

Many thanks for your suggestion, yesterday my ST1100PT started loosing coolant from an overfull expansion tank. As per attached picture, that was exactly my problem, a small split in the hose end. The Honda mechanic suggested a head gasket - I'd much rather change a hose!
Thanks again, you saved me heaps of money:thumb:IMG20200302185223.jpg
 
Georgevn said:
Many thanks for your suggestion, yesterday my ST1100PT started loosing coolant from an overfull expansion tank. As per attached picture, that was exactly my problem, a small split in the hose end. The Honda mechanic suggested a head gasket - I'd much rather change a hose!
Thanks again, you saved me heaps of money:thumb:
Click to expand...
Yep, that's a very common failure point on the ST11. Happened on both of mine. One way to minimize this is to run a longer hose, which will increase the radius of curvature, thus reducing the stress on the hose. There's enough room in front to allow a bit more hose length. I think I ran fuel hose for mine.
 
The original hose lasted 30 years and 100k km for me ... I don't know much about silicone pipes, can they stand up to superheated (120 degrees C) coolant?
 
Silicone trivets can stand up to 600ºF so making suitable hoses for a cooling system should be possible. But 100Kkm @ 30yrs isn't bad. A silicone hose could outlast you.
 
jfheath said:
Did the OP, @CompressorStall, get his problem fixed, I wonder?
Click to expand...

I've been wondering about him too. His last post on the subject was September 11, 2019 when he posted - "I'll have some time to tear into it on Friday before heading to eastern Ohio for some riding" - and then the last time he visited the site was 9 days later on September 20th, without commenting on this thread. So the concerns may be more involved than just whether he sorted the overheating problem out.
 
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