ST1100 overheating issue

[the cueball]

Hi.

a few weeks ago I was sitting in traffic and noticed the temp gauge getting higher and higher without the fan kicking in… right up into the red zone and nothing.

so far I have:

checked the fuse - all good.

jumped the fan to check that it switches on - it does.

replaced the temp. Sender unit.

replaced the thermostat (OE Honda) and o ring!

I thought it was all ok….bike runs great, no loss of power, temp sits just before halfway when riding.

but it happened again today - in traffic, a bit of steam from the front and no fan.

it dumped a bit of cold coolant out the rear of the bike - I’m guessing from the overflow, but it was cold to the touch.

so what now? I’ve exhausted my limited knowledge and once again defer to the the experts…

please help!

 

[John OoSTerhuis]

You didn’t say anything about it, so I’ll ask the obvious question, did you check the coolant level at the radiator? Sounds like the common ‘crack in the coolant expansion hose at the thermostat housing nipple’ issue. Coolant‘s pushed to the expansion tank but isn’t drawn back during cool-down.

John

 

[STFlips]

maybe the pump is not circulating the hot coolant over the temp sender or a blockage?

 

[Al st1100]

You didn’t say anything about it, so I’ll ask the obvious question, did you check the coolant level at the radiator? Sounds like the common ‘crack in the coolant expansion hose at the thermostat housing nipple’ issue. Coolant‘s pushed to the expansion tank but isn’t drawn back during cool-down.

John

and or seepage from the outlets and / or hoses over the years .... you know how they get corroded over the years

 

[the cueball]

I have done a full coolant change, and flushed the radiator a few times and rode around 2k since that.

made sure that the radiator was full to the cap and done my best to get all the air out the system.

can’t see any other leaks anywhere apart from the loss today at the rear..

 

[dwalby]

replaced the temp. Sender unit.

I thought it was all ok….bike runs great, no loss of power, temp sits just before halfway when riding.

did you replace the temp sender unit in the T-stat housing, or the thermal switch in the radiator? The sender in the T-stat housing has nothing to do with the fan coming on, the thermal switch is what causes that to happen.

normally the temp should not be close to halfway when riding, provided you're going 45mph or above. It should be towards the lower end, so that sounds a little suspicious as well but nothing to be concerned about for now. It may be an indication that the coolant level is a bit low though.

Agree with John's comment to double check the overflow hose, if you've put 2k on it since the coolant change you may have burped enough coolant out of the system to cause the problem to return again. Double check the coolant level at the radiator cap.

 

[Al st1100]

If the fans did not go on, it's a fan problem. you replaced the temp sender but not the fan switch at the bottom of the radiator. Also make sure the radiator is grounded.

 

[the cueball]

Sorry, maybe I’m getting my bits mixed up.. I replaced the switch at the bottom left of the radiator, next to the drain plug - radiator fan switch.

I use the bike to commute each day, so it’s in heavy traffic 30mph and slower usually, hence the temp gauge being half way.

when I get out on the motorway it does go down to around the quarter.

I guess I’m stripping it down and checking hoses again then??

should I get a new radiator cap too just in case?

 

[dwalby]

the overflow hose attaches to the radiator cap area of the radiator, so you need to remove all the plastic bits to get to the radiator cap, then you can check both the hose connection and the coolant level. I'd check the overflow hose first and if its cracked, then your problem is identified. If its good and the level is still low, then it could be blowing past the cap, or leaking from one of the hose connections, but you'd think there'd be some evidence of those types of leaks.

One more thing to test that Al mentioned regarding the radiator grounding. Do a continuity test from the base of the radiator fan switch to battery negative, it should be almost zero. When the switch closes, that completes the path to ground to make the fan turn on, so if there's any corrosion in the ground path that could also prevent the fan from coming on.

 

[kiltman]

Ideally, as dwalby states, you should remove the plastic to view the overflow hose, however, if you stand on the left side of the bike and turn the bars to the left you can just see the radiator cap. In front of the cap pointing downwards is the overflow hose connection. If that hose is compromised you will see cracks or a crack in the rubber in the first 1/2” of the hose below the clamp. You may also see dried up coolant crud. If you do, there is an easy fix, but removal of plastic is necessary. Once the plastic is removed, disconnect the overflow hose from the rad fill stem. Cut back the hose until it’s free from cracks. You can safely cut an inch off and reconnect, if more than an inch then a new hose will be needed.

 

[the cueball]

As far as I can tell the hose is ok.

I cleaned and inspected them all when changing over the thermostat.

however, I’ve now noticed the small clip holding the hose has snapped, so although the hose is staying on, it’s a bit loose…

I’m guessing as pressure is building up the coolant could be getting out that way and causing an issue?

I’ll inspect the hose again just to be sure and get a new clip ordered up… my macgyver fix of a cable tie probably won’t hold it either!

 

[Ron]

I’ll inspect the hose again just to be sure and get a new clip ordered up… my macgyver fix of a cable tie probably won’t hold it either!

Give it a shot! Basically a freebee.

When there is a leak in the overflow hose, the vacuum to pull the coolant back into the radiator is lost. Typical sign is full overflow tank but low level in radiator.

 

[Bush]

"should I get a new radiator cap too just in case?"

Yes, install a new rad cap as well. If it isn't holding pressure, the coolant will boil sooner, causing it to puke out the overflow hose. What is in the bottle already will be cold, as you described.

 

[Al st1100]

I’ll inspect the hose again just to be sure and get a new clip ordered up… my macgyver fix of a cable tie probably won’t hold it either!

Give it a shot! Basically a freebee.

When there is a leak in the overflow hose, the vacuum to pull the coolant back into the radiator is lost. Typical sign is full overflow tank but low level in radiator.

cut the hose back about an inch, should be enough to get a tight fit . You could clamp it with a mini zip tie not a regular one. Check the nipple on the radiator it gets plugged. But If it was just filled it should not have lost that much coolant. The fan switch If I remember correctly is one wire. Ground the wire to the radiator and make sure the fan goes on, the radiator has a grounding wire somewhere.

 

[the cueball]

Cheers guys.

parts are ordered, some on back order with Honda U.K. so it’ll be a couple of weeks before I can look at the bike again I’m afraid, but I’ll report back and update the thread - hopefully with good news!

for now though, I’ve got to jump on the other bike and head off to Italy for my latest tour!

 

[the cueball]

I’m back!

I managed to get a few hours with the bike today, so I carried out:

check the rubber hose from the thermostat to the overflow and there was a few small cracks at the top, so snipped about an inch from it and secured it with the new clip.

I then topped up the system with antifreeze, made sure the level was correct in the overflow as well.

put the new Honda cap on and went for a ride.

came back and let the bike idle for ages until it was right up in the red zone - no leaks of anything and the fan was on, but turning slowly… not like a fullblast as you would expect…

it seemed to bring the temperature down slightly… but certainly wasn’t working like I would expect or as fast as it does when I jump it.

I’m in the office for the next few days, I’ll give it a run and see how it goes…

 

[Uncle Phil]

Usually when the fan kicks in it's blowing pretty good.
Sounds like your fan maybe on it's last legs.

 

[Upt' North]

If the motor was seized it would probably blow the fuse when it kicked in.
So the motor may be going south. Can you connect the fan upto a 12 v source and just compare the fan speed.
This would hopefully help diagnose where you go next. The fan on my 11 was never that noisy but it did its job pretty good.
Upt'North.

 

[moosulkwanman]

Had an over heating issue couple years back, radiator fan would not turn on due to a wire that had rubbed bare, design problem, (wondered if others had this problem, ) and shorted out , if my memory is correct. Honda mechanic was baffled. But will never forget how difficult it was to get to that connection and make that repair, finally had to use silicone caulk to reinsulate the wire, now that the fan will run, no problem

 

[the cueball]

When I jump the fan/ground it it comes on full blast like i would expect it to. - very fast, full power etc.