ST1100 Temperature issues

Joined
Mar 4, 2017
Messages
7
Location
Havant
Hi,

I have an 1991 ST1100 and the temperature is starting to do strange things. It takes a while to heat up and then all of a sudden it will heat up and go into the red, even when moving, although when moving it will stay just under the red. I can't hear the fan coming on either. But it weird that it will stay cool until it been running for 10-15min then go strait to the red a few minutes after that.

Does anyone have any idea as why this would happen?

Many thanks in advance :)
 
Joined
Jun 3, 2006
Messages
3,512
Location
British Columbia
Bike
2021 RE Meteor 350
There are several reasons why an engine will overheat, but let's start with the simple, most common cause for the 1100. Sounds to me like you have a low coolant level in the rad.

A very common problem is a split in the overflow hose at the rad filler neck. Check your overflow reservoir and see if it seems overfilled. The split hose allows coolant to exit the rad into the reservoir, as it expands, but when the engine cools, the split in the hose allows air back into the rad, rather than coolant being drawn from the reservoir. The fix is to cut off about an inch of the hose and reattach, but blow through the hose first to clear any crud from inside and then top off the rad. Clean the reservoir and add coolant up to the lower line. Use ONLY a non silicate coolant. Honda type 2 is a good choice.
 

Slydynbye

Will ride for Pie
Joined
Sep 3, 2007
Messages
1,596
Location
Fremont, California
Bike
2000 ABSII
STOC #
7331
Have you checked coolant level?
As has been said before, the overflow tank is a poor place to check coolant level.
You need to look inside the radiator cap to see the actual level. Also you will probably need to replace the overflow tube that goes from the top of the radiator to the overflow tank as they tend to split at the top.

Edit...Bush beat me to it. What Bush said.:rolleyes:
 
Joined
Mar 13, 2012
Messages
5,046
Location
soCal
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'97 ST1100
STOC #
687
it could be one of several things, start with the simple things first.

1. strip off the plastic and check the coolant level in the radiator (NOT the overflow tank) and top off as needed.
2. while in there, check for split overflow hose at radiator cap neck, and repair if needed.
3. run bike and check for proper fan operation.

if fan doesn't work, and needle still goes into the red, remove wire lead from the thermo switch in radiator and ground to clean metal (not painted) on frame or engine. If fan comes on, you have either a bad thermo switch, or your water pump isn't flowing enough water to the radiator. If fan doesn't come on, report back for how to further troubleshoot inoperative fan.

Jumper thermo switch wire to ground to keep fan on all the time, and see if needle falls back to normal or stays high. If it stays high then you have insufficient water pump flow. If it comes back to normal you have a bad thermo switch.
 
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Joined
Apr 30, 2014
Messages
141
Location
Las Vegas, , Nevada
Bike
94' 1100 ABS
I had the same problem that baffled me. I changed and checked everything. In cold weather mine would not red-line and seemed fine, in warm weather it looked like it was going to over heat. . Mine ended up being a bad radiator. I would guess that over the years the previous owners let the radiator sit for long periods of time without proper antifreeze protection or just water. The bottom half of the radiator had severe corrosion and was plugged. A new OEM radiator is over $450, ouch!!! You can find brand new after market radiators with better flow on e-bay for about $105 shipped. I would also make sure the t-stat is working. Hope this helps.
 
Joined
Mar 20, 2016
Messages
1,201
Location
Auckland, New Zealand
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2005 ST1300
STOC #
8901
Not to suggest any of the previous suggestions are wrong, but I have an alternative theory about the fault. If you have a thermostat that is stuck slightly open, you would get the slow heat up due to coolant reaching the radiator when it shouldn't, and then overheating due to low flow to the radiator when the thermostat should be wide open. If you start the cold bike and keep a hand on the radiator, it should stay stone cold for a couple of minutes, then get quickly too hot to touch, If it slowly heats from the time the bike starts, then the thermostat is stuck open, and should be replaced.
 
Joined
Sep 10, 2011
Messages
2,211
Location
West Michigan
Bike
'98 ST1100
STOC #
8470
Should be easy to check to see if the radiator is plugged - disconnect the upper and lower hoses and stick a garden hose in the upper inlet and see what kind of flow you can get. But don't open the water spigot too much; you don't want to "over pressure" the radiator. If flow is good, my bet is maybe low on coolant or a funky thermostat. A Stant 13868 fits.
 
OP
OP
Joined
Mar 4, 2017
Messages
7
Location
Havant
Ok all sorted. I tested the fan by earthing the lead and it worked fine. So I checked the level in the radiator and it was empty. I topped it up and ran the engine and it turned out the jubilee clip had broken on the bottom of the large hose that connects the thermostat housing to the radiator. I got a new jubilee clip and it is not spot on.

Thanks for the help guys :)
 
Joined
Sep 10, 2011
Messages
2,211
Location
West Michigan
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'98 ST1100
STOC #
8470
Or hose clamps, but that's not nearly as descriptive as a jubilee clamp, I suppose........

Good to hear your ST1100 is back on the carriageway.
 
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