Overheating Problem

My 2001 ST1100 has recently developed an overheating problem. It's absolutely fine on the open road but if I hit traffic, it starts to overheat very quickly. The fan is coming on, but it's not coming on until the needle reaches the top of scale, which is too late by my reckoning. It does go into the red if I let it. Have checked the coolant level and it's fine. Can anybody offer any advice?

Check several locations...yes, you have to remove a bunch of plastic. Check the radiator cooling fins for accumulated bug residue, tar, mud, etc. If it is plugged it won't cool. Consider the age of the coolant also. Check the radiator cap seals for cracks on the two seals, also for goo buildup underneath and in the immediate area where it attaches; look for crusty buildup also, that's a sign that there is corrosion in the system. Also inspect the hose that goes back to the overflow/expansion tank, make sure it isn't cracked or plugged. While the cap is off, start the bike and watch for waterflow around the time when the fan kicks on. If you have waterflow, the thermostat is opening and your problem may be a failed temp sending unit (I've had this happen several times) or bad connector causing the fan to come on late. If you see no waterflow, the thermostat is either failed or you may have a bad water pump.

When you said you checked the coolant level did you check at the radiator cap or the overflow tank level?

I had the fan switch sensor (the one on the bottom left of the radiator) go wonky. The fan wouldn't come on until the temp gauge was almost to the red. There's a test in the manual to verify the switch is closing at the right temperature which mine failed. I replaced the sensor and now the fan kicks on a bit over the halfway mark as it is supposed to.

Wow, Oldbikefixr sure covered all the bases. Only thing I would add, is Mother Honda wants the radiator coolant to be changed every 24,000 mi or every 2 years (I looked in my 1300 service manual - i know you have an 1100). The corrosion inhibitors in radiator juice get used up or become ineffective if you never change it (we will NOT discuss how I know this). Your bike is 15 years old, if the coolant has been maintained regularly, the chances of corrosion in the engine are slim.

=superstar;1969317]My 2001 ST1100 has recently developed an overheating problem. It's absolutely fine on the open road but if I hit traffic, it starts to overheat very quickly. The fan is coming on, but it's not coming on until the needle reaches the top of scale, which is too late by my reckoning. It does go into the red if I let it. Have checked the coolant level and it's fine. Can anybody offer any advice?[/QUOTE]
I went through this scenario and it took me three months to find out I had a bad ground to my gauge. Do the simple stuff first. One of the easiest is to hook up an ohm meter to the temp sender by the thermostat. The fan will come on when the ohm meter reads 28 ohms and shuts off at 31 ohms. If it does that, and your needle on the gauge is in the red zone, then take off the plastic and the gauge cluster and attach a new ground wire to the centre pole of the gauge, to a good ground on the bike, see if that makes a difference. It doesn't hurt to check the overflow tube as others have suggested.i actual rode the bike for a day with an ohm meter connected to the sender. I believe the thermostat will open up around 38 ohms. When you're riding hi way speeds, does the gauge indicate under half? When it goes into the red is that when you're in stop and go traffic? Does the fan cycle off and on when the needle is in the red zone? If yes then check the ground wire to the temp gauge. ( I replaced, both the fan and temp sensor, all the coolant hoses, water pump, thermostat, rad cap, and gauge only to find out that it was a bad ground.)

The fan should "kick in" when the temp needle is at the "12 o'clock" position - not at the top of the scale. Looks like you have a problem, there. First thing to check is that the cooling system is full. If it's full , then you may have a bad fan motor switch. But it's also possible the thermo sensor is giving you a bad reading on the temp gauge.

When you are on the highway, what reading do you have on the temp gauge ? If it's at the bottom of the normal range, the temp sensor is probably OK.

You guys have given me some great info - thanks. I will start checking out the things you all have suggested. Just to answer a couple of questions, I checked the coolant level at the reservoir on the right hand side of the bike (not the radiator cap). When it's on the open road, it's sits between 1/3 - 1/2.

Checking the level in the overflow reservoir doesn't tell you if the cooling system is full, you must check at the radiator cap. Take the plastic off and verify if the coolant level is up to the radiator cap. A low coolant level would explain your symptoms. While you're there check the hose to the overflow reservoir for cracks near where it attaches below the radiator cap.

superstar said:

You guys have given me some great info - thanks. I will start checking out the things you all have suggested. Just to answer a couple of questions, I checked the coolant level at the reservoir on the right hand side of the bike (not the radiator cap). When it's on the open road, it's sits between 1/3 - 1/2.

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Check your level at the rad cap. If the fan cycles on and off when the needle is in the red zone, I suspect a bad ground at the instrument cluster

agree with the advice given so far, but wanted to chime in because the symptoms are similar to what I was seeing a few years ago that turned out to be my water pump impeller blades had rusted away due to poor coolant system maintenance. Mine never went fully into the red, but got very close before the fan kicked in, and sometimes the fan didn't kick in. Since mine never went into the red, I didn't bother troubleshooting further and just left it the way it was and made sure it never went into the red, which it didn't. A year or so later I replaced the timing belt and water pump, and that's when I noticed the bad impeller. Its gotten better since the new water pump, but my gauge still acts erratically sometimes in the mid-range, so there does seem to be an issue with the temp gauge reading accurately as these bikes get older. Others have reported similar gauge weirdness.

So as has been recommended the first step is to verify the coolant levels are correct at the radiator cap (mine was, and the symptoms were still present). Then do a resistance check on the temp sender when the needle hits the red zone. Its also easy to test that in boiling water off the bike as well.

The spec on the temp sensor is

50C - 130-180 ohms
80C - 45-60 ohms
120C - 10-20 ohms

The spec on the fan thermo switch is:

98-102C - switch closes

Keep in mind that the temp sensor is next to the engine at the thermostat housing, while the fan thermo switch is down low in the radiator. If your water pump isn't properly circulating the coolant, you could have a large temperature gradient between the hot coolant coming out of the engine (temp sensor) and cooler coolant that has been sitting a while in the bottom of the radiator. That could explain why your fan comes on late relative to the gauge reading.

To the above three posts. And to add : You are running too high on the highway. Now to figure out why. Check the radiator level by removing some plastic ( side panels & "shelter" ) . It doesn't take that much time. Also check the antifreeze concentration. Even if it's strong enough, the rust inhibitors may be worn out. I hope your water pump impellar doesn't look like dwalby's .....

How long have you had it, and when was the last time you did a cooling system flush? Don't open the bolts on the heads, instead blow air down the radiator neck to get all the old coolant out. Flush with water, repeat, use a radiator flush, flush, then flush with distilled water. Add coolant. Replace thermostat while you're there.

superstar said:

My 2001 ST1100 has recently developed an overheating problem. It's absolutely fine on the open road but if I hit traffic, it starts to overheat very quickly. The fan is coming on, but it's not coming on until the needle reaches the top of scale, which is too late by my reckoning. It does go into the red if I let it. Have checked the coolant level and it's fine. Can anybody offer any advice?

Click to expand...