Over heating need advice

Last summer I purchased a used 95 ST1100 with 131,000 miles. It is my first liquid cooled bike. It had some major electrical, carb problems and the water fitting on the right head was corroded to the point it was falling apart. The PO told me that he replaced the left one 3 years ago. While I was replacing it I flushed the old dirty water, and it was just water, out of it. The PO told me that he never used anti freeze, just plain water.
While doing the fitting and hoses I replaced the radiator cap.
I finally have the thing pretty well sorted and it runs great, EXCEPT, for trying to overheat. When running on the open road the gage reads about 1/4 of the way up.
When running in city traffic and even slow stop and go on the freeway it will come up to the point where the fan comes on (very quickly) and if the speeds don't pick up it will keep climbing, even with the fan on. The other day it got up to the bottom of the top white mark and I pulled off the road and let it cool down, yes the fan was running. It was a pretty warm day (80deg) but I was doing between 25 and 35 mph on the freeway when it just kept climbing.
I have a few concerns.
While t-shooting the electrical I temp installed a voltmeter. When the fan comes on, at idle, the volts will drop from about 14 to about 11.5. This seems like a really heavy draw for the fan. I have a honda shop manual for it, BUT, nowhere does it give any specs on the fan motor and the draw.

I am wondering if the tubes in the radiator could be partially plugged and/or the passages in the block/heads, because of the extended use of straight water. If so, can I use a commercial coolant flush to clean it? Or is the radiator trash?

I am also considering that the water pump might be in bad shape because of the lack of good coolant. I have seen aluminum waterpumps with the housing pretty well ate away from lack of good coolant, and they would not pump enough water to keep the engine cool.

Any advice on this is very much appreciated.

BTW, it doesn't leak any coolant...

Herb1949 said:

I am also considering that the water pump might be in bad shape because of the lack of good coolant.

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Mentioning having drained water only, I'd concur... the impeller is made of stamped steel and its blades can silently corrode away... similar reports have been posted, cause was either use of tap water or simply (very) old coolant...
At that mileage I'd go for the t/belt + spanner & idler pulley anyway, replacing (or at least inspecting) the w/pump would add only 20 minutes to the job...

A partially clogged radiator could also be a cause, this would however show by the outside of the fins being badly corroded.

Besides those no internal passage blockages have been reported on a SC26 plant...

The voltage drop to 11.5V with fan running seems OK if the bike has the 26A alternator.

ST1100Y said:

Mentioning having drained water only, I'd concur... the impeller is made of stamped steel and its blades can silently corrode away... similar reports have been posted, cause was either use of tap water or simply (very) old coolant...
At that mileage I'd go for the t/belt + spanner & idler pulley anyway, replacing (or at least inspecting) the w/pump would add only 20 minutes to the job...

A partially clogged radiator could also be a cause, this would however show by the outside of the fins being badly corroded.

Besides those no internal passage blockages have been reported on a SC26 plant...

The voltage drop to 11.5V with fan running seems OK if the bike has the 26A alternator.

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Some good advice given! At a minimum, try the coolant flush. With the previous owner's negligence towards proper coolant, one must wonder if the timing belt had ever been done... hmmm? After the coolant flush, if there is no improvement, go for the complete timing belt, water pump routine stated by ST1100Y above. At that point, you may want to take the radiator to a certified shop and ask them to check it out/ flush or repair if possible. Hope you get the issues sorted out.

With the bike on the center stand, let it warm up. When the gauge reaches about the 12 O'Clock position, the radiator fan should start and then the temp should fairly quickly decrease. If the fan doesn't come on, of course that's a problem. If the fan does come on, but the temp doesn't decrease, you may have some corroded impeller vanes in your water pump. take a look at the pic of the impeller that was in the water pump I rebuilt at the " I rebuilt my first water pump" post.

With 131K miles , I wouldn't be surprised, especially if the antifreeze wasn't replaced regularly - the anti rust inhibitors wear out over time.

Mine had similar symptoms, but yours sounds a little worse in terms of how high/fast the temp needle climbs. I neglected my coolant and my waterpump impeller fins corroded, reducing the available coolant flow. My impeller is the one Jim referenced in his post. I'd assume the pump is bad, do the timing belt, pump, pulleys maintenance, and have the rad checked while its off the bike for that maintenance. The parts aren't cheap, but given the age/condition of the bike it will be money well spent. Look up the Gates timing belt references here too, its identical to OEM and costs a lot less.

I've seen a broken thermostat cause overheating and the infamous overflow hose leak. When the bike is cooled off and you open the cap, is the coolant level all the way to the top of the neck? If not you may have a degraded over flow hose. They go bad right where the 180 degree bend occurs just off the neck. Coolant will be pushed to the over flow tank, but due to the degraded tubing, only air is pulled back when the engine cools, leaving the radiator incompletely filled.

The fact that the fan is running would suggest that the t-stat is opening and allowing hot coolant to enter the radiator. The overflow hose leak check is a good idea, make sure the rad is full before going to the next step.

Good advice from Martin, Tom, Jim, Doug, and Jeff!

I'd check coolant levels at the radiator AND reserve tank first. Couldn't hurt to do a proper flush, but...
Then ask the PO if the timing belt was replaced and when/mileage; AND if the ST exhibited the same 'running hot' symptoms for him.
Depending on all that, proceed to the water pump removal/impeller inspection and radiator check. FWIW

John
via iPhone 6

Just to expand on my answer above ( I was in a hurry this morning when I first posted ).

It sounds like your symptom is overheating at lower speeds, but not on the slab.

Recently when doing some digging about water pumps, I found an article about a Toyota car that had your symptom - only overheating at low speeds. When the mechanic removed the water pump to inspect it, he found the plastic impeller had broke loose from the water pump shaft !! But it wasn't overheating on the road, only at low speeds.

Apparently the "Ram Air" cooling effect through the radiator along with enough "Hydronic Flow" was enough to keep the engine cool on the road at higher speeds. That's why I suspect you may have a corroded impeller , especially with the miles on your bike. And at 131K miles, you are due for a timing belt change, if it hasn't been changed yet. So it won't be too much more work to pull the pump if you need to replace the timing belt.

See my post about rebuilding the pump yourself.

dwalby said:

Mine had similar symptoms, but yours sounds a little worse in terms of how high/fast the temp needle climbs. I neglected my coolant and my waterpump impeller fins corroded, reducing the available coolant flow.

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Doug : Almost like yours !!



Check this out

Yes, its the highly efficient, low drag version. Adds extra HP by removing that inertial load at the pump.

Just a quick note to say thanks for this thread...I rode my bike from Indy to FL earlier this week and have noticed the same thing...when I'm running on the slab the temp stays over on the cool side of the gauge but when I got off into stop/go riding on city streets at times it would roll all the way up to near the red. I noticed this a bit before I left on my trip and did a coolant/overflow bottle flush and replaced the radiator cap but it appears I need to dig deeper into the issue as outlined in this thread...

My trip back to Indy is on Sunday so I'm hoping for no traffic backups on my way home...appears that as long as I can keep moving the bike stays cool enough!

The other issue that comes to mind are the reports of the fan coming loose from the fan motor. The shaft spins but the fan itself does not or it spins too slowly.

Check the coolant level at the radiator cap before heading home. You'll have erroneous readings if the temp sensor is not immersed in the coolant.

smunderdog said:

Just a quick note to say thanks for this thread...I rode my bike from Indy to FL earlier this week and have noticed the same thing...when I'm running on the slab the temp stays over on the cool side of the gauge but when I got off into stop/go riding on city streets at times it would roll all the way up to near the red. I noticed this a bit before I left on my trip and did a coolant/overflow bottle flush and replaced the radiator cap but it appears I need to dig deeper into the issue as outlined in this thread...

My trip back to Indy is on Sunday so I'm hoping for no traffic backups on my way home...appears that as long as I can keep moving the bike stays cool enough!

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Does the fan come on when the temp gauge reaches around the 12 O'Clock position ? Does the fan ever come on ?? If it does, can you see the fan blades spinning ??

Jim Van said:

Does the fan come on when the temp gauge reaches around the 12 O'Clock position ? Does the fan ever come on ?? If it does, can you see the fan blades spinning ??

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+1 on impeller- a quick test, when its getting hot (at idle) does it feel like the fan is blowing very hot air. If not increase idle speed to about 2,000 rpms and hold it. does the fan blow hotter air and does the temp gauge go down ?? the increased rpm will increase in circulation (like driving faster) Indicating a restricted radiator or bad impeller. putting water thru the radiator via a garden water hose will give you an idea if the radiator is clogged, water should flow fairly easily.

John OoSTerhuis said:

Check the coolant level at the radiator cap before heading home. You'll have erroneous readings if the temp sensor is not immersed in the coolant.

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Thanks John - didn't know where the sensor was located. Just filled it before I left when I replaced the coolant but will see what I have there now.

smunderdog said:

Thanks John - didn't know where the sensor was located. Just filled it before I left when I replaced the coolant but will see what I have there now.

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temp sensor is in the tstat housing, next to the rad filler cap. Fan switch sensor is in the lower portion of the radiator.

Will have a bit of time tomorrow morning to check a few of the items being brought up and will report back...thanks for all the input thus far!

So I stayed at a Holiday Inn Express last night. No really....I'm staying at a Holiday Inn Express. Popped the plastic off the bike this morning and found the infamous overflow hose cracked at the radiator filler neck. Took care of that and will replace the entire run of hose when I get home. Coolant was not to the top of the filler neck so that explains the temperature sensor readings. The overflow tank was "full" of coolant so now my question is - once I refill the radiator to the top of the filler neck do I need to siphon out the overflow tank to bring it's level back into spec? I would assume it would just eventually blow out of the overflow tube attached to the tank...so is that the only downside to not siphoning it?

By the way - after cutting the end of the cracked overflow hose I was having a little trouble getting it back on the nipple and didn't have any silicone grease with me. Please make a note that whipped butter from the hotel breakfast counter works.