ST1100 - She's Giving Up Smoking Like A Cigar But Now She's Hot!

Uncle Phil said:
Here's 'new' oddity - the neutral light comes and goes.
The bike will start when it is in true 'neutral' but the light does not come on.
Bulb has been replaced and it worked for a while.
IIRC, the neutral switch circuit and the temp sensor circuit are in the same harness ..... hmmm ... :think1:
Problem is I am running out of time as I'm off to ArkanSToc tomorrow.
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Well, a diode failure would be permanent...
Intermittent could be a faulty/dying switch, loose cabling, loose ground connections...
For peace of mind I'd use one of the "spare ST's" (IIRC are there a couple on the premises ;) ) and deal with the culprits after the trip...
 
Just spitballing out loud, in case it helps...

New engine, old issue.... thus it's quite safe to rule out the engine.

You've swapped coolant before, and well coolant is coolant.

That then narrows it down to a rad issue, blocked or pinched rad hose/tube, the thermo sensor, the wiring or the temp gauge.

You can remove and test the thermo sensor with an ohm meter and boiling water, if you know the values you'd expect to see at temps.

If you replace the thermo sensor and it still happens, it's gauge or wiring.

I'd swap the gauge to see if it's sticking once it gets hot or if a resistor or winding in it has gone south.

After that it would seem to be a wiring issue. Corrosion, bad ground etc would certainly result in the resistance changing. A wire heating may cause that too.
 
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Uncle Phil said:
The 'gauge' (hence the sending unit which is the one that came with the engine - 23,000 miles) seems to be indicating properly.
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Well, I'd understand the gauge being the clock/instrument in the instrument cluster vs the probe being the thermistor screwed into the t/stat housing...
I'd check all contacts, connectors and also the small Philips screws holding the cables on the contacts at the backside of the gauge...
It's the 'problem' gets worse the longer I ride.
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Just to humor us: did your "new" replacement engine show any traces of rust-water on the inside of the coolant stubs?
There had been cases of corroded impellers in the past...
Either you have insufficient flow due to a restriction/obstacle inside, or you don't have enough coolant being pumped, or you cannot radiate enough heat into the atmosphere...
There ain't so much possibilities left... except instrument error of course (see other thread)
 
What about the possibility of water pump debris trapped in the rad from the original engine/waterpump? grenading. Might be worth pulling the rad and flush it with a hose, over a bucket and see if that reveals anything. If the original engine is handy, it might be worth pulling the timing cover and checking the pump for catastrophic damage, just to give a clue.
 
With the cap off and engine running, the 'flow' looks really good - lots of coolant moving.
The 'pee' hole in the thermostat had quite a stream going before the thermostat was open - means the water pump was doing its job.
The problem was 'solved' and now it is back with the new engine install - doubt if it is the engine.
There were no signs of corrosion, etc. at the water ports for the new engine.
I replaced the water necks/o-rings while I was in there.
My 'instinct' tells me the thermostat (which is fairly new) is not opening enough to allow the proper coolant flow.
My reason is it seems to work for a while, then on a longer ride, the engine heats up and cannot cool back down to where it should be.
 
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Neutral switch - help me here as my memory is failing.
The neutral light is not lit now and the bike will not start unless the clutch is pulled in though the bike is in neutral.
Is that diode or neutral switch (I know the bulb is good)?
 
Uncle Phil said:
Here's 'new' oddity - the neutral light comes and goes.
The bike will start when it is in true 'neutral' but the light does not come on.
Bulb has been replaced and it worked for a while.
IIRC, the neutral switch circuit and the temp sensor circuit are in the same harness ..... hmmm ... :think1:
Problem is I am running out of time as I'm off to ArkanSToc tomorrow.
Click to expand...

I had the nuetral light issue it was the blue green wire nuetral switch wire that ran under the gas take tank. It had rubbed through and was grounding to the engine. Just a though! wish I had a great solution for you.
 
You could pull the thermostat and run without it to test. If your overheat issue goes away, then that's the problem. If not, I would suspect the radiator has something in it that is blocking a cooling channel. I have seen that in a car I had, sometimes the flow was fine, sometimes a blockage (in this case rust) would flow into a channel and block it.
 
DJDixon said:
You could pull the thermostat and run without it to test. If your overheat issue goes away, then that's the problem. If not, I would suspect the radiator has something in it that is blocking a cooling channel. I have seen that in a car I had, sometimes the flow was fine, sometimes a blockage (in this case rust) would flow into a channel and block it.
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I've thought about that and that may be the next move.
But then I'm thinking if that is the case, I could install a brand new one (for the same amount of work) and if it fixes it I wouldn't have to tear into it again (Uncle Phil's Parts House has plenty on hand! ;))
 
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I used to get cars in tha would overheat when put under load. Coolant flow looks fine when opening the cap. Since your rad is a cross flow (the cooling tubes run horizontally) the top tubes are flowing well and those are the only ones you can see flowing. A cross flow rad plugs from the bottom to the top.

Suggestion: when the engine is running the temp of the rad should be evenly hot from top to bottom. If you have cool spots, or hot spots, then your rad has lost enough cooling area for it to cool the engine efficiently.

Better way to check this would be with a temp detecting device of some sort. But your bare hand will give you a good idea.
 
When I had the fairings off quite a while ago I ran the bike in on the center stand until three bars [which it remains at] and there's no doubt flow [heat] is predominantly through the upper half maybe of passages.
I'm guessing that that likely corresponded to a partially open thermostat, and that when the stat fully opens flow would increase through the lower circuits of greater resistance.
I did idle it well over an hour in a traffic mess a couple months back in about 28C [83F] and it held within the three bars.
I wonder if sediment could settle where flow is lowest and block some passages or if it's just fouled on the coolant side. I'm not sure what maximum pressure the radiator could be subjected to but I would connect some hoses and back flush it into a pail and see if anything comes out.
Could try some kind of cleaner / descaler through hoses and a submersible pump in a pail. I've had success and failure with that in boiler heat exchangers. Those were SS but there might be something compatible for aluminum.
All this probably if I was going to condemn the rad and buy a new one anyway.
 
The inlet on a cross flow rad is at or near the top of one side of the rad and the outlet will be at the bottom on the other side. So after running for even a relatively short period of time at operating temps the entire rad should be an even temp. If not then that section of the rad is plugged.

There are coolant flush chemicals available but for them to work the coolant has to carry the solution to all parts of the cooling system. (go to your local auto parts store, make sure it’s aluminum compatible, most of them will be, but better make sure) If the tubes in your rad are plugged the solution can’t get thro and it won’t work on the plugged tubes.

These chemicals work very well, just drain enuf coolant off to get the canfull into the rad (don’t add to your overflow tank, must be strait into the rad.) Take the bike for a half hour ride, rinse with distilled or RO (reverse osmosis) filtered water until the water coming out is clear and that will get you the best flush available. Then you can re-check your rad if it worked or not, and then you can make a decision on what to do.
 
Uncle Phil said:
I've got a heat gun - that's a good way to check the radiator!
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It would be very odd if turns out that the Evans reacted with some traces of the prev, regular coolant, resulting in some crud/residue clogging some of the narrow radiator tubing...
(few years back I noted a slight temp increase in my '96 Toyota, corrosion caused expansion of the aluminum fins was squeezing the tubes -> reduced flow volume)
I guess some FLIR thermography would ease/speed diagnosis...
 
Not sure about connections on the ST1100 but on my ST1300 those locations are consistent with where I could detect most flow / heat as I described. As can be seen from the picture they hardly lend themselves to providing equal pressure differential across the circuits, so it didn't surprise me to feel hotter upper circuits and cooler [to cold on the bottom] circuits with the bike on the center stand.
I think in this situation it's two different engines / same rad with higher than normal temperatures [?] so I'm more inclined to think it's a few blocked passages.
 

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First off I haven't read the whole cooling thread. Nor do I know anything about ST1100s. Although I have followed a few. Just wondering if the water pump is driven by the smooth side or tooth side of the timing belt. If the original belt is still on and the pump is driven by the smooth side it could have stretched and be slipping on the water pump at higher RPM/load. Just a thought. Sorry if this has already been brought up.
 
If memory serves, it is the smooth side of the belt that runs the water pump. I would think it would have to be remarkably stretched to not turn the water pump, and in that case, the engine timing would likely be quite off as well.
 
Had the same temp sensor issue with my 2000 GW. Gauge on dash reading very high. Went through 2 oem sensors in 5000 miles. The new sensor worked for a few thousand miles. Replaced it with cheap aftermarket. No problem since. I believe it’s the same part number as your st1100.
 
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Does the fan come on when it is supposed to? If so and the temperature does not go down I would suspect that the thermostat is not opening enough. At least with the Evans coolant you won't boil over and the higher temps won't hurt the engine. I've run Evans in a motor that the water pump impeller failed and was able to ride the bike in the desert almost 20 miles severely overheated and the engine was not harmed at all.
 
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