Another Victim of the Stat issue

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Jul 16, 2013
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Halifax, Nova Scotia Canada
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St1300
On my second highway ride on my new to me 2003 St1300, the thermostat seems to be stuck partially closed, causing over heating over 100 Km per hour, was able to limp home at 98KPH, holding 5 bars, stat ordered, rain on Saturday, weekend project ahead.

Many thanks to previous articles here, as I have the same symptoms has in previous threads.
 

dduelin

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The ST1300 thermostat never seems to fail closed or partially closed thus causing overheating or a gauge display of more than 3 bars. It normally fails open causing cool running issues and gauge displays of less than 3 bars.

I am not disputing your comments and experience, we have seen this before but it's rare. The only time I helped with an overheating issue it was actually a problem with the electrical connections to the coolant temp sensor causing an incorrect gauge display when the coolant temp was actually normal.

When you examine the thermostat housing focus on the condition of the wire to the sending unit tapped into the housing and the green wire clipped onto a terminal affixed under one of the housing cover bolts.
 
OP
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Halifax, Nova Scotia Canada
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Kool, thanks for the input, the problem is exactly as another member described, I have a stat ordered $46, and while in there will replace it. Will document, and check the wiring, thanks for suggestion, love this forum! I feel it is a stat issue the rad is cold except by the input from the engine, only a small hand sized part of the rad is hot, the rest cool to the touch, will also flush and clean the system while it's apart.
 

dduelin

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Kool, thanks for the input, the problem is exactly as another member described, I have a stat ordered $46, and while in there will replace it. Will document, and check the wiring, thanks for suggestion, love this forum! I feel it is a stat issue the rad is cold except by the input from the engine, only a small hand sized part of the rad is hot, the rest cool to the touch, will also flush and clean the system while it's apart.
If the radiator is cold for the most part it doesn't sound like it's running hot at all and 5 bars is an incorrect reading.
 
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If the radiator is cold for the most part it doesn't sound like it's running hot at all and 5 bars is an incorrect reading.
In my mind that would be a good indicator of a stuck SHUT thermostat.....doesn't open to allow coolant into the radiator........I think he's got it right....or I'm thinking backwards.......................ff
 

dduelin

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In my mind that would be a good indicator of a stuck SHUT thermostat.....doesn't open to allow coolant into the radiator........I think he's got it right....or I'm thinking backwards.......................ff
Well he will find out soon enough.
 

BakerBoy

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In my mind that would be a good indicator of a stuck SHUT thermostat.....doesn't open to allow coolant into the radiator........I think he's got it right....or I'm thinking backwards.......................ff
Same deduction here--stuck shut thermostat is a reasonable explanation. Unless there's a fault in the coolant temperature sensor or temperature circuit, the high indicated temperature would be due to the thermostat sticking closed (or debris in the thermostat lines somehow causing the same effect) and the coolant recirculating directly back into the engine, bypassing the radiator, leading to overheating if too much power is required.

As I recall, the coolant temperature sensor is on the recirculation (hot) side of the thermostat housing, not in the radiator (cold) side. And as dduelin noted, a stuck closed thermostat is very rare in the ST (I can't recall ever reading about one).
 
OP
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There are 149 km on her, was owned by an older retired gentleman, and then a middle aged guy, both rural, so mostly highway miles, the bike is in very good shape overall, the deal who did the inspection could not believe the miles to condition of the bike, looking as good as it does.

My thoughts are with the flush, and stat replacement the problem should be solved, I had no problems at all during the first 10 days of ownership, steady 3 bars, this just started Thursday of last week.

Coolant level is good, and coolant in reserve does heat up, and the fluid level rises when hot, I also have a clamp that leaks slightly when I hit 5 bars, from the pressure of the increased heat this will be replaced during the repair.

I will also clean out the rad of bugs, and correct a few bent fins (not severe, but does not help)


in my eyes all these things, plus the earlier thread I this that exactly matches my conditions

https://www.st-owners.com/forums/showthread.php?89199-ST1300-overheating
 
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While your in there verify water pump flow. before you reassemble the bike you should boil some water and verify sticking t-stat. (not a bad idea to check new stat as well)
 

ST Gui

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With only 149km on the clock it would seem a 2003 bike has done a lot of "sitting around" and I could easily imagine how the thermostat could end up stuck shut.

Whatever the cause here's hoping you're on the road soon.
 
OP
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After the delay of the parts guy not ordering the o-ring, I finally got the thermostat, and o-ring. Replaced stat, flushed system, checked old stat in boiling water, it barely opens. Run bike in driveway, steady three bars, off and on coolant fans cycle. No leaks, everything tightened Looks like I got it. Too wet for a highway run tonight, but will reassemble her tonight, and ride to work tomorrow. Will advise final outcome tomorrow.
 

Mellow

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good to hear it will be back on the road soon.
 
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