Article [13] ST1300 - Thermostat Failures

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Joe
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Background:
A somewhat common issue with the ST1300 is a stuck thermostat.

Symptoms:
The temperature gauge on the ST1300 should warm up to 3 bars and stay
there under most circumstances.

The thermostat always sticks in the open state which is good because it
should never cause an overheating situation.

The symptoms of a stuck thermostat are most noticeable when the
ambient temperature is at or below 50 degrees. When the thermostat is
stuck open, the bike may still warm up to 3 bars while not moving however,
as soon as the combination of the ambient temperature and forward motion
continues to cool the bike, the gauge will drop to below 3 bars. It's not
uncommon for no bars to show on the gauge.

Many also report a dramatic decrease in gas mileage during this period.

Causes:

There have been 3 possible causes stated on this site but nothing official
has ever been proven.

  1. Coolant Quality - Some have noted the coolant used in the bike
    during setup may not be high enough quality.
  2. OEM Thermostat Quality - Some have stated the OEM thermostat
    did not appear to be a high quality product.

    Here is a pic of an OEM thermostat in the stuck open state:

  3. Manufacturing Process - Many have noticed paint over spray in
    areas where coolant exposure and heat cycles would break down the
    over spray and allow them to circulate throughout the system -
    collecting on the thermostat itself - many have noted corrosion and
    buildup on the thermostat which supports this theory.

    Here is a pic of some paint over spray from the manufacturing
    process as well as a pic of some of that over spray that has
    collected in the coolant bottle:


Solution:

  1. Over spray removal - checking metallic-to-rubber radiator hose
    connections for any paint and over spray and removing it is the first
    part to this solution. The use of Scotchbrite for over spray removal
    and cleaning the overflow bottle are keys to this step.
  2. Complete flush - Flushing the system thoroughly with water should
    help remove any contaminants which did not come out during the
    draining of the coolant.
  3. Thermostat and Coolant replacement - Some have used the OEM
    thermostat and some an aftermarket one, some have used the Honda
    50/50 coolant mix and some have used other brands. Both of these
    approaches appear to work.
  4. O-Ring Replacement - When replacing a thermostat, be sure to
    replace the o-ring along with it. Some aftermarket thermostats come
    with a new o-ring, but the diamater may be smaller than OEM. Given
    how inexpensive an OEM o-ring is, replacing with a new one is cheap
    insurance.
(If you have corrections, clarifications, additions to this thread please PM
us or post in the suggestions thread.)
 

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Reno
thanks for the description,,,,my 06 with 18k is starting to burn fluid??..the bars stay @ 3 and I've never had any drips on the garage floor....
I do smell burning coolant every now and then...

Mike
 
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Joe
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thanks for the description,,,,my 06 with 18k is starting to burn fluid??..the bars stay @ 3 and I've never had any drips on the garage floor....
I do smell burning coolant every now and then...

Mike
That is typical when the temps start to drop during the onset of the winter/cooler months... It's usually the hose clamps just need to be tightened. Unfortunately, you need to take the plastic off to get to them.

You may want to check the weep hole on the right front side of the engine block to see if any coolant or oil is coming out of that.
 
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Just checked in,,,it's been a while,,,,thanks for the clamp check,,,I will get to it in the next week,,,,

Personal matters have kept me away from the 2 wheeler for sometime now....

:bow1:
 
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New owner of an 2005 ST and had it out today. I let it warm up until I had 3 bars, then took it out on the highway and it immediately dropped and stayed at 1 bar. The temp was 37 degrees. Does this sound normal in your experience?
 

ChucksKLRST

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New owner of an 2005 ST and had it out today. I let it warm up until I had 3 bars, then took it out on the highway and it immediately dropped and stayed at 1 bar. The temp was 37 degrees. Does this sound normal in your experience?
No your thermostat is stinking open. Bike should warm up to three bars and then stay at three bars.
 
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I was afraid of that, but was planning on doing a coolant change/flush as part of my 'new bike' program anyway. Any clear choice on best brand for a replacement thermostat?
 
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I went with a Honda replacement. So far, after one day, it's working great! :) Time will tell. I couldn't believe the crud that came out of the radiator and overflow bottle. No way that any T-stat could've survived that. I gave the whole system 2 thorough flushes before replacing the T-Stat.
 

BakerBoy

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I went with a Honda replacement. So far, after one day, it's working great! :) Time will tell. I couldn't believe the crud that came out of the radiator and overflow bottle. No way that any T-stat could've survived that. I gave the whole system 2 thorough flushes before replacing the T-Stat.
I agree Bill...the pics Joe included in post #1 of the radiator and overflow bottle were from my bike. When I flushed it with distilled water, it still brought out more 'stuff'. Writeup is here. Additional pics are here.
 

Tom Mac 04a

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I went with a Honda replacement. So far, after one day, it's working great! Time will tell
When I replaced mine @ 12k , I went with OEM ( cause I had one )... The stock replacement has worked / lasted almost 2x already. BTW, did change over to Prestone Extend Life.
 
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I used hose water. I know, not prefered, but two full flushes, cleaned overflow bottle, then removed radiator and flushed that several times, as well as spaying the fins as clean as possible, Then drained as well as possible. By the time I put in the new coolant and thermostat, there wasn't much water left. It's certainly alot cleaner than the crud I was running through it before!

I feel like it's a new bike! New windshield motor, new thermostat , flush and coolant, fresh oil and gear oil, new plugs. Next is a new air filter and valve check.
 

saddletramp8511

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Is there a posting somewhere on flushing the cooling system....how to do it....dumb question maybe but never did it soooooooo......Bill
 
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I have the Turbo Tom and I think the bike runs a tad cooler than with the OEM. Other than taking a little bit longer to warm up it's been flawless. Also, my thermostat failure had nothing to do with "crud" IMO. Just a bad stat. Honda just had a bunch of them that were defective. The flushing isn't all that critical as I see it. I just drained the bike and brought the radiator in the house and rinsed it out. I think the coolant I drained out was still good but I got rid of it and used the Prestone.
 
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