Overheating...Slowly(Solved Sep 2020)

[scottie21uk]

Hi

Ive recently bought a 2002 st1300 with 80k miles.

It is overheating. Comes up to 3 bars after about 5 miles of riding and then immediately skips to full heat with a flashing top bar.

I know ill have to check the coolant level but what gets me is the fan doesn't come on.

Is it a fairly audible fan on the st1300? Does it stay on with the engine off? If not sounds ike the fan isn't kicking in, Ive checked the 30 amp fuse but all seems fine.

Any advice?

 

[leonides]

looks like a closed thermostat.

 

[Larry Fine]

I would also check the coolant level in the system, not just the overflow jug.

It sounds like the gauge peaks after the thermostat opens.

 

[TerryS]

I think you'll find the fan operation and the water temperature readout are two separate functions. I've been looking at something similar on my FSC600 scooter and there are two circuits within the one water temp sensor, one drives the dash display, the other is read by the ECM and that decides whether to run the fan or not.

If the temp gauge suddenly changes to maximum temperature then more likely you have a wiring issue between the sensor and the gauge or within the sensor. A high reading means low resistance between earth-gauge-sensor-12v source.

You can get a small IR thermometer gun and check the coolant temperature when the engine is warmed up (I aim at the meaty part of the radiator) and that will tell you whether the bike is really overheating. For reference, around 80C is the normal point at which the thermostat should be open and hot coolant reaching the radiator, and if you are moving (i.e. not sitting in slow traffic/idling) then the coolant should stay pretty close to that. The fan switching temperature is normally around 100C and the "whoops we're way too hot" flashing gauge would be north of 120C. I know these things because my VFR800 had a direct readout of degrees C rather than a sectored gauge.

If the thermostat is really stuck closed the radiator won't heat up much at all, if it is stuck open it will heat slowly from the moment the engine starts, and if it is normal then the radiator will stay mostly cold until the engine reaches 80C then the radiator will receive a wave of hot coolant and get hot quickly.

 

[SMSW]

Read this thread. It might help with this problem. Bottom line is you will have to replace the thermostat or the temp sensor. Go with Honda Type 2 aunt freeze, but call around if you have multiple Honda car dealerships. I found a $10 variation in price for a gallon.

 

[Al st1100]

Thermistors (coolant temp sensors) are fairly bullet proof. I would first make sure the fan spins, could be locked up. If thats ok get a couple of jumper wires, disconnect the fan and power the fan with 12 volts. Check the coolant at the radiator cap not the bottle and you can use any extended life A/F, it will mix with all coolant.

 

[CYYJ]

It is overheating. Comes up to 3 bars after about 5 miles of riding and then immediately skips to full heat with a flashing top bar.

Hi Scottie:

Welcome to our forum community.

@SMSW gave you a good tip in post #5 above, when he provided a link to another thread with a discussion of overheating. Do take the time to review that discussion.

To troubleshoot your problem, you need to approach it in a "logical order of probability" manner - this to avoid chasing down unlikely causes whilst missing the most likely causes. So, here's a list of things that I would look at, in the following sequence, if I had your problem:

1) Check the coolant level in both the overflow bottle (just ahead of your left foot) and at the radiator cap. To get to the radiator cap, you will need to remove the fairing panel on the right side (not difficult). If you find the coolant level in the radiator is below the very top of the cap, be aware that you will need to fill it, put the cap on, start the engine, rev it a little bit, stop the engine, and refill it again. You will need to do this several times.

2) Check the condition & attachment of the hose that goes from the overflow tit at the top of the radiator cap to the overflow bottle. Make sure it is properly attached at each end, and not obstructed.

3) Inspect the overflow bottle - make sure it is properly filled. There are marks embossed on it, but they can be difficult to see if the bottle is dirty. It's an easy job to remove the bottle and clean it, then highlight the embossed marks with a black marker to make it easier to check in the future. That requires removal of the right faring panel - the process is pretty much the same as removing the left fairing panel.

4) Once you are certain that the radiator is full of coolant and the overflow bottle is appropriately filled, and the hose between those two is correctly fitted and not obstructed, then (and only then) should you start checking the radiator fans for proper function. That's easy to do. Put the bike on the center stand, start the engine, and leave it alone for about 10 minutes. It's quite easy to hear the fans whirring when they come on - which they will eventually do if the engine is idling and the bike is not moving forward. If the fans operate, that rules out any problem with coolant temperature sensors.

5) If the coolant levels are known to be correct, and you have confirmed that the fans work, but you still have the overheating problem, then (and only then) should you consider investigating the thermostat.

My guess is that you have low coolant. Do come back and let us know what you find.

Michael

PS: Like @SMSW said, go to a Honda automobile shop to buy a jug of premixed Honda Type 2 coolant. Chances are that it will be cheaper at the auto dealer, and chances are that a Honda auto dealer will be closer to you than a Honda moto dealer. The ST 1300 requires a special type of coolant, and since you are new to the bike, the safest thing to do is just use the Honda Type 2, rather than going shopping for an aftermarket brand that meets Honda specs.

PPS: Here's a link to a post that explains how to remove the fairing panels: ST1300 - Fairing Removal

 

[scottie21uk]

Guys,

Excellent advice. I will go through the full coolant checks first and work back from there.

Really appreciate the replies and the detail. I was always told Pan riders are the most helpful out there.

I will get a look at it this weekend and report back.

cheers

Scott

 

[ToddC]

You always meet the nicest people on a Honda...........!

 

[scottie21uk]

So finally managed to get a look at this today.

Coolant was low....So i toped up and started engine. Initially some coolant leaked from the bottom of the bike. I took off the lower cowl. hose to expansion bottle seems fine. Leake appeared to be coming from a bolt directly under it.

Anyway it dropped a bit of coolant then seemed to stabilise. No more leak and expansion bottle still full.

Checked the fan operation and it is coming on and off. temperature was stable at idle. No leaking, expansion bottle full so i thought i must be fine.

Rode bike for about 3 miles and temp jumped up once again. Came home and when i arrived the temp was still at full although i noticed the fan wasn't on.

watched a few moments and fan seems to come on independent to the temp gauge.

Took a infrared temp reader to the radiator. Radiator temp sen to shoot up quick to 100 degrees. Fan cuts in and it drops to about 80 and this cycle continues However the tempt gauge still reads at the top end.

if i leave the bike for 20 mins the bars drop to 3 and then at an hour they are back to zero.

Where now guys?

 

[heffly]

I would say the radiator running at 80 to 100 is normal, fan on at 98 to 100 and off at 80 to 82 is good. Sounds to me like a temp sensor issue, if no other electrical problems. I always recommend checking ground connections when the bike is apart.......if i had the bike down this far down i would replace the thermostat as well just as a PM item...jmo

 

[SMSW]

The easy things to do, in order, are add juice (you did that), change thermostat and check hose clamps, change sensor on back of the stat housing. As I said elsewhere, I went in expecting to change all of the hoses (preventative medicine), clamps and probably the sensor along with my failing thermostat and O-ring. When I got to the stat housing by pulling the front wheel and radiator, I chickened out on everything behind the stat housing. I did not want to approach this task from above. (And, I think this happened during my riding season - going in from above is a multi day task.) BTW, if you do replace the t-stat, and see scratches on the center post, that is a sign of impending failure - meaning a permanently stuck stat. Should you change the stat, I'd suggest you pull the big hoses off the stat housing and clean up the spigots before putting everything back together. Don't forget a new stat o-ring.

 

[TerryS]

My guess is an electrical fault in either the temp sensor, the wiring to the dash gauge, or the earth. High temperature equates to low resistance in the sensor, so a breakdown in the sensor would explain that. The temp sensor has two independent internal circuits, one for the ECM (which then decides on fan operation) and the other for the dash readout, so a high dash reading but no fan operation is entirely possible.

Actual temps of over 80C is normal (that's what the thermostat is aiming for as a minimum) and 100C is where the fan should be starting/stopping so it sounds like the physical cooling system is probably OK. 120C is about the upper allowable limit for safe operation and the gauge should be registering VERY high at that point.

 

[CYYJ]

Where now guys?

Hi Scottie:

Good advice has been given by other forum members in their posts above - it's time to take a close look at the coolant temperature sensor and the wiring associated with it.

You are going to need to do quite a bit of disassembly to get to the coolant temperature sensor. Because of the amount of work (disassembly) needed to get to that sensor and its wiring connector, you might as well do a thermostat replacement and (perhaps) replace some cooling system hoses while you are in there. Your bike is 20 years old, that is a very strong argument for replacing coolant hoses before they fail catastrophically.

Below are some photos that might help you understand where the temperature sensor is and how the coolant plumbing around the thermostat works. If you do not already have a Honda Shop Manual for the ST 1300, I do strongly recommend you get one, it's almost essential to have one when doing this amount of disassembly.

We have a forum specific to ST 1300 thermostat and cooling system issues, here it is: ST1300-Thermostat. Also, if you browse through the forum entitled ST 1300 Articles, you'll find some excellent illustrated "how-to" guides that explain how to disassemble to get access to the interior of the engine. We also have a forum called ST 1300 Leaks (it deals primarily with coolant leaks) - I suggest you browse through that forum before you start work, because once you have everything apart, there will be other little tasks that are simple to carry out that you can do to prevent future coolant leaks.

Below is a photo showing the thermostat, thermostat housing, and associated hoses - I suggest you plan on replacing the thermostat and the two big 90° hoses, as well as the O-ring on the thermostat casing. The part numbers shown are correct for my 2012 ST 1300, double-check to make sure they are appropriate for your 2002 bike. There were changes made at the 2007 model year, I don't know if these affect the cooling system or not.

Because you have to remove the radiator to get access to the thermostat, now is also a good time to clean the radiator (inside and out) and check the condition of all the hoses at the front of the bike.

See also this post that discusses sealing up the galley plug - if you disassemble to the state shown in the third photo below, you might as well seal up the galley plug as well: Galley Plug Leak and Fix

Thermostat components


Thermostat Location (note the ground wire & connector - check this when you are in there)


Temperature Sensor Location
Photo was taken from above, with fuel tank, airbox, & throttle bodies removed

 

[scottie21uk]

Once again thanks for all the advice. Due to a hectic work schedule ive just got a chance to look at it this week.

In doing so i noticed the battery was a little weak. So i purchased a new one, Installed and problem solved. No seems to heat up correctly fan kicking in as it should and does not overheat.

 

[jfheath]

That's good news. But it's always good to see another batch of Michael's well documented photos !

But can anyone explain that behaviour ? replacing a weak battery fixes temperature readings ? If the engine is running, the bike is getting the power it needs - irrespective of the state of the battery. Unless in replacing the battery, a dodgy earth has been distrubed.

I really would go round your earth points - undo them, clean up the contacts, check the wires. Go back to the earlier replies and check the electrics mentioned there. Come to think of it - its about time I checked mine again.