No temp indication on the dash, ECU doesn't seem to know engine temp.

[STD-1300]

So I start my bike up 2003/4? ST1300 and all is well, Idles at 2000rpm from a cold start as usual, the problem is after 3 minutes or so instead of dropping to 1000rpm it climbs to, 2500, 3000+.

There are 0 bars on the engine temp gauge so I think the ECU still thinks the engine is stone cold, and is giving it cold engine fuelling which is causing the climbing RPM as it comes up to temp.

The bike I will add, also seems to ride completely fine other than the very high idle making slow speed difficult.

Where do you think I should start? I'm not massively clued up on the cooling system of bikes but IIRC coolant pumps don't run until a certain temp is reached, meaning the radiator might not be circulating no matter how hot the engine gets?

 

[Larry Fine]

Where do you think I should start? I'm not massively clued up on the cooling system of bikes but IIRC coolant pumps don't run until a certain temp is reached, meaning the radiator might not be circulating no matter how hot the engine gets?

No, the water pump spins with the engine. The fan comes on when the radiator sensor switch calls for it.

The gauge is controlled by a second sensor, a variable resistor, which could be bad or have a loose wire.

 

[STD-1300]

I see, that makes sense.

I think I'll start by checking the thermostat and the sensor, it gives resistance figures for a working sensor in the workshop manual.

If it's neither then like you say it is probably a bad wire.

 

[Willsmotorcycle]

I had the high idle after a minute until about three, @Igofar identified it as (my words "wax valve") dirt on the linkage. I pulled the air box and there was dirt, cleaned and lube and all was well. You have a few more symptoms, smarter riders will be along soon.

 

[vstrom.zrxdude]

Check for coolant sensor wires having insulation baked off.my 06 had this problem last fall.reinsulated wires,2 of 3 were shorted together.gauge worked fine in uses 1 of the 3.other 2 for ecu

 

[wjbertrand]

Wonder if a mouse got down into the V of the engine and chewed the temp sensor wire? The sensor is located near the front of the engine, down in the V under the rubber heat blanket.

 

[vstrom.zrxdude]

No rodent damage.Insulation was flaking off wires from sensor plug about 4 inch back.The heat cooked wires.further back was like new

 

[vstrom.zrxdude]

Here pic of wires need to cut open to find

 

[STD-1300]

OK so whipped the fairing off, checked the coolant level, expansion tank is empty... popped the radiator cap off, radiator is completely empty...

filled it up with water, ran the bike, everything gets hot, circulating as it should, get 3 bars on the dash, high idle is fixed, after warm up runs at it's normal 1000~ rpm.

wiped it down trying to find the leak and nothing, after 5 minutes it starts pouring out.

It appears to be coming from this fastener here, but it's hard to see with the radiator on it could easily be from the thermostat housing or any of the pipework above it.

I'll follow up with a video once it's done uploading.

 

[STD-1300]

Here is the video, I think it needs to build up enough pressure or something, then once it goes (30s~ into video) it leaks quite fast, also makes a pretty horrible noise.

 

[970mike]

Take a look at your thermostat O-ring and your water pump O-ring as that is the area you have circled.

 

[mortenk]

The ST is notorious for leaking coolant where the hoses connect. You may try constant pressure clamps or maybe replace your hoses and clamps as old hoses tend to get stiff over time.

 

[wjbertrand]

Yeah, my money is on a loose hose clamp.

 

[STD-1300]

So I put the radiator on with just the essentials plumbed in so I could pull it down as far as possible and get a view of the leak and also removed the bracket that runs across the front of the thermostat housing.

I can't pinpoint the leak but I can see a drip coming from the back of the thermostat housing, what I saw running down the front of the engine previously was just where it had pooled in the V and was overflowing.

A leaking hose sounds right on the money from what I can see.