2t Aprilia RS125 - running temperatures

[c_dug]

This morning I eventually put my little Aprilia back on the road after sitting unused for probably two full years now, maybe 3.

I've really not ridden it much at all and so perhaps it's always been this way, but according to the dash temperature it never really warmed up. When I first switched it on it showed 71°c which is obviously wrong, then dropped down to mid/low 60s when I started it up.

It did fluctuate a bit on the ride, but I never saw above 72°c at the absolute highest, and it would drop down to maybe 66ish or thereabouts at times.

It ran perfectly the whole time, I probably covered 20 odd miles, I didn't give it the beans for a good few miles just to be safe.

I'm guessing it shouldn't be showing 70°c before it's even started so something is up, what should I be checking?
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[xX-Alex-Xx]

Temperature sensor is the first place as it’s showing the wrong temp before you fire the engine. You’ve got it set to Celsius not Fahrenheit yeah?
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DILLIGAF

[P.addy]

[c_dug]

Yep absolutely certain it's in Celsius.

Can I check the temp sensor somehow? Or do I just have to replace it and hope for the best?

Does it have any knock-on effect other than showing the wrong temperature on the dash? I presume the thermostat is separate?
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[Kickstart]

Thermostat is separate.

Check the connection first and that it is clean, and the block connectors in the loom, but sensor would be my guess to.

All the best

Katy
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[1198]

Would a Google search show expected resistances at various temperatures so you stick an multimeter across it then warm it up / cool it down?

[jeffyjeff]

I would check the electrical connections at the temp sensor and any intermediate connections up to and including the gauge. The high temp at start up suggests a faulty sensor or electrical continuity to earth (too much current flowing through the gauge). You can test the gauge by disconnecting the wire from the sensor and touching it to the engine case. Expect the gauge to peg cold when the wire is disconnected, and peg hot when the wire is touched to the engine case.
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History shows again and again how nature points out the folly of men - BOC

[UnknownStuntm...]

Not a 125, but I spent far more of my life than I like trying to find out why an otherwise mint 250 constantly showed the wrong temp.

New thermostat, sensor, etc. I gave up in the end.

Electricity doesn't seem to be a strong concept in Italy.

[c_dug]

I had a quick 5 minutes spare to have a cursory look this morning

I popped the connection off of the top of the sensor, the connection was just a spade connector and felt very loose, not sure if that's normal or if it's been replaced at some time in the past? It didn't feel very well attached anyway.

When I popped it back on it felt a little better, and the gauge slowly dropped to around 40°c. Might have gone a wee bit lower if I'd left it longer but I was booked into the tyre shop and had to get going. That's a clear improvement over the 70 odd it showed yesterday!

On the 5 mile ride to the tyre place it climbed pretty quickly to around 61, then slower to 65. It only ever touched 70 briefly at traffic lights. This seemed a bit more normal at least.

Is 65ish normal running temperature for these bikes, or does it still seem like I need to do a bit more investigation still?
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[Kickstart]

Hi

A spade connector is usual there.

Thermostat opens at 70 degrees I think.

All the best

Katy
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[jeffyjeff]

[stevo as b4]

Two strokes like to be kept cool generally, with a lot of generalizations.

I know that 55degrees coolant temperature will always be better than 75 degrees coolant temp on a two stroke. If you ride your Aprilia gently for at least 10min after starting it from cold it will have opened the thermostat by then if it was going to open which is the important thing, regardless of what the number on the gauge says.

[Old Git Racing]

Ran my TZ at 60 degrees. warm up is important, not having a thermostat in could lead to a cold seize if too many beans are applied to soon.

OGR
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2022 Tiger Sport 660 2019 Street Twin 2003 K3 gixxer 1000 1998 Srad 600 track hack

[c_dug]

Looking into this further at the moment, I've installed a new sensor and have checked all of the connections up to the clocks and I'm still getting the same odd readings.

There's no obvious corrosion on any of the connections between the sensor and the guage cluster. I'm wondering if it might be a grounding issue as I also have intermittent issues with the dashboard indicator idiot light, but they don't seem to share a ground judging by the diagram:

https://4.bp.blogspot.com/-_D3o1Sx2x1k/U0-4k7kT79I/AAAAAAAAFXc/T109odQLJuM/s1600/Rotax+123+wiring+diagram.jpg

Any thoughts/suggestions?

Edit: Actually on second look at the diagram it does look like there is a shared ground for the indicators and temp guage, the horn is a wee bit weedy too and is also on the same ground. Looks like I have a culprit. Time to find the ground point!
____________________
I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[c_dug]

Ok, so measured with my meter and I have 0 resistance on the sensor wire, and have a good ground between the connector right up at the clocks and the negative terminal on the battery.

I'm beginning to think it may be the digital display playing up. Not that much else it could be!
____________________
I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[jeffyjeff]

I see a 10 pin connector block in that circuit. Any chance of a wonky terminal crimp, or possibly a damaged male-female terminal connection?
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History shows again and again how nature points out the folly of men - BOC

[c_dug]

Could be possibly but it all looked in great condition, nothing looked out of place and no visible corrosion or any sign of damp at all. Plus, I've measured beyond that, at the final 4/5 pin that goes into the the back of the digital gauge and there was no resistance at all on that wire.

The sensor works by dropping resistance as it heats up, but if anything it is doing the opposite. I think it must be an issue with the digital gauge itself.
____________________
I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[Campbell SOUP]

Have you found any documentation that says how much voltage should be getting sent from the dial to the temperature sensor? Measure between the sense wire and the negative wire on the gauge and compare.

Most temperature sensors increase in resistance with temperature, is the Aprilia rs125's sensor different?

[c_dug]

Err, no it's a pretty standard sensor, maybe I have it backwards!

Not sure on the line voltage either, I've been looking for any spec at all on it but found very little.
____________________
I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[jeffyjeff]

Did you try grounding the sensor wire to the case or cylinder to see how the gauge reacts? If the gauge pegs one way or the other, that will tell you how the circuit is engineered. I think the gauge will peg hot when the sensor wire is grounded. If it only arcs part way, that will confirm beyond doubt that there are other issues with the circuit.
____________________
History shows again and again how nature points out the folly of men - BOC

[Robby]

Single wire sensor? If so, it's completing the circuit by grounding through the rad. Look for corrosion where the rad bolts on to the frame.

[jeffyjeff]

[Robby]

No idea, I normally see temp sensors at the top left-hand corner of radiators on bikes. Could be cylinder head mounted, in which case you want to be sure that the engine is well grounded and doesn't have a thick layer of rust and alloy corrosion on its mounting bolts. Or run an additional earth strap from engine to battery negative, which is my usual fault-finding shortcut.

[jeffyjeff]

[Robby]

It might, but spark plugs are stupidly high voltage and that cares a lot less about corrosion. Similar thing for ignition pickups, where the quality of the signal isn't that important. As long as a signal can get through to the CDI or ECU, they work.

A temp sensor is trying to constantly measure resistance in a circuit. If there is a load of corrosion in the circuit, then it is going to read more resistance. Add in the fact that you have corrosion, different metals, heat changes in those metals, stuff moving around (so you might sometimes get a better connection than other times) and a load of vibration and it's no surprise that readings will wander around a bit.

Also worth noting that bikes are surprisingly shit for this. Cars seem to get away with a couple of chunky earth straps that just work, and failure is usually down to the strap breaking or rusting away. Bikes have loads of little earth points all over the place, nearly always involving at least two different metals (and sometimes 5 - copper wire, aluminium eyelet, alloy engine, mild steel frame, stainless steel bolt). Galvanic corrosion is an acceptable sacrifice at the altar of lightweight, shiny parts.
Then, just for fun, the earthing points are hidden behind bodywork and the manual gives you a vague indication of where you might find one.