NX250 coolant temperature

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scrambler
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Registriert: Fr Sep 14, 2012 8:50 am

NX250 coolant temperature

Beitrag von scrambler »

The carbs of all NX250 versions (even the 29 HP AX-1) are identical, except for the jets. The 1988 (249cc) version got 138/38 main/slow jets (12,5KW: 145/38), the 1989-1990 142/38. The 239cc from 1991 onward 140/35 (12,5KW 145/35).
The cooling system of the Nixe is well dimensioned and very dependable, overheating and other problems are rare. With my 249cc version and the stock 142 mainjet I have never seen the temperature warning light in 15 years (ok once, when I was curious whether it works at all and tested it by heating the thermo unit with a blowtorch) and the fan is running very rarely (only when going at very low speed for some time).
So usually a cooling temperature gauge is just a gadget, if everything is stock. But if the airbox or muffler is modified the jetting might need to be adjusted. In this case one can utilize that the coolant temperature is sensitive to the main jet. I tried a 138 main jet once and the coolant got really too hot at full speed. After switching back to a 142 main jet I got 10-15 degree less. I measured it with a trailtech Vapor (it shows the max temp and max speed during that trip).

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Or you could get yourself a thermo radiator cap. Radiator caps of car and motorcycle are pretty much standardized - as far as I know there are only two types, „big“ and „small“ head – and the NX radiator needs a big head cap. The only other difference is the max pressure before the internal valve of the cap will open – it’s written on the cap: 0.9, 1.1, 1.3 or 1.8 kg/cm2 - the NX cap is labeled 1.1

Attention: chinese thermo caps proved to be very unreliable, often they fail after a few km, resulting in massive loss of coolant

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scrambler
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Re: NX250 coolant temperature

Beitrag von scrambler »

I wanted to add where the temperature is measured. It would be possible to insert a hose adapter into the cooling hose. But I use the space of the sensor for the red warning light. It is located at the left side of the cylinder head. It has a PT1/8 '' thread – no kidding. Must have come from the early days of engine construction - so I am not surprised that the American Trailtech is available with a 1/8 sensor. The Acewell speedo I bought for my NX had a M6 sensor, luckily Acewell also offers 1/8 sensors.

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scrambler
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Re: NX250 coolant temperature

Beitrag von scrambler »

If you want to keep your original speedometer, there is the trailtech temperature gauge https://www.ebay.de/itm/Trail-Tech-TTO- ... SwD-5eWdJT. It works with a battery, so no changes to the wiring harness are necessary. A 1/8 '' sensor fits in the cylinder head and with an M12 to 1/8 reduction (sold seperately) you can also measure the oil temperature.

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daleipi
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Registriert: Sa Dez 08, 2018 5:18 pm

Re: NX250 coolant temperature

Beitrag von daleipi »

I still find it VERY interesting that the XN250 has no oil pressure sensor at all...
jonathan
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Registriert: Fr Sep 13, 2019 12:11 am

Re: NX250 coolant temperature

Beitrag von jonathan »

as far as I know, the only common problem with this engine is failed main bearings, and I'm not sure how common this actually is, or whether it was a model year issue. Oil pressure would be the best indicator if the mains were on their way out, but if it registered a sudden drop, it would indicate complete failure/cracked case, so all it would do is confirm what you already knew if it happened when riding it. I've had a few old classic cars that had tell-tale lights that told you something or other had broken, but by the time the light came on it was usually too late. A good example is the old VW aircooled that had an alternator warning light that came on if the fan belt had snapped or was slipping. Usually, people would drive from miles without realizing and fry the motor 9no cooling). The way round this was to rig up an electric fuel pump and put the alt warning light in the circuit so if you're belt did snap, the fuel pump would quit and you'd coast to a stop a mile or so down the road!

Oil temp is worth knowing, especially if you're not 100% certain the water cooling system is working properly. For pressure, you'd need to measure it at the main bearings somehow.
daleipi
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Registriert: Sa Dez 08, 2018 5:18 pm

Re: NX250 coolant temperature

Beitrag von daleipi »

jonathan hat geschrieben: So Jun 07, 2020 10:14 pm as far as I know, the only common problem with this engine is failed main bearings, and I'm not sure how common this actually is, or whether it was a model year issue. Oil pressure would be the best indicator if the mains were on their way out, but if it registered a sudden drop, it would indicate complete failure/cracked case, so all it would do is confirm what you already knew if it happened when riding it. I've had a few old classic cars that had tell-tale lights that told you something or other had broken, but by the time the light came on it was usually too late. A good example is the old VW aircooled that had an alternator warning light that came on if the fan belt had snapped or was slipping. Usually, people would drive from miles without realizing and fry the motor 9no cooling). The way round this was to rig up an electric fuel pump and put the alt warning light in the circuit so if you're belt did snap, the fuel pump would quit and you'd coast to a stop a mile or so down the road!

Oil temp is worth knowing, especially if you're not 100% certain the water cooling system is working properly. For pressure, you'd need to measure it at the main bearings somehow.
funny. I tuned and restored aircooled Volkswagen for years. sold my last one, a beetle convertible, some time ago. NEVER had a snapped belt. heat-killed some No3-cylinders nonetheless due to the idiotic placement of the original oil cooler (and a full shelf of motors). serious motors always had a front mounted oil cooler.
for the oil pressure warning light - we had a rear fog light mounted in the footwell. you never missed a flicker! then again, most engines where dry sumped.

still miss a oil temp and press indicator. would feel more complete ;-)
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