Question about engine coolant temp When in very slow driving and many stops in...


Question about engine coolant temp. When in very slow driving and many stops in town, my Tracer is between 96-105 degrees Celsius. The fan starts and stops in cycles.

But on highway it is 70-72 degrees.

In cold weather and rain it falls under 60.

What's wrong?

%d comments
  • Fan start at 104 and stop at 99 ....+/- 1degr C..As I said; Everything is OK

  • When the motorcycle is moving, Cold air flow besides the engine,and cools all parts,not only cooling system.(radiator)therefore, the temperature is lower. sorry for my bad english.

  • If you are really worried (and I was when I first got the Tracer) some of the flashes people are doing give you the option of kicking the fan in a little earlier. Yamaha use a non water based coolant that has a much higher boiling point than water so that the bike is able to run a it hotter. As a mechanic I do agree the rang from cold highway riding through to stop start city summer riding is large but as said earlier once the engine is warmed up, as in the metal components and the oil the coolant temp, as long as it stays within a reasonable range is not so important. We are all used to sitting on or in vehicles that have gages that are not that accurate or reactive. You would be amazed if you actually had the same type of Guage in your car how much it jumps up and down.

  • Thanks for reply

  • Somewhere I have a link to an interesting caterpillar cooling system design pdf. Need to find it. There is loads of cooling system design stuff on internet. System is 2 part. Engine primary loop has centrifugal pump circulating water through the coolant galleries in the engine block and back to the pump. Coolant warms very quickly. In the primary loop there is a thermostat that starts opening about 92 deg c and is fully open at about 105 deg c. The thermostat opening is proportional to coolant temperature and it modulates the water flow back into primary loop or into secondary loop. Secondary loop contains radiator. The heat dissipation of the radiator is proportional to cooling air speed and is limited by ambient temperature. If the temperature exceeds alarm limit cooling fan is turned on. Temperature probe is in secondary loop, not primary. The thermostat should keep primary circuit happy. Radiator cap provides pressure of about 1.7 bar to stop coolant boiling. Rad cap also allows leaking into expansion bottle to allow for thermal expansion of the coolant and during cooling a second valve in the rad cap allows coolant from expansion tank to return to the secondary system to prevent radiator being buckled under vacuum conditions.

  • Thanks! As an automation engineer I do like the details in your text. I will read your link too.

  • What he says. The bikes behaving perfectly normal. Rad and stat along with a cooling breeze do most of the work. Fan is only really needed in traffic.

  • over the last few years I have been working on and off trying to solve cooling issues on this 65 litre, v16 1.8MW engine offshore on a FPSO.

  • side view

  • now that is a radiator. Actually, not just engine coolant, the heat exchanger on the top cools the exhaust gas to below the surface temperature ignition point in the high exposion risk area (of there was a hydrocarbon leak).

  • Det är lika på min.

  • All engines on a moving chassis cooled by a radiator work like that.. Nothing is wrong !

  • When I read all replies, it seems to that my question is about fan temps and hysteresis. I described in my text that the fan seems to work as it should.

    But I wondered why the thermostat lets the temp fall below 60 deg C in cold and rainy weather. Is that working temp optimal for the engine? Please explain if you know why.

  • My bike is working at 70 in normal conditions. In colder weather about 65 and fan kicks in at 90-100

  • The temperature transmitter in in the secondary loop. If you use a infrared thermometer on the engine block it will be running at 100-105 deg C, even when the temp gauge shows 60C. The thermostat will be allowing hot water to intermingle into the secondary circuit. If you took the thermostat out you would see the sensor showing the true engine temp but then the warm up time would be huge and engine damage (through differential expansion) would me more likely.

  • Trying to find proof of my belief that the temperature sensor is in the secondary circuit but some show it in the thermostat housing. If it is in the secondary circuit then it will give the fan the signal when the forced air cooling is insufficient.

  • Looks like I'm wrong about the temperature sensor being on the secondary loop. I'm sure it was on the radiator on the 350YPVS. According to the workshop manual on the Tracer it is on the back of the block. That suggests that the temp reading really is the engine temp. The manual does say that the fuel injection system considers the water temperature as well as air temp, O2 sensr etc when it gives a squirt of fuel.

  • unfortunately there is no decent system description in the manual.

  • that makes me want to drop a K type thermocouple into the thermostat housing just to check with a datalogger.

  • David Watkin Thanks for good explanation.

  • Ok! Please be back in this thread with result.

  • Working away in India at the moment. Get home in a week or so.

  • Take the Tracer to India next time

  • Boeing 777 much more comfortable.