Cooling water temp is always low?

[h106frp]

What would a reasonable cooling water temperature be? I've been messing with my external dash instruments and noticed that with the default 125cc bike the temps are always very low (<60 C). If i pull the clutch and rev the bike for ages i can force it up to 100 C but as soon as you start moving it cools really fast. Always though a reasonable running temp was around 90-100 C for a road bike, most thermostats open around 85 C.

Is this a bug or do race bikes somehow run really cool?

Thanks..

[HornetMaX]

Depends on the bike I guess. A 125 can probably run really cool, but a 990 is a different story.

In GPB you also have the head temperature, what does it say ?

MaX.

[EdouardB]

Here's my answer in the other topic:

To be honest below 60 on a 125 is just fine.

In real life on the TZ250 the temperature is anywhere between 45 and 55/60°C depending on the weather. I checked with my mechanic (who worked in GP) after I ran at 45°C with very cold weather and he told me it was a bit low so we put some tape on the radiator to raise it to 50

Anywhere above 50°C on a racing 2-stroke, you start losing power progressively (and above 80° it's really terrible).

On a road 2 stroke (TZR, RD/RZ, etc...) it's ok to run warmer.

[EdouardB]

Speaking of the thermostat and temperature here are some words from Jan Thiel who designed the Aprilia 125 GP engine about the testing results back then with external cooling:

No, a thermostat was never used.
On the dyno the lower the temperature, the more HP!
I do not know the lower limit, if something 'strange' happens if you go too low.
But at a certain piont you might get fuel evaporation problems.
At Aprilia HP still improved going from 45° to 40°.
And at Bultaco I used tap water for cooling, about 20°, with good results and without any problem.
Lots of water moving rapidly was clearly the best.
Some people believe cooling the exhaust duct 'too much' would cost power.
This proved to be nonsense.
The more we cooled the more HP!
Reducing wall thickness also proved to improve HP.
The limit is mechanical reliability.
Which makes me think that fixing the cylinder to the crankcase at its bottom is all wrong!
The combustion forces should not stress the cylinder!

[EdouardB]

Also I confirm that TZ250, TZ350 and TZ750 (and probably the 500 and 125 too) don't have a thermostat, it's useless.

[EdouardB]

Here are some other wise words from a professionnal snowmobile racer who makes his own 2 stroke engines. Apparently you can go really low...

Only for those really interested in engines, this is getting a bit more technical.

We have sucessfully tested coolant temperatures as low as 50 degrees F (10C) on the dyno . Colder than this seems to cause a misfire with our race fuel possibly from incomplete vaporization and we run the risk of what we call a "cold seizure" caused by the piston heating up and expanding faster than the cylinder. Our fuel is 116 octane r+m/2. The difference between 10C and 50C coolant temperatures is around 4HP
The difference from 10C to 80C is 8HP on our 440 cc motor so you can see there is a big advantage to having lots of cooling. We also have the advantage of racing in winter temperatures that dip to -30C at times and we cool our race sled with ice so it is easy to keep it cool, however under sustained running the coolant out of the motor temperature stabilizes at around 80F (26.6C) . We run an auxillary electric pump to boost the flow and also cool the motor down to below 10C whenever there is a restart. One of our problems is that we have difficulty starting the motor cold if the coolant temperature gets below -10C. We have a handy "squirt bottle " with regular 87 octane that helps us start a real cold motor otherwise we keep the race sled inside a heated trailer. My advise is cool the motor as much as you can and run as much water through the motor as possible. There is no such thing as "overcooling" in summer weather temperatures.

[h106frp]

Thanks for all the input, checked and it does change for the different bikes so i scaled my gauge to the warning temp to give sensible deflections. I can confirm if you overheat the 125 in game you do noticeably lose power, at 100C it can barely drag itself along.