what is normal operating temp

[red350]

What is a mormal operating temp for an rz?
I know that the temostate opens fully at 185 degress F, according to the yamaha book, but what temp is to hot?
Mine runs between 180 to 200. is this to hot.

[ricar]

200 is too hot.

[RZ250350OZ]

An example from racing 2Ts - any temp over 55C (131F) and the engine starts losing power.

[tobster]

if the thermostat opens at ~80C, then 55C seems mighty low for thrashing time. So TTS, what temp would you wait to see on the water temp guage (assuming you had a digital readout) before it is safe to rev the engine to the redline?

[Smoker]

OEM thermostat opens at 85C/185F, closes at 71C/156F.

[Bare]

2 of mine open at 80C,. Might be anomalies, might not?

[red350]

So what are u all saying should we run with no thermostat at all?

[RAL]

on my acewell dash on a run the dash show a steady 82c this is with a new stat, so i also want to know if this is the correct running temp?
i did 80 0dd miles yesterday without any probs!.
AL.

[jimrd]

red350 wrote:

So what are u all saying should we run with no thermostat at all?

of course you need a thermostate

Really need it when starting the bike up it warms up before take off
and in the spring and fall the rad will cool the engine at high speed

wihout a thermostate you increase the four corner cold siezure on the piston

and the use of the thermostate forces the water around the jugs uniformily

on race cars we remove the thermostate and install a blanking sleeve to help prevent hot spots in the motor.

[aaronmvrider]

on the 125 and 250's they tape the radiator to keep heat in the engines.... on cold days

[RZ250350OZ]

if the thermostat opens at ~80C, then 55C seems mighty low for thrashing time. So TTS, what temp would you wait to see on the water temp guage (assuming you had a digital readout) before it is safe to rev the engine to the redline?

Hi Toby,

Yamaha put in the higher-value stats so the engines get warm quickly, and warm throughout the block (differential rates of expansion of differing materials such as alloy and steel are taken into account) so that the engines are 'idiot proof', if you like.

The thing is that Yamaha didn't care that in doing this, the engine runs 30°C warmer than optimum, and that it loses power and efficiency. The idea is to get plenty of heat into the engine at all times, to avoid the spectre of cold seizures brought about by differential rates of material expansion, soon after start-up.


So the ultimate answer is that if installing a thermostat housing such as we produce, i.e. one that starts opening at 43°C and is fully open at 50°C, and if running it with iron-liner bores such as on the RZ350, the idea would be to run the engine for at least five minutes once up to temperature before giving it the berries.

Once the engine is warmed through to 55°C, it will operate at optimum efficiency, and develop the most power. This is true of ALL two-stroke engines.

With regard to the RZ350, the stock rad is not up to cooling the engine to a constant 55C in normal running ... it doesn't have the capacity to do this, except perhaps in cold weather.


Using the stock Yamaha stat/designed operating temp is not a problem, it's just inefficient. You might lose a couple of horsepower when running the engine at 85C compared to 55C ... but Yamaha were not concerned about that. Because they're not racing the things. But notice the massive cooling on GP bikes ... it's there to keep temps to around that 50 to 55C mark because that's where optimum power can be had.


Our custom bypass thermostat housings including thermostat are USD$195. Pic below.



This is how we run the stat with our RS500 radiators, which have a 46mm core, with a sealed crossflow divider which forces the coolant to make two passes across the rad - from right to left across the top half and then vice versa across the bottom half. This is done to prevent coolant short-circuiting.



Cheers,
Steve

[nikfubar]

I have heard that an RGV thermostat fits and they open at 60c

[Stroker]

Gee 60c that is must lower an the OEM one.... Might be a good upgrade

[peddro]

KTM have a few thermostats which are cheap, both 55 degrees and work fine.

Bypass thermostat, you just need to block off one of the 2 outlets which is very easy!
Part No.:- 54835013044
£23.20p plus Vat.



Or the Inline thermostat
Part No:- 54635013144
£36.10p plus Vat.



Best regards
Peddro.

[tobster]

nikfubar
well 60C is at least closer to 55C. Presumably the stock Yam radiator will struggle to keep the engine coolant at 55C, therefore need a better/bigger rad etc?