Engine temperature - cooler is better, right?

[Viking]

Morning all,

This philosphical question is brought about by the discussion TLoML and I had last night.

She is saying that the Aprilia engine designers designed the engine to run at an optimum temperature range, somewhere between 75 degrees C (where the thermostat opens) and 95 degrees C (where the cooling fans kick in), and that by changing the fan switch to a lower temperature I will be reducing the engine's optimum temperature range. With the effect that the engine may not run as well as the engineers designed it to.

I want to change the fan switch because I don't like the idea of the engine running very hot before the fans switch on. I can recall that engines prefer to run cooler than hotter, and that engines can be damaged by running too hot for too long.

Given that the riding I do is mostly low speed commuting, I'd prefer to keep the engine cooler - especially on hot summer days where the ambient air temperature can be 35 degrees C or higher. (As an aside, it's been a fairly cool 15 degrees C some mornings and the engine temperature can still get to 95C and stay there for quite some time.)

So, who is right here?

To be fair - I haven't seen any posts (either here, on ARS or AF1) saying that the stock fan switch is too hot and will cause engine damage in the long run, but I have seen posts on AF1 from people saying that they've installed the lower temperature switch out of personal preference.

Finally, I heard that the early Falcos had the low temperature switch but changed to the high temperature one somewhere in the middle of the production run. Whilst the RSV-R started with the high temperature one and changed to the lower temperature switch. Is this correct?

If you've read this far, you deserve a medal!

Cheers!

[D-Rider]

mmm that's a good-un.

Think I'll have to side with TLoYL. The engine will have been designed to run within an optimum band where clearances will have been optimised.
Unless the fans fail to cool it sufficiently and the temperature keeps on rising, I guess all is fine. I presume that the lower temp switch is for use in those higher ambient situations where temperature will keep rising despite the best efforts of the fans - cutting the fans in earlier will not stop the problem but it will delay it somewhat - hopefully enough for the traffic situation to have improved so that you can start riding fast enough to get some serious air through the radiators.

..... well, that's my speculation anyway.

Not only that, but I've learned never to disagree with anyone's "better half" (particularly my own!) - so I was never going to back your arguement anyway.

There again, I'm pretty sure the lower temp switch is not going to give any real problems - the engine is designed to run over a wide range of temperatures - not just at this "optimum" point.

[Gio]

I want to change the fan switch because I don't like the idea of the engine running very hot before the fans switch on. I can recall that engines prefer to run cooler than hotter, and that engines can be damaged by running too hot for too long.
Cheers!

Can't speak for the Falco, but my Blackbird always ran better the hotter it got, the fan on that used to cut in at about 115c.

When I ride the Falco in London the temp never drops below about 90/95c and I've only heard the fan fire up once and am glad about that as its fecking noisy

[ancientd]

Bike engines are designed to run at a specific temp range, if you deliberately set out to lower the temperature you will have problems, you will use more fuel, engine could run irraticaly and you will stand a much higher chance of emulsifying the oil and will get a white skum inside the engine casing. I have a Thundercat, which in standard trim is over cooled, the temp gauge hardly moves, which is common on Cat's, as a result I run the bike with the rad partially blocked off so that it is considerably less efficient at cooling the engine, hence the temperatuere rises and the gauge rises to its mid range and the bike runs much sweeter.

[Samray]

The only thing that might alter the optimum engine temperature is altitude?, certainly not the ambient temperature.

[Gio]

Bike engines are designed to run at a specific temp range, if you deliberately set out to lower the temperature you will have problems, you will use more fuel, engine could run irraticaly and you will stand a much higher chance of emulsifying the oil and will get a white skum inside the engine casing. I have a Thundercat, which in standard trim is over cooled, the temp gauge hardly moves, which is common on Cat's, as a result I run the bike with the rad partially blocked off so that it is considerably less efficient at cooling the engine, hence the temperatuere rises and the gauge rises to its mid range and the bike runs much sweeter.

I'm glad you posted that Ancient, my son has a thundercat and he lives in London, 5 mile ride to work and he's been saying its playing up. Even there his temp gauge barely moves off the bottom scale.

[Viking]

I've been keeping an eye on the temperature gauge for the past couple of days now.

If I can get a good run to work, the temperature stays between 77 and 84 degrees C. As soon as I start getting stuck in traffic, it tends to stay between 86 and 96 degrees.

Ideally, I'd like to keep the temperature below 90 degrees, hence the low temp switch.

I think I'll install the switch and see what happens.

Oh, I'm aware of running engines too cold. Believe me, that's not going to happen here.

[lazarus]

I might have my doubts about Italian engineering, particularly when it comes to electrics, but I cant believe that Aprillia wont have done careful work to determine the engines best operating temperature range. Co-incidentally, their temperature range is much the same as that of other engine manufacturers. Some are higher (Merc for example) and the only ones I know of that are lower are raw water cooled marine diesels at about 50 deg operating, and thats for a special reason. So what makes you think that the posters on RS know any better (or anything like as much) as the engineers who designed the engine?

A cold running engine is less efficient (laws of thermodynamics), risks internal corrosion because the oil doesnt get hot enough to get rid of water (coffee coloured gunge you used to see on the inside of the oil filler cap on cars) and increases wear (most of which occurrs during warm up). The only gain would be the power being consumed if your fan is permanently running as you imply.

[falcomunky]

Well, considering the engine is the Swiss made Rotax and the electrics are Japanese, (I think), then any doubts about Italian engineering go out the window!
The Rotax is one of the few bike engines I know of where they reach 100k+ and still keep on keeping on! I bet there aint many litre Jap bikes that do as well...
As fer the temp range, mine runs anywhere from between 70-100' under 'normal' use; Warm ambient temperatures simply means she gets hotter that little bit quicker. Not a problem as long as the fans do kick in!
My old zx6r B1 ran within the same tolerances as did my T595 and zx7r before that and they never had any mechanical probs...