Engine Temperature going up and down
 

On the way home last night, via M25 (empty apart from a gritting lorry :evil: ), I was trundling along at a steady 90, and noticed that the engine temperature was going steadily up and down from 80-81 degrees, up to 87 and then back down again. It kept repeating this pattern regardless of whatever speed I tried - 70, 80, 90 and even a bit more :oops: , but it still kept repeating the pattern.

Is this normal :?:

I suspect that there is some sort of thermostat opening and closing, but would have thought it would have been a bit smoother than this, seeing that the load on the engine was constant.

That's perfectly normal and I think you're right about the thermostat opening and closing.

Mine does this too.

Not specific to the SV, but in general engine terms that type of cycling is not unusual.

Probably what made it more pronounced is that at higher speed and low air temperature, the thermostat will have been only just cracked open, the coolant flow through the rad will be very slow so it cools a lot (maybe 15-20degC), most coolant flow will be on the 'stat bypass circuit. When the coolant warms up the 'stat opens up a bit more and a slug of cold coolant gets pushed through to the engine, which then shuts the 'stat again.

It's often quite tricky to get the transition smooth when designing the coolant system, but with slightly higher air temps the problem disappears to a large extent. Under normal circumstances you'd expect a temp drop across the rad to be about 7degC which won't normally cause the 'stat to close again. :wink:

Interestingly I was in the south of france for 2 weeks and returned home on Sunday night. below the Lille area of France in the North all the way down to Nice etc the temperature has been in the 40's. When I rode down in 2 days in daylight and rode back in daylight in 2 days to Lille, the temp read a steady 88 degrees with very very hot weather and the bike fully loaded with tailpack panniers etc. After ferry trip and back in blighty which was much cooler and now was dark and slightly dampish, the temp fluctuated from 84 to 90 cycling up and down over a period of around a minute. I was riding in the exact same speeds and styling.

Until I read this thread I was starting to worry that something had been damaged on the ferry.

I think that's perfectly normal when maintaining a "constant" speed... don't pay too much attention to it.