I was bored this weekend, so I got obsessed with oil temperature. This made me believe that I need not worry about my GRiSO's oil temp unless it rains. Which is pretty much what others here have said, so no news really.
I've always liked to have an oil temp dipstick on my air cooled Ducatis. I think they look much nicer than the usually cheap plastic dipsticks and they also provide some useful information. So, when I got my new GRiSO before Christmas I also looked for an oil temp dipstick. My local shop found a "RR", from Louis, [You must be registered and logged in to see this link.]
This cost approx. 80 EUR which really is quite expensive. There is an almost identical product out there labelled MotoGadget, for half the price of the RR. I've used both and never notived any difference except cosmetic. However, this time only RR appeared to have a match for the block thread and the depth of the sump, to be able to function as a dipstick. So RR it had to be.[You must be registered and logged in to see this image.]
Having learned that the GRiSO is over-cooled I also made a cover for the oil cooler air inlet. I then went for a relaxed cruise around the local back roads.
To my surprise the gauge showed a full 130C, and that was riding at a measly 60-90 km/h for some 30 minutes, in dry conditions and air temp +10C. Hmmm. A bit high. I removed the cover, rode on and saw the temp drop ten degrees, to 120C. Still high. While I know that the GRiSO is known to run quite hot (I normally see 60-70C on the Ducatis in similar conditions), surely not this hot? I checked the oil again, Motul 7100 10W60, and found the level to be right between the marks.
This made me suspicious of the gauge. So I decided to get som references.
Around the house I found an left over MotoDetail gauge, a pre-historic steak thermometer with a cracked glass, and the wife's digital cooking thermometer, which I used as a reference. Rigged them in water and noted their readings every minute during heating up from +50C to +100C, at a rate of approx +2 degrees/minute, and cooling back to +85, at a rate of approx -0,5 degrees/minute.
(I'd like to say that the decision to stop at +85C was motivated by fancy thermodynamic theory but in reality it was then my patient wife finally claimed back the saucepan and thermometer)[You must be registered and logged in to see this image.]
Result: All of the gauges proved to be reasonably accurate when given time to stabilize, on average devating no more than 3 degrees from each other. However, they differed in terms of lag. The MotoDetail struggled to keep up with heating up and lagged 9-10 degrees behind all the way from +50C to +100C. And that was at a heating rate which probably is slower than during real riding conditions. The RR did better, only lagging 1-2 degrees behind.
1. I can trust my posh RR oil temp dipstick.
2. I can also trust my cheap MotoDetail dipstick, but have to remember that it thinks slowly = underestimates heating engine.
3. The oil temp in my GRiSO 8V is well above the crucial +100C even in our quite chilly Swedish spring weather. As long as it's dry, as some of you have pointed out. I too am convinced that wet conditions changes that dramatically: A few years back we rode our Ducatis across Denmark, pressing to make the AutoZug train from Hamburg. This was in April and the air temp was around +5C. My oil temp hoovered around 60-65C. It started to rain and the oil temp dropped into the 40s....
So, probably that's that. I can forget about oil temp until it starts raining and then slot in my oil cooler cover if needed.
The only other possiblity would be that my almost zero-mileage engine is running tight and therefore hotter than it will in the future. However, that logic feels a bit 1960s and... surely moderns Guzzi engines are not built that way? Are they?