I think this is an accurate explanation. I've noticed that my threshold, based on the gauge reading, is around 205°--which is the temp normally reached in summer riding, only exceeded in heavy stop-and-go traffic (230° max). IOW, it will climb to 205° and mostly stop at that point as long as I'm not stationary for more than a normal interval in city riding.

In highway riding mine would rarely exceed 180° in 50-60° air, 205° at 95°. Get into the city and it may go higher in winter, not much in summer.

I don't know if it is errant as much as the graduations are not in round numbers. I look at the graduations as being linear, and based on my tests they are so at least at around 205° (mid-point graduation between 180 and 230). I can't say above or below that since I haven't checked it. Once warmed-up I stay between 180-205° 99% of the time, even comparing summer and winter.

Well, it has been in the 2-3 times I've compared readings between the fairing gauge, IR thermometer, and meat thermometers--the latter two read as the oil is drained, not after hitting the drain pan, as that cools it very quickly. In these informal tests the temperature has been within a few degrees.

I agree and have always thought of this phenomenon this way. The oil-temp will indeed decrease radically when riding in rain, but I never thought of it being the water directly causing the sender to emit false data.

I monitor both oil and front-head temps and I've seen differences of as much as 90-100°, with 50-70° fairly common. I can frequently see the head temp at 270° in summer traffic, higher in gridlock, with oil temps at 205°.

I don't monitor the rear head temp in real-time, but checking with the IR thermometer shows the rear to run around 50° hotter when at normal operating temp. What are you seeing?

For two years I had the PCV-AT with a switch that allowed me to toggle between a lean (14.6) cruise-range and a rich one (13.5). I really didn't see much of a difference, always <10° measured at the front head. With that setup I ran the leaner configuration 99.9% of the time, and now with the PV run it at all times, although I do have the richer map loaded in the tuner module in case I really need it. Lately in these hot (95-100°) days we've been having, my front-head temp stays between 225-235° as long as I'm running >45mph, which I consider very acceptable. I would like oil temps to stay around 180°, but that isn't going to happen, at least on my Harley in summer.

Thanks for your interesting input.

 

Disregard....question already answered...

 

 

iclick, what I've observed is that there is not a simple answer to your question. The variance between front and rear is ever changing with riding condition variables, but I have noticed some consistencies. Beginning with the first start up and warm up, I see the exact same rate of increase and temp, front and rear. When I start moving I see the rear heat up at a slightly faster rate, at 45 MPH or below I only see 5-15 degrees hotter in the rear cyl, at highway speeds above 65 MPH I see 20-30 degrees hotter rear cyl, under normalized condition. Now then when I come to a stop, the front will rise to meet the rear temp quickly and equalize in about 2 minutes or two traffic lights, and both CHTs will climb above 340 within 3-4 min. The temps will come down again very slowly, front and rear will remain in an equalized condition even moving slowly in town. When I do get back up to traveling speed, the front drops very slowly, way slower than the time it took to heat up, even moving fast on the highway it drops slow. I posted something similar in another thread but I don’t remember the round about values that used, I don’t want to contradict myself. Although occasionally I see a difference of up to 30 degrees, basically I see the front and rear temps are the same or only a couple percent difference for a majority of the runtime when driven normally (no extremes in driving style). Unless you are traveling long distance on the highway at high RPMs, you wont see the big difference in rear temp for very long. I guess I would say I’m beginning to question the traditional concern for higher rear cylinder temps. Granted this is only my bike, but I know the front and rear are tuned the same at stoich in the cruise range and transitioning only to 13.4 out at WOT/upper RPMs. At a glance my results may not be too impressive, but on a lean tune, @ 95F, normalized at highway speeds turning 3k RPMS, I’m typically seeing 220-225F oil temps, and I am positive my gauge reads accurately, at the same time my rear CHT will be about 300F and my front about 275F. With everything the same except 2.5K RPMs, the oil normalizes at about 205F. Also not running synthetic, plain Jane HD 20-50. Another consideration is that my test platform is an 06 with a 5 speed, so at 75 MPH on I-95, I’m turning in excess of 3K RPM. Important because in my observation, RPM is the second most influential variable relative to oil temp, the first is tune condition. Anyone with a six speed has a definite advantage in combating oil temps, at least on the highway, because they will be generating less heat at a lower RPM, and moving faster.

 

About three years or more ago I checked front and rear CHT at the base of the spark plug with an IR thermometer on several occasions, and it was as much as 50° hotter on the rear, but usually the difference wasn't that high. That was with the stock cams, and I haven't checked since installing the 255's in early 2009. I haven't noticed any difference in oil temps since that time.

I know I'm repeating from my last post, but my oil never exceeds 205° in 95°+ weather as long as I'm moving along >45mph and I don't have a strong tailwind, which can run temps up as much as 10° higher at interstate speeds. It hits that midpoint line between 180 and 230° on the gauge and mostly stops there, which I assume is when the cooler is fully open. CHT stays at 225-235° under these conditions, but at city speeds with some normal stop-and-go it will go to 250° or so, and 330° was the highest I've ever seen in really bad gridlock on a 100° day. I rarely see >280° on this bike, and above about 290° makes me nervous. When CHT hit 330° that one time, oil temp stayed at 230°, and to date neither has gone higher. OT will hit 230° several times per year in summer traffic, but it takes a while to get up there. I hope I'm using figures that are consistent with past posts, as all this is from memory.

When engine temps (OT or CHT) climb above normal I find that they will never go back down to a "normal" level. IOW, if I'm tooling along the backroads running 225° and hit traffic, letting CHT's go up to 250°, once I get moving again it will never go back down to where it was before, maybe within 10-15°, the same going for oil temps. If they climb to 220-230° they will settle at maybe 210° after quite a while of riding >45mph. I don't quite understand this, but you apparently see the same phenomenon.

I ran fossil oil during break-in, but changed to synthetic after 1700 miles, at which time my oil temps consistently ran ~10° cooler in the same conditions. Most report similar cooling effects after changing.

I don't use 6th gear until I'm going around 62mph, higher in a headwind, and I haven't noticed any difference in oil temps, gas mileage, or CHT by shifting to 6th. My Power Vision has an instand MPG gauge that doesn't change much if any when I use 5th instead of 6th between 60-65mph. Keep in mind that my gearing is lower than yours in gears 1-5 and I'm turning 67mph at 3000rpm in 5th gear (GPS speed).