I drove 165 mi from Sacramento to Fresno last evening between 7 and 10 pm. Lowest temperature shown on MFD was 37°F. Weather was dense fog with zero visibility at times. I kept defroster going the whole trip to keep the windows clear (high relative humidity). I turned 40k mi enroute. As soon as I got home I backed the Prius in the garage to change the oil. I have pipe insulation in the front grill in winter to help keep the engine warmer. For some reason I did not have the Scan gauge plugged in. I reached underneath to loosen the oil drain plug. Everything was cool to the touch - the oil pan and filter. I changed the Mobil 1 double size oil filter and changed the oil with Mobil 1 synthetic. While fuel economy is lower during cooler weather, I did not expect the engine to be so cool. Not complaining, just an observation.
When your Scan Gauge is plugged in and you do similar freeway driving in cold ambient temps, what engine coolant temp does your gauge report?
That doesn't sound right. After even a few minutes the oil ought to be nearly as hot as the engine's nominal operating temp, about 180°F.
I made about a 20 min trip just the other day when the ambient air temp was in the lower 40s (°F). Under normal conditions, the Scanguage will indicate at least 82 or 84°C after 20 min, but with the temps down in the 40s and lots of fog, it didn't rise above 68°C. That is still warm to the touch, but nowhere near the thermostat opening temp of 82°C. I think the dense fog and freeway speed sucks a lot of heat out of the system. I remember my first experience with carburator icing occured driving down Hwy 99 towards Fresno under similar conditions back in the early 80's. The engine runs very cool; even in the summer with 100°F temps, the highest temp I have seen on the SG is 92°C which is only 10°C above the thermostat temp.
The opening temp spec is 82°C, so the thermostat is supposed to open somewhere in the range of 80°C to 84°C. Further it is supposed to be fully closed when the temp is below 77°C.
You are correct Patrick. I'm not sure where I got the 88°C number from - but I thought that was the opening value. You are right it is nominally 82°C.
So it sounds like perhaps the OP's thermostat is stuck open? That should cause a significant MPG reduction. (BTW, how are you guys inserting the "°" symbol?)
I don't know if it is or not. I think that it may be due to the dense fog and low temperature conditions. It would be a good idea to monitor it with the SG just to make sure. Shift-Option-8 on a Mac. I don't know what the combination is on a PC.
If the OP managed to run the last few blocks with the ICE off it would explain why it was cool to the touch. The oil pan and oil filter are in the air steam, not blocked by grill blocking. I find the engine will cool off very fast if it turns off while I'm driving. I've seen it drop below 60C, and when I drive into my garage (after stopping to open the door - it's Mexican, Manual) sometimes the coolant temp is down below 55C. I force the engine to not start by turning off the heater for the last few blocks (A/C Auto off).
The correct engineering notation is 82°C. It is usually written as 82C becasue text editors cannot insert symbols.
I stand corrected. I have used 82C for forty years based on what my school physics teacher taught. However, it turns out you are not quite correct either because there should be a space between the numeric characters and the units thus 82 °C.
Per internatioinal standards, a temperature is written 82 °C (Celsius). The degree symbol and capital C are separate from the number. The temperature scale is named after Anders Celsius (Sweden) who invented the scale. There is no excuse in 2008 for not following the standards of typography.
Uh.... Probably most of the kid now a day do not even understand the concept of CR (carridge return)..... much less seeing a type writer... Now, texting on their cell... that is a different story...
