Summer Vs. Winter Mpg

[rocky2]

I know that the discussion of winter vs. summer MPG has been brought up but has anyone determined why in the winter the MPG drops,

We got one of the first RX400h so we were able to drive it in the summer in the Midwest. Our immediate MPG was 28+ city, and 24 hwy at 75 – 80, maybe 25 mpg at 65.

In the winter, below 50 degrees, our city MPG dropped to 24 mpg and hwy stayed the same. Now it's warm again and were back to the 28+ city.

We are still happy with the 24 MPG city in the winter because the ML320 our RX400h replaced was getting 14 city MPG and 19 hwy. The RX400h is a much more comfortable vehicle to spend time in. Additionally, to get the same performance I am getting from the RX400h I would have had to buy an ML500

I have spoken with both my dealer and Lexus about this winter vs. summer issue and really have not received an explanation.

As an aside I have no issue with the mileage representations or marketing claims from Lexus or Toyota. Before we bought the RX400h it was well documented that there was a greater disparity in the claimed US Government EPA MPG figures of hybrids and vs. non-hybrid vehicles. My dealer even pointed this out before I took delivery of the vehicle. Considering we were one of the first to take delivery from our dealer, its clear early on there was no attempt to deceive the public that the RX400h was capable of the matching the EPA mileage figures.

Bottom line, I have a vehicle that is as fast as a V8 ML500 or BMW X5, gets better mileage, and cost less, and from my experience needs less visits to the dealer.

[rexmiami]

I took delivery of my 400h on 6/3/05 so I have driven it during all 4 seasons. My mileage also droped about 2-3 mpg when the temperature droped below 50 degrees. I have not heard any official explanation from Lexus, but I think that as the temperature drops below 50 the engine runs more to keep the internal temperature at the proper level. Also the passenger heating system runs more often which uses more energy.

Maybe next winter I put on my longjohns and drive with the heat off to see if I can boost the mpg.

[skyfish400h]

I took delivery of my 400h on 6/3/05 so I have driven it during all 4 seasons. My mileage also droped about 2-3 mpg when the temperature droped below 50 degrees. I have not heard any official explanation from Lexus, but I think that as the temperature drops below 50 the engine runs more to keep the internal temperature at the proper level. Also the passenger heating system runs more often which uses more energy.

Maybe next winter I put on my longjohns and drive with the heat off to see if I can boost the mpg.

I know you are joking, but before anyone thinks that putting yourself out will make much difference remember that the batteries in the back seat are also very sensitive to temperature and are at thier best at about 70 deg (same as you).

So don't put yourself at exteems to get better MPG, because the batts working well is your best shot at greater effciency... that's why you bought the hybrid system.

[katzjamr]

The catalytic converter has to run at 800F for low emissions so the engine runs much longer in the winter for that reason, and to heat the cabin