increasing MPG's in the winter

Priuschat has an engine block heater available: PriusChat Shop : Toyota Prius Engine Block Heater [Prius EBH] - $59.00

Last winter I saw my MPG drop down to 44 (I admit I'm not a very patient driver). I'm actually considering picking up one of those.

 

Hi Ct...,

Yea, its going to be a bummer to be back in the 40 something MPG, in the 0 degree weather, after finishing the last tank at 69.8 (77.0 computed).

But the engine block heater does help. Keeping track of tire pressures helps. Pump the tires up each week, as the weather gets colder each week. Besides the engine warming up, the battery and tires also need to warmup to give good mileage results. And both are delayed by cold weather. Unfortunately there is little one can do to help warm those up. I have a black rear deck cover, which helps with solar gain (when available). Which also reduces extracting heat from the engine into the passenger compartment on the way home. In the morning, however, everything is just cold.

 

I agree that a block heater is a valuable wintertime accessory. In fact, I use it all year 'round when I have somewhere to plug in. Problem is, I'm like you -- I moved into a townhouse development last year and have no easy way to plug in. The only times I routinely plug in these days are when I'm at my part time job site or my fiancee's house.

For further information on the five stages of the Prius' warmup sequence, see this. Some highlights: There are two transition points in the sequence that are at least partially tied to temperature. Probably the more significant of those is the transition from stage 2 to stage 3, which occurs with an ICE temperature of 70C (157F). The ICE will not shut off with the vehicle moving in S2. It will shut off in S3 under certain circumstances (described in detail in the linked paper), and in S4 (which also requires 70C) it will shut off whenever it is not needed for propulsion. In the dead of winter, it can take a long time in city driving to reach 70C, especially if you're running the cabin heat. The block heater reduces the time to reach that threshold. In addition, many of us block the grille in the winter to reduce engine heat loss. Search for "grille block" for numerous threads if you want to find out more. Finally, the hard-core fuel economy fanatics among us (like me ) bundle up and run without cabin heat as much as we can tolerate it. I've seen engine temperature drop by 10-15F just sitting at a red light while running the heat. Once ICE temp drops below 70C, S2 behavior returns.

The other transition point is from S1 to S2. The five stages paper says it makes that transition at 40C (104F). But several of us have observed that it is not strictly temperature-dependent; it has a time component too. Without a block heater pre-heat, it takes a little over a minute, seemingly without much regard for baseline engine temperature. In the winter, I've seen the transition with an ICE temp below 90F, whereas in the summer it can climb to over 110F before transitioning. On the other hand, an EBH shortens it to as little as 30 seconds, so there is at least a partial temperature component to it.

I would not let it run at a standstill just to warm it up. That wastes fuel. If it's going to run anyway, you might as well get some propulsion from it. The only precautionary note is not to push it hard during S1. As the five stages document describes, it is still using battery power to move until S2 is reached, and to push hard will quickly deplete the charge. It doesn't harm the car, but the ICE will have to run more to recharge the battery.

I think I've seen mention of an oil dipstick heater, but I don't recall any reports of whether it helps. And I wouldn't think one that can run off a battery, if it even exists, would give you much power and heat; the EBH is 400W. The latter is the overwhelming choice for a preheating device.

Finally, one other thing to consider: an EV switch. Read this for how I use it and to get a sense of whether it might benefit you. Also, research it thoroughly to understand how not to use it, and realize there is at least a small risk of potential warranty issues, as I mention in that discussion.

Sorry for the long-winded response, but you seem interested in a deeper understanding than many of how cold weather might affect fuel economy. And I had some time this morning before starting work.

 

More important then the EBH do some grill blocking with foam insulation in the winter.

 

My first 7 winters with a Prius in Minnesota, I didn't do anything. MPG was still way better than other vehicles on the road anyway.

On winter 8, blocking the grille caught my interest. That only took a few minutes and was cheap to do, so there's no reason not to. Photos in the User-Guide.

EBH (Engine Block Heater) has proven worthwhile for those that have tried. Do searches. You'll find lots of experience with that shared here.

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The simple answer is that you don't have to do anything to warm the ICE. The control system does it for you. If your engine needs heat, the Prius will run it as needed.

Block heaters and grill blocking are techniques to improve mileage by reducing the loss of heat. They help with mileage, but are by no means necessary for the safe operation of your Prius.

Btw, the block heater for the Prius is not an oil dipstick type of heater. It attaches directly to the engine block and fits into a spot designed for it.

Tom

 

I did some grill blocking last Wisconsin winter using pipe insulation and velcro ties. Gray car and gray insulation. Actually looked very good. One each on the upper and lower grill pieces. Managed to hold 48 mpgoverall through the first winter which, given the car that was brand new I thought highly of. Now it's middle of the hot season and I still have the bottom one on. Wish the car had a temp guage so I could tell if that's a good idea but since the motor doesn't run all the time I'm thinking that keeping the heat is a good idea regardless of season. Now getting 52 on my standard commute with reformulated gas. 55 with the good gas from up north.

Grant

 

Grant,

Get a Scangauge (~$150) and it can display up to four simultaneous parameters for you (including several temperatures).

JeffD

 

When you say good gas? No ethanol?

 

Actually is gas without ethanol. Definite improvement in performance and mileage. SE Wisconsin is both 10% ethanol and reformuated with something (MTBE?) for air quality. Even makes a difference in my mower so not surprised I do better with the good stuff. I don't know what difference just 10% ethanol would make without the other additive.

 

I believe it makes the engine run cooler.

 

If you have access to a garage (a heated one), that would help w/ the winter temps.

Other than that, I think it is kind of a tough it out till warmer weather gets here. I face the same cold weather problem w/ my diesel truck - less mileage in the winter, cold weather starts on those frosty mornings. I sometimes use the oil pan heater to start this beast especially when temps are @ 20 degrees or colder.

This coming winter will be my Prius first cold weather exposure. it will be interesting to see how it responds in terms of mileage. Once I get 10,000 miles on the ODO, I will probably switch over to a synthetic 5-w-30 oil.

Dbcassidy

 

I have found that true LRR tires help MPG in cold weather. See the attached data on my experience with three different tires. The Two LRR tires (Michelin MXV4+ and Nokian WR) noticeably improved winter MPG over the original GY Integrity tires.

JeffD