Pre-heating the Prius Transaxle and Engine for better fuel economy
 

I'm eyeing the transaxle for pre-heating because unlike the engine, it warms up slowly. The graph below shows the relationship between fuel economy and temperature for the Gen 1 Prius. I think this has to do mostly with the transaxle and high voltage battery, both of which are more efficient when warm.

I'm also going to install a high wattage circulation tank heater to try to get the Prius into stage 4 right on startup. Stage 4 simply put is when the engine shuts down anytime it's not needed. Normally the engine runs until it reaches 70˚C whether it's needed or not and runs rich while doing it.

I have not found anyone preheating their Prius transaxle yet so I think I'm blazing a trail here. Please let me know if you see anything out there.

From Bob's transaxle study:2003 Prius - Cold Weather and Transaxle

So it must be worse at lower temperatures.

The following graph shows the effect of cold on mileage in the gen 1 prius:

http://www.hybridexperience.ca/Pages...0vs%20Temp.gif

I have a tank/circulation engine heater which I plan to install in the transaxle coolant circuit. The Prius has a separate cooling circuit in the transaxle/inverter which uses the same coolant as the engine. there is a drain plug in the bottom which I may be able to tap and a series of hoses on the upper side which feed the MG2 electric motor.

What I don't know yet is if the coolant has to be forced through with the coolant pump or if it will circulate by convection through the internal passages.

I'm also interested in preheating the transmission oil via the pan. For this I may have to fab something custom to get the heating I want.

Added chart for reference (Thx Bob):

http://hiwaay.net/~bzwilson/prius/pri_tt_09.jpg

Manitoba publishes some worthwhile reports, for some reason. But under what circumstances was this data collected? Is it just trip fuel economy data from .mb's fleet of Priuses, lumping together trips of different kinds on different routes? It looks like it, and it looks like it's not instantaneous fuel consumption in kilometer #10, for example, but trip fuel consumption for a 10km trip. Therefore, it doesn't really show how long it takes for instantaneous fuel economy to reach its peak, i.e. how long it take to warm up the car.

Why does .mb's fleet get better fuel economy when it's 4.1-23.9°C out, and FE drops when it's hotter than 24°C out? I dunno, but I bet it's because the battery is too hot to provide excellent regenerative braking.

My gut feeling is that you'd get more mileage out of preheating the battery (by grid charging, perhaps?) or the ICE, but heating the tranny can't hurt.

I have thought about this in my Jeep. When it's about 5°F you can barely shift from 1st to 2nd without stopping. I was looking at immersion heaters for this but the ones I found said 10w for every quart of oil. The smallest heaters they made were 120-150w. By their ratings I would need 20-30w.

Phillips & Temro have quite the variety of heaters, but I have no idea how to order from them.

Since the Prius uses antifreeze the circulation heater should work fine.

I have seen oil pan heaters that you put onto the bottom of the pan somehow.

Good luck
Don

To be frank, I don't know how the data was collected but it seems to be from a data logger of individual trips. Any way I have experienced this effect myself. The efficiency slowly increases long after the engine is at temp. Probably part external engine components, part battery, part transaxle, part bearings.

I have noticed a big difference in rolling resistance when the tranny is cold. This has a continuous effect until it's warm so my hunch is that it makes a substantial difference. I would love to be able to grid charge the battery as this would give a double whammy by warming the battery and giving you way more assist. But it's a much more expensive proposition. It's on the wish list for sure.

I'm already preheating the engine coolant and will install a block heater soon.

I looked through their catalog yesterday. Yummy. They have diesel warmers for running #2 all year, and many many interesting heating gadgets. I picked up a 1500 watt Series 8000 heater. They seem to be better built than the Kats versions. I got mine at a Lordco auto parts store. You have to ask to look at the catalog because my guy didn't even know they existed and at first told me they didn't carry them. Turns out they had one in stock for about $65.

Found them for you at JCWhitney:

http://www.jcwhitney.com/jcwhitney/p...29&zmap=10837G

I've been disappointed with them. After a year, the cord breaks at the heating pad.

I'm think of alternative solutions.

Bob Wilson

ps. When the work, they help but their failure rate is too high for my taste.

Water bed heating pad!!!

I agree that those pad heaters are flimsy. The magnet style are overpriced for their output and a hassle if you have to remove them every time. There are hard elements that can be bolted on though which must be very durable.

The catalogs are here:

Heavy duty catalog link including the tank style and oil pan heaters:

http://www.fuelinjection.net/zerosta..._zerostart.pdf

Main catalog:

Zero Start Product and Applications Guide

Ahhhh!

Just found a good solution although it requires taking off the pan: Immersion oil heaters. Braze on or weld on adaptors available.

[IMG]http://ecomodder.com/forum/member-or...pan-heater.jpg[/IMG]

Too bad they don't screw in to the drain plug. Wait... do they? Will ahve to check my threads.

Ain't those an bit large?

They aren't too big.