Coolant Temperature Hack. Better MPGs!

Click on this link for an automatic version.
http://priuschat.com/forums/gen-ii-...-automatic-coolant-temp-hack-better-mpgs.html


This is probably the easiest hack I have done that requires getting under the dash.

First you need some supplies.
1 - 1k POT
1 - 240 Ohm Resistor
1 - SPST Switch
2 - wire taps
some wire
a bread board of some kind or make some kind of mount to solder your components together.
a knob and a place to mount your switch and POT.

All credit goes to ken1784, Bob Wilson, and Hobbit and is based on this post here.
http://priuschat.com/forums/prius-modifications/36342-another-thermistor-hack.html

Here is what I'm going to make. ken1784 I hope you don't mind me stealing part of your picture.


This little contraption get connected to the coolant temperature.


Pin 19 is where THW is pointing and its a white wire. Pin 28 is where E2 is pointing and it is brown I think?



First you need to remove the the lower glove box. Just open it and on the right hand side remove the pneumatic arm that is attached to it. then just pull the glove box out. Now you should be able to see the ECM. It has the white connectors. the one with the gray connectors is the Hybrid unit.


Here is what it looks like with the connector removed.



Find the right wires and tap into them. The green arrows are pointing to the wires.



Once you have the wires tapped hook everything back up and mount your POT somewhere. I'm leaving mine in my breadboard for now until I make an order from digikey to get the parts I need. Here is what my temporary setup looks like.



Here is a video of the hack in action.
[ame=http://video.google.com/videoplay?docid=-3162050563074112733]Coolant Temperature Hack for Toyota Prius[/ame]

I have not got a chance to really test it from a cold start but I can say I can instantly get into a glide when I reach 35mph. I have not tried to get into S4 yet where I can start a glide from below 35mph.

I do know with this setup you must monitor the temperature all the time while this circuit is on or you may cause the car to panic if the temp gets too high. You have to continuously lower the POT to keep this from happening. I made mine this way so I can still "monitor" the actual temp. You could bypass the the whole coolant temp and set your own temp with the POT but then it would be a fixed value and you would not know how hot or cold the actual temp is getting.

I will report back when I get a few trips in with this hack.

 

A 555 timer would work that way but the better solution would be to use a PIC to monitor and control the circuit so you could have a constant 160F until the ICE actually reached 160F then the circuit would stop faking the temp. Then it could monitor it so if the temp drops below 160F the circuit kicks in and fakes the temp to 160F again.

If I forget to monitor the temp as it gets higher the fan will kick on but the actual temp would be much lower so there would be no real danger. I cant fake a cooler temp unless I cut the thermistor and put my POT in its place. I think this would be a bad Idea because there would be no real protection if the thing got too hot. At least the way I did it there would not be any damage besides clearing a few codes.


Well I tried it out for the first time and all I can say is that it works and works well. I don't have any hard numbers because I did not take my normal course home but I was able to get into warp stealth and S4 almost instantly.

One thing I noticed is that a good warp stealth temp seems to be between 160F and 170F. In between those temps I was able to draw about 50 amps off my Hymotion pack. If the temp was above about 170F I could only draw about 20 amps. I don't know if this is a temp related fact or if its related to how much juice is in the battery. I will have to do some more tests to find out.

 

Well I finally got a good number with this hack. Normally I think I can get about 235MPG on my way to work without this hack. Today I was able to keep it in WS much longer. The result is a trip to work with 377MPG. I wont find out for sure if this can help me overall until I head back home this evening.

 

If it was left on the Prius would think it was over heating and kick on the fans and give you warnings like in my video. There should not be any damage but you don't want to let the car think its over heating. Its like yelling FIRE in a theater when there is no fire.

 

You control how fast or slow the temp rises or falls with the POT but as the coolant gets warmer the temp will rise unless you manually lower it.

Because you can damage the engine? Because priority number 1 for the Prius is low emissions?

 

Well I should let you know on my way home I was able to get 212MPG compared to my 195MPG on my previous trips. I think this hack may help me stay above 200MPG if I'm lucky.