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.

Could you put a 555 on it to run for 12 minutes at start?

Can you post more on the 2nd screen your using?

Curiosity question.... engine overheating protection: does the radiator fan have a temp sensor of its own to start the radiator fan (say you forgot to manage the coolant temp and let it go too high)

Thank you for an interesting video.
It shows the engine temperature means nothing.

Ken@Japan

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.

Would your design be safe to turn on and leave on? I have A.D.D, and A.D.H.D., so there is a chance that I might forget to oh look! A rabbit!

Unless there was a visual reminder that it was bypassed, I KNOW it would be left on for a few days...

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.

I saw your vid. Is this an immediate thing, or does it take time for that to come up?

Now, who can tell us why Toyota didn't design the car to do this automatically?

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?

OK, I have little electrictical experience, can you explain how the POT controls the temp? Can the minimum temp be permanent setting?

Easy
Basic Ohms Law.
You put 2 resistors in parallel, say 100 ohms each. Than the total net resistance for that circuit is 50 ohms.

In the case of the Prius heating circuit the Temp sensor is a Thermistor, that is a temperature sensative resistor that changes its resistance with a change in temp. If you start out cold and the thermistor reads, well lets say 10k ohm ( Just a number picked out of the air, but it will work for this example)as the temp heats up the thermistor resistance will either drop or increase depending on the thermistor type.

The Prius wants to see a specific value of resistance when warmed up. That indicates to the computer that all is correct and the ICE can now stop running just to heat uo the engine block and catalytic converter.

By adding the "POT" or variable resistor in parallel you can fake out the computer into seeing a FALSE resistance indication that the system is up to temp and it will shut off the ICE, thus saving you gas.

Tha problem, as indicated, as the engine really does warm up, the thermistor will still change and combined with the POT's value could add to a resistance value that completly fakes out the computer, and can shut you down, thinking that there is a overheating problem, when in reality its just running just fine, but the Thermistor data is grossly incorrect!

Simple, now lets put a man back on the moon!!

Hope this makes some sense!!!

73 de Pat KK6PD

NICE
I think i am going to have a try at this!

is there any damage that can happen when you go to S4 or S2 and skipp the startup warmup of the engine?....

Correct me if I am wrong, but I don't think this is used to skip the initial startup warm up. I think it is used in his case (because he is Warp Strealthing so much with that extra battery) to keep the ice from coming on ..But I think it could benefit all drivers in keeping the ice from coming on during stops around town when the motor is warm already..Just my opinion of course..

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.

Do you know what is the voltage @ 170 degrees....to use a pic chip that would be useful....also...................235 vs 377MPG.....is that per tank???

It's an interesting observation.

The Prius thermostat starts to open at 82C(180F) and we see the typical temperature is approx 86C(187F) after complete warm-up and such temperature is used to be recognized as an optimum temperature.
The thermostat is closed at 170F, and it is still in a warm-up stage.

Ken@Japan

I personally am thinking of this because of the way my wife leaves my car after she drives it, usually green, if I can get into the stealth mode and run it down from the green instead of the car just burning it off.

Perhaps it has to do with EPA regs? Meeting California emissions?

Or just an engineering oversight? No one thought of it in the rush to get the car developed? This happens all of the time with sales asking for things and engineering getting bad information.