Possible temp sensor hack

NHW11 Prius Temperature Hack

Bob Wilson

 

Yes, Bob Wilson has put a great deal of time and energy into the idea. He can tell you more than you ever wanted to know about it I'm sure.

Just remember that it involves tampering with an emissions related part of the vehicle and may increase over-all emissions (yes, thermistors on the engine block are considered part of the emissions portion of the vehicle). There are reasonable discussions ongoing regarding the legality of these types of modifications (compliance with federal Clean Air act which prohibits tampering with emissions related aspects of the vehicle). In states that do OBD2 emissions testing it could cause you to fail an emissions test.

It is possible that such a modification could cause the vehicle to prematurely exit normal warmup mode which could cause a significant spike in overall emissions. In theory it could (depending on the design) fail to warn you when your engine temperature is legitimately too high.

Don't forget that a very significant part of a PHEV is that you should be able to increase mileage without increasing emissions (a conversion isn't going to save you money at this point, might as well at least save the environment, eh? ).

Not trying to spoil your fun or anything here, just trying to point out a few things to consider. It's more than meets the eye--which is usually the story when it comes to hybrids.

Andrew

 

Hmmm...I'm not aware of any such hack for the Gen1 Prius. There are Gen2 modifications that do this but they involve tampering with the catalytic converter temperature sensors. That /will/ significantly increase emissions and certainly violates all kinds of federal laws.

Unless you want to significantly increase your emissions (by a factor of 10 to 12 times) you're best off just letting your engine warm up normally. Demanding power from your gasoline engine with a cold catalytic converter is a very bad thing to do from an emissions perspective.

Andrew

 

The another thermistor hack works on Gen1 too.
The temp sensor (THW) pin is B-14 of the engine ECU.

Ken@Japan

 

Yes, yes. I get that--but the problem is you can't cut the fuel pump on an Enginer kit because it doesn't output enough electricity. You'll stall unless you are extremely careful (Great idea in concept, poor idea in application). That much current transfer simply wont cut it if you don't have the gasoline engine to assist.

What you would be looking at would be a selective way to prevent the gasoline engine from initially starting until your battery ran down. What I'm saying is that when the gasoline engine /does/ start (and believe me it will unless you are going very very slow or have lots of stop signs / stop lights), you end up kicking out a weeks worth of regulated emissions over a matter of seconds because you didn't let the catalytic converter warm up in the first place (yes, a weeks worth give or take a few molecules). Even just one cold engine start will ruin your emissions. Try driving in EV mode without any engine starts for a week. Sure, maybe you can do it once or twice--but consistently over long periods of time?

I realize this is all counter-intuitive and it seems like im trying to rain on your parade, but trust me--I am as gung-ho about driving on electricity as anyone is here (heck, I have a $10,000+ conversion kit in my car just so I can drive on pure electric up to 70 MPH). It just irks me (and clearly it irks CARB as well given how strict they have been) very much when people sacrifice one of the crowning achievements of the Prius (Super ultra low emissions standards certification) to get a few extra MPG. I'm trying not to rant here--how am I doing?

Andrew

 

Yes there would be an advantage to a block heater. Block heaters are by far the most economical way to save money on gasoline (in the winter, obviously).

As for the engine start question--think of it like this. When you start your car normally in the garage the Prius is not under load. That means it can go through a controlled warmup sequence where it effectively puts the car into a "flame-thrower" mode to super-heat the catalytic converter as fast as possible (it adjusts ignition degree, fuel injection rate, and various other timings to heat the cat as fast as possible). It burns a lot more fuel in this mode but it /substantially/ reduces emissions by this rapid warmup of the catalytic converter. This is why the car will heavily favor the electric motor when you first turn the car on--it's driving purely on electricity while the gasoline engine super-heats the catalytic converter to reduce emissions.

If, on the other hand, you wait until you are in traffic--the engine cannot go through this "flame-thrower mode" because it has to contribute power to the vehicle (which, no--due to the way its designed it cannot do flame-thrower mode and drive the car at the same time). While it may eventually end up in flame-thrower mode, the damage is already done by that point (large amounts of emissions produced without a warm catalytic converter = bad news bears).

Again, I realize this is counter-intuitive, but you are /significantly/ better off (from an emissions perspective anyway) letting the car warm up first for this reason. That is why even 10 or 15 ICE starts on a warm catalytic converter are better than 1 start on a cold catalytic converter in traffic. Remember, once the converter warms up the overall regulated emissions of the vehicle are effectively moot (there still will be emissions, but far /far/ less).

Andrew

 

Yeah, you're probably best off with just the block heater. Unfortunately I don't know of any instructions for the Gen1 either...

I'm sure Toyota has one though since block heaters are required for all cars sold in some frigid countries. Maybe contact the Prius Chat store?

I don't know if you want to have the charger and the block heater going to the same plug--I think the charger is already pulling close to the maximum current for a standard outlet. Generally speaking you want the block heater to turn on about 3 hours before you drive the car (much more and it can decrease the life of the heater, much less and you don't get as much benefit from it).

Andrew

 

The block heater hole is in the same relative location on the engine. You can either reach up to insert or take the windshield wiper pan off and reach down. Regardless, it is not a fun job ... but only needs to be done once.

Bob Wilson

 

Why not just warm up the catalytic converter ahead of time, using a heat tape or heat pad (similar idea to the block heater, but in the case for the catalytic converter)? It sounds like, from the above discussion that there is a temperature sensor in this loop (heating of catalytic converter), I also was told that engine fluid is ciculated around/through the catalytic converter to heat it (but I have not confirmed this). Any idea where the temp. sensor is for the catalytic converteris located, if there is one, I know or was shown the O2 sensor so I know its location.

 

How does using less fuel increase emmissions?? I've heard your argument before but I totally disagree with your figures. What do you base you "factor of 10 to 12 times" on??? If one implements this hack and uses less overall fuel, wouldn't this offset overall emissions? Do you work for an oil compay?

 

You are asking reasonable questions here. The answer has to do with whether the fuel is used cleanly or dirtily. You can do a quick think-through with easy made-up numbers just to get the basic idea: suppose your hack cuts fuel use in half (which is silly, but an easy made-up number), but the cold catalyst is only one-sixth as effective converting emissions. Again, a made up number. For this example, you produce 3 times the emissions (1/2 times 6) even though you are using less fuel.

Andrew really did explain this in his earlier posts, but you might have skimmed those parts.

It is a reasonable question to ask the basis of Andrew's figures. In my made-up example I had to make up two factors: how much fuel your hack could save, and how much the cold starting reduces catalyst efficiency. Andrew also needs estimates for those two factors, and can probably explain what they are based on and why they are realistic (not just pulled out of the air like mine).

I'm not sure whether you meant to say you "disagree" with Andrew's figures, or just question them. I mean, I can see that you question them, which is reasonable, and it makes sense to ask him for the supporting evidence. Saying you 'disagree' with them sounds more like you have different figures of your own with supporting evidence for them, but in that case it would be fair to be asking for your calculations and evidence too.

-Chap

 

The bottom line or the point I'm trying to make is that people throw out figures with no data to support them and they state those figures as facts. I can do a study (with my biases) and make the data support my predetermined conclusion. He can do a study with his biases and make the data support his predetermined conclusion. The OP was trying to save gas. Emissions were not his concern but suddenly this post got hijacked to berate him about emissions???