Just as a test, tonight I plugged in the block heater and

i used to live in Alaska where block heaters were a requirement, so the benefits of one is undeniable.

but even in temperate climates of Wa St. it can still benefit one if used properly.

Since we have already established that the pre heating does increase economy, then use it like you use any other car in cold weather.

I think simply turning on the block heater 15 minutes early before leaving in the morning would do just as well. Or is that not enough time.

I think that only in the more severe climates would leaving the thing on all night be neccessary. but for temperatures in the 30's and 40's would it be neccessary?

its too late for me to try this (its been in the 70's and 80's for the past 2 weeks) but maybe we need to see how effective short pre heating times would be.

is 15 minutes enough? or 60? or 5?

obviously if it takes too long, then it wouldnt be a feasible idea. but i think someone in Minnesota or Canada who still has chilly nights should try this to see how effective different pre heat times would work.

let us know.

 

In the most bitter cold, my '89 Honda Civic always started. But it started much more easily when plugged in. My subjective experience suggests an hour makes a small difference, and a few hours makes a big difference. We're talking 30 to 40 degrees below zero. Obviously, less time is needed at milder temperatures. Above zero F. it was not needed at all, and above freezing it would be silly to plug it in.

 

at 30 to 40 degrees below zero ALL CARS should be plugged in. to not do so is inviting a whole host of problems.

I lived in Alaska for 2 years and experts there estimated a reduction of engine life up to 90% when vehicles were not plugged in ALL the time when not running.

When building the Alaska Pipeline, all heavy equipment and vehicles were started when they arrived and ran the whole time they were there.

some ran for 5 years straight never being turned off because the cold was so severe that too much damage could occur on startup. And there was no AAA or local garage where they were.

 

ok... we need to understand that a 400 watt heater if left running for 4 straight hours would probably boil the water.

we need to get some measurements for one thing. how much water are we preheating?

a 400 watt heater running 100% for an hour would put out 1366 BTU's.

a BTU is the amount of energy needed to raise 1 pound of water 1 degree Faranheit

so lets say we are preheating 2gallons. so that would be about 16 pounds. so 400 watts will raise the temperature of the water 85 degrees farenheit in one hour.
so its rather apparent that a 4 hour turn on is waay too much. Plus the amount of water preheated i doubt would be anywhere near 2 gallons. so there must be a thermal cutoff that heats the water to a certain point. Does anyone know what that point might be? or what the optimum water temperature would be? we need someone to drive around till the car is warmed up and measure the temperature somehow and that may not be an easy task as the top of the radiator would be cooler than what we need. I would think that about 120 F is about right??

now we also have to consider how cold it is outside and how fast that would dissipate heat because of that. because it is a closed system, the cooling will not be terribly dramatic and if the preheated water is insulated at all, then it may not be much of a factor.

unfortunately i do not have the information neccessary to even hazard a guess on that scenario.

but its my opinion that excessive engine wear aside, the block heater would never cost you what you would lose in mpg.

at 50 mpg and 2$ a gallon, its costs 4 cents a mile. the reduced gas mileage will add up real fast especially if the reduction is as much as 10-25% as people have reported.

 

I think the block heater only solves *part* of the extra gas at startup. I have found that even with a 5 min stop for an errand when I restart the mpg takes a hit because the CAT cools rapidly and demands to be reheated. On the coldest starts this winter +/- 5F the heat comes on before 5 minutes.YMMV.

 

yes the engine does cool rapidly because it is used so seldomly. in fact, its my observation that with out the electric preheater, the engine would run cold nearly all the time.

that is why i suspect that the preheated part is only a very small part of the total cooling system. it probably works similiar to the cooling system in a regular car where the coolant flow is trapped in the engine jacket until it heats up enough for the thermostat to open. the only difference being the electric preheater that warms the water faster. I think that if given enough time, and charge, the water will preheat to a certain temperature before starting the ICE. oh course, i think the problem lies with starting in severe weather conditions where either

1) the temperature is too cold to overcome with the available charge of the battery.

2) demands on the charging system are too heavy too soon and the ICE is forced to come on before being properly warmed.

and like in a regular car, we are not talking about the entire mass of the engine, only the upper intake area. keep in mind, that it takes less than a minute to sufficiently warm up the block. the problem we have is that we need to heat the block to a very high temperature to be able to cool intake air fast enough to be useable in an engine because on a part of the exhaust is reused. Most of the air is cold fresh air which cannot be circulated through the exhaust because it would crack the exhaust. so we wait a minute to heat up the engine, then the engine heats up the water, the water heats the air, then the intake air is warmed before compression resulting in a lower moisture content and a leaner burn.

The Prius ICE runs less seldomly, so it uses the preheater to get the water up to the operating temperature. Then intake air is circulated through the water jacket which gets heat initially from the preheater but eventually from the engine.

so as you can see, it is not the preheaters job to heat the engine, just the water.

 

thanks for the data input. do you plan to continue measurements?

i would be interested in seeing how the measurement stack up over time. at least 2-3 days more anyway.

your data doesnt seem linear considering the temp changes

30 min=+22
***60 min=+3***
90 min=+13
120 min=+10

this measurement needs more data to support. the block heater must be running on a duty cycle (where it cycles on and off) to keep from creating hotspots. it would appear that the temp cutoff is probably somewheres around 110. higher temperatures happen because of hotspots.

also im curious as to what type of block heater you are using.

also, maybe measuring temp every 10 min might give a better picture of what is happening