Probably depends on the engine displacement, temp the heater can get the coolant to, outside temp, and trip length. Iirc, the amount of fuel injected on startup is proportional to coolant temp, since this is used by the ECU to guess at how warmed up everything is, so I'm guessing it's pretty significant. I'm also guessing for short trips to the store it could make a huge difference, but for longer highway trips, not nearly as much.
Originally Posted by FormulaTwo
I think if i could get that type of FE i would have no problem driving a dildo shaped car.
I should be an EBH salesman, because I believe it works extraordinaly well in reducing excessive fuel consumption on cold startup.
Just a rough estimate: with the EBH on for a sufficient amount of time to operate at peak temp, the time to closed loop is within 20-30 seconds; whereas, closed loop on a cold start under similar conditions would take up to a minute or more. Say, open-loop idle is 1.5 gph and closed loop is 0.6, then there's the savings. The throttle input should be proportional to gallons-per-hour figure when moving to give you an idea of fuel consumed. I even operate it in the summer to reduce startup wear and quicker C-loop.
I have found on my short 11 mile commute I get about 5 mpg better (according to SG) with a warm engine compared to cold. So I would agree that if you have a lot of short trips the benefit would be more noticeable, for longer trips the FE gain wouldn't be as noticeable, still there, just not as prominent.
And this doesn’t take in to account the added benefit to the engine itself or the operator.
If you're doing a lot of short trips with cold soaks in between, it'll be a bigger relative benefit than with fewer, longer trips.
This PDF tries to quantify the fuel savings, but you have to take it with a grain of salt (they're selling them). Also, it focuses on the benefits of short trips (because it looks better presented that way):