Pre-warming diesel engine with glow plugs

[Piwoslaw]

I found some info about how my engine uses its glow plugs: the on time depends on the temperature of the coolant.

Temp. (*C)	Time (s)
-30	16
-10	5
0	0.5
10	0.25
18	0
40	0

Would it be worth while to somehow extend the on time, so that even when it's relatively warm outside, they still pre-heat the cylinder for at least 5-10s? Or would the drain on the battery be greater than the gains from having warmer cylinders?

Going along that line of reasoning, if a block heater and/or coolant heater were wired to run off of the electrical system for, say, 5 minutes after a cold start, then would the extra load on the alternator be greater than the benefits of shorter warm up time? I know, I know: the best is a plug-in block heater, but there are situations when you either don't have an outlet handy or don't have the time to plug in.

[Daox]

A plug in block heater is usually at least 300W and it takes hours to heat up an engine. Putting a 25A load on your alternator for 5 minutes isn't gonna do squat unfortunately.

If you really wanna look into preheating the engine I'd follow what Toyota did/is doing with their coolant thermos on the Prius, or the exhaust heat exchanger. I do think the coolant thermos idea could be implemented fairly inexpensively with a bit of thought from the guys here.

[Piwoslaw]

The coolant thermos is a good idea when you are running errands, but if you commute, or just do long oneway trips with hours before the return, then it's just more coolant to warm. But it should be mandatory on taxi cabs!

[99metro]

I used to have a glow plug relay bypass switch so that I could turn off the glow plug relay and the starter would get full battery voltage while cranking.

With that in mind, perhaps using a manual toggle switch so that you could keep the glow plugs on as long as you like. Maybe even set up a 3 way toggle switch "Auto", "Off". "Manual On".

[Daox]

The coolant thermos is insulated fairly well. I park the Prius in my garage each night at around 5pm. When I start it up the next morning at 5am, my engine gets up to roughly 100F (38C) almost instantly.

Unfortunately, I don't have a scangauge right now or I'd get you actual numbers since it has been cooling off. I'm sure its a bit cooler than that now.

[tasdrouille]

I don't think it is worthwile to increase the glow period unless you have trouble starting your car. And in such case something probably is wrong with it.

In my car there 3 things to consider when talking abour glowplugs: pre-start, afterglow and coolant plugs.

The table you posted refer to the time the plugs glow to warm up the chamber a bit. But depending on the temperature, the plugs will continue to glow after the engine is started to help it run smoother when it's really cold. Ideally if you don't mind the engine caughing and clacking a little you could reduce the afterglow. And then there are the coolant plugs, on my car there are 3 which warm the coolant up faster, I unplug them all the time but when I don't have access to plug my block heater.

I think external warming solutions are the best option.

[MadisonMPG]

What kind of work would it be to do the "Prius" to a regular engine? I get the main idea, but I don't know the parts or the electronics that are involved.

[Daox]

There are varying levels of complexity you could build into a coolant thermos. The Prius system is fairly complex and efficient. Here is a layout of the system:

[MadisonMPG]

Ooh, that may be a little more difficult than I thought.

[vtec-e]

That top pipe coming out of the flask is feeding the return pipe to the engine is it not? So by my reckoning, the flow control valve coloured green is to divert coolant away from the flask to the radiator when the flask is up to temp. It would then switch over and take hot coolant from the flask to the engine upon starting. There would be some software responsible for that i'm sure. The lines feeding the rad arent shown but i'd say they connect to that green valve somewhere.
That return pipe on the front of the engine is the exact same as on my yaris. It returns coolant from the cabin heater and in fact, the branch off that to the top of the flask is also on the yaris. Only on the yaris its for the external block heater that prefers to dump heat into the radiator......hmmm..
So it might be worth getting a scrappy valve and flask off a prius?

ollie