Re: Do cooler operating temps reduce mechanical losses? - Saab 900 Bulletin Board - Saabnet.com
NG900 & OG93 |
Vintage Models |
Clubs & SOC |
Other Cars |
Member Photo Galleries |
Member Directory |
*Buddy Registry |
*Mileage Registry |
What's New |
Photo of the Month |
[Main C900 Bulletin Board | Post Followup | BBFAQ ]
[ Prev by Date ] Member Login / Signup [Latest Member Gallery Photos]
Re: Do cooler operating temps reduce mechanical losses?
Posted by Ari [Email] (more from Ari) on Tue, 14 Jul 2009 04:19:15
In Reply to: Do cooler operating temps reduce mechanical losses?, mag [Profile/Gallery]
, Mon, 13 Jul 2009 02:54:45
Actually, running the engine cooler makes it less fuel efficient. I'm talking about coolant temps here - from a combustion standpoint, hotter is better. But you've got little control of that.
The engine is designed to operate at a given temperature. At that temperature, the clearances are as close to the design targets as possible (tight but not too tight), the oil is thin enough (less drag), and the gasoline is vaporizing, and not condensing on the intake walls and burning poorly.
I'd think that the water pump actually pulls more power from the engine when the thermostat is open - it is pushing fluid through more pipes, with more drag, and the radiator has lots of internal drag. Some folks use 'water wetter' which reduces the surface tension of the coolant and can reduce some drag. But the cooling system is one of those unfortunate necessities. Throwing away heat in a radiator is a waste of energy and aerodynamic drag, but there are no good ways to recover that energy today. As to the waterpump load, you're pretty much stuck with it.
There are two parts to the alternator. One is parasitic drag - some power loss just spinning the alternator unloaded, flex in the belts, heat in the pulleys. Not a lot, but some. The major part of the alternator is the electrical load. Yes, the more current you pull from the alternator, the more energy it sucks from the engine. When the engine is running, only peak current loads come from the battery - the alternator provides most all of the car's electrical needs, and recharges the battery. But for the alternator to produce CURRENT, it consumes mechanical power from the engine.
The cooling fan should only be running when the car isn't moving, or moving very slowly. The cooling fan's job is to replace the airflow over the radiator you'd normally get when the car is moving. Given that one of the greatest power losses in a car is aerodynamic drag, and drag increases with (the square) of speed, the cooling fan is the most energy-efficient way of cooling the engine. Of course, it doesn't get you where you need to go.
So yes, any electrical load - cooling fan, AC clutch, stereo, lights - all suck down engine horsepower. A cooling fan pulls about 25 amps at high speed - at a nominal 13.5 volts, that is about 337 watts, or about 0.43 horsepower.
The internal combustion engine is maybe 30% efficient. Electrical needs, cooling needs, all contribute to the inefficiency. Of course, it takes energy to pull air through an air filter, and even the energy lost to pulling air past a partially open throttle takes a surprising amount of power. There are ways to recover some of this power, for example, it's more efficient to run a small engine at wide open throttle than a big one at closed throttle, as it improve pumping losses. And a turbocharger recovers heat energy that would normally be lost down the tailpipe. But many other ways to save a few percent from the engine adversely impact the life of the engine, or driveablilty, or add lots of weight and cost.
The best way to make the whole system (car) efficient is to use as efficient an engine as possible, and then use it sparingly. Losing 400 pounds of sound deadening, or smoothing the surfaces as much as possible all help.
A buddy of mine did some fuel economy 'races' back in the '80s with a Sonett III. The Ford 4-cylinder in the Sonett was no high-tech engine - it was an old pump engine with a carb. But he was able to get 50 mpg out of the car on a 200 mile race in New England, including the 'hills' in Vermont. Of course, he leaned the mixture out to the point of just about melting the engine down, and a K&N filter for less drag. He ran the narrowest tires he could find at 50 psi. He removed the side mirrors, and taped over the radiator. He cooled the engine by running the interior heat at full. And he drove the car like the accelerator had a hand grenade under it, and stayed off the brakes, period. It was the aerodynamics, skinny tires, and gentle, gentle driving that saved the gas. The minor engine mods saved a few mpg.
posted by 75.11.4...
Posts in this Thread:
- Do cooler operating temps reduce mechanical losses?, mag , Mon, 13 Jul 2009 02:54:45
- Re: Do cooler operating temps reduce mechanical losses?, Ari, Tue, 14 Jul 2009 04:19:15 <-- Viewing This Message
- Let's leave the politics aside ..., mag , Mon, 13 Jul 2009 21:41:35
- Re: Do cooler operating temps reduce mechanical losses?, mag , Mon, 13 Jul 2009 13:48:16
- I have never used ethanol,, tibbidoh , Mon, 13 Jul 2009 15:46:26
- Re: I have never used ethanol, mag , Mon, 13 Jul 2009 20:13:08
- Re: I have never used ethanol - me either, oldsaab, Mon, 13 Jul 2009 17:09:44
- Re: I have never used ethanol,, Justin VanAbrahams , Mon, 13 Jul 2009 16:35:33
- Re: Do cooler operating temps reduce mechanical losses?, tibbidoh , Mon, 13 Jul 2009 07:00:39
- Re: Do cooler operating temps reduce mechanical losses?, Landjet , Mon, 13 Jul 2009 05:18:29
Post a Followup
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
This is a moderated bulletin board - Posting is a privilege, not a right.
Unsolicited commercial postings are not allowed (no spam). Please, no For Sale or Wanted postings, SERIOUSLY.
Classifieds are to be listed in The Saab Network Classifieds pages.
This is a problem solving forum for over 250,000 Saab owners, so expect to see
problems discussed here even though our cars are generally very reliable. This is not an anything goes
type of forum. Saabnet.com has been a moderated forum since 1988. For usage guidelines, see the
Saabnet.com Mission and Purpose Page. Please remember that you are
not anonymous. Site Contact | Site Donations | Other Sites by SP -
Your address is: 18.104.22.168 - Using CCBot/2.0 (https://commoncrawl.org/faq/) - Logged.
Site Members do not see red text instructions, bottom of the page anchor ads, or box ads.
Click here to see all
the Site Membership Benefits!