Pulse and Glide with an auto

[kickflipjr]

I just started trying out "the pulse and glide" with my car. I go up to 50 or 55 and then put the car into neutral (no shuting off the engine) drift down to 35(so I can still keep the car in final gear) . Do a small rev match and put the car in Drive. I don't think I am going o kill my tranny by doing this...right? So does this have a mpg gain or is it more troble then its worth.

[MetroMPG]

It's a good question.

I once did a little experiment and calculated that using P&G between 70 and 90 km/h, leaving the engine running through the glides netted a theoretical gain of about 8% in my car (5-speed) over steady-speed FE at 80 km/h.

http://metrompg.com/posts/pulse-and-glide.htm

It's theoretical because: I didn't average the comparisons over a set distance, I was just looking at instantaneous readings (subject to more error).

So I'd take that with a BIG grain of salt.

If I had to bet, I'd wager it's pretty close to being a wash, since the automatic isn't as efficient in the pulse as a manual.

Edit: only way to know for sure is to do a little experiment. Where's your MID? :)

[kickflipjr]

I am looking for a car first. I will get a computer for that one. ok.

[MetroMPG]

Right! Forgot about the car search.

[zpiloto]

I just started trying out "the pulse and glide" with my car. I go up to 50 or 55 and then put the car into neutral (no shuting off the engine) drift down to 35(so I can still keep the car in final gear) . Do a small rev match and put the car in Drive. I don't think I am going o kill my tranny by doing this...right? So does this have a mpg gain or is it more troble then its worth.

I tried this with mine but can't locate the data for it :confused: I abandoned it pretty quickly after a couple of runs because the FE was about 3% lower. I think with an auto the only way to be succesfull with P&G is engne off. Although METRO saw a gain with his 5 speed. Sounds like we need someone else to test it:) YMMV.

[kickflipjr]

I never tried P&G before because I thought it was too much work.

So, metro do you kill your engine when you P&G?

I would say killing the engine on auto with P&G is way too much trouble (no bump starting).

YMMV=Your mileage may vary (I had to use wikipedia)

[MetroMPG]

Oh yeah, I kill the engine all the time.

I've got a momentary kill switch attached to the shifter, because I make it one movement: ease off gas, push/pull the shifter into neutral (no load, so no clutch used). I let the engine drop to idle, pause another second or 2 (to let some more hot coolant flow away from the hot areas), then hold the switch with my thumb until the motor stops.

You're right: having to key off & key start definitely adds to the work.

But it's like anything else. After you do it enough, it becomes automatic and you don't really think about it while doing it.

[omgwtfbyobbq]

I know that when coasting down from 65mph, leaving the car in gear results in twice as much energy lost compared to putting it in N. And as long as the rpm is under say, 1.2-1.5k, the engine will idle even if it's in gear, so given a choice between having the more drag on the car, with the engine idling in both situations, then it seems like coasting in N could increase mileage by a fraction of what the transmission losses are. Also, for an auto, I don't have to rev match, since it does that stuff itself, like shifting into a gear higher than dropping down into the gear it's supposed to be in so there's not as much of a shudder. But your tranny may be different so YMMV.

Actually, depending on what year your Saturn is, you may be able to coast in N w/ the engine off w/o messing up the bearings in the auto tranny. I'd suggest contacting Saturn and asking if you can tow your model in N.

[kickflipjr]

I already know its ok to coast w/ the engine off on my car(I think i read it on this site somewere), and i do coast down hills almost daily.

I think this is a last ditch effort to get good mpg before I get a different car.

[omgwtfbyobbq]

I'd bet you can pull 40+mpg out of it np compared to just cruising at ~50mph, but then again, i don't know your route, so you may have already hit the upper limit in terms of that and the average speed you want to travel at.

[red91sit]

When you do EOC or p&g your car, does your temp gauge skyrocket? I did it a few times in my car, but when i restart it i find the temp gauge nearly pegged :O this seams real bad for the car, so I usually dont' do it.

[MetroMPG]

I P&G'd for abot 25 miles both ways yesterday. My normal coolant temp is 192-195. The SG1 recorded a peak temp of 210.

The temp spikes when you P&G because you load up the engine and then kill it before it has the chance to dissipate the extra heat generated in the pulse. So you have a mini hot-soak event every time the coolant stops circulating.

By the time I re-start, the "average" coolant temp has probably dropped a few degrees below the normal operating temp - I sometimes see mid/high 180's on the gauge for a few seconds when I restart.

So.... I try not to kill the engine immediately after loading it up. I let it idle in neutral for a count of 3 at the start of a glide, and then kill it. It probably doesn't make a huge difference for hot-soak.

[Peakster]

But it's like anything else. After you do it enough, it becomes automatic and you don't really think about it while doing it.

That is very true. It almost killed me to stop hypermiling because it felt so natural to do so. I tried P+G when there was little traffic at night, only I did it at 30-35 mph and turned off the engine while gliding. It was a lot of work though and I stopped because it's getting too cold outside (the heater turns cold when the engine isn't running).

[MetroMPG]

Peakster: do you have your grille blocked? That'll help.

[psyshack]

P&G should not effect coolent temps if at all. There might me some smallish spikes here and there.

With a sealed or semi sealed cooling system thermal dynamics force the bulk of the collent around and in the cooling system. Water pumps mainly circ. the cabin hot water loop. This is not to say they dont help with the flow of water to and from the rad. and block.

If a car is showing signs of over heating while P&Ging. I would check the thermostat and rad. cap. And if that ok and your still seeing alot of temp spikes or over heating action a good flush might be needed for the block, head and rad. I would do a flush very gental like. Getting dirt out of the system is hard on the water pump seal.

[red91sit]

P&G should not effect coolent temps if at all. There might me some smallish spikes here and there.

With a sealed or semi sealed cooling system thermal dynamics force the bulk of the collent around and in the cooling system. Water pumps mainly circ. the cabin hot water loop. This is not to say they dont help with the flow of water to and from the rad. and block.

If a car is showing signs of over heating while P&Ging. I would check the thermostat and rad. cap. And if that ok and your still seeing alot of temp spikes or over heating action a good flush might be needed for the block, head and rad. I would do a flush very gental like. Getting dirt out of the system is hard on the water pump seal.

I'm more afraid that maybe the transmission is heating up the coolant excessively in the neutral cruise? I just did a whole cooling system flush and refill, so it's not that. The only time she ever overheats is during P&G I think it's too old for P&G anywyas, so I'm going to focus on normal driving economy.

[psyshack]

Really? Say you have a hot engine- take the radiator cap off and run it- see the coolant shooting into the radiator? Shut it off- see the coolant not shooting into the radiator any more? I think it would act the same if the heater circulation was stopped.



How do you do a harsh enough flush to affect the water pump seal?

Ok how to explain this.

Have you ever heated something up in a microwave and noticed the lid has either popped off the container or is bulging a lot? This is pressure. Then you pull it out and set it on the counter and the lid then pulls down as the food and moisture cools? This is a basic vacuum.

As the water heats in the water jacket in a car it expands. IE the reason radiator caps have a psi rating. As the water is cooled in the radiator it goes into a vacuum if you will. So when the thermostat opens were does the water want to go? Twords the cool vacuum. Also if you ever take a radiator cap off at the wrong time you will get burnt bad due to the psi. The thermostat can be closed say just after the hot water got in the radiator. If you have a 12 psi radiator cap and 10 psi in the radiator,, guess what you just got burnt. If the water has had a minute to cool nothing will happen when you take the cap off. You might even see the fluid level rise a slight amount. The water pump will help some no doubt. But basic psychics rule the roost on this one.

The water pumps real reason for being is circ'ing the heater core. The heating system is on the high side if you will. The pump creates differential pressure to move water thru the heater core. We know there is pressure drop across the heater core. So enough psi has to be made to flow the core. If you shut the motor off the core cools with air being blown over it. No pump no flow. With equal static psi on both sides of the coil.

As for the water pump seal and flushing the system. If you have a cooling system full of dirt and other stuff. You have major problems. Dirt is the number on killer of mechanical seals and lip seals. The other killer is no water. Dirt eats up the sealing surfaces and a seal will fail fast. Running one dry will ruin it also. The water is what makes the seal and it also cools the seal surfaces. If a seal is ran dry what water is in the sealing surface will boil making these tiny explosions between the seal surfaces and causing pitting. Soon as you have pitting from over heating or running dry the seal surfaces or scratchs from dirt. The water tension will not make the seal and psi will force the water out between the sealing surfaces.

Standard materials for mechanical seal are buna or viton for the elastimers with carbon type material and either a ceramic or durametalic matrial for the sealing surfaces. Tis goes for full face seals or lip seals. Most of these basic seals have a max temp rating of 220 degrees F. Most of these seals have a max psi rating from 125 psi to 175 psi in basic config's.

I hope this helps.

psy

[onegammyleg]

Ok how to explain this.

Have you ever heated something up in a microwave and noticed the lid has either popped off the container or is bulging a lot?

psy


The top didnt pop off , what shall i do next ?

http://www.jaydahl.com/cheap%20draft%20photos/cheap%20draft%20-%20cat%20in%20microwave.JPG