convertor lockup and synth. diff juice?

I've been working some bugs out of the fuel economy end on my 1991 Z71. I've paid very close attention to transmission shifting on reasonable acceleration up to highway speeds, and it shifts 1-2-3-4 like it should, when it feels like it should.

I know these units employ a lockup torque convertor. is there a way to know when the TC locks up? the tc locking up on the highway helps fuel economy, right? can I "feel" the tc locking? or is there another way to know?

Also, I've heard good things about full synthetic differential fluid, with many claiming they get a gain in MPG by changing out both diffs. How much truth to this? I'm looking for every easy MPG I can get!!!

thanks!

b
Reply to
Hamilton Audio
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if it has a tach, you should see RPM drop by 2-300 when it locks

when locked, you should be able to 'crowd' the throttle a bit without the RPM's increasing, while crowding the throttle, tap the brake with your left foot, the RPM's should immediately jump up 3-400

Reply to
Gary Glaenzer

Reply to
David J and Lynne J Shepherd

thanks

I try to make it short and to the point

Reply to
Gary Glaenzer

no tach, but will be installing one to be sure of this. when does convertor lockup usually happen? particular speed? only highway speeds? cruising at a specific "load" on the engine?

the truck shifts cleanly in and out of each gear, and I'm sure I "feel" the convertor unlocking when accelerating from say 90 to 100 km/h on the highway...

once the tach is in, I'll double check as you say to...thanks for the advice!

Reply to
Hamilton Audio

depends on speed, load and of course throttle opening

on a 91, 4th and lock-up usually happen so close together that you can't separate the feel

the throttle-crowding / brake test once it's in 4th at about 60 is the best test

Reply to
Gary Glaenzer

G already hit the TC question; I'll tackle the synthetic question. Switching to synthetics in ALL drive units (engine, tranny, TC, front and rear diffs) will net you a 5-10% increase in fuel ecomomy. I've seen this in all of my trucks. But you're still calculating your fuel economy incorrectly so you won't know the difference anyways.

Doc

Reply to
"Doc"

you're killing me man!! I've got it down pat right now (so poop on you :) Resetting the odometer /right at/ half a tank will yeild around 150 or so KM on the nose. Same with 3/4 to half. can't tell full to 3/4 or 1/4 to E cause the gauge is not calibrated, and won't go right to full, and goes well past empty.

I would notice a difference now :)

b
Reply to
Hamilton Audio

Stugats,

You foolish, foolish man. I've told you FOUR TIMES how to correctly calculate fuel economy. Your method is far too insensitive to pick up any increases/decreases in fuel economy. Added to the fact that your fuel guage is not calibrated correctly it's even worse. I've got news for you, GM fuel gauges read differently from full to 3/4, from 3/4 to half and from half to empty. I get 200 miles from full to 3/4, 100 miles from 3/4 to 1/2, and 100 miles from half to empty.

So, using my fuel guage, I get 23.53 MPG on the first 1/4 tank, 11.76 MPG on the next quarter, and then 5.88 MPG on the last HALF tank. If I keep my tank always full will I always be getting 23.53 MPG? Oh yay!

Considering that fuel economy normally varies by +/- 5% every single tank, how the hell are you supposed to calculate a 7% increase with the 5% variability using your method? I get between 14.6 and 16.5 MPG per gallon in my truck. Same roads, same heavy foot, same gas station, same pump, same city:highway ratio. I AVERAGE every 5 tanks to get my average fuel economy.

I'm really trying to be nice here but you're trying my patience. Do you not own a calculator? I'll re-write the instructions AGAIN with some little pointers for you to make it easier to remember.

1) Fill gas tank to full (leave it at the first pump stop, do not top off). 2) Reset trip. 3) Drive it to at LEAST 1/2 tank, preferably 3/4 tank. 4) Fill it up to full at the same pump you did in step #1. 5) On your receipt you'll have the number of litres you dumped in her. 6) Using a pen, write your km's at the top of the receipt before you put it in your wallet. 7) Reset trip meter. 8) Repeat.

When you get home, pull out a calculator and divide the number of km's by the number of litres of gas you dumped in her. Use ALL DECIMAL PLACES for maximum accuracy.

Doc

P.S. All future posts WRT this topic that do not have CALCULATED figures per the above method will receive a hearty flame.

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Reply to
"Doc"

Exactly right. The longer between fillup's, the better.

Reply to
Tony

Doc,

Your wasting your breath. Some people were not meant to calculate MPG and you have stubmled across one.

Without some sort of static measurement it is impossible to get relibable/reproducable MPGs. Unless you either fill the tank/refill the tank and measure how much gas was put back in divided by total miles driven OR run her completely dry on level ground, refill a specific amount of fuel and divide the fuel consumed buy the mileage driven, its' just not going to work. According to Stugat's method, I am getting 40+ MPGs on my first 1/10 tank. (300 miles to the F mark, then 100 to E). Oh yeah, "Poop on you" LMFAO.

Derek

Reply to
derek

I used the second (run dry, fill with 5 Litres, run dry) method on both my vehicles. My 2L petrol sedan, (now stolen) got 11.5 litres per 100 Km. my 2.8L TD SUV gets 11.25 litres per 100Km.

the difference seems to be the SUV in top gear can rumble along at 3200 revs for 100KmH, but the petrol needs 3600 revs, thats 400 revs more for the same speed, and diesels are more economical anyway.

rhys

"derek" wrote

Reply to
rnf2
3200 RPM cruising on a diesel????? you *sure* about that? if your cruise RPM's are that high for 60 MPH (100kph) you need some seriously higher gears. my wife's isuzu turns about 2800 RPM doing 75 and it's got 4.30's in the axles. my pickup with 3.73's turns about 1800 RPM again at 70 MPH

-Bret

diesel's are more economical because there is simply more BTU's in a gallon of diesel than gasoline.

Reply to
Bret Chase

I think mines 5. something (5.37?), that'd mean turning the engine 5 times for every 1 on the wheels, as opposed to 3.7 turns of the engine for every one of the wheel on your pickup. not sure exactly what mine is anymore have to go look again at the notes I made. If I can find them, since it's been a while since i looked everything up and worked out it's perfomance.

5 gear manual '88 Bighorn

rhys

Reply to
rnf2

Final drive is 5.37? I doubt it.

You have to take into account the transmision gearing as well as the rearend gear.

Reply to
Tony

I have a 1993 K1500 w/5.7 liter and I can definitely feel the converter lock. And, after adding that Flowmaster muffler, I can hear the difference. It seems like it kicks in after I've reached cruising speed, where I'm not putting a lot of strain on the engine to get up to speed. I noticed, just recently, that I can feel it kick in even when I'm not in overdrive. It will go through the first three gears and then I'll feel that kind of smooth kick, which drops the RPM's. It seems to lock about 2-3 seconds after reaching a steady cruising speed.

One thing that I've never been able to find out is what the life expectancy is on the lock. I had one go out in a previous truck and it gave the computer a brain-hemmorhage. It kept trying to lock and compensate for the decreased RPM's (which never decreased since the lock was dead) which made the engine radically fluctuate RPM's as I was driving. It was embarassing!

-Derek

Reply to
Derek Schwartz

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