35mpg? What am I doing wrong?

[anarchyx34]

My first 2 tanks with my 1.6TD were 35mpg, which, is slightly disappointing considering my driving is a good 75% highway at 65-70mph.

Now, I have been using my a/c I'd say about 35% of the time, but I'm not sure how much of a difference it would make in fuel economy. Some cars I've had show no difference at all with the a/c on. I bet on this car it does make a difference, but I'm not sure what i should be expecting.

I did make another post a while back about my engine is lacking power. While this is still partly true, I did notice that on cooler nights it feels 10x better. On hot days, a/c on or off, it's a slug, which I'm guessing is normal.

One thing I would like to re-check is my pump timing. I set it to 1mm when I put it on, but I would like to go back and double check that now, just to make sure. Otherwise the engine runs perfectly smooth, starts up immediately, even when cold and never smokes, only a teeny bit if I'm WOT at high revs and it's cool out.

Oh and my alignment is perfect, my brakes arent dragging, and my tire pressure is at 30psi. Any ideas?

[745 turbogreasel]

How wide the tires?
Ac takes about 10 HP , so subtract that from your available HP, and figure the compressor is only on about half the time the AC is on.  In a low power car, you willl take a good hit.  worth noting is on the freeway, opoening the windows can create an even greater load through aerodynamic drag...hence the new cars where you open the window and still have poor ventiilation.

[anarchyx34]

They're factory sized tires. 185mm wide IIRC.

[Powjetta]

Check your timing it is critical to power.  I just set mine from .31 up to .39" and it runs much better.  I also went over the throttle, made sure it was wide open with someone pushing the pedal and then I also backed off the stop about 1.5 turns to coincide with the stop in the pump.  This made a big difference.  Do you have a boost guage to check turbo help?  Then also check to make sure you have some kind of cold air intake, the hot air under the hood is really bad when it's hot outside.  Hope this helps,

[anarchyx34]

I will recheck the timing this weekend. The throttle was opening all the way when I installed the motor but I'll double check it. Are you talking about backing off the stop screw so it opens more than it did before? Because I think I'm hitting the stopper before I run out of pedal travel. Oh and I did temporarily connect a boost gauge once and it is making 9psi like its supposed to.

I am running a "hot air intake" at the moment because I couldnt get my hands on a factory TD airbox in time. I'm sure that's not helping much and it's loud as all hell. Drives me nuts on the highway .

[Powjetta]

Yes the stop screw on the pump.  I loosened the lock nut and backed out the screw a couple of turns until it seemed like the throttle lever was binding and then turned the screw back in to take the load.  This won't do much for economy but it gives the power at WOT.  This gave me 5 extra mph on several hills around here.

[shwartzbewithyou]

The fact that it never smokes unless WOT would make me wonder a bit.  I know we all don't want to be driving smoke stacks but no smoke at all isn't normal for a diesel.  I would check the pump and where the max fuel screw is at.  You may be throwing in more air than the required amount of fuel, this would cause you to lean into the pedal a bit more but not really use the extra power as efficiently so you may be throwing away your fuel.
Just a thought.


I'm so tired it hurts.

[anarchyx34]

Air filter's clean and the fuel filter's only got 1000 miles on it. No air bubbles.

[jtanguay]

I think its the '92 trans.  Mine runs at about 2900-3000 rpm doing 100km/hr... it sucks and I want to change it!!! :evil:

though I had an automatic golf... (3 speed) and it was 3500 rpm doing 100km/hr... doing 120, it was having a mad gas guzzling fest!!! :lol:

[irdiver]

i was getting about 32mpg on my TD and just noticed last night that the oil leak i thought was from my turbo return is actually from the head gasket... hummmm   so check that, bad compression = bad milage!

[anarchyx34]

Filled up the tank again today, this time got 38mpg. The only difference was very little a/c use.

[Doug]

I'd be looking for a fuel leak. Once I had the water trap leaking a steady drip. Also have seen the fuel pump leak from the drive end seal down the inside of the timing case cover to drop out on the road. If the engine is always a little oily it is a tough one to spot unless you are looking.

[veeman]

Have you tried increasing the air pressure on your tires?  Sounds silly, but going from 30 to 35 or 3 psi might help slightly.

Others have recommended this to me in the past...seems to work but makes the ride a bit more "jarring"...

[anarchyx34]

Checked for a fuel leak earlier, nope, nice and dry.

I would increase the tire pressure more, but the roads here are awful and it might suck having that much air in the tires. I have an idea why though. I'm still using the gas "AUG" trans, which might not have the most optimal gearing for the highway. I finally got around to installing a tach tonight so I'll see tomorrow when I hit the highway what my revs are.

[anarchyx34]

Damn. 3800rpms at 70mph. That is a bit high isnt it? My top speed is also only 90mph before I hit the fuel cutoff. So I think a trans swap is in my future. Oddly enough, according to the charts, mexican built GL's are supposed to come with the AON trans, but mine came with the AUG trans, which is supposed to come with german built cars. Mine might've had a trans swap before I owned it.