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Horrible mpg 6.5 TD!!! help please

foxdenfarms

foxdenfarms

1994 C3500 6.5TD
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Location
Cherryville, NC
My 94 3500 2wd is getting horrible mileage towing and empty. I am only averaging around 200 per tank mixing empy driving and towing 10k
 
my first thought would be to look for fuel leaks. some of those oil drips underneath might be more fuel than oil. next would be bad injectors
 
I suggest you have your boost turned up too high for the factory asthma attack turbo.

A mechanical wastegate is like a belt drive supercharger always sucking power and MPG form your engine. For example unloaded having 6PSI of boost at steady cruise throttle is just wasting fuel.

Some have turned down the boost and improved their MPG's.

Others like me have found a better turbo and increased MPG's by 30% towing. Yes 7MPG to 10.4MPG on hard grades with the GM3 vs. A Team Turbo. This is due to the lower exaust back pressure of 1 to 1.1 vs. the GM4 that gets up around 1 to 1.5 depending on boost. Anything over 14 PSI is heating the air more than compressing it to get higher boost on a GMx turbo.
 
I was thinking of doing the dual tstat and what is TCC? It is an auto and it doesn't leak a drop and doesn't burn anymore than it should this truck will only sometimes when cold starting will puff a small cloud of whitd only sometimes. I dont know what to do I know pulling it won't get great but I should do better than 10 hell if this is the case I should have stayed with my big block dually!! It will when it is cold not want to move when you put it in gear the rpm's just won't raise and it just won't move and ill have to put it in nuetral and rev up to 2k then back to drive. This is my first 6.5 so I dont know what performance should be so I dont know if it is normal but it does seem to struggle some with my tandem 20ft aluminum horse trailer and four horses. Dont know what is normal with them.
 
dont waste money on the dual t-stats.

Bill heath likes single, due to the single blocking the bypass port off and sending 100 percent to the radiator, unlike the duals.

Leroy (username Burning oil, commented above) has wrangled a deal on 195 degree genuine AC delco thermostats for the single t-stat system. I would vote buy a t-stat from him, it will do nothing but help.

If you are too cold, the TCC (torque converter clutch) wont lock up, and this would drastically hurt mpgs. if this is the issue, a new t-stat will fix it.

you are definitely not doing good for a 2wd 6.5L. granted the auto sucks more fuel than the 5 speed manual, but not that much more. unless i am pulling into the wind with a big load, I never fall below 10 mpg loaded, and with no trailer, many of mine are 20 mpg capable.

so, something is definitely wrong, and the guys here can help you figure it out! btw, welcome to the site.
 
My truck will fluctuate engine temps pretty good, it will usually stay around 185 empty pulling up a grade loaded it will creep up to around 210 and if it is hot outside it will steady creep up sitting still.
If the tcc is bad what are other symptoms? Because it is real aggravating putting it in gear and rpms bog down to around 500 and won't move.
 
Need more info, anything else you have observed?
Thinking outloud: Fuel delivery? What PSI do you have? Exhaust/xover pluged? IP on its last legs? Brakes draging?

I lean toward fuel delivery, snoty tank sock, dirty filter or pluged lines.
 
Well I mean I have checked the fuel flow to the filter while the truck is running and has good flow I put my lift pump on a switch so I could be sure it was on I have not checked the sock but I can It would be easy since my truck is a flatbed. Clogged lines I do not know would make sense because there is good pressure to the filter.
What are the symptoms for the tcc I am interested in maybe persuing that because it would make sense eith it have problems moving when cold.
 
Well you say engine is bogging, only things I can think that would do that is Fuel delivery, air intake and not as likely, but a pluged exhaust (assuming engine is healthy)
Put the engine under load a see what fuel PSI #s are.
 
TCC could bog the engine if it were to stay engauged, not likely though unless its on a manual switch maybe?

My full manual 4l80E will bog unless I turn off the TCC switch.
 
Ok when it is cold ill put it in drive and push the gas and the rpms will drop and it will not move same with reverse I have to put it nuetral and rev it up so that it isn't at idle when I put it in drive so it will move, the only exhaust that I have on it is the factory downpipe and is is d amaged like they all are but it isn't bad at all from the downpipe back there is nothing no exhaust, air filter is a cone filter
 
Trans fluid level? Very dirty trans filter? Bad/worn pump in trans.....
Im just guessing, its hard when not there to see it. Post a video of it.
 
I just pulled my front wheels off and it does need pads and the wheels dont spin free I can spin them by hand but they will not turn without pressure not free like I would think they would. But I dont know what is normal on these trucks. Also when I start it the ses light will stay on until the motor will abruptly idle up to a grand then down to idle then it will go out.
 
Engine should not bog even if brakes were locked up, but obviously would hurt MPGs.
A video might help alot.
 
High idle sounds like crank sensor or coolant temp sensor. Wheels should free spin if you give them a good turn, I usually don't get more than 1/2-1 rotation. Check the rear drums too, pads falling off and wedging has happened.

Sent from: Source Unknown
 
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