Attention: TDR Forum Junkies 
Last winter I was discouraged with the mileage I was getting and thought most of the mileage claims were creative fiction. I made a couple of 200 mile trips at 60 mph and the best mileage I could get was about 20 mpg. I have not had any solo trips with long mileage for 5 years (pull the fifth wheel mostly).
Thinking that the timing might be off, I drove to Wentland Diesel in Oregon for a timing check. They pulled the pump and checked it on the pump stand. The pump timing was right at the spec of 14 degrees. I had them set it at 14. 5 degrees. They also found that the overflow valve was weak and changed it.
The technican remounted the pump and stated that the TDC pin on the engine that pops into the pump gear was off. He determined the true TDC by using a probe into the cylinder through the injector hole and measuring the piston travel. He reset the TDC pin before remounting the pump. He could not estimate how many degrees the TDC setting might hae been off.
All the use of the truck up to the last week has been towing with mountains and more headwinds than normal, but I thought that the mileage might have increased some. This week I made a solo 650 mile trip and got the first good reading on mileage.
This weeks trip was done at 65 mph and crossed the Cascades twice. The mileage was a calculated 22. 6 mpg. Since I changed the timing I have heard that 16 degrees is probably the best value for the 12 valve engines with better idleing and better low end response.
If you are discouraged with your 12 valve mileage, consider checking or changing the timing. My experience also shows that using the TDC pin to set TDC can have an error of several(?) degrees.
Thinking that the timing might be off, I drove to Wentland Diesel in Oregon for a timing check. They pulled the pump and checked it on the pump stand. The pump timing was right at the spec of 14 degrees. I had them set it at 14. 5 degrees. They also found that the overflow valve was weak and changed it.
The technican remounted the pump and stated that the TDC pin on the engine that pops into the pump gear was off. He determined the true TDC by using a probe into the cylinder through the injector hole and measuring the piston travel. He reset the TDC pin before remounting the pump. He could not estimate how many degrees the TDC setting might hae been off.
All the use of the truck up to the last week has been towing with mountains and more headwinds than normal, but I thought that the mileage might have increased some. This week I made a solo 650 mile trip and got the first good reading on mileage.
This weeks trip was done at 65 mph and crossed the Cascades twice. The mileage was a calculated 22. 6 mpg. Since I changed the timing I have heard that 16 degrees is probably the best value for the 12 valve engines with better idleing and better low end response.
If you are discouraged with your 12 valve mileage, consider checking or changing the timing. My experience also shows that using the TDC pin to set TDC can have an error of several(?) degrees.
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