I believe I am having issues with my 6 speed manual... i have a good size rear main seal leak... 6 speed manual... lately i've noticed.. my fuel milage slipping... but it gets better after about 2 or 3 hours of hauling a medium load.... i don't get it...ill be towing a trailer and albeit i know 6s isn't a pulling gear after about 1900 rmps it will pull okay when you ask it too... but not the first 2 or 3 hours of my voyage... anyhow... i've had a few back yard guys look at my truck and they are all suggesting... im getting oil from my rear main seal to my clutch??? Is that even possible?  Truck has been a hwy truck since 50000 km where i bought used ... back then it had a BD Power Diesel chip with no settings on it... so i removed it asap... fuel pump has been replaced. No clutch work ever.. opinions please.... could it be an injectore?   I mean my clutch isn't covered in oil... and my drive way has a little oil spot where i park... this isn't a huge oil leak... i don't add oil between oil changes

 

sorry ill add that i am at about 340000km... now not sure what that is in miles?  Maybe around 200 000

Edited October 30, 20159 yr by somethingnuw

Is your clutch slipping? (RPMs go up while speed doesn't change, or speed barely goes up)

With that many miles it's entirely possible the factory injectors are getting tired. Mine changed night and day after 180k on stock injectors.

Can you see oil coming through the slot in the bell housing? If yes, the trans need pulled and the rear man replaced asap. While you're in there you can see if the clutch needs replacing.

I would think if your clutch was slipping enough to make a noticeable difference in mileage you would know it was slipping, How are you checking the mileage to know it is worse the first 2 or 3 hours?

As far as towing in 6th many say dont many do. I am one that does and so far with no ill affect. It will get the tranny hot however and that will put some stress on it. I will do at no more that half throttle. Any more than that you need to catch 5th. Many schools of thought on that. Ran mine with a Banks Tuner with no settings on it either, 

For the main, I agree with T Faoro.  

For the mileage, I would expect the injector pump is getting worn as well as injectors getting tired.  What is the boost pump?  Do you have a pressure gauge?  If so, what fuel pressure?