Blue Smoke - Posted for Sobczak

[TDRadmin]

TDR Friends and Experts (posted for Sobczak who is unable to post due to limited access to computer at this time):



I recently purchased a 1992 D350 from an original owner. At higher elevation (7,000') the truck has a lot of blue smog and runs rough on start up. AFter it warms up, there is no smoke. The engine has 56,000 original miles and has been serviced regularly to the best of my knowledge.



I changed the oil filter, air filter, fuel filter, and adjusted the valves. This truck is a dually with a Getrag 5-speed and a 4:10 rear axle. What might be causing the blue smoke?



Thank you.



Adam Sobczak



* * *



Robin

TDR Admin



(Note: this has also been forward to the TDR staff for input. )

 

[1stgen4evr]

Unless the truck started doing this after the filter changes, I would think it just needs a road trip. That is really low miles and lots of years. If it runs good any time, it will run good all the time when it gets broke in.



James

 

[Forrest Nearing]

you need to advance the timing.



(and drive the snot out of it)

 

[cerberusiam]

Thats pretty much normal for cool high altitude starts for these trucks. It is just unburned fuel from the cold cylinders. A timing advance may help some and make sure the KSB is doing its thing also. As long as the smoke quits when it gets warm and you don't get any white smoke while driving I would not worry about it.

 

[dpuckett]

Timing advance cured the blue cold smoke in my 92. It fogged for skeeters in Feb (though, ironically, we almost need it as warm as our "winters" are around here. )



I agree- 56K for a 92 is a LOT of sitting. If it doesnt clear up after some hard driving, it's time to check out the fuel system- start with testing the injectors, and go from there.



Daneil

 

[Adam Sobczak]

Adam Sobczak

RE Blue/White smoke in a 92D350

Thanks for the tips. The original owner did drive it empty but very little.

What is a "sweet spot" in RPM'S ? Empty at 60mph it is around 2200 with the 4. 10 rear axle which seems quite high. Towing a 12000lb 5th Wheel I try to stay around 2000 RPM.

Adam Sobczak

 

[1stgen4evr]

The sweet spot is in a sense hypothetical but it is a reality that you can use to good advantage. It is relative to RPM as you note but there are other factors which you 'tune into' to decide for each individual application. From an engineering stand point, the sweet spot is the result of a 'couple' as it is stated. In any multiple rotating mass there will be certain points of harmony and other points of dis-harmony. The couple you are seeking is the point where everything is working together to provide the smoothest operation.



Translation: you decide.



James

 

[cerberusiam]

Sweet spot - the rpm frequently defined as the point of peak engine efficiency which generally occurs slightly above peak TQ.





In my experience, it occurs at 1900 to 2000 rpms on both of my trucks. Depending on how the truck is setup this can vary.