Engine/Transmission (1994 - 1998) blue-ish smoke when cold

[Moparsean]

Just did my head gasket (factory) this weekend for a lingering external coolant leak and was very pleased to find cross-hatch still in the cylinders. But my question is this. I have always had some blue smoke on cold start ups... probably from all my bombs so far to the truck. You have to really look hard when its warmed up to see any at all. I have never set or checked the timing (have the tools) as it seems to run very well,would a bump in timing clear up some of the start-up smoke or make it worse? I know it will clear up white,but how about blue? its fuel,not oil. The pump is factory... yes it has 446k on it,could that be going south,how far can they go? I run bio diesel 50/50 in winter and 100 percent in summer. I think this is keeping it alive. Opinions?

 

[Vaughn MacKenzie]

When doing your head job it's possible you disturbed the fuel system and are drawing air somewhere. There is an odd O-ring on the hard line from the tank where it goes into the prefilter/heater, this tends to be brittle or crack. You should also check your prefilter and heater. . . the heater can go bad and when it does, it lets air in around the electrical connector.

Did you happen to go with a thicker headgasket such as . 010" over? This can contribute to startup smoke. I replaced the virgin head gasket on my '96 around 355,000 miles and after that it always had a little more startup smoke than before & never could resolve it. A couple theories. . . I am told even though the cylinder walls may look great (mine did) the rings could still be worn, and replacing the HG may "disturb" things enough to decrease cylinder sealing resulting in cooler combustion (causing smoke). Just by reinstalling the head bolts and torquing the down the cylinders may be distorted in a slightly different way than they were originally, because Cummins bores them with torque plates, so this can compromise cylinder sealing a bit. Have you noticed any increase in blowby or oil usage since your repair?

 

[Moparsean]

The smoke was the same as before the repair,it has always had this minor thing,but it does get less and less as it warms up. The fuel heater is by-passed. I use almost no oil,its fuel. I'm thinking of checking timing anyways,just wondering if anyone had a decrease is blue - ish smoke by doing a timing bump.

 

[PRattenbury]

The blue smoke is normal. The mechanically controlled pumps are set to perform optimally when warm. When the engine is cold there isn't enough heat to burn all the fuel delivered by the pump at idle. So it gets sent out the pipe and smoke is produced. Timing won't help that.

 

[DZinger]

I have had this on numerous gassers over the years and I am sure it probably applies here as well. Blue smoke, as you are well aware, is from burning oil. On the gassers I had, this was a result of worn valve stem seals. Oil was slipping past them until the engine warmed enough for them to swell slightly. Hope this helps!



Don

 

[Champane Flight]

Normal

Mine has smoked from day one when it is cold if I do not plug in. Give it a little longer to warm up and try this, when you get to a main highway, ease into the throttle just enough to produce a black haze, then back off, your blue smoke should be gone. . The blue smoke is fuel and oil, it is called cylinder wash, it takes place during incomplete combustion of cold engines. When you push a little bit more fuel to the engine you burn off the unburnt fuel, and seal off the cylinder. Mine is capable of smoking out entire neighborhoods if I take RPMs up while cold.....

 

[Missouri Mule]

It does state in the service manual that a defective fuel injection pump or misadjusted pump timing could "cause blue or white fog like exhaust".

Maybe your bio-diesel is causing the blue smoke on start-up. Also your 370 hp injectors could be causing it.

 

[Woodenhead]

Timing may help a little but I say get used to it. The 370s are well known for being cold smokers. My timing is at 16. 5deg (or at least it was and I think it slipped again but that's another story). I've done timing, head gasket etc. and right now have a fresh set of 370s and it still smokes when it's cold. I'm sure your high mileage pump doesn't help either but I have about 1/2 the mileage you do and I'd be willing to bet it smokes just as

much. I think Vaughn had a pump pack it in with about that many miles.



I do think mine smokes a little more since the head gasket and o-rings but I had 0. 009" cut off the head and put on a 0. 010" over head gasket. Since the head is flat (no combustion chamber) the 0. 010 over gasket probably lowered my compression a bit making for more cold idle smoke.



I'm with Vaugh on checking the fuel heater and other connections. That's solved many problems for many people over the years.



Do you have issues with stumbling when accelerating with a cold engine?



Mike

 

[Vaughn MacKenzie]

I missed seeing the 370 injectors in Sean's signature, swapping those out for something else like DDP sticks would definitely help.