Truck Repair: Cummins 444 smokey when cold, viscosity of oil, oil pressure

Question

Engine Right hand side Hi there,
We have 1989 Cummins 14ltr @444hp. It runs very well, has good oil pressure etc. However when cold, it is extremely smoky. It is the STC type of engine, and I know the oil pressure regulates the injectors, but I am not sure which way to tackle this. Most of my local mechanics seem to know lees about the STC engine than I do!  

Answer
Hi Richard,
It is probable that the viscosity of oil when cold plays a part in the snoky exhaust. My advise is to ask you to first replace your engine oil with multigrade winter lube oil preferably SAE 10-40 W and also replece the oil filter. If this does not solve the problem, you may need to service your STC control valve or  replace with new one. Replecement may be a better option as servicing the valve may not give desired result.

One of the primary function of STC is to advance the injection at starting and acceleration to prevent smoky exhaust.

You may feed me back on the result.

Best of luck.