Q. What oil should I use, and do the two strokes tolerate synthetic oil?
A. Detroit two cycles demand the right oil if you expect them to last.
straight weight oil is a must. I understand that Chevron Delo 100 is first choice with Shell Rotella T a very close second. Personally I use Shell Rotella T SAE40, but would use Chevron Delo 100 SAE40 if it wasn't special order around here.
The details from Detroit Diesel (edit at one time were) found here (only 4 cycle stuff there now):
And the two cycle oil info was as follows:
2.2 TWO-STROKE CYCLE ENGINESThe new most up to date oil info for Detroit Two cycles comes from MTU Detroit Diesel, and can be found in this PDF
The lubricating oil requirements for On-Highway applications of Series 53, Series 71, and Series 92 two-stoke engines are outlined in this section.
SAE Viscosity Grade: 40
API Classification: CF-2
Lubricating oil for On-Highway applications for two-stroke cycle engines must meet the
□ 1.0% Ash Maximum as measured by ASTM D 874
□ 7.0 TBN minimum as measured by ASTM D 2896
□ 700 ppm zinc minimum as measured by ASTM D 5185
At ambient temperatures below freezing (0°C [32°F]), sufficient starter cranking speed may not be achieved to start the engine with SAE 40 grade oils. Where starting aids are not available or at very cold temperatures (-18 to -32°C [0 to -25°F]) even if starting aids are available, the use of multigrade SAE 15W-40 or monograde lubricant SAE 30 will improve startability. These lubricants must possess a HT/HS Viscosity (measured by ASTM D 4741 or equivalent) of 3.7 cP minimum. These oils must be replaced with monograde SAE 40 lubricants as soon as ambient conditions permit.
3.5 SYNTHETIC OILS
Synthetic oils may be used in Detroit Diesel engines provided they are approved by a POWER GUARD Oil Specification (PGOS). For two-stroke cycle engines; only synthetic oils which do not contain viscosity improver additives may be used. The use of synthetic oils does not necessarily ensure the extension of the recommended oil drain intervals beyond the limits.
It's not as easy to read as the perhaps now out of date DD info quoted above, but worth reading none the less.
Here's the reply I received (on 12-21-09) form Castrol when I asked about synthetic oil for the two cycle Detroit:
Please be advised we do not offer a synthetic oil for Detroit Diesel twoClear as mud?
Stroke engines. Over the years for Detroit Series 53, 71 and 92 engines we
have recommended our Assuron 40 which meets the noted Ash, TBN and Zinc
requirements that are also noted in Section 2.2 of Detroit's Lubricating Oil
Requirements for their Two Stroke Engines. "At ambient temperatures below
freezing" other viscosity grades (SAE 30 and 15W-40 are recommended but
"these oils must be replaced with monograde SAE 40 lubricants as soon as
ambient conditions permit.
If your Detroit Diesel 4-53T requires synthetic oil recommended by the
original engine manufacturer we recommend you follow their guidelines.
If the original engine manufacturer does recommend that a synthetic
blend may be used please confirm with the original engine manufacturer that Castrol
Assuron SAE 40 meets all required specifications.