There isn’t really a predetermined timeframe for changing oil in gas engines. The useful life of the oil depends on the type of gas, the capacity of the sump, the working conditions, the load, the temperature, the air-gas relation, the characteristics of the oil itself and of the condemnatory limits established by the manufacturer.
For example, manufacturers such as Caterpillar recommend changing oil after 750 hours whilst others, such as Guascor-Dresser, recommend changing in engines running on natural gas after 1,200 hours and in engines running on biogas after 700 hours.
Fundamentally, there’s never a good time to change the oil and it shouldn’t be predetermined by a calendar or number of hours, but by its status, which is highlighted during routine analysis.
Below you will find a table with the condemnatory limits suggested by different manufacturers.
| Analysis | Typical values of the majority of manufacturers | Waukesha | Caterpillar |
|---|---|---|---|
| Viscosity | +/- 20% new oil | -20%/+30% new oil | + 3 cst new oil at 100ºc |
| B.N. | 50% new oil and >2 | 50% new oil and >2 | 50% new oil |
| A.N. | +2.5 of new oil | +2.5 of new oil | +2 new oil |
| Iph | >4,5 | ||
| Nitration | 20 ab/cm | 25 ab/cm | 20 ab/cm |
| Oxidation | 20 ab/cm | 25 ab/cm | 20 ab/cm |
| Insolubles | > 1% | > 1% | |
| Glycol | >200 ppm | Undetectable | Undetectable |
| Water | >1000 ppm | >1000 ppm | >5000 ppm |
| Fe | 20 ppm | According to tendency | According to tendency |
| Cr | 5 ppm | According to tendency | According to tendency |
| Sn | 5 ppm | According to tendency | According to tendency |
| Al | 10 ppm | According to tendency | According to tendency |
| Ni | 3 ppm | According to tendency | According to tendency |
| Cu | 15 ppm | According to tendency | According to tendency |
| Pb | 20 ppm | According to tendency | According to tendency |
| Mo | 5 ppm | According to tendency | According to tendency |
| Si | 4-7 ppm | According to tendency | According to tendency |
| Na | 25 ppm | According to tendency | According to tendency |
| Ca | 50% new oil | According to tendency | According to tendency |
| Mg | 50% new oil | According to tendency | According to tendency |
| B | 50% new oil | According to tendency | According to tendency |
| Zn | 50% new oil | According to tendency | According to tendency |
| P | 50% new oil | According to tendency | According to tendency |
| Chlorine | >800 ppm | > 900 ppm |
Table. Suggested condemnatory limits (standards are omitted)
