Here's why:
* Additives: Car diesel often contains additives that aren't suitable for heating oil systems. These additives can cause damage to fuel pumps, injectors, and other components in heating oil systems. They can also produce unwanted byproducts during combustion, leading to issues like clogging and increased emissions. Heating oil typically has its own specific additive package designed for optimal combustion and system longevity.
* Legal Restrictions: Many jurisdictions have regulations governing the use of fuel in heating systems. Using car diesel may violate these regulations and lead to fines. The fuel taxes may also be different, leading to legal issues.
* Different Specifications: While they share a similar base, car diesel and heating oil have different specifications, primarily relating to the sulfur content. Heating oil usually has lower sulfur content, which is crucial for minimizing emissions and preventing corrosion.
* Warranty Issues: Using an incorrect fuel can void warranties on heating oil systems.
In short, while there might be some superficial similarities, the differences in formulation and legal considerations make using car diesel as heating oil a risky and potentially costly proposition. Stick to using fuel specifically designed for your heating system.
