Simple implementation of CSV (or any other character delimited file) writer.

DelimitedFileWriter.cs

class Car
{
  public int CarId { get; set; }
  public DateTime ManufactureDate { get; set; }
  public decimal SomeDecimal { get; set; }
}

class DelimitedFileWriterExample
{
  static void Main()
  {
    using (var delimitedFileStream =
        new DelimitedFileWriter<Car>(
          "C:\\abc.csv",
          arg => new[]
            {
              arg.ManufactureDate.ToString(),
              arg.CarId.ToString(),
              arg.SomeDecimal.ToString()
            },
          () => new[]
            {
              "ManufactureDate", "CarId", "SomeDecimal"
            }))
    {
      delimitedFileStream.WriteObject(
        new Car
          {
            ManufactureDate = DateTime.UtcNow,
            CarId = 5,
            SomeDecimal = (decimal) 4.23890
          });
    }
  }
}

public class DelimitedFileWriter<T> : IDisposable
{
  private readonly char _delimiter;
  private readonly Func<T, string[]> _getObjectStrings;
  private readonly Encoding _encoding;
  private readonly FileStream _fileStream;
  private readonly StringBuilder _objectStringBuilder;

  public DelimitedFileWriter(
    string path, Func<T, string[]> getObjectStrings, Func<string[]> getHeaderStrings = null, Encoding encoding = null)
    : this(path, ',', getObjectStrings, getHeaderStrings, encoding)
  {
  }

  public DelimitedFileWriter(
    string path, char delimiter, Func<T, string[]> getObjectStrings, Func<string[]> getHeaderStrings = null, Encoding encoding = null)
  {
    _delimiter = delimiter;
    _getObjectStrings = getObjectStrings;
    _encoding = encoding ?? Encoding.Default;

    _objectStringBuilder = new StringBuilder();
    _fileStream = new FileStream(path, FileMode.Append);

    if (getHeaderStrings != null && _fileStream.Length == 0)
      WriteObjectString(getHeaderStrings());
  }

  public void WriteObject(T objToWrite)
  {
    if (!_fileStream.CanWrite)
      throw new Exception("Cannot write to file.");

    WriteObjectString(_getObjectStrings(objToWrite));
  }

  private void WriteObjectString(string[] objectStrings)
  {
    _objectStringBuilder.Clear();

    for (var i = 0; i < objectStrings.Length; i++)
    {
      _objectStringBuilder.Append(objectStrings[i]);

      if (i < objectStrings.Length - 1)
      {
        _objectStringBuilder.Append(_delimiter);
      }
      else
      {
        _objectStringBuilder.Append("\r\n");
      }
    }

    var bytesToWrite = _encoding.GetBytes(_objectStringBuilder.ToString());

    _fileStream.Write(bytesToWrite, 0, bytesToWrite.Length);

    _fileStream.Flush();
  }

  public void Dispose()
  {
    _fileStream.Dispose();
  }
}