You do not need a guarantor for your car's COE renewal. However, if you are getting a COE renewal loan, you may need a guarantor for your bank loan if you are below the age of 21, or do not have the minimally required monthly income.
The minimum requirements are as follows: $2,000 of monthly income, no trace of bankruptcy, age not exceeding 65 years old. Approvals are on a case-by-case basis.
If you want to find out more about COE renewal loans, you can find out all that you need to know here: http://www.motorist.sg/article/23/how-to-renew-your-coe under ‘Getting a Loan’.