OK so I work in a kitchen and I was wondering, one of our ovens fans went out a few days ago, and we have a guy who comes in and does basic maintenance work around the kitchen and what not, to help save money on replacing stuff... but here is my question, the fan went out on the oven and he said he greased the fan and everything and says it is completely safe to use. We found out today that he used 30 weight engine oil to lubricate the fan in the convection oven, he claims that all we have to do is run the oven and burn off the horrid smell that is coming from it, basically the smell is like your car overheated and started burning oil, he claims it is perfectly safe and has done it at several restaurants that he has done repairs for, is this safe or do we need to replace our oven, or at least take it apart and remove the oil traces

When a motor locks up due to a lack of oil the proper procedure is to pull the motor and replace the bearing, but sometimes you can get away with it. He should have used turbine oil on all motors except that one. ( It comes in a plastic bottle at all appliance parts stores for about $3.00.) He should have used a food safe oil when the motor is exposed to food. To use 30 weight oil will cause the motor to fail again. You may need to get at the motor and clean it with soap and water to remove the oil.

As far as safe....I doubt that it would be approved by any inspectors that would come in. I also have to wonder how it makes the food taste and if it adds any toxins.

I think the restaurant you are working for A) doesn't care at all about the health of its customers, B) doesn't care about the taste of its food, and C) doesn't think the inspector will come in.

Sure doesn't sound right from at least 3 standpoints:
Odor onto the food.
Toxin(s) in the food.
Thirdly, could this also be a fire hazard?

The attached spec sheet indicates a flashpoint for a typical 30W oil, at 430 degrees.
http://www.hess.com/docs/us-safety-data-sheets/hess-10w30-motor-oil.pdf?sfvrsn=2

Replacing the motor would be the minimum action to take in my opinion, and I am not very confident that the odor (depending on how long the oven has been used) will ever be eradicated.
The boss should consider using qualified/certified craftsmen who are insured for these maintenance needs. I think that most insurers investigating a claim like yours, would throw in the towel and get this behind them fast, especially if the facts and odor are as you have described.