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Have 2 questions. 1) when adding air to the tires do you go by the tire specs or do you go by the tag on the cars door? 2) Does it hurt the motor if you mix synthetic oil and conventional oil.

3 Answers

1- Use the tag on the door. The tire specs tells you the maximum pressure your tire can tolerate and it is not safe to put that much in a tire because when you drive, the tires heat up and the pressure goes up and you might blow up the tires.

2- In case of emergency, it can be ok, but otherwise, do not do that.

Thanks for the reply. Airing the tires up hasent been to much of a problem usually there isnt to much of a differance in the tires and the tags, sometimes 15 lb differance. But with the oil ive been curious because i might be a qt. low of 1 type of oil but i have a qt. of the other sitting in garage.

you'll take the chance of hurting your engine to save the price of a QT> of oil?

  1. the pressure spec molded into the tire sidewall is always the MAXIMUM rated cold pressure for the tire. You don't want to ride on maximum pressure. It's perfectly safe, but it would be a very rough, rattly ride. (like riding on wagon wheels). The door sticker states the correct pressure for your vehicle. The difference between these can sometimes be as high as 50 psi.
  2. No it won't hurt.

1) on the spare tire if its a space saver, they often have their pressure rating on it. on regular tires that's usually the MAX pressure - so you should just follow the tag on the door (on most cars), the fuel filler flap (on some cars) or, even better, the car's manual (on all cars - it'll pretty much always match what's written on the door).

2) I wouldn't do that, it probably won't cause damage 99% of the time but I wouldn't risk it...

This post was modified 3 days ago by Dan