the other day i checked my tires in the morning and it low so i went to get air in the afternoon when it was fricken hot. then the next morning i checked the psi and all of my tires were missing 4-5 PSI. So which is the real PSI reading?

 

Measure tire pressure and add air when the tires are cold not hot. Cold means when the car hasn't been driven for a while, such as overnight. Heat causes gas to expand, thereby increasing the pressure.

 

but if i set my tires to 35 PSI in the morning, wont they expand too much when they get hot?

 

It's built into the system. Yes, the tire pressure rises as the tires heat up.

 

thats why your tires say COLD PSI. it compensates for the temp/psi increase. if you drive on them and then fill them up then put afew more psi into them. but if you keep leaking air from them then take them to a tire shop ya might have a screw in the thread, or a leaky valve stem.
my valve stem just craped out on me the other day driving to work

 

How cold is it getting at night?

If you have a temperature drop of more then 5C overnight you could loose an pressure as cold air is more dense and therefore less pressure.

But also get your tires checked if you can

When I bought my civic I had to take it back the next day cause every valve stem was put in improperly and it was leaking a lot. The dealer had bought a warranty on the tires but it did not cover the stems, however he paid with his own money to fix it.

 

o well thats bs about the valve stems.LOL at least here in the US most large tire chains offer free plug service and free valve stem replacement. i just had one stem replaced by a tire shop free of charge. now to patch a tire i think they charge a few bucks if you didnt buy the tire from them. but a simple plug is free. probably had some stupid kid on the tire machine. i never go to the tire shop after 2pm if at all posible! they always have the idiot on the balance machine and never balance my tires right!