Recently my car after sitting for 10-15 minutes while running at idle will gain a bar (4 total). If I start driving within 10-30 seconds it’ll go away. I know people have experience with this and was wondering what it can possibly be. Thanks

 

Maybe you have air trapped in your coolant system? Bleeding may help.

 

put the heater on full- it should be absolutely piping hot coming out the vents by the steering wheel. If it's not, you've got air trapped in the system.
darcy

 

I replaced a couple of coolant hoses going into the water pump about a month ago and had to burp the system which took about 1 1/2 hours. It just started doing this a couple of days ago and I believe there isn’t any air in the system.

 

I did try this and it is blowing hot. Any other idea what it could be?

 

With the AC on, do the fans come on?

 

Weak fans, our cars are getting old. You can get replacement motors(condenser and radiator) for a 1992-1997 Accord 4 cylinder from any auto parts store. Much cheaper than the $350 for the OEM ones.