hey guys i am working on a buddies car its a i believe 94 civic 4dr auto
the problems he thinks the car is over heating on him here is the list of stuff
he did
he as the fan on constant he to the thermo out and a new cap
the rad looks good but i drove it today for about 20 mins the car didnt over heat but the needle varys if i go down hill it drops all the way if i cruise on the street its cold and as soon as i hit the freeway it went back up i am not sure what to look at first
i will try to check the sensor for the gauge it might be bad
and i also think the cap he has is no good,it doesn't seam to release any pressure
i turned the car ran it for about 2mins and when i got to take off the cap it releases the pressure even if you let the car sit it still does it when you take the cap off
well thanks for any help

 

any one??