I have a Jegs liquid filled fuel pressure gauge mounted under the hood and when it gets hot the gauge shows a lower pressure,sometimes real low depending on how much heat.Anyway i borrowed a non liquid filled Stewart Warner pressure gauge and set my fuel pressure off of that and really don't even worry with mine anymore.Something for you to check out,take some ice in a bag and put it on your pressure gauge and let it cool for a little bit and watch the gauge change.