Just engineering up my Dolphin which has sat in the hanger since way back in v2.x
First off the additional new 2 small slots in the April update gives the Dolphin 9 optionals which is fantastic, since outside the unobtainable Cobra MkIV it has more slots then any other small ship, and even beats some medium ships like the AspX (8) or Type-6 (8).
Second I have found this bug as well.
If I maximize the speed of the Dolphin, and turn it 90 degrees to the horizon on a planet and simply go in circles (Joystick pulled fully down) my maximum temperature is about 62%, dropping to 18% if I leave the joystick in idle (but travel at full speed)).
If I start changing the angle to my horizon so that it is less than 90 degrees (while still going in circles, but trying to keep the planet horizon in view), then the temperature starts to increase. At less than about 70-80 degrees things start to get quite toasty and at about 45 degrees the temperature will climb very rapidly. If I then resume the original 90 degree angle to the horizon (or become horizontal) the Dolphin will cool down from that overheating state.
In any case the issue can be seen by setting your Dolphin to maximum speed and then trying to circle around, keeping the planet horizon centered (well slightly below so you don't crash), but your angle to it at about 45 degrees.
Hmmm....it doesn't seem to work every time, just most times. Entering into a turn after reaching maximum speed appears to work most of the time though.