Coolant inlets and outlets Coolant inlets and outlets megals (Automotive) (OP) 3 May 16 04:59 What's the basic principle regarding the relative size of coolant inlets and outlets? Smaller outlets to maintain pressure in the engine? Also is there any advantage in fitting outlet(s) in the head near cylinders known to run hotter and plumbing them to the return lines to the radiator to equalise temps? RE: Coolant inlets and outlets MikeHalloran (Mechanical) 3 May 16 16:04 Grossly oversimplifying in the interest of clarity: Smaller outlets minimize the use of metal while keeping the coolant velocity not too high. Larger inlets are needed because centrifugal pumps don't suck very well. Pretty much everything you can think of has been tried. Chevy went with 'reverse circulation', or something odd, in the LT1, which worked ok once you got all the air out of the system, and got lots of dependable power. Then they went back to 'normal circulation' in the LS1...7, and got lots more dependable power. Clearly, it's not simple, and it's not easy, so a few rules of thumb are not going to cover the subject. Mike Halloran Pembroke Pines, FL, USA RE: Coolant inlets and outlets BrianPetersen (Mechanical) 3 May 16 16:17 Gas bubbles (steam from overheating, whether at local hot spots or generally throughout the engine, or from a wee bit of head gasket leakage) want to go "up". Venture in the opposite direction at your peril! Plenty of head gaskets also act as flow-control orifices for the cooling system. Never ignore the need for gas bubbles to escape upward and out.