'93 225 Running Hot on Start - Up

When the engine is warming up, the temperature rises into the 180 degree range and then frops to normal (140). In the past it has just gone to the 140 degree point without rising first.<br /><br />I assume the problem is either thermostats or the pressure relief valve (don't know if I have this right). I understand how thermostates work, how does the pressure relief valve work? I have replaced the thermostates in the past, but not the pressure relief valve.<br /><br />The motor has 10 psi of water pressure at idle and a good water pump.

Re: '93 225 Running Hot on Start - Up

In 1997 they added slots to the pressure relief valve to bleed out air and allow the block to fill with cooling water quicker. Get a new one and a seal, they are cheap.<br /><br />The "blow off" or pressure relief valve is a plastic cone that is spring loaded against the block. When water pressure rises to a certain point, the valve comes off the block and water blows out overboard. That allows more cooling water to enter the engine at high speed, keeping it at operating temperature.<br /><br />Make sure the thermostats are operational, test them according to the service manual and make sure you have a factory water pump kit installed correctly, # 5001594 for the 20" shafts and #5001595 for the 25-30" shaft motors.