I replaced the complete water pump and complete thermostats in my 88 SPL. still got some over heating after 10 minutes. Water was coming out the pee stream enough with the muffs on. I removed the 2 hoses going to the thermostats to see how much water was being pumped out and it isn't streaming strong but enough and it is warm water. I don't think it is stong enough to push it through the thermostats though to have them open up. Is there a certain preasure that should be present? When it over heats the heads are hot but the thermostat casing is just warm. Maybe check the water pump...again?