1986 Mariner Magnum 150 Temp issue

kakarot

Recruit
Joined
May 29, 2016
Messages
5
I have an 86 Mariner 150 that is showing it is running very warm to hot at higher speeds. It has a new water pump kit, rebuilt poppet valve, 2 new 143 thermostats (tested good) new temp sender and seems to have no problem moving water out the tell tale hole. By the time I idle from the ramp to end of the no wake zone (approx 150 yards) the temp is showing at almost half and rises to 3/4 on any acceleration headed to H unless I back off the throttle. The water temp today was 90 as this is a power plant lake and is generally warm. At the advice of a local Merc service center i have removed the thermostats and put in blanks in their place just to test, made no difference except that I get a tell tale stream immediately instead of having to wait for them to open. I tested the water temp coming out of the tell tale with a laser thermometer with the gauge at a little over 3/4 and the water was at 148. The stream is constant, no sputtering or any signs of issues there. Im starting to wonder if this isn't a gauge issue. My alarm horn seems to have fallen apart at some point in the past so I cannot rely on that until I get it replaced. Has anyone ever had a gauge read incorrectly or is there something I am overlooking?
 

Dukedog

Captain
Joined
Oct 6, 2009
Messages
3,235
get tha warning horn workin'.... very few gauges are "right on"... laser temp gun tells tha truth.. point it next to your temp sender (port head) ta get an idea of what tha gauge is showin' compared ta actual temp
 
Top