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Engine temp not reading high enough

mschen

New member
"I have been trying to figure

"I have been trying to figure out a water temp issue with my 5.7 mercruiser (Raw water cooled) At the end of last season the temp gauge seemed to stop reading, it only reads the minimum 120 and I replaced the sending unit, no help, then the gauge, still no help. I checked the thermastat and discovered that the previous owner was not running one! I installed a 170 degree stat and still no noticable temp rise. I ran a new wire from the gauge to the sending unit, still no change. I then boiled water in a pan and using the original sending unit wire and tested both sending units with the heated water and the gauge rises and reflects an accurate water temprature. While doing these test I am running the motor on a garden hose. The thermastat housing (sender is mounted in the side of it) does not seem to get warm at all, but the manifolds and risers are warm to the touch. I would think even at idle the internal engine temprature would rise enough to show a reading on the gauge. The water coming out of the exhaust ports on the outdrive is pretty warm to the touch after running for a while? Any help would be greatly appreciated!"
 
"In my experience any engine s

"In my experience any engine should warm up to full operating temp at idle using a garden hose within about 10 minutes or so. At that point the guage should read normal temp if all is working correctly, and the T'stat housing, manifolds, and risers should all be quite warm to the touch. The manifolds will be the hottest.
Did you get the T'stat in correctly? (Button end down, cone shaped end up.)Make sure you have enough water flow so that there is water escaping the muffs when the engine is running.
There is always water bypassing the T'stat housing so as to assure flow to the manifolds and risers, even when the T'stat is closed.
The water leaving the exhaust ports will be quite warm (even hot) and may look steamy. It gets very hot by being in contact with the hot manifolds, then heated even more by direct contact with the hot exhaust gases.
Make sure you run it for at least 10 minutes or more. You won't hurt it as long as it has a good supply of cooling water.
Rod"
 
"I'd bet the t-stat is ups

"I'd bet the t-stat is upside down.
Also, you should be running a 140F t-stat with raw water cooling... open system, no pressure to surpress localized boiling in the water jacket."
 
After some internet searching

After some internet searching and talking to my local marine mechanic we discovered there is a plastic spacer/diverter that should be in the thermastat housing that was missing when I installed the thermastat the first time and the stat was not positioned in the housing right without this part which allowed the cool water to flow directly into the engine and it never had a chance to get to operating temp. The previous owner must have removed this as well as the thermastat. Also it is a 140 degree stat that I had put in not a 170. hopefully this will help someone out a lot quicker than my ordeal! I am going to get the part tomorrow and I will let you all know how it turns out! Thanks for the help!!
 
"be aware the thermostat sits

"be aware the thermostat sits above the sleeve. the good news is, You havent harmed the engine. you just took the sender out of the warm side."
 
"Just wanted to let you know t

"Just wanted to let you know that I got the thermostat sleeve and put it in Saturday, now the temp is running around 145-155 on the hose after initial warm up. Only problem is after it ran fine Saturday, I started it yesterday (Sunday)and after a few minutes it stalled (never done that before)It will start right back up and run for a few minutes, but then will stall again?? I think it is an unrelated issue perhaps fuel filter or water seperator..any thoughts"
 
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