Temp Reading

d-reed

Member
Oct 23, 2018
53
Western Ma.
Boat Info
1996 Sundancer 250 DA
Engines
Gen 6 454 carb Bravo 1
So I just repowered my 96 Sundancer with a new 7.4. Boat runs great but I was wondering what the coolant temp should be when running in the water? The gauge is reading just under 100 deg all the time. When I shut the engine off and let it sit for 10 min and turn the key on it will read 175 deg or so. As soon as I start the engine it will slowly go back down to 100. I am thinking this is normal. I have an open system, and it has a 160 deg. thermostat. It has 2 temp sensors in the housing, 1 must be for the gauge and the other for the overheat alarm?.

Thanks.
 
Should have a 160deg thermostat which would result in a 175deg running temp. Put a temp gun on it just to verify it's not the gauge. If not the gauge, then something is not right, thermostat is hanging open or was installed incorrectly - there are a couple of different housings and install configurations, so it's hard to diagnose without pictures. Regardless, get to the bottom of it, not good running an engine that cool.
 
I will go home at lunch time and get a picture of the setup. New t stat, not sure how it could be installed differently? I will run it later and put my temp gun on it and see where its at.
 
Running at 100* is definitely NOT normal. But the question is, is it the gauge that's faulty or is it something else? I suspect it's something else. Do as Bill mentioned and go back and check your install, first.

2 sensors... yes, that is correct.
 
There is a round plastic piece, looks like some kind of restrictor that goes into the housing. I would have to say the gauge is fine because it does read correctly when the engine is shut off. I also remember when I started it for the first time in the driveway with the ears on it, they slipped off a little and the temp started to climb. I shut it off and re attached them and the temp went back down. I may have that installed wrong. I guess I need to find a picture of the setup. going to take it apart today. Thanks guys
 
d-reed, If you have the Tstat cover with four hoses then your problem is an easy fix. The plastic spacer is installed and then the Tstat is installed on top. Then the top gasket is last to be installed. The Tstat is not installed first. It looks strange but is right. I had the same problem that someone installed it incorrectly. I have a repair manual and this is the correct installation... Good Luck... J
 
d-reed, If you have the Tstat cover with four hoses then your problem is an easy fix. The plastic spacer is installed and then the Tstat is installed on top. Then the top gasket is last to be installed. The Tstat is not installed first. It looks strange but is right. I had the same problem that someone installed it incorrectly. I have a repair manual and this is the correct installation... Good Luck... J
I went home at lunch time and took it apart. The spacer was in the wrong place! Ran it up to temp and it seems fine. Man I am 52 years old and I am a Ford Certified Tech and have multiple ASE certifications and I put it together wrong. lol. Boats, WTH! Thank you for your input.

PS, I think something is breaking while I am at work and its sitting in the driveway on the trailer!!!
 
Easy to do. Bet it was nice not having to raise the cab to get back in there!
 
Happens to all of us - but be happy the issue was easily "fixed"!
 
Good deal - I will say the Mercruiser thermostat setup is overly complex, some have the sleeve, some have these balls, every engine seems to have a different housing. Sure there was a method to the maddness or maybe I am getting to be a gumpy old guy, but go figure...
 

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