Overheating. Almost done saga.

Pirate Lady

Pirate Lady

Well-Known Member
Jun 2, 2020
7,537
Chesapeake Bay, Middle River
Boat Info
Sundancer 250 ‘91
Engines
7.4 Bravo 1
This week be 2 months. We fixed or replaced…
Intake manifold gaskets
Carburetor
Thermostat
Thermostat housing
2 temp sensors
5 coolant hoses
Bilge pump hose (found a hole in it)
Impeller
The big pump on front of engine.
Flushed engine multiple times, cleaned that out like new.
Pulled outdrive ….
Replaced the hose going from lower vent holes thru transom to impeller (bravoitis)
Bellows cables everything in there inspected or replaced.
Fixed loose wire going to trim switch starting to cause electrolisis.
Bravo 1. In excellent condition after 30 years. Engine too, 560 hours.
Previous owner used once a week to fish on Saturday morning then kept in a boatel.
I swear we did other shit too.
Thank god for friends. Total cost $1200.
mechanic buddy/friend test ran today, all seems good. Tomorrow we going down river out to the Bay and run the piss out of it to see if we got it all.
Wish me luck.
 
Good luck. I was in a similar boat (pardon the pun) about a month ago. Fortunately, thanks to a great honest mechanic, she is all sorted out after years of neglect. Safe and does everything I ask of her on the water.

I hope the same for you and it sounds like this will be the case.

Please let us know how the shake down goes.
 
Setback #??? Hell, i lost track.
Boat running great but gauge is bouncing up and down 10 - 15 degrees depending on how you tap it. We went from a 145 to 165 thermostat.
but it seems to be pushing the 170 that we dont want it going over.
Decided to go back to a 145 and change the corresponding sending unit.
one more day!
Mechanic says he can fix the gauge. Dont know how. Original teleflex, dont want mis-matched gauges or the work of replacing them all so if he can repair, all good.
 
Pirate Lady said:
Setback #??? Hell, i lost track.
Boat running great but gauge is bouncing up and down 10 - 15 degrees depending on how you tap it. We went from a 145 to 165 thermostat.
but it seems to be pushing the 170 that we dont want it going over.
Decided to go back to a 145 and change the corresponding sending unit.
one more day!
Mechanic says he can fix the gauge. Dont know how. Original teleflex, dont want mis-matched gauges or the work of replacing them all so if he can repair, all good.
Click to expand...
Send me a pic of the gauge please
 
7923E9F0-54DC-49A0-8005-C918678F0326.jpeg
 
Way back in the day before all this overheating shit, with a 145 thermostat the gauge was pegged on the line between 130 and 170. Since we fixed it all and changed to a 165 it’s pushing 170. Don’t like it.
 
If I recall properly, salt water wants the 145 thermo so salt doesn't precipitate out.. if your in fresh water - you can run the 165. closed cooling is probably a different story altogether.

engines apparently like the warmer temps and are more efficient. I recently swapped to the 165 because I dont have to worry about salt.

actual engine overheat temps are I think are near 200..
 
I might be able to find you the gauge but you may want to be sure it’s not just a loose ground at the sensor. A bad connection will make the gauge jump around. I’m also unsure if a sensor and a gauge have to be matched. I will look on Wednesday when I go back to the boat
 
Oh man I feel you on the long term mechanic dance Pirate.
Mines costing way more though!
 
Ours are always at 170 on the nose (and again now after the major overhaul we did). Salt water.
 
I'm usually in the 150 range in saltwater (but Mpi not carbed).
 
Last edited:
Mine r
Black Valkyrie said:
Ours are always at 170 on the nose (and again now after the major overhaul we did). Salt water.
Click to expand...
Mine also runs at 170 all day long, also salt water, closed system. That's a great temp for efficient combustion. Performance boats will run even hotter. Markrsimon is correct: overheat is at the plus side of 200.
 
markrsimon said:
If I recall properly, salt water wants the 145 thermo so salt doesn't precipitate out.. if your in fresh water - you can run the 165. closed cooling is probably a different story altogether.

engines apparently like the warmer temps and are more efficient. I recently swapped to the 165 because I dont have to worry about salt.

actual engine overheat temps are I think are near 200..
Click to expand...

You are correct 145 thermostat for saltwater cooled and 160-170 for a closed system. Remember that the cooling system can only cool the engine down by ~100 degrees from the sea water temp. The upper bay right now is low 80's, last weekend at Fairlee Creek it was 84 in the creek and 82 in the channel just off of Tolchester. So running 170-180 is not running too hot. The boys up in Canada how a bit cooler waters, so their temps will run cooler then here in the bay.

It was mentioned that the sender and gauge need to be "matched", that is 100% correct. So be careful if you have to swap out the gauge and make sure there is no thread sealant on the sender if it is a single pole sender, the body is the ground in that case. Good luck with the test run, it sounds like you should be good.
 
SKybolt said:
You are correct 145 thermostat for saltwater cooled and 160-170 for a closed system. Remember that the cooling system can only cool the engine down by ~100 degrees from the sea water temp. The upper bay right now is low 80's, last weekend at Fairlee Creek it was 84 in the creek and 82 in the channel just off of Tolchester. So running 170-180 is not running too hot. The boys up in Canada how a bit cooler waters, so their temps will run cooler then here in the bay.

It was mentioned that the sender and gauge need to be "matched", that is 100% correct. So be careful if you have to swap out the gauge and make sure there is no thread sealant on the sender if it is a single pole sender, the body is the ground in that case. Good luck with the test run, it sounds like you should be good.
Click to expand...

That's interesting. We sit at 154 on port and 152 on starboard whether the water is 84 or 64 degrees, freshwater lake, raw water cooling.
 
dwna1a said:
I might be able to find you the gauge but you may want to be sure it’s not just a loose ground at the sensor. A bad connection will make the gauge jump around. I’m also unsure if a sensor and a gauge have to be matched. I will look on Wednesday when I go back to the boat
Click to expand...
Let me know if you have that gauge, then we can PM about how to send it. Thanks.
 
We are changing back to 145 today. I read this in an old thread from 2011 when doing some research....

"I read somewhere that salt water engines have to run at 145 degrees or the salt will crystalize and build up inside the engine block and exhaust. The merCruiser manual calls for a 140 thermostat for the 454 and 502 motors. My 454 has a 160 in it and it wants to overheat on the garden hose muffs....cools fine at 165 in fresh open water. The 160 may make my hot water heater core work better but I don't really need that hot of water. I'm dropping mine back to 145 for this summer to see if it eliminates the hose problem. My 350 runs fine at 145 in my CV-23"
 
mobocracy said:
That's interesting. We sit at 154 on port and 152 on starboard whether the water is 84 or 64 degrees, freshwater lake, raw water cooling.
Click to expand...
Same here. 160° thermostat, raw water cooled in salt water. Mine runs at 156-158° all season long. Bay Water temps range from 60-80ish.
 
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