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2006 Merc 350 MAG running temp.?

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skinut1

Contributing Member
I have a 2006 Crownline 240EX with a 350 Mag Mercruiser and Bravo III drive. My temp gauge reads 160 degrees with the needle straight up. My boat runs at 180 degrees which is a little to the right. It makes me nervous with the gauge leaning to the high side. A friend told me that was fine and the fuel injected engines need to run at 180 and not 160. I know my chevy 5.3 litre p/u runs straight up needle at 210 degrees and doesn't get to the red till about 240. Is all OK with this or do I need to change the thermostat since I am assuming it has a 180 thermostat in it and may need a 160 ?
Thanks for the help !!!
Great Site .
 
1. a 160 degree thermostat will run on average between 160 and 170. If running hard or at high rpms especially in hot weather and warm water it could run around 180 ish

If it is running at 180 at idle in cool ambient temps and cool water then you have an issue.

First you need to confirm the temp like with a infa red temp gun........~$15 - $20.

point it at the temp sender and exhaust manifolds and get some numbers.


So what is not right? Is it the gage, the sender, the thermostat?

Also what is the condition of the impeller? How many years has it been in use?

WHat conditions do you use the boat in? Salt water? Fresh water?

The other point is you have to have enough water coming in and also the same amount going out. If either is weak, low flow or blockage coming in or blockage due to rust in elbows going out this will cause high temps.

So there is no easy answer..........need more info as much as you can give
 
It is run in a clear deep fresh water lake in North Arkansas. It stays at 180 when idleing or running hard. I am going to replace the raw water inpeller and seal as I have a small drip at the pulley shaft. I haven't replaced the impeller in the drive leg. I have only had the boat for 2 years though. It would run at 180 even when idleing if it had a 180 thermostat, right?
Thanks for your help Jack !
 
You don't have an impeller in the outdrive.

All bravo outdrives use engine driven water pump impellers
Alpha out drives use out drive driven impellers.


If it stays at 180 on the gage no matter what, then I would say either the gage is bad or the sender is bad but I will add it may be the gage just reads 10 +/- degrees off..........

It should get warmer when running hard as much as 20 degrees especially if you run hard and come to a stop very quickly.

No marine engine I am aware of runs anything more than 160 degree thermostat (pleasure boats)

So if you run any thermostat and lets say it is a 160 as yours is.

If everything is perfect the gage should read 160-170 at idle

Most boats of older designs run a 140 - 143 degree and almost every gage will read 150 degrees when fully warmed up and at idle when all systems are running correctly.
 
After looking at the parts diagrams for your engine, I notice that there is 2 different tstats used, (160 degree and 170 degree), depending on whether you have a 6 point drain, 3 point drain, or single point drain system. Can someone explain why?
 
Interesting.........maybe he has the 170 and if so that explains the 180 constant temp...........and if so that solves the temp mystery.

It looks like based on the parts diagram if the thermostat is mounted horizontally it is a 170* and if it is mounted vertically it is a 160*
 
Last edited:
kghost said:
Interesting.........maybe he has the 170 and if so that explains the 180 constant temp...........and if so that solves the temp mystery.

It looks like based on the parts diagram if the thermostat is mounted horizontally it is a 170* and if it is mounted vertically it is a 160*
Click to expand...

Yeah, that's the only difference i'm seeing. Next time I'm on the phone to a Merc service rep, I have to remember to ask about this.
 
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