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Discussion Starter · #1 ·
Hey guys I know there is a thermostat question jut about every week on these boards but I'm not finding a clear cut answer.

I'm running a 91 350 mag/alpha and its running great, oil is fine, plugs look fine, and its holding a constant 170 water temp all day, but I seem to blow alot of steam, i pulled the t-stat and found out its a 160 t-stat (I think) is this my culprit? some say I should be running a 160 t-stat and others say I should run a 140. I have no serial number on my engine (long story) so I can't look up what t-stat is was originally equiped with. any ideas? is this even my problem? I have no idea how old the manifolds/risers are
 

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Discussion Starter · #3 ·
Fyhr Factor said:
That's strange, No serial # on your engine..??
I'd like to hear the long story... :winker:
Haha well really its not a long story as to why there is no serial #, so much as the hell it took to register the boat in my state.

basically the number plaque was lost when the motor was rebuilt. and they did a new sticker package on the rebuild. so anywhere there should have been a serial number (top of flame arrestor, outdrive, etc.) was lost. the boat resided in IN and they don't require serial numbers on motors for registration. so it was no big deal that it got lost, however the wonderful state of ohio where I love does. one of those little things I never thought about till I already purchased.
just thinking about the hoops I had to jump through to register the boat brings back headaches. it took 5 months to transfer title and complete registration :dead1: my wife always brings it up the minute I talk about trading up boats to deter me :laugher:
 

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I'll tell you with 1,000,000% certainty your engine was equipped from Merc with a 140 stat. While in there inspect/replace all t-stat gaskets, t-stat spacer, and passages for blockage.

Re-run and check steam.
 

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Discussion Starter · #8 ·
thanks guys, cfm since your 1,000,000% certain I'll roll with the 140 :bigsmile: I figured as much but I've been going with the "ain't broke, don't fix it" mentality.

p.s. ya sorry I left that out, it is in fact carberated. :winker:
 

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Discussion Starter · #9 ·
okay now what's the deal. went ahead and dropped in the 140 t-stat ran the thing on the hose and it runs even hotter, like the t-stat isn't even opening. pulled it out, popped it in some hot water and it works fine. what would cause this to happen? :confused1
 

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how long since you put an impeller / water pump in? and what kind of an exhaust do you have? Did you by chance find any little bits of rubber when you replaced the thermostat?

you migt also be looking at manifolds and risers - as they fill up with rust and scale they restrict water flow. I might at the very least inspect them with an eye to replacing if they're significantly corroded inside. If needed, new exhaust is cheap insuarance compared to the cost of a new longblock and new exhaust. just my two cents...
 

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Mine runs very hot on the hose also. Only way to accurately test it is in the water. I also ran into problems with the hose that runs through the transom being clogged up.
 

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Should not run hot on the hose at all. "MAYBE" a tad warmer but thats it. Mine idles all day long at 140-150 on the hose and 140 in the water 24/7
 

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88maxim said:
Mine runs very hot on the hose also. Only way to accurately test it is in the water. I also ran into problems with the hose that runs through the transom being clogged up.
I beg to differ. My boat runs 150 degrees all day long in the water but will continue to creep up in temperature (180-190) when on the hose. Dont think the hose provides enough volume or perhaps it is sucking air. But before he gos replacing things, id try it in the water. My .02
 

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Discussion Starter · #14 ·
just replaced the impeller this spring. I didn't find any rubber bits or anything. no idea on the age of the risers/manifold used to run it on the hose all the time on the old 160 t-stat and it would run 170 constant. ran it this time on the 140 and it just continued to climb by 175 I decided something was up so I shut it down. maybe I'll just reinstall and see what happens :confused: again the ony thing that changed was my t-stat, and the only reason I changed it was because It was running 170 and blowing a little steam.
 

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How hot was the water when it opened? Could you have possibly put it in upside down? Do you have a good flow of water out the exhaust? Do a compression check for a possible head gasket failure. At least pull the plugs and look for super clean ones. Possibly even try it with no thermostat just to see what happens. There are lots of places that things can get clogged up. You would not believe how much sand was in my block and heads the last time I had mine apart.
 

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Discussion Starter · #16 ·
well just for giggles I put it back in and it definately ran better...not sure why but I'll take it, still a little warm running around 165, not sure where to go next. it only blows a little steam so I'm not sure how concerned I should be. :confused:
 
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