operating temperature for a 1995 350 magnum

[e2firefighter]

Ok, here goes...... I have a 1995 Harris Kayot Ultracat equipped with a 350 magnum. The boat is in excellant shape and everything works except for the temperature guage. I grounded out the wire coming from the sending unit and the guage maxed out. As it was explained to me, this tells me my guage and wiring are in working order? Ive also changed the thermostat (160) and sending unit. The guage still doesnt move above the bottom number which is 120. Even after running at WOT i can immediately touch the water from the exhaust, exhaust risors and thermostat housing and its barely hot. The water temperature here on the Ohio is around 80-85 degrees. My boat is running rich and i can here it missing between the 2200 to 3000 rpm range. Im beginning to think im not getting up to operating temp. Is that even possible? Any help would be appreciated.

 

[NHGuy]

Re: operating temperature for a 1995 350 magnum

I'd say get one of those handheld IR thermometers and check the temp at the sensor, it should be right on the thermostat housing, starboard side.
If you did not get a thermostat gasket with a bit of metal in it that could be your problem. The metal piece carries the ground from the motor to the t-stat housing. If you want to test it without diss assembly just ground the sensor body or the thermostat housing when the motor is warm and see if the temp gauge moves.
The cooling system always sends water through the exhaust water jacket-so there's always semi warm water in the elbows and the exhaust manifolds. That could be why the water you feel coming out isn't scalding hot. When the motor is warm and the thermostat is fully open the water from the engine gets mixed into the water that goes to the the exhaust and then out of the boat. Engine make more heat when they are doing work, so at idle even with a hot motor there isn't as much heat in the expelled water as there would be under a load.

 

[e2firefighter]

Re: operating temperature for a 1995 350 magnum

I'd say get one of those handheld IR thermometers and check the temp at the sensor, it should be right on the thermostat housing.
If you did not get a thermostat gasket with a bit of metal in it that could be your problem. The metal piece carries the ground from the motor to the t-stat housing. If you want to test it without diss assembly just ground the sensor body or the thermostat housing when the motor is warm and see if the temp gauge moves.
The cooling system always sends water through the exhaust water jacket-so there's always semi warm water in the elbows and the exhaust manifolds. That could be why the water you feel coming out isn't scalding hot. When the motor is warm and the thermostat is fully open the water from the engine gets mixed into the water that goes to the the exhaust and then out of the boat.

Thanks for the response NHGuy,

I already tried grounding the sending unit body with a wire and it did nothing. Last week, in hopes that i installed a faulty thermostat i replaced it yet again (this time it was a 190 degree). I also took the sending unit out and connected a mechanical temperature guage in its spot. The mechanical guage started out at 100 degrees and after a warm up it fluctuated between 100 and 130. After i shut down, i heard lots of tinging and popping and everything felt hotter. Even though the mechanical guage didnt reflect this (perhaps because it wasnt in liquid), the residual heat must have brought it up to around 190 degrees because i heard the thermostat open and a short rush of water. The guage then reflected 160 degrees. Im thinking the thermostat isnt even opening during operation but im not overheating which doesnt make sense so..... Now what? Just to throw something out there, if i have a water pump in my out drive and one on my engine what sypmtoms would i have if one is/was failing?

 

[NHGuy]

Re: operating temperature for a 1995 350 magnum

Maybe I jumped the gun...is this boat new to you? Do you think it ever lived in salt water? How long has it had this cooling issue?

Find the cooling diagram and reconfirm all the connections and gaskets, there are gaskets that manage cooling water flow where the exhaust manifolds meet the elbows. And there are a number of hoses that need proper routing.
There is a good representation of the thermostat housing and the hose routes and the gasket attitudes in the manual. If your thermostat housing has a bad chamber, a rust hole or a piece of junk in it, that could cause things to go wrong. That would surprise me, my 23 year old one looks fine.
Also some, like mine, use spring loaded check balls in the elbow hose outlets. If yours has those they need to be free to move in the hoses.
The pinging and popping sounds like cooling water is not getting in the motor at all. Pull the big hose to the engine water pump and check for blockage. You really need an IR gun. Maybe someone on here can recommend a test for the water circulating pump that's on the motor. If you can't test it remove it for inspection unless someone comes along with a better method.
If you end up pulling the water pump do your best to clear out any junk in the water passages, use sticks, bent coat hangars, air pressure, forceps, anything that will remove any thing that's not motor.
Oh, here's a test for before you take off the water pump.
After you run the motor (on muffs) and before the thermostat opens, remove the engine drain plugs from below the spark plug holes and see what comes out. You will need to probe in those holes with a piece of metal to break up any rust scale once the plugs are out. If it's dry you gots to find why.

 

[Oshkosh1]

Re: operating temperature for a 1995 350 magnum

I'd say get one of those handheld IR thermometers and check the temp at the sensor, it should be right on the thermostat housing, starboard side.

X2...Start with that. You can "spot" check many different areas. Water temp sending unit, Cylinder head(individual cylinders), water jacket, manifolds etc...

 

[e2firefighter]

Re: operating temperature for a 1995 350 magnum

Maybe I jumped the gun...is this boat new to you? Do you think it ever lived in salt water? How long has it had this cooling issue?

Find the cooling diagram and reconfirm all the connections and gaskets, there are gaskets that manage cooling water flow where the exhaust manifolds meet the elbows. And there are a number of hoses that need proper routing.
There is a good representation of the thermostat housing and the hose routes and the gasket attitudes in the manual. If your thermostat housing has a bad chamber, a rust hole or a piece of junk in it, that could cause things to go wrong. That would surprise me, my 23 year old one looks fine.
Also some, like mine, use spring loaded check balls in the elbow hose outlets. If yours has those they need to be free to move in the hoses.
The pinging and popping sounds like cooling water is not getting in the motor at all. Pull the big hose to the engine water pump and check for blockage. You really need an IR gun. Maybe someone on here can recommend a test for the water circulating pump that's on the motor. If you can't test it remove it for inspection unless someone comes along with a better method.
If you end up pulling the water pump do your best to clear out any junk in the water passages, use sticks, bent coat hangars, air pressure, forceps, anything that will remove any thing that's not motor.
Oh, here's a test for before you take off the water pump.
After you run the motor (on muffs) and before the thermostat opens, remove the engine drain plugs from below the spark plug holes and see what comes out. You will need to probe in those holes with a piece of metal to break up any rust scale once the plugs are out. If it's dry you gots to find why.

Ok, ill try these ideas out as i have no recourse. I purchased the boat two summers ago from the original family owners and its obvious it has been babied big time! The meter reads 87 hours and i was told it has never spend a night on the water and always been in fresh water. From the looks of things, i have no reason to disbelieve. I suppose the cooling issue was there from the get go but i payed little attention to it as i was not overheating..... I just assumed someone yanked the thermostat out totally until i checked this year. Inside the thermostat housing is clean too. I cannot recall if i have those check balls or not but i'll look. Also, i have a manual so i'll double check the hoses and gaskets. However, with the exception of me adding a through transom exhaust, nobody has ever been too far into this motor so i doubt that's the problem.

Oh, the boat is kept on the water. Can i pull the lower drains when im afloat? If not, that test just might have to wait til the season is over.

 

[e2firefighter]

Re: operating temperature for a 1995 350 magnum

One more thing, would changing my thermo from a 160 to a 190 change my WOT rpm from 4200ish to 5100ish? Perhaps its irrevelant but its just something i noticed today. Or perhaps an inaccurate tach too as its the original

 

[e2firefighter]

Re: operating temperature for a 1995 350 magnum

Maybe I jumped the gun...is this boat new to you? Do you think it ever lived in salt water? How long has it had this cooling issue?

Find the cooling diagram and reconfirm all the connections and gaskets, there are gaskets that manage cooling water flow where the exhaust manifolds meet the elbows. And there are a number of hoses that need proper routing.
There is a good representation of the thermostat housing and the hose routes and the gasket attitudes in the manual. If your thermostat housing has a bad chamber, a rust hole or a piece of junk in it, that could cause things to go wrong. That would surprise me, my 23 year old one looks fine.
Also some, like mine, use spring loaded check balls in the elbow hose outlets. If yours has those they need to be free to move in the hoses.
The pinging and popping sounds like cooling water is not getting in the motor at all. Pull the big hose to the engine water pump and check for blockage. You really need an IR gun. Maybe someone on here can recommend a test for the water circulating pump that's on the motor. If you can't test it remove it for inspection unless someone comes along with a better method.
If you end up pulling the water pump do your best to clear out any junk in the water passages, use sticks, bent coat hangars, air pressure, forceps, anything that will remove any thing that's not motor.
Oh, here's a test for before you take off the water pump.
After you run the motor (on muffs) and before the thermostat opens, remove the engine drain plugs from below the spark plug holes and see what comes out. You will need to probe in those holes with a piece of metal to break up any rust scale once the plugs are out. If it's dry you gots to find why.

Ok, just an update even though im really stumped. My symptoms do not make sense. Ive tried everything you suggested (minus the iR gun and the lower drains) and came up empty. I tested the new thermostat in a pot of boiling water and it opened up right at 160. I confirmed that all the hoses and gaskets are installed and are in the correct location. My impeller is functioning because water is coming out my exhuast bypass at appoximately 4+ gallons per minute which is what i was told the capacity of the raw water pump should be. I even took the circulation pump off and apart to visually inspect and flush everything. Everything, including the ports going into the motor were in great shape! Why isnt this thing getting to operating temp? It seems my thermostat isnt opening but its not overheating. Could this be some kind of air lock? If the thermostat spring wasnt submerged in water would it still open? ........Ill try the iR gun this Friday.

 

[e2firefighter]

Re: operating temperature for a 1995 350 magnum



this is exactly what i have. Should i be concerned that the "o" ring and sleeve is no longer present on my boat?

 

[Fun Times]

Re: operating temperature for a 1995 350 magnum

Yes you definitely should be concerned that the "o" ring and sleeve is no longer present on your boat.

With out them there it will do exactly as you're describing above. PS, even before i had seen you ask if they should be there, i was going to chime in and ask if the O' Ring or cork gasket was in place correctly as that is what your symptoms appeared to be to me.

It is important you put the 160 degree thermostat back in and make sure you only use a OEM mercruiser gasket between the T/housing & intake manifold. Mercruiser gasket part number is 27-530451. It's a specialized design gasket not normally found on aftermarket gaskets to my knowledge.

http://www.mercruiserparts.com/Show...c=STANDARD+COOLING+SYSTEM(DESIGN+III+-+ALPHA)

 

[e2firefighter]

Re: operating temperature for a 1995 350 magnum

Yes you definitely should be concerned that the "o" ring and sleeve is no longer present on your boat.

With out them there it will do exactly as you're describing above. PS, even before i had seen you ask if they should be there, i was going to chime in and ask if the O' Ring or cork gasket was in place correctly as that is what your symptoms appeared to be to me.

It is important you put the 160 degree thermostat back in and make sure you only use a OEM mercruiser gasket between the T/housing & intake manifold. Mercruiser gasket part number is 27-530451. It's a specialized design gasket not normally found on aftermarket gaskets to my knowledge.

http://www.mercruiserparts.com/Show...c=STANDARD+COOLING+SYSTEM(DESIGN+III+-+ALPHA)

I think that solved it!! After looking inside my thermostat housing there was in fact a sleeve and a cork gasket but the thermostat was on the wrong side of it. As the thermostat was just sitting atop the intake manifold, that left a 1" gap between the ceiling of the housing and the top of the thermostat which was basically acting as a huge bypass.

Thanks for everyones help.