Temp Gauge Reading? Wrong? TOO HOT?

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enginesilo

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So I just got my boat a few weeks back and have been out 3 or 4 times. The temperature gauge is acting up a bit and I wanted to feedback and advice.

The boat is a 2005 Sea Ray 180 Sport with the 3.0L Mercruiser Engine. It has bout 27 hours on it and was like brand new when I got it at 23 hours.

Here is the scenario:
  • When the boat is off and the key is turned in the off position, it reads 130. The gauge starts at 100 so it stays 30 degree's above.

  • When the boat is running and fully up to temp, the gauge reads 190 to 195 degree's.

Now if I leave the boat and let it get fully cold, like the next day, the gauge will usually still be stuck at the hottest temp the boat ran at when the key is in the off position. If I turn the key to the on position, the gauge will fall all the way down to 100, which is zero on this gauge. Now if I turn the key to the off position right after turning it on, it will go to 130 and stay there.

So basically when the engine is cold, the gauge reads 130, but when I turn the key on it goes down to 100/zero and climbs as the engine runs to the 190+ mark.

I was told that this engine should be running around 160. Think the gauge is reading 30 degree's off and that is why it is in the 190 range? Since the cold engine keeps the gauge at 130 when off and not 100, it makes sense, but I want to be sure I am not running at 190+ degree's.

Is there an easy way to test this? If I run it on the hose and put a thermometer in the water coming out the back would that be a quick way to test, or would the water loose too much of its temp on the way out? I was thinking of sticking a digital thermometer in the water to see if it is over 160 degree's since that would tell me immediately. Also considered buying an infrared thermometer but don't want to spend the cash if there is another way to do it with something I have around.

Could it be running too hot? Could it be the gauge? Could it be the sending unit? The boat has 27 hours so the impeller is young, and I considered changing it but would rather try to test other ways before going through that trouble. The running temp stays on the spot consistent at the 190 range so that leads me to think that it isn't the impeller.


Any feedback and opinions will be helpful.
 

RJLeuwen

Seaman
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Re: Temp Gauge Reading? Wrong? TOO HOT?

There is an alarm that will sound if your engine reach's 200 deg.

Most likely the gauge is off or the wires on the temp sender and the temp sensor are reversed.

sender is for the gauge.

sensor is for the alarm.


RJ
 

enginesilo

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Re: Temp Gauge Reading? Wrong? TOO HOT?

Thanks RJ,
So it is definitely not sounding an alarm, unless the alarm was not functioning.

I don't have a manual yet, so is there any way I can go about testing this? Would my test of measuring the water temp with a probe thermometer out the back work to see the temp, or will the water loose some heat on the way out? I figure this will at least tell me if it is running in the right temp range.

Does the manual tell you how to go about testing the gauge, and the sending unit, and sensor? Any tips on how I can possibily do this will be great.
 

RJLeuwen

Seaman
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Re: Temp Gauge Reading? Wrong? TOO HOT?

The alarm should sound with the key in the on position (engine off)

The alarm will sound for 3 things.

1. High water temp.

2. Low oil pressure.

3. Lower Uint lube low.

Don't think you'll get an acurate reading in the exhaust water out the back of the boat.
Best bet is IR thermometer aimed at the thermostat housing where the sending unit screws in, should have a tan wire on the sender and a tan with a blue tracer stripe on the sensor.

RJ
 

enginesilo

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Re: Temp Gauge Reading? Wrong? TOO HOT?

NO alarm so I am thinking it is more along the lines of the gauge or sending unit.

I might just bite the bullet and get an IR from the store if I can't find one to borrow. On the 3.0L, where is the temperature sending unit? If I am looking at the engine and out the back of the boat, is it on the left hand side towards the lower side?

What type of tests could I run on the sending unit? Other than shooting the IR near this area?
 

Robj

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Re: Temp Gauge Reading? Wrong? TOO HOT?

You can verify it with an infrared thermometer, one of those temperature guns. Sounds like you gage is off. Is it still under warranty? If so I wold get it fixed, if not I would try replacing the gage. Yes the correct operating temperature is about 160 degrees F.

Have a great day,

Rob.
 

enginesilo

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Re: Temp Gauge Reading? Wrong? TOO HOT?

Thanks for the reply. Nope, not under warranty any longer so I am going to try to diagnose on my own. A member, Jerry, suggested some tests of removing the wires and grounding to see if the gauge drops to zero, and pegs full. Going to test these first. I am also ordering an Infrared Thermometer as the next level of testing if I can't get anywhere testing the gauge.

Thanks for the tips so far guys!
Anyone else have any other feedback or ideas?
 

bruceb58

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30,454
Re: Temp Gauge Reading? Wrong? TOO HOT?

Ignore any reading that you have with the key off. It means absolutely nothing.

Testing the water temp that exits the boat also tells you nothing as it is the water circulating within the engine that is what you need to know.

As a previous poster mentioned, the only good way to verify what the guage is telling you is to use an infrared thermometer at or near where the temp sender is.

If the boat is 3 years old, it is time to be replacing that impeller. That impeller has been in there 3 years and you do not know how the previous owner cared for the boat(run on muffs all the time). The number of hours on the engine is not what matters. The fact that the boat has been sitting alot without being used(low hours) is actually worse for the impeller.
 

enginesilo

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Re: Temp Gauge Reading? Wrong? TOO HOT?

Thanks for the feedback. I am going to give the gauge a test anyhow to see if that is the issue. Also, I am getting an Infrared Thermometer to shoot around and see what type of temps the engine is actually running. Where is the sending unit on a 2005 Mercruiser 3.0L? Is it on the lower left hand side if I am looking at the rear of the boat?

How hard is it to change an impeller on these engine's? I've read that it is easy for some, and other's have had a hard time with it.
 

enginesilo

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Re: Temp Gauge Reading? Wrong? TOO HOT?

UPDATE

So I managed to borrow a nice Craftsman Infrared Thermometer from a friend. It is the $80 one listed on their site, and says it could have up to a 4 degree inaccuracy which seems reasonable enough.

I temperature shot the engine in various spots and saw various temperatures.

So let me ask, where does the current temperature sensor sit in the engine? Is it on the bottom side near the crank area? From my picture below can someone explain which side it is on (Starboard or Port?)

I IR tested all along the bottom side of the engine where I expected the crank to run and it read about 160 to 170 from the front to the back. If I IR tested the engine on the top side, it would read a little higher. For instance all around the top valve cover and the bolts it was in the 165 range, but the right hand bolt on the valve cover towards the bow read about 190. Seemed like the port side of the engine was slightly hotter than the starboard. Look at my picture below and the arrow on the right is where it read 190, where as the left arrow only read about 165.

engine.jpg


So overall, most of the engine shot at 165 in the crank area. I pointed the IR right near the spark plug area and it was in the 170 to 175.

Is the engine not supposed to read over 165 in any area of it? Does this mean that I may have an issue with my thermostat or something?

Any tips appreciated.
 

bruceb58

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Re: Temp Gauge Reading? Wrong? TOO HOT?

Not positive but your temp sender is probably on the thermostat housing on that engine. You should be measuring where the temp sender is located.
 

enginesilo

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Re: Temp Gauge Reading? Wrong? TOO HOT?

Can you tell me exactly where the thermostat housing is? Is it on the starboard side about half way down and centered on the engine? I am totally new to I/O's and Mercruiser's
 

jerryjerry05

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Re: Temp Gauge Reading? Wrong? TOO HOT?

Your left arrow is almost pointing at it.It's at the front where the hose's meet.You will get different heat readings all over the engine as heat is generated in different spots.I/E exhaust manifold /risers..Just change the guage and be done with it.Jerry
 

Don S

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Re: Temp Gauge Reading? Wrong? TOO HOT?

engine.jpg
 

enginesilo

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Re: Temp Gauge Reading? Wrong? TOO HOT?

Thanks to you both for the responses!
I am going to try the IR gun once more directly at the temperature sensor area to see if it is accurate in the 160-170 range.

Seems pretty consistent so it might be the gauge, just want to be sure it isn't actually running too hot and am doing damage. I will give it a go, and also try the gauge tests.

Anyone have any idea what new gauges cost, even a ball park idea? I'll probably have to call a local dealer.
 

nickcasa

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Nov 18, 2007
Messages
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Re: Temp Gauge Reading? Wrong? TOO HOT?

new temp gauge is $30 or so at any marine store, but shoot the gun like the other guy said where the two hoses meet, you should see 2 gold sensors with wires on them, thats where you want to check.
 
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