Mercruiser 3.0 Possible Overheating Issue

[onegoodoleboy]

Ok... I am relatively new to the boating world and have learned alot from these forums... So Thanks to all..

I have a 2004 Mercruiser 3.0 with a Alpha One Outdrive. I recently had to pull the motor, due to a broken starter bolt. After watching many You tube video's and reading my manual extensively, I was able to pull it and put it back in with very few issues. The only problem that I am having is when I put the water hose (with rabbit ears) on it, and let it run for about 10 minutes, the temp gauge shows that it is climbimg over 200 degrees. I then shut it down and pulled the thermostat out. Now the motor never heats up. So I put in a new thermostat and it still is slowly climbing over 200 degrees. I have felt the water exiting the transom plate and it is not scalding hot. I also have touched the water in the thermostat housing and it is not scalding hot. I have also touched the motor and intake, and have not found any evidence that the motor if over 200 degrees. I have also verified that water if coming into the thermostat housing, but I understand that this may be possible from the city water pressure forcing water thru the block.
1) Is it possible that I kinked a water line when I put the motor back in?
2) Could the sending unit be bad?
3) Is it possible that the new Thermostat is faulty also?
4) any other things I could have screwed up?

 

[Bondo]

Re: Mercruiser 3.0 Possible Overheating Issue

Ok... I am relatively new to the boating world and have learned alot from these forums... So Thanks to all..

I have a 2004 Mercruiser 3.0 with a Alpha One Outdrive. I recently had to pull the motor, due to a broken starter bolt. After watching many You tube video's and reading my manual extensively, I was able to pull it and put it back in with very few issues. The only problem that I am having is when I put the water hose (with rabbit ears) on it, and let it run for about 10 minutes, the temp gauge shows that it is climbimg over 200 degrees. I then shut it down and pulled the thermostat out. Now the motor never heats up. So I put in a new thermostat and it still is slowly climbing over 200 degrees. I have felt the water exiting the transom plate and it is not scalding hot. I also have touched the water in the thermostat housing and it is not scalding hot. I have also touched the motor and intake, and have not found any evidence that the motor if over 200 degrees. I have also verified that water if coming into the thermostat housing, but I understand that this may be possible from the city water pressure forcing water thru the block.
1) Is it possible that I kinked a water line when I put the motor back in?
2) Could the sending unit be bad?
3) Is it possible that the new Thermostat is faulty also?
4) any other things I could have screwed up?

Ayuh,.... Welcome Aboard,... #1,... Anything is Possible, the line runs up, 'n over the intake, so it should be easy to check...

#2,... Sure... Plumb in a mechanical gauge, to see if it's readin' right....

#3,... Again, Sure, anything is possible... Any chance some ole broken chunks of impeller blades got lost in the system,..??

They tend to hang, 'tween the drive, 'n t-stat housin'...
Pull the drive, 'n replace the impeller, while it's off, back-flush it with yer hose, from the t-stat housin', Back...

 

[HT32BSX115]

Re: Mercruiser 3.0 Possible Overheating Issue

Howdy,

Welcome aboard!

It is possible that you have a kinked line but you can easily check that by removing the raw water supply hose from the transom to the T-stat housing and see how much flow you have.

You didn't mention the raw water pump impeller at all. If you have not replaced it or inspected it, now would be a good time. It's usually the first source of problems. Also, if it has ever failed before it may have sent impeller fragments down-stream that are caught in the hoses or power-steering oil cooler (if installed)

Since the cooling water from the pump exits wholly out the riser, you should check your exhaust manifold and riser to see if it is clogged by rust. [If the cooling water cannot get out overall flow is reduced and will cause overheats]

Finally, get yourself a Harbor Freight infrared Heat sensor and measure the temp at the t-stat housing, intake manifold etc. you may not have an overheat at all.

It could be in your gage, sender, or gage wiring. (and you should check this stuff first)


Regards,


Rick

 

[onegoodoleboy]

Re: Mercruiser 3.0 Possible Overheating Issue

Thanks guys.... I have a little more info.
I used a barrel tonite instead of the water hose and rabbit ears. The lower unit was not taking in any water. I had no water at the thermostat. The temp climbed over 200 with or w/o a thermostat. I presume my impeller is bad?

I did check the gauge by grounding it. It checked good.

I also used an Infrared gun and the temp at the thermostat was approx. 180 degrees when the gauge read 200.

 

[achris]

Re: Mercruiser 3.0 Possible Overheating Issue

In a drum, the water level needs to be around the cav plate. Any lower than that and the water pump won't pick up the water. One interesting test, put the muffs on again, and without the engine running see if water comes up to the thermostat housing. It shouldn't... If it does, that indicates the water pump blades are not sealing on the housing, allowing water to by-pass... and it shouldn't do that.

Chris......

 

[Bondo]

Re: Mercruiser 3.0 Possible Overheating Issue

Thanks guys.... I have a little more info.
I used a barrel tonite instead of the water hose and rabbit ears. The lower unit was not taking in any water. I had no water at the thermostat. The temp climbed over 200 with or w/o a thermostat. I presume my impeller is bad?

I did check the gauge by grounding it. It checked good.

I also used an Infrared gun and the temp at the thermostat was approx. 180 degrees when the gauge read 200.

Ayuh,.... Always,... Always, start there, Whenever there's an Overheat issue....

 

[onegoodoleboy]

Re: Mercruiser 3.0 Possible Overheating Issue

Thanks Chris.... I added more water to tank and now it is pumping but still climbing to about 210 at idle after about 10 minutes. It is pumping water out of transom plate.... but it isn't even warm.... maybe 20 degrees warmer than tank water. I will put rabbit ears back on and see if water comes out at thermostat housing with motor not running.

 

[onegoodoleboy]

Re: Mercruiser 3.0 Possible Overheating Issue

Using rabbit ears with water on.... no water comes out of thermostat housing with boat motor not running.... Impeller ok then?

 

[onegoodoleboy]

Re: Mercruiser 3.0 Possible Overheating Issue

Any good way in verifying that my Sending unit is good?

 

[achris]

Re: Mercruiser 3.0 Possible Overheating Issue

Any good way in verifying that my Sending unit is good?

Only with an IR gun, or substitution with a known good one.

Chris.......

 

[onegoodoleboy]

Re: Mercruiser 3.0 Possible Overheating Issue

Thanks Chris... I checked thermostat housing with IR gun... It checked 150 max when gauge showed 200.

 

[achris]

Re: Mercruiser 3.0 Possible Overheating Issue

Thanks Chris... I checked thermostat housing with IR gun... It checked 150 max when gauge showed 200.

Well, there you go. Now you need to determine which is faulty, sender unit or gauge...

 

[onegoodoleboy]

Re: Mercruiser 3.0 Possible Overheating Issue

Well I put un a new factory temperature sending unit. Temp still gets to 200 deg on gauge. I checked my wiring by grounding the sending unit wire, it pegged. I also used an IR gun on engine and nothing over 150 degrees no where. I have water coming out the starboard side transom plate but just a water mist out of port side. Should i have water in both sides? I believe the only other thing that can be wrong is the actual gage in the dash?

 

[achris]

Re: Mercruiser 3.0 Possible Overheating Issue

Water out of only one side it not a problem. It just means it's the easier path for the water to follow. If you take the exhaust pipe off (you need to pull the engine first), you'll see that they are from the same place anyway.

Chris........

 

[onegoodoleboy]

Re: Mercruiser 3.0 Possible Overheating Issue

Still not fixed!

Below are some facts:

1) I am utilizing a barrel full of water with the lower unit lowered well below the pump inlets.
2) I have replaced the temperature sending unit, no change.
3) I have replaced the thermostat with a factory replacement (160 degrees).
4) I replaced the spark plugs MR43LTS with R44LTS.
5) I have tested my water temperature gauge, and it is good.
6) I have grounded out the tan wire going to the temperature sending unit and it pegs the temp gauge, therefore my wiring is good.
7) I also ran a wire directly from the gauge to the sending unit and it still went 180 degrees plus.
8) I have removed the thermostat and there is no issue with overheating.
9) I have removed the inlet hose to the thermostat housing, and started the motor and I have good water pressure there.
10) I have removed the exhaust hose to the thermostat and started the motor, water is coming out of the thermostat very good. there is also some water flowing out of the hose, is this correct?
11) I have good discharge water coming out of the transom plate on the port side, but only a spray coming out of the starboard side. The port side water coming out, maybe 20 - 30 degrees warmer than what it is taking in.

With all this being said, what do you guys reccomend that I do next? Could I still have a bad impeller?

 

[achris]

Re: Mercruiser 3.0 Possible Overheating Issue

Water pump output test. Also (long-shot) I'd put a section of clear hose in the water inlet (between transom and thermostat housing) and make sure you have a good solid water stream (no bubbles)... Are you referring to the Merc service manual?

Chris.......

 

[onegoodoleboy]

Re: Mercruiser 3.0 Possible Overheating Issue

Thanks Chris.... Yes I am.... I am getting worried, I just spoke with a mechanic, and he said that I may have blown a head gasket?

 

[achris]

Re: Mercruiser 3.0 Possible Overheating Issue

Yes, that's also possible. But no big deal. Replacing a head gasket on those engines is pretty simple...
Have you done a compression test? Or a leakdown test?

Chris.....

 

[onegoodoleboy]

Re: Mercruiser 3.0 Possible Overheating Issue

i have not done either....

 

[onegoodoleboy]

Re: Mercruiser 3.0 Possible Overheating Issue

If I had a blown head gasket, would the temp with the IR gun be reading high?