Merc 3.0 I/O couple questions

Pet982

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Apr 9, 2013
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I have an 07 3.0 with 113 hrs on it and now the season is winding down I wanted to address some minor things that I noticed of the summer.

We bought it brand new in 08, its moored and used mostly in a brackish river.


Issue 1

Trim sender has an erratic gauge. I took the starboard sensor apart and cleaned it with all parts are good and clean. I tested the rotor with a MM and get continuity across it on the very top and bottom of one side. The gauge now will show down with the out-drive fully down and fully up in any other position and will jiggle around when the drive is moving.

I see the rotor is available from Merc. does that sound like it will fix my problem?

Issue 2

This summer it seemed to me that it ran a little hotter then it has in the past. At speed over 15 mph it would be around the 185 mark but at idle/headway it would drop to the 175. My IR thermometer shows the motor in the 170 range.

On the hose it stays at the 175 and in the past I swear it would be just above the 150 mark. I took the T. Stat out and ran it on the hose with it out. Full water pressure gauge would not raise above 100 with the hose at 1/4 open it stay at the 160 mark.

I tested the t-stat on stove (its the original factory 160) it would start to open at 176, fully open by 180 and be closed again at 160. I ran this test 3 times with the same results.

The impeller was changed 2 years ago only because its was 8 years old and I probably should.

The elbow is original and I have taken it off to inspect its condition yet.

Every spring the water pump on the block seems to get stuck to the case and tap with a rubber mallet fees it and away we go.
 

Grub54891

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Jun 17, 2012
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Put a new thermostat in, they are cheap enough. Replace the circulating pump with a marine style. The pump you have sounds to be automotive, the rotor gets rusted to the housing in plain water. A marine pump has a stainless rotor to prevent that issue. And check the elbow too. Brackish water can corrode things.
 

muc

"Retired" Association of Marine Technicians...
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1. If the trim sender wires look good, no cracks in the insulation. I would try the rotor 1st.
2. Thermostat is starting to bad. Might want to replace it.
3. Might want to start running some non-tox antifreeze through there during winterizing. And start keeping a close eye on the circ pump weep hole. Having to "tap' it in the spring isn't normal.
 

muc

"Retired" Association of Marine Technicians...
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Put a new thermostat in, they are cheap enough. Replace the circulating pump with a marine style. The pump you have sounds to be automotive, the rotor gets rusted to the housing in plain water. A marine pump has a stainless rotor to prevent that issue. And check the elbow too. Brackish water can corrode things.

Saw a lot of cast iron impellers back when we had to do the check for MerCruiser service Bulletin No. 2013-05R1. But I have no idea about 3.0L engines because I never see those. I'm guessing this is one of the reasons MerCruiser now requires antifreeze during winterize.
 

alldodge

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MerCruiser now requires antifreeze during winterize.

IMO only, bet Merc says to use AF to help save some DA's from not draining everything and getting a busted block.

All marine engines I've worked on have brass or stainless, but I'll never say I've done as many as you have

That said, if the original poster needs to hit the water pump, it needs to be replaced
 

Pet982

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Apr 9, 2013
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Thanks for the input. Should I stick with Merc/Quicksilver for the T stat or is aftermarket ok (I know marine only)?

Does anyone know the P/N of an OE kit with the gaskets?

I Don't know why but I've stopped putting antifreeze in the block 19 years ago and even before then I only added 1/2 gal into the block and manifold just in case.

This one since new would stick. The first couple of years it would break free right when she started for the first time. (thought it was the power steering pump at first but the dealer found nothing when it was under warranty wrong with it) Then it evolved to starter couldn't spin it over that's how I found what was locked up and took the pump off to free it up. The impeller looked fine with no rust (SS). Now if the belts are loose enough she will crank and the belts will slip. But all it take is a tap with a mallet, and I mean a tap like was freeing a stuck window sash. It never sticks until the next spring.


Replace the circulating pump with a marine style. The pump you have sounds to be automotive, the rotor gets rusted to the housing in plain water. A marine pump has a stainless rotor to prevent that issue. And check the elbow too. Brackish water can corrode things.

If its got an automotive pump in there then Merc installed it on the assembly line.
 

13crazyhorse

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Apr 4, 2010
Messages
147
IMO I have found good aftermarket parts like Sierra to be as good as Mercruiser for sometimes a fraction of the cost, your call. I never could figure out why somebody would winterize a 5K engine without taking a few minutes and $10 worth of antifreeze to run through it then drain everything. I know I'm gonna get blow back on both of these opinions so have at it.
 

muc

"Retired" Association of Marine Technicians...
Joined
Jul 7, 2004
Messages
2,064
Thanks for the input. Should I stick with Merc/Quicksilver for the T stat or is aftermarket ok (I know marine only)?

Does anyone know the P/N of an OE kit with the gaskets?

I like OEM and the added cost isn't much compared to the consequences.

I suggest searching for parts with the engine serial number.
 
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