Merc 3.0 Overheating

[tedstur]

Greetings. I have been combing these threads looking for answers. My boat is getting hot. It shoots up to 175 at idle and goes up from there if I give it more gas.

Mercruiser 3.0, Serial number 1A000334 (2004 ish), freshwater boat.

These are the steps I have taken thus far:

1. New impellor - old one looked fine, but replaced it anyway
2. Oil change
3. New thermostat
4. Replaced the temperature sensor
5. Removed and inspected the water pump - looks great, it did not need to be replaced

That leaves the exhaust manifold... which I hate to do. Before I try to tackle that job, any other advice for me? Is there a way I can test for water flow before I take off that manifold?

Also, can I remove the exhaust manifold, clean it, and put it back on OR is it 100% that if it is gunked up I will need to replace it?

THANKS for any and all input.

 

[Chris1956]

Check your compression. A leaking head gasket can also cause overheat.

Was the boat always used in freshwater? Exhast manifolds in salt water only last 10 years at most.

 

[tedstur]

Yes, original owner had it on a lake in Orlando, no trailer. I have had it on a lake just outside Orlando. I have taken over to the intercoastal once, just for three days. So... no saltwater.

I will check compression next. Good thought, though the oil is clear and there is no sign of water in the oil.

 

[Chris1956]

Compression can leak into the cooling passages, causing overheat. You can run it and check for pressure in cooling system. Not sure offhand how to do that, though.

 

[airshot]

The 3.0 can have warp issues between #2&3 so a comp check is a good idea. Also be sure the hose from the outdrive to the main water pump is clear. Have had that hose get clogged up in the past. Had my head resurfaced a few years back. Mine was hard to start, not bad enough to overheat

 

[tedstur]

So I finally got to the boat and did the compression test. 145 across all 4 cylinders. That is down about 8 pounds from a few years ago when a shop did a comp test on it.

So... I will pull all the hoses and check them next. Bleh.... I hate that job as it will probably be futile, but it is the next step.

 

[kenny nunez]

Most times the riser is what causes water flow problems rather than the manifold body. If you have a water hose supply try connecting the hose to the manifold inlet. The water should free flow through it.
A leaking head gasket builds up enough pressure where it overcomes the pressure from the water pump. Add a piece of clear hose on the incoming supply hose. If the head gasket is the problem the water will disappear in the clear hone with the boat running on plane.

 

[tedstur]

I pulled the hoses, no problem. Water is entering the supply hose. Exhaust manifold is in good shape, as is the riser.

I just notice that the two water outlets on the transom are not both spewing water, just the one. Here is a video of it:

Not sure what to make of that. Could it blocked AFTER the riser? Seems strange that it would be.

 

[Scott Danforth]

I just notice that the two water outlets on the transom ......

Not sure what to make of that.

tilt the boat a bit to the other side and water will come out the other idle relief port hole.

you are over thinking that.

 

[airshot]

Pull the riser apart and see if the flappers are in place, if the come apart, they can create partial blockages....had that happen to mine.

 

[Scott06]

Greetings. I have been combing these threads looking for answers. My boat is getting hot. It shoots up to 175 at idle and goes up from there if I give it more gas.

Mercruiser 3.0, Serial number 1A000334 (2004 ish), freshwater boat.

These are the steps I have taken thus far:

1. New impellor - old one looked fine, but replaced it anyway
2. Oil change
3. New thermostat
4. Replaced the temperature sensor
5. Removed and inspected the water pump - looks great, it did not need to be replaced

That leaves the exhaust manifold... which I hate to do. Before I try to tackle that job, any other advice for me? Is there a way I can test for water flow before I take off that manifold?

Also, can I remove the exhaust manifold, clean it, and put it back on OR is it 100% that if it is gunked up I will need to replace it?

THANKS for any and all input.

Have you verified the 175 plus is accurate with an ir thermometer? Do you have a ps cooler Is it clear of debris. There is a test to verify water flow up to engine I think you want to see 3 qts in about 15 seconds .

 

[rolmops]

Your problem may be as simple as a thermostat not opening up when it should. Just for fun, remove the thermostat , run the engine and see what happens to the temperature