a few questions about 3.0l merc after first run of the year.

[beason]

I did a little work on the engine, and boat in prep for this year. new plugs, starter, prop, and bilge float were completed by me. Bellows, impeller, gimbals, and shift cable were all done by a reputable shop. I went from a 21p prop to a 19p prop.

I started it here on the muffs before we left, and it fired up as soon as i hit the key, so i felt pretty good about it.

got the boat in the water, and made sure there wasn't any water coming in from the bellows, etc. Then went to fire it up. It took a bit to fire, and i ended up having to give it a little gas to get it to fire. Once it started it ran good. we did a little pass up the river, and checked for water again, before heading out to the lake. I noticed that it was not spinning as fast on the starter as it was here at the house. I can only assume this is because of the water resistance.

I was seeing temps of about 150 at cruising speed, but it would climb closer to 170 at WOT. I was seeing speeds right at 40mph and rpm about 3500. I think. Ill have to look at the gauge again to verify. These were both on the dash, no GPS speed.

Every time i shut off the boat it would diesel. and would be semi hard to start again.

I did notice better takeoff and a lot faster planing with the new prop, and i didnt see a drop of water in the bilge, so those are both +1!!

Sorry for the long post, so ill summarize.

merc 3.0l on a 99 searay 180

40mph @ 3500rpm @ WOT Is this acceptable?

what would cause dieseling, and having to give it throttle to start? None of the work i did messed with the carb adjustments.

slower spin on start up from the starter, in the water, opposed to on the muffs. Is this normal as well?

 

[FourWinns86]

Re: a few questions about 3.0l merc after first run of the year.

I think you're running a little hot, my 3.0 was around 160 at cruising then eventually started to overheat until I put a new impeller kit on and now it runs at 120 when cruising all day long (31 mph)

 

[beason]

Re: a few questions about 3.0l merc after first run of the year.

thanks for the reply. The water was pretty warm, but im not sure how much effect that has. The impeller is brand new. They just replaced it last weekend. Could it be caused by something else?

 

[Don S]

Re: a few questions about 3.0l merc after first run of the year.

Being a 99, you should have a 160? thermostat in it. Under power, 170 to 175? is normal. 120 is too cold and would indicate you need a new thermostat.
The 160? thermostats START opening at 160.

Your dieseling problem could be idle rpm, (needs to be under 750 rpm) and you need to let it idle and cool down for a minute or two before shutting off.

You should also have a Max WOT rpm of 4400 to 4800. If not, you could be over propped and that in itself can cause an overheat.

When was the last full tuneup, timing check, and idle mixture adjustment?

It all has to work together.

 

[beason]

Re: a few questions about 3.0l merc after first run of the year.

Being a 99, you should have a 160? thermostat in it. Under power, 170 to 175? is normal. 120 is too cold and would indicate you need a new thermostat.
The 160? thermostats START opening at 160.

Your dieseling problem could be idle rpm, (needs to be under 750 rpm) and you need to let it idle and cool down for a minute or two before shutting off.

You should also have a Max WOT rpm of 4400 to 4800. If not, you could be over propped and that in itself can cause an overheat.

When was the last full tuneup, timing check, and idle mixture adjustment?

It all has to work together.

Thanks for the reply Don, i was hoping you would come along.

That makes sense if the thermo is a 160, that is about right. I know the gauges aren't extremely accurate, so the 150 line could be 160.

I was idling at the line just over 1, so that would be 1100? that is a bit high. Ill adjust the idle. Does this need to be done in the water, or will muffs work?

I did notice the temp shoot up pretty high once when i stopped to pick up the down tuber. I will remember to let it idle a bit, just dont like them/rope in the water and the engine running.

It may have been 4500rpm. ill have to look at the gauge again. I didnt write it down, and could be wrong. I know it was between two numbers, so it may have been 4-5 instead of 3-4. My back was hurting pretty good on the way back, and i was just trying to get back to the ramp.

I dont have the info on a tuneup, although i know the PO had it in the shop for other things, and im pretty sure they changed the engine oil, and replaced the trim senders.

how hard would it be for me to do the tuneup? I can get a timing gun. Would a can of seafoam do me any good? the engine only has about 220 hours on it.


So, if it was 4500rpm, i should be good on that and the speed. right in the sweet spot. So the prop i got is good.

the temps are within range, so that is good as well.

All that is left is the dieseling and high idle.

thanks again in advance to all who reply. Im learning as fast as i can!!

Edit: the manual states to back the idle screw off the lever. then screw it back in until it touches, and then 2 full turns after that. Should i set it back to factory, or just adjust from where it is? How accurate is the dash tach?


any ideas on the hard start? would high idle do the same there?

 

[FourWinns86]

Re: a few questions about 3.0l merc after first run of the year.

Being a 99, you should have a 160? thermostat in it. Under power, 170 to 175? is normal. 120 is too cold and would indicate you need a new thermostat.
The 160? thermostats START opening at 160.

Ok sorry Don, I was just going by my situation, I have an 86 3.0 and it was at 120 all day, are you saying I should be replacing my thermostat?