1991 Mariner Magnum II 150HP Coolant and Exhaust system details needed

[andrey_2004]

Hello experts!
My recent project has been to rebuild the 1991 Mariner Magnum II 150HP (2.5l V6 outboard). Problem was that the 1st piston/cylinder overheated and melted. I got the motor in this condition, and there were a few possible explanations to the failure. 1 - Thermostat failure, and 2 - top crank oil seal leakage. Second is what I am leaning towards since it would cause a lean condition only on this cylinder. If it was coolant failure, then at least the next cylinder would also be affected base on how severe the first was. Anyhow, the repair was a success. Block was bored to 0.015 (1st cylinder only), and the rest were honed. Heads machined flat as well as top block surfaces. We also replaced most gaskets that came in the gasket kit, and water pump was rebuilt. Carbs were not touched or re-adjusted. Reason for that was that plugs were perfect and cylinder/piston condition for the rest 5 cylinders was good before re-build. Motor now has original 5 piston assemblies (including original rings) and only 1 new piston assembly on cyl 1. Reason for not replacing rings was like I already said good condition, good gaps and good compression (and of course the high price for new rings $420). Wiesco rings did not fit Mariner pistons ($120 for those).

My concern is that during start-up, for first 20 seconds or so, we have exhaust fumes coming out of pee hole and when I removed thermostats, the smoke is there also, then water comes up and flows just fine. Water pressure is very good, and thermostats are working well. Water coming out of pee hole is very warm - 180 degrees or so. Should it be this hot? It makes sense because the water line is connected after the thermostats, and so if those are closed, then there is very little water seeping through, but when motor is warm, water comes out of pee hole after it flows though cylinders, so it is hot. We also have a constant water leaking though tiny hole on the poppet valve all the time, which accumulated inside the motor covers - is this normal? We did install a new poppet diaphragm and 2 large gaskets. Everything else is original. Oil flows into every cylinder just fine.

So to summarize, I am looking for answers on the fumes inside cooling lines, pee hole water temperature, and poppet valve hole water discharge. I will give more details if needed. Many thanks in advance!

 

[Dukedog]

So to summarize, I am looking for answers on the fumes inside cooling lines, pee hole water temperature, and poppet valve hole water discharge. I will give more details if needed. Many thanks in advance!

Ya got something very wrong if exhaust in coming from tha pee discharge hose/stat openings. Probably a gasket (hopefully) somewhere. Next you have not isolated tha original problem. A single cylinder mess up is usually one of these three things, "electrical" (timin for that cylinder, cross/double fire etc,) issue, fuel delivery (usually carburetor) issue, coolin' issue.. Water temp discharge after stats open in no way should be that hot. Stats should open at around 143 degrees. Max timin'? Original electrics? Water comin' from tha tiny hole at tha poppet indicates something wrong in there as well. This could have also been tha original problem or a contributor to it........Your good water pressure? On tha hose or in tha water" What is it ? At idle, at speed?

Checkin' all that will keep ya busy for a little while. Get back to us.....

Ya shoulda done a tad more research on parts. Those rings (real Merc) are around 240 retail (under 40 bucks per pair) for all 12 from pro marine. Is your motor a 3 3/8's bore or 3 1/2 inch bore? Reason I ask is a Mag II (XR4) is a 2.4 and a Mag III (XR6) is a 2.5. Both were built in that year......... .

Coolin' dia here. Tha very first one is for older motors. Yours will be tha last one on tha right in tha second row.......

https://www.google.com/search?q=merc...w=1329&bih=665

Exhaust is simple. out tha hole and down to tha bottom. Exhaust chest might be your "leak" That's a place where water and exhaust can meet (divider plate n gasket) if something there is not right. Only other place is head gaskets and/or crack. Normally either of these conditions will show water in a cylinder also.......

 

[Faztbullet]

More likey the stablizer/advance module took out #1

 

[Dukedog]

Forgot 'bout that one. WTH! I'm old....................I've earned that right!.

 

[andrey_2004]

Thanks Dukedog and Faztbullet! Here is more info/thinking... Dealer told me that motor is a "175HP" but labeled as 150hp because of the crank vs. prop rating. My piston cost me $230 ($225 at Boats.net) and rings kit is $419 at Boats.net ($475 at dealer). So it has 3-1/2 diameter cylinders. Motor SN 0D038327. The 150HP model parts are all much cheaper.

Motor is on a 1995 Bayliner 25ft Deck boat.
After rebuild, we tried to use muffs, but hose water flow rate was not good, so we took the boat into our lake and tested there.

Smoke only comes out of 'pee' hose, and NOT cylinder heads. We had to disconnect the thermostat hoses to see it, or feel the pressure of exhaust by hand. When everything is connected, there is no actual visible smoke, but we can feel pressure at pee hole for first 15-20 seconds or so depending on idle RPM's. Coolant hose connects both heads at top, then comes down and tee's off into smaller hose going to 'pee' and the second larger hose to very bottom of motor and into the warm water discharge channel. So, the only way for water to flow good at idle into pee hole is when thermostats are open. When they are closed, water 'spits' out as it seeps through thermostat bleed holes at idle. This pee hose connection explains the slight pee 'delay' at start, because air needs to first get out of cylinder heads, and at idle, water is not getting there that fast. Hose routing also explains why water feels hot (not burning hot). I will measure the exact temp of it next weekend. But comparing to a 105 deg water at home, I think it will be somewhere between 130-150 deg. (When water was flowing out of thermostat holes, no air was coming out with it. So if there is a a leak, then it would only be at the exhaust chest.) Also, when we had both thermostats and hoses disconnected from cylinder heads and started the motor, after a 10-15 second delay, water came up as it filled the block, and there was NO bubbling, meaning nothing is leaking in there. With a thermostat and hose disconnected, water slowly was coming out of CH hole, and when we increased RPMs, flow increased. We then place a finger on top to see if it resists, and it sprayed water all over, meaning pump is working.


Head gaskets are new, both block cylinder top surfaces machined down flat, and so were head covers. Cylinders did not show any presence of water by checking plugs after running it on a lake for about 20 minutes.

We already ran the motor on a lake for about 35 total minutes before my first post here, and did not have any overheat condition. All plugs were oily (wet) after running the boat at about 25mph, and were slightly warm. They are Marine cold plugs (flat) as recommended by dealer. We stopped multiple times and splashed lake water over the block and it was not evaporating fast, drying evenly across all cylinders. I am beginning to believe that there is no coolant issues other than poppet valve, but I'm afraid of being wrong after already spending close to $1,500 for parts. I will check the surface temperature of each cylinder and water temperature next weekend and will post it here. Will check both idle temps, and after running it at higher RPM's. I do have a timing gun, but forgot to check with it, so will also do that.

What is the stabilizer/advance module? Could you help with a p/n? I would rather replace it right away.
Again only 1st cylinder had severe overheat to the point that aluminum holding the cylinder sleeve 'shrinked' down and so sleeve was sticking up by 0.008 - reason for milling the whole surface down.
Older gentleman at machine shop said he has not seen anything like this before, and said it was most likely caused by lean condition resulting from oil seal leak. Right now spark plug on that cylinder looks just like the other 5 after running it.

Sorry for so many details, but I'm trying to give out every detail I ran into...

 

[Dukedog]

Ya might start usuin' ProMarine. Most of their stuff is top shelf and some even come in Merc packaging.......Plugs BU8H or BUHW's?

First your "dealer" doesn't know his Merc/Mariners. They quit rating tha horse power at tha crank in '83//'84. Everything after that is prop rated. That's a given. If your motor is a carbureted 2.5 150 its an Mag III (XR6) Its tha only production carbureted 2.5 150 they build. Not tha MAG II which is tha piston port 2.4.fat block for that year.

Second ya need a water pressure gauge and good, solid temp readings. Address tha poppet drip deal.

Alrighty then. Your not in as much trouble as ya think. Tha "pressure" you feel at tha discharge before tha stats open is coming from tha adapter plate. There is a hose that ties into tha adapter plate then "T's" into tha discharge from tha port head. That part works in conjunction with tha pressure in tha adapter plate.

Tha module (get rid of it, over priced and not necessary) is one of tha two that are about 2 1/2" X 3 1/2 inches. One will be tha oiler module with a bunch a wires. Tha one you want will have 3. A blk (ground) a white/blk, a red/white wire. Blk probably termed close to tha box. Tha other two will go to tha switch box. Red/white will be piggy backed on same color wire on tha top of tha switch box..Disconnect tha one goin' to tha module. Tha white/blk may or may not be that way. If it "LOOKS" like two individual white/blk wires its because its made up in a joint right above where they are termed on tha two switch boxes. Joint will be under tha plastic shield and/or taped. If it is tha easy way to fix it is to make a short jumper with a piece of tha white/black to tie tha two switch boxes together. That jumper is all that's needed when tha module goes away...... Once ya get rid of tha module set max timin' at 22 degrees advance and lock it down. Some say go as much as 25 degrees but I only do that if tha flywheel is indexed and I know tha value of each cylinder.

May not be clear enough but if not let me know..

JAN. Your "older gentleman" is kinda on tha right track but this is not in anyway uncommon with these motors when it comes to a piston failure. Tha TRICK is ta figure out which scenario caused it........Sometimes ya gotta bite tha bullet and "fix" everything that might have been...........

One other thing..I use tha Mercury Marine (aka Merc Net) website for all my stuff as far as look up. It shows your serial number as invalid? It matches an exact number to THAT motor. Not a serial group like most...........

 

[andrey_2004]

The spark plugs are BU8H.

After leaving motor in up (tilted up) position for a week, i had very hard time starting it. Eventually it started running, but a bit rough. I tried to check timing with timing light gun, but do not see marks at all on CYL1. I have a feeling that flywheel is not positioned properly with the 6-8 screws. Will check that.

I found the Idle advance module, and there are two wires going to it. The red/white and black/white. Single wires each - not two. What are the "two switch boxes" that I am tying together? and which wires are being connected together? There is only one for timing and the other is for oiler module. In addition to the jumper (once I know what to jump out), do I just leave the red/white disconnected?

Also, not sure if it is necessary, but here is what we have on this boat:
Oil storage tank. On motor oil tank. Oil line coming out of oil pump and connecting into a T right where fuel line connects. What concerns me is a label next to fuel tank camp saying to premix oil 50:1 ratio. I have a feeling that is done only if that oil line doesn't connect to fuel line, but not sure. There is plenty of oil inside cylinders as they get fouled, and I can even see it 'drip' on cylinder 4.

Bought XR6 service manual online, and motor looks slightly different than mine. I still think mine is a XR4, and the motor cover also says Magnum II.

Trying to set the idle also, as we have to push the throttle a bit to hold it somewhat steady, but I think timing might be the issue, so I will resolve that first.

(I somehow now wish a good mechanic could come out to adjust this thing .... )

 

[andrey_2004]

Just to clarify, it would not start because plugs would get fouled fast, and gas was not coming (possibly because it was tilted). Anyhow even though I don't like to use starting fluid, I had to use it for about 2 minutes until motor finally could run on its own.
In regards to too much oil in cylinders, the secondary (on board) oil tank is always pressurized, and so I think that oil might be leaking into motor when it sits.

 

[Dukedog]

The spark plugs are BU8H.

After leaving motor in up (tilted up) position for a week, i had very hard time starting it. Eventually it started running, but a bit rough. I tried to check timing with timing light gun, but do not see marks at all on CYL1. I have a feeling that flywheel is not positioned properly with the 6-8 screws. Will check that.

It has to be trimed all tha way down and use tha enrichner to start after pumpimg tha bulb up.

I found the Idle advance module, and there are two wires going to it. The red/white and black/white. Single wires each - not two. What are the "two switch boxes" that I am tying together? and which wires are being connected together? There is only one for timing and the other is for oiler module. In addition to the jumper (once I know what to jump out), do I just leave the red/white disconnected?

Tha switch boxes at tha two mounted on tha starboard side with all tha wires going to them. Top left stud on each will have a blk/white wire on them. Disconnect both. Make a jumper from one of tha blk/white that you removed. Tha jumper will tie both boxes together at tha studs you removed 'em from. Your better off to completely remove tha module. Neither of those two wires go to tha oiler module nor tha red/white


Also, not sure if it is necessary, but here is what we have on this boat:
Oil storage tank. On motor oil tank. Oil line coming out of oil pump and connecting into a T right where fuel line connects. What concerns me is a label next to fuel tank camp saying to premix oil 50:1 ratio. I have a feeling that is done only if that oil line doesn't connect to fuel line, but not sure. There is plenty of oil inside cylinders as they get fouled, and I can even see it 'drip' on cylinder 4.

Not sure 'bout this. Never seen that before!


Bought XR6 service manual online, and motor looks slightly different than mine. I still think mine is a XR4, and the motor cover also says Magnum II.

Trying to set the idle also, as we have to push the throttle a bit to hold it somewhat steady, but I think timing might be the issue, so I will resolve that first.

(I somehow now wish a good mechanic could come out to adjust this thing .... )

You said it was a 3.5 inch bore. That's a 2.5 which is a MAG III, XR6........ MAG II, XR4 is 3 3/8 inch bore 2.4. That's tha way it is.......So is it 3 1/2 or 3 3/8 ????

There ya go..........Never ever use ether in a 2 stroke. It WILL kill it. use fuel oil mix.........

 

[sam am I]

In regards to too much oil in cylinders, the secondary (on board) oil tank is always pressurized, and so I think that oil might be leaking into motor when it sits.

Nope, by the nature of the design, they can and will hold pressure for some time. In both tanks in fact.

The oil BTW, has to first mix w the gas, then go into the carbs. You don't have a direct path of oil into the cylinders w these carb'd motors. Only Gas/oil mix.

 

[andrey_2004]

Just an update... Eversince the motor overhaul last season, I have learned much about this motor which still runs very strong. We have been riding it at 5,000 - 5,300 RPM most of the time as we pull kids (a lot of kids ) on tubes and banana boats. Not sure how much longer the partially overhauled motor will last, but it has now worked for quite some time. All minor/major issues have been resolved. Thanks for all the help!