Mercury Black Max 150 wont cool motor

[hemijosh426]

I recentley bought a boat in a bunch of pieces and put em back together. I bolted a 1986 powerhead to a 1991 25inch lower unit. It starts right up 150- 155 compression in each cylinder, and i cleaned carbs. I did notice the carbs leak as if the needle and seat are bad in the middle set of carbs. The main problem is that I cant get water to flow thru the motor. I replaced the impeller, and when i fire it up i cant feel the heads getting cool and there is no pee stream. Water flows out thru the prop though when the motor is running. I pulled plugs out to see about the flooding problem due to needle and seat and the one lower plug on the left side if looking from the back had some water spots on it. So i compression checked it and it came out with 150 just where it was before i tried running it. That leads me to think its not a blown headgasket, but maybe water from somewhere else?

Does anyone have any ideas what else to check? Thanks

 

[sschefer]

Re: Mercury Black Max 150 wont cool motor

Never seen a stock 150 ever pump 150lbs compression. You would need to be running 93 octane fuel at a minimum. Are you sure your gage is correct?

 

[j_martin]

Re: Mercury Black Max 150 wont cool motor

Pressure gauge would help a lot, but for now I'd venture that the poppet valve is stuck open, or assembled wrong.

 

[Dukedog]

Re: Mercury Black Max 150 wont cool motor

Never seen a stock 150 ever pump 150lbs compression. You would need to be running 93 octane fuel at a minimum. Are you sure your gage is correct?

Yeah, thats kinda high for a stocker.
Start by makin' sure all tha hoses goin' ta tha tell-tale or clear of tiny varmits and/or bug larve. If that don't work, replace tha whole pump assy. not just tha impellar. Replace t-stats. Poppit

If not tha head (check for being flat) or head gasket, check divider plate (flat, cracks) and gaskets...........Replace gaskets with new. Thats a given when ya pull tha divider plates...............

 

[nbnewbie]

Re: Mercury Black Max 150 wont cool motor

check base plate compatibility

 

[Dukedog]

Re: Mercury Black Max 150 wont cool motor

check base plate compatibility

Shouldn't make any difference other than exhaust holes (block ta adapter). We cross breed 'em all tha time without any problems...................

 

[hemijosh426]

Re: Mercury Black Max 150 wont cool motor

Where are tstats and poppit valves? The gauge is brand new, but that doesnt mean its accurate i will try an old gauge tommorow morning. I thought that seemed high. Why does water flow thru the prop but not the heads?

 

[Bravo]

Re: Mercury Black Max 150 wont cool motor

Where are tstats and poppit valves? The gauge is brand new, but that doesnt mean its accurate i will try an old gauge tommorow morning. I thought that seemed high. Why does water flow thru the prop but not the heads?

The water flows outta the prop most likely cause its not getting pumped up to the block. I can't remember for sure, but does that particular impeller have a removable keyway on the shaft? If so, did you make sure it got reinstalled? I'd make sure of it. The shaft may be turning, but the impeller isn't kinda thing. Always start with the easy things first. Like stated before, check for blockages and dirt dobber nests. I'm always fighting those damn little boogers around my house. Also good advice and cheap insurance to replace the whole impeller housing assembly when you change the impeller. Just my .02

 

[Bravo]

Re: Mercury Black Max 150 wont cool motor

BTW, tstats = thermostats.

 

[nbnewbie]

Re: Mercury Black Max 150 wont cool motor

The POPPET VALVE is a device in the cooling system which opens or closes in response to the pressure in the water cooling system. Generally the pressure in the cooling system increases with increasing engine speed. The poppet valve--a name which really just describes the shape of the valve and not the fact that it is associated with a pressure controlled response in the cooling system--is usually arranged so that when the pressure rises the valve opens and permits greater flow of cooling water. If this device is stuck in the "low" pressure mode (closed),
it can cause overheating in the outboard motor.

not consistent with what i've found here which is it?

 

[Dukedog]

Re: Mercury Black Max 150 wont cool motor

Where are tstats and poppit valves? The gauge is brand new, but that doesnt mean its accurate i will try an old gauge tommorow morning. I thought that seemed high. Why does water flow thru the prop but not the heads?

Water pressure guage? Where is it tied into tha system? Whats tha pressure readings? OEM manual? Two of tha main ingredients for workin' on this stuff for tha inexperienced.................

 

[SuperNova]

Re: Mercury Black Max 150 wont cool motor

The POPPET VALVE is a device in the cooling system which opens or closes in response to the pressure in the water cooling system. Generally the pressure in the cooling system increases with increasing engine speed. The poppet valve--a name which really just describes the shape of the valve and not the fact that it is associated with a pressure controlled response in the cooling system--is usually arranged so that when the pressure rises the valve opens and permits greater flow of cooling water. If this device is stuck in the "low" pressure mode (closed),
it can cause overheating in the outboard motor.

not consistent with what i've found here which is it?

That whole post is incorrect, sorry. The "poppet" valve is better known as a "pop-off" valve and it is a pressure control valve. It is normally held closed by spring pressure and when water pressure in the block overcomes the spring pressure, the valve is pushed open and bleeds off some of the pressure. If it is stuck open, it will not allow the block to fill completely. It is found on the lower part of the engine block just in front of bank 1 (right side standing behind the motor) and it is under a round metal cover that is about 1.5 inches in diameter and held on by two? 1/4-20 bolts (7/16 head).

 

[hemijosh426]

Re: Mercury Black Max 150 wont cool motor

Water pressure guage? Where is it tied into tha system? Whats tha pressure readings? OEM manual? Two of tha main ingredients for workin' on this stuff for tha inexperienced.................

Forgot to add it was a compression gauge. If you read the posts above we are talking about how 150psi seems high for stock compression. I have a manual, but I was at work when I asked the question. I will be taking the manual with me to work today and trying to study it, but I always like to ask the pros first because they know the little tips and tricks to every aspect.

All of my lines are clear, I took off the hose on the right side of the motor that points down and blew thru it and i heard the wind noise coming thru where the exhaust smoke hole is in the backside of the lower unit right below the powerhead. I guess its an exhuast smoke hole, its about 3/4 inch diameter on the left side of the motor.

I also removed the top left side 2 bolts where housing bolts to for a crossover cooling hose and looked inside and it was dry.

I made sure about the removable key when i installed the impeller the first time, but to make sure Im going to drop lower unit to see if anything changed.

So when water flows out the prop is that making it to the bottom of the powerhead and back thru the exhuast, or is that just passing thru the water pump and back out the prop?

THANKS FOR EVERYONES HELP!

 

[Faztbullet]

Re: Mercury Black Max 150 wont cool motor

it will not allow the block to fill completely

99% correct but block will fill with or without a poppet valve...

 

[SuperNova]

Re: Mercury Black Max 150 wont cool motor

I also removed the top left side 2 bolts where housing bolts to for a crossover cooling hose and looked inside and it was dry.


THANKS FOR EVERYONES HELP!

If I'm not mistaken, there should be an identical cover on the top right cylinder head, that crossover tube runs between them, and there should be thermostats under both of them.... Could be wrong though.

As far as the pop-off valve, I was told by a Merc mechanic (when I was having trouble with my tell-tale) that if that valve is stuck open, the engine will not fill completely and you may not get a good stream from the tell-tale. Doesn't mean he knew what he was talking about, though.

 

[Dukedog]

Re: Mercury Black Max 150 wont cool motor

Thats a 2 part ?. Do you have a water pressure guage and where is it installed if you do. Had nothing ta do with compression. Should have been a t-stat under that housing if its tha one I think your talkin' about.

Best thing ta do with all tha unknowns of this motor is start from square one. Bite tha bullet. Get new OEM pump kit, T-stats and poppet kit (including donut and grommet). Install tha new stuff just like tha book tells ya.

Ya also need ta take a peek inside tha hole you said showed signs of water. if its got intrusion tha piston top will be really clean compared ta tha other ones. If thats tha case do not run tha motor till you get that fixed.........

Like FB says. Block stll fills but you don't have tha same pressure with a poppet thats working. ie: hot rod coolin' systems DON"T even have a poppet.........

 

[j_martin]

Re: Mercury Black Max 150 wont cool motor

If I'm not mistaken, there should be an identical cover on the top right cylinder head, that crossover tube runs between them, and there should be thermostats under both of them.... Could be wrong though.

As far as the pop-off valve, I was told by a Merc mechanic (when I was having trouble with my tell-tale) that if that valve is stuck open, the engine will not fill completely and you may not get a good stream from the tell-tale. Doesn't mean he knew what he was talking about, though.

He knew what he was talking about. There's other water outlets besides the poppet valve and the thermostats. At low rpm, if the poppet valve is stuck open, the water will drain out faster than the block is filling. It's being filled by a positive displacement pump, not a centrifugal pump, so flow is almost entirely dependent on rpm. The upper cylinders will overheat, as well as the temp sensor, and the telltale will steam.

Poppet closed, at idle, and the block will fill to the thermostats with about 5 lbs pressure. T-stats open may drop it to 2 lbs, but will cool and flow nicely. If the poppet is stuck open, or mis-installed, the block may not fully fill with water at idle.

Most of this can be discerned with a WATER PRESSURE GAUGE. Sorry for yelling, it's important.

hope it helps
John

 

[nbnewbie]

Re: Mercury Black Max 150 wont cool motor

don't be sorry the whole post is not incorrect and it came straight from mercury marine tech support but then they might not know what they're talking about either something to consider is that when everything is working properly on this v6 it is my understanding that incoming water frrom the water pump first goes straight up the inside center of the block and is routed from the top of the center of the block to everything else stats, cyl walls, heads, pop-off valve, telltail, exhaust, and out the prop hub it is for this reason that i think someone would want to know if they are getting water to the top center of the block and other than perhaps a visual check from an outlet of some sort a water pressure guage is the next best thing once you have determined there is adaquate water at the top center of the block the engine should run at a proper temp if it doesn't you can then diagnose what it is about the cooling system that is not working i agree that 150 psi cyl compression is high but i would think it unlikely that that alone is the root cause of overheating the shaft key on the impeller is a good thing to check right while you're there make sure the impeller blade tips are facing the correct direction

 

[Dukedog]

Re: Mercury Black Max 150 wont cool motor

a water pressure guage is the next best thing

Not tha NEXT best. Its tha FIRST thing ya need when lookin' for coolin' problems. Maybe John needs ta yell a little louder..................

 

[j_martin]

Re: Mercury Black Max 150 wont cool motor

don't be sorry the whole post is not incorrect and it came straight from mercury marine tech support but then they might not know what they're talking about either something to consider is that when everything is working properly on this v6 it is my understanding that incoming water frrom the water pump first goes straight up the inside center of the block and is routed from the top of the center of the block to everything else stats, cyl walls, heads, pop-off valve, telltail, exhaust, and out the prop hub it is for this reason that i think someone would want to know if they are getting water to the top center of the block and other than perhaps a visual check from an outlet of some sort a water pressure guage is the next best thing once you have determined there is adaquate water at the top center of the block the engine should run at a proper temp if it doesn't you can then diagnose what it is about the cooling system that is not working i agree that 150 psi cyl compression is high but i would think it unlikely that that alone is the root cause of overheating the shaft key on the impeller is a good thing to check right while you're there make sure the impeller blade tips are facing the correct direction

Koine Greek doesn't use capitalization or punctuation. Is that what this is?