Mercury Black Max 150

[DaleBurris]

Just bought a boat with a Mercury Black Max 150. 1990 model and it runs great but I am having a heating issue. I have replaced the Water pump, Thermostats and Poppet Valve and it seems better but still wants to heat up a little if I am just barley crusing. I can run it up to 35MPH or faster and it cools right down. I did a compression check and it is all great......Any ideas where to go next? I am really lost now. Thanks in advance, Dale.

 

[Diamond Dave]

Re: Mercury Black Max 150

What do you mean by heating issues? Is the alarm going off? Or are you getting a high gauge reading? I believe your motor does not start to **** until the thermostats open. So if you?re feeling the stream of water being discharged and it?s hot that would be normal. If the thermostats open at say 140 then the water being discharged is going to be 140.

I have a 95 150 Black max that I?m working through a over heat issue as well.

 

[sschefer]

Re: Mercury Black Max 150

The 135/150 motors will run about 145-150 at idle and 130-140 at cruise in 60 deg water.

One typical mistake is to leave the slinger washer off. This is the one that looks like a garden hose washer and slides over the drive shaft ending up on top of the water pump housing. If you don't put it on, water floods the mid.

Another problem is with correctly seating the stainless steel tub in the water pump housing. There is a tang that fits in the indent and if it is not aligned, you'll loose volume and thus cooling even though pressure looks good.

A misaligned water tube will cause you problems, as well as a replaced tube that is just a little bit longer and jambed into the pump.

Believe it or not, that tube could fall completely out and you would still have water pressure but experience overheating problems.

I've probably fixed 10 of these types of problems this year alone. All caused by first time pump rebuilders that were too frustrated to go back and do it again. I make them watch me do it as a condition of free labor because I hate doing it too!

 

[Diamond Dave]

Re: Mercury Black Max 150

The 135/150 motors will run about 145-150 at idle and 130-140 at cruise in 60 deg water.

One typical mistake is to leave the slinger washer off. This is the one that looks like a garden hose washer and slides over the drive shaft ending up on top of the water pump housing. If you don't put it on, water floods the mid.

Sschefer,

What holds the slinger washer in place? What keeps it from riding up the shaft?

 

[DaleBurris]

Re: Mercury Black Max 150

The gauge is reading high and the alarm is going off. Once that happens I just get up to about 35 mph and it cools right back down. I am really lost at this point.

 

[DaleBurris]

Re: Mercury Black Max 150

The 135/150 motors will run about 145-150 at idle and 130-140 at cruise in 60 deg water.

One typical mistake is to leave the slinger washer off. This is the one that looks like a garden hose washer and slides over the drive shaft ending up on top of the water pump housing. If you don't put it on, water floods the mid.

Another problem is with correctly seating the stainless steel tub in the water pump housing. There is a tang that fits in the indent and if it is not aligned, you'll loose volume and thus cooling even though pressure looks good.

A misaligned water tube will cause you problems, as well as a replaced tube that is just a little bit longer and jambed into the pump.

Believe it or not, that tube could fall completely out and you would still have water pressure but experience overheating problems.

I've probably fixed 10 of these types of problems this year alone. All caused by first time pump rebuilders that were too frustrated to go back and do it again. I make them watch me do it as a condition of free labor because I hate doing it too!

Thanks for the info and I did double check all that and it all seems good. I went as far to do a compression check just to make sure and all cylinders are around 125-130. I am at a total loss now. It does not run hot really quick either it take a little while to get there.

 

[Diamond Dave]

Re: Mercury Black Max 150

Well like I said I?m working through a similar issue with my 150 Black max EFI motor but I?m not an outboard expert by any stretch of the imagination. So with that being said I think the issue might be in the pump regardless of the fact that it?s new. If it cools down when you?re running you?re forcing water through the cooling system so I would have to say that there isn?t any restriction in the system.

Did you put the pump in yourself or did you have certified marine Tech do it?

 

[sschefer]

Re: Mercury Black Max 150

The 135/150 motors will run about 145-150 at idle and 130-140 at cruise in 60 deg water.

One typical mistake is to leave the slinger washer off. This is the one that looks like a garden hose washer and slides over the drive shaft ending up on top of the water pump housing. If you don't put it on, water floods the mid.

Sschefer,

What holds the slinger washer in place? What keeps it from riding up the shaft?

Nothing, but it doesn't.

 

[Diamond Dave]

Re: Mercury Black Max 150

Nothing, but it doesn't.

Thanks sschefer.



Dale, I would get a heat stick or a laser thermometer and check the head temp when the gauge says it hot. Maybe the sender or gauge is out of calibration and giving a false reading. What is the temp gauge at when you're at speed? If it really is getting hot at idle it sounds like its not making enough pressure to pump or its bleeding off somewhere. That?s all I can really think of. Keep posting someone will help you figure it out. When you do please let us know what you found. Thanks,

Dave

 

[sschefer]

Re: Mercury Black Max 150

Thanks sschefer.



Dale, I would get a heat stick or a laser thermometer and check the head temp when the gauge says it hot. Maybe the sender or gauge is out of calibration and giving a false reading. What is the temp gauge at when you're at speed? If it really is getting hot at idle it sounds like its not making enough pressure to pump or its bleeding off somewhere. That?s all I can really think of. Keep posting someone will help you figure it out. When you do please let us know what you found. Thanks,

Dave

Dave, it sure sounds to me like its the water pump. That gasket kit comes with a bunch of different gaskets. The parts catalog shows which ones to use for your pump. Sometimes it's difficult to tell but if you put the wrong one on, it will fit but you won't pump water like you should.

That fact that it cools down at 35mph tells me you're finally making enough pressure to open the poppet which is really late. I think it's supposed to open aroun 1800-2000 RPM and the temp should fall off immediately. I don't think it's the poppet because the thermostats should hold you around 145-150 at idle and they're not and the poppet isn't even a player at idle pressures. If the poppet were stuck open, you'ld be running really cold at idle.

The poppet is a water dump so to speak. When it opens the water flows free out of the engine taking the heat with it. At idle the flow through the engine is restricted to what can flow through the thermostats. When the temp reaches 143 degrees, they open and let water out of the engine. There should be enough volume to adequately cool the engine and that doesn't appear to be the case.

 

[Faztbullet]

Re: Mercury Black Max 150

The gauge is reading high and the alarm is going off

1) Temp or pressure guage??
2) What did the old impeller look like when you changed it?
3) Was it missing any pieces? Was housing scored/worn?
4) Is this a brackish/salt engine?
5) Is barcode decal on port head shrunk?

 

[DaleBurris]

Re: Mercury Black Max 150

Thanks for all the help. I am going to double check it but the water pump that was in it was in great shape, The housing was not messed up or anything. It does have a good stream coming out at idle so that makes me think that it is not the water pump. I am just at a loss with this.

 

[Diamond Dave]

Re: Mercury Black Max 150

I have a 3 cylinder 25 hp Yamaha on my johnboat; the pee stream was coming out hard enough to push your hand out of the way put the motor was still overheating at RPM above idle. I pulled the head off and found the water passages where 90 percent clogged.

If mine still gets hot after I replace the poppet valve I will triple check I have the right water pump installed. After I can say it has the right pump and it?s installed correctly I will pull the heads and check the water passages. I believe the poppet valve is stuck not allowing the hot water to exit. I won?t be able to make repairs and test until the weekend put I will keep you posted. If you figure yours out let me know. Thanks,

Dave

 

[DaleBurris]

Re: Mercury Black Max 150

I have a 3 cylinder 25 hp Yamaha on my johnboat; the pee stream was coming out hard enough to push your hand out of the way put the motor was still overheating at RPM above idle. I pulled the head off and found the water passages where 90 percent clogged.

If mine still gets hot after I replace the poppet valve I will triple check I have the right water pump installed. After I can say it has the right pump and it?s installed correctly I will pull the heads and check the water passages. I believe the poppet valve is stuck not allowing the hot water to exit. I won?t be able to make repairs and test until the weekend put I will keep you posted. If you figure yours out let me know. Thanks,

Dave

I will and thanks again for the help

 

[hkeiner]

Re: Mercury Black Max 150

If you don't solve the problem with the good advice you already received above and you are looking for more advice, my advice is to install a pressure gauge on the motor and see what it tells you. Depending on what the pressure gauge shows at various RPMs, the below linked guide may help you narrow down the likely causes.

http://forums.iboats.com/attachment.php?attachmentid=26806&d=1240515681

How to install a pressure gauge: http://www.diy-boat.com/index.php?option=com_content&task=view&id=151&Itemid=49

 

[Diamond Dave]

Re: Mercury Black Max 150

Thats good stuff bro, Thanks,

Dave

 

[DaleBurris]

Re: Mercury Black Max 150

If you don't solve the problem with the good advice you already received above and you are looking for more advice, my advice is to install a pressure gauge on the motor and see what it tells you. Depending on what the pressure gauge shows at various RPMs, the below linked guide may help you narrow down the likely causes.

http://forums.iboats.com/attachment.php?attachmentid=26806&d=1240515681

How to install a pressure gauge: http://www.diy-boat.com/index.php?option=com_content&task=view&id=151&Itemid=49

Thanks

 

[Diamond Dave]

Re: Mercury Black Max 150

If you don't solve the problem with the good advice you already received above and you are looking for more advice, my advice is to install a pressure gauge on the motor and see what it tells you. Depending on what the pressure gauge shows at various RPMs, the below linked guide may help you narrow down the likely causes.

http://forums.iboats.com/attachment.php?attachmentid=26806&d=1240515681

How to install a pressure gauge: http://www.diy-boat.com/index.php?option=com_content&task=view&id=151&Itemid=49

The diagnostic trouble chart is a great help thanks. Can you or someone verify the conditions that we should run these tests?

It makes sense to me that this would be a static test. Lower unit in the water below the pickup, not on the hose correct? I mean if you?re forcing water through the pickup you?re going to get an inaccurate reading right? Also these test are done in neutral not in gear running across the bay or whatever. Is it safe to assume that is the way these test should be preformed? Thanks,

Dave

 

[JW007]

Re: Mercury Black Max 150

Please let me know what the solution to your problem was. I have exactly the same engine and the same problem.

Thanks, Johan