Hot Merc 200hp

[222Aquasport]

1986 Merc 2.4 liter 200hp s/n 6625359<br /><br />Hi Guys,<br />OK here's my situation. I bought a used 200hp merc that was rebuilt (don't know by who. The motor is clean and seems to be in good condition. The powerhead has 132 psi in all holes and starts and runs strong (sounds nice and tight. The problem that I have is it seems to run hot (200 deg F)but the hot horn doesn't go off (it's must be the 240F sender, I checked it in boiling water, didn't go off, checked it with a heat gun,a and got it to close and pass voltage, unsure of temp). So I checked the thermostates, only seals with washers that have a 3/8" hole (common mod right?). I checked the pressure relief valve, diaphragm looks good, rubber seat looks good, stem looks good, don't think it'd the problem. So I took off the lower unit and bought a genuine Quicksilver pump kit. Cleaned and inspected the pump mounting plate (if that's what it's called,the part between the drive shaft bearing and the pump. It all looked good. New o-ring, gasket, cleaned and lubed the shaft seals (seals not in the puimp kit, would have been nice to have them also, maybe you should consider adding them to the kit). Oh yeah, I also used some silicone sealant on the gasket just to make sure it sealed nice on all the thin lands around the shaft bearing. New lower pump plate and gaskets, housing and cup, new impeller, all the parts in the kit. Went together real nice. Checked the seal in the pump housing to make sure it was in there (pre-installed into the housing). Put the lower back on and took it for a test ride. So here's where I'm hoping for some advice. I've checked and replaced all of the maintenance stuff, but the motor still only makes about 10 psi at 5000 rpm. It doesn't seem to be creating normal pressure. As far as I know the motor is stock. I've checked through just about everything I can think of, but I have limited experence with Merc motors. I've built lot's of different motors, so taking it apart isn't a problem. So here's my question: What is the best way to test for what might be wrong? What's the most likely, or common cause for low water pressure? With everything that I've eliminated so far what could cause such low pressure (at idle takes about 30 seconds for water to come out the "tell tail" and gauge (second gauge just to make sure) reads 2 psi. The motor runs great, so I don't think water is getting into the combustion chambers, no leaks external. One thing worth mentioning, I do get a good amount of cold water out the right (starter motor side) nostril (don't know what call them, their the two slots right below the (exhaust plate?)powerhead, ok don't laugh, doing my best to describe them, what do they do, where do they connect to?) Here's some of my thoughts, Mismatch of parts between the powerhead and midsection (is this possible)?<br />Cracked block (can't see how without a leak somewhere)?<br />Bad gasket between midsection and exhaust plate or other?<br />OK Guy's your my last hope, and information, drawings, documentation, recomendations that might help me solve this low water pressure problem.

 

[JerseyJim]

Re: Hot Merc 200hp

I have a 1985 200hp merc blackmax. When I start the engine on the muffs, mine takes about 30-60 seconds for the thermostat to open up and water to come out of the tell-tale. WHen it comes out, it comes out HOT. <br /><br />What makes you think the engine is running hot? Can you touch the block behind the flywheel while the motor is idling? If you can hold your hand there for a few seconds and not get burned (mine is about 100degrees to the touch) then the motor, water pump, and thermostat are operating just fine). <br /><br />I dont know where you are gettin 200degrees from, or the statement 'the motor only makes 10 psi' ... What makes 10psi?? <br /><br />You shouldnt be revving the engine at 5000rpm on the muffs in my opinion - there isnt any back pressure and i just dont feel comfortable with a garden hose providing enough water for the water pump at that rpm.<br /><br />Your telltale shouldnt be shooting out like a firehose - but mine comes out in a steady stream once the thermostat opens.

 

[JerseyJim]

Re: Hot Merc 200hp

btw my CC is a 222 model as well. What year is yours?

 

[RJS]

Re: Hot Merc 200hp

The thermostat kicks in at 140 F. Like Jersey Jim says, the water won't come out intially, but will take some time until the engine heats up. The water will feel out out of the pee-hole. If it's at 200 F, it will scald you if you touch it. If it's at 140 F, it will feel hot, but you can touch it. Try getting a kitchen thermometer and a styrofoam cup, fill up the cup and measure the temp.

 

[kingsbiship]

Re: Hot Merc 200hp

I also have a 200 B/Max that runs very hot...<br />but it's only at WOT. I made the passages for the water larger at the bottom of the p/head, also<br />a little larger under the exh. cover, without much gain. Your pressure is low because there is no restriction (as in thermostats, etc.) separate<br />the thermo outlets (remove the tee fitting) mite <br />help! good luck

 

[Dave Clark]

Re: Hot Merc 200hp

Did you check the water pressure from the top of the block? At this point you can measure the pressure from the pump, through the riser tube, through the adapter plate and up through the center of the block. At the top of the block there is a 1/2" plug that can be removed to attach a gauge. If you have low pressure at this point it could mean that the pump is not producing flow, or their is no restriction provided by the pressure relief valve. While at low RPM's the thermostats control the temperature by opening and closing. At low RPM the pressure relief valve is closed, or cracked open a little. As RPM increases the pump pressure increases, the thermostats can not provide enough flow and the pressure relief valve starts to open. So at higher RPM the pressure relief valve actually controls the temperature by regulating water flow.<br />DO NOT UNDERESTIMATE the fitting of the pressure relief valve plastic shaft into the rubber bushing in the block. Remove the plastic piece and fit it by hand into the rubber o-bushing. It should be a little loose, and not restrict the movement of the valve. Remove the o-bushing to see if it has grooves in it, that could be a sign that it is binding.<br />A possible restriction (rare, I doubt this is your problem):<br />I have heard that at the top of the riser tube there is a rubber bushing that holds the riser tube into the adapter plate. Sometimes the edges of this bushing start to cover the inside of the tube. Since it is not easy to get to this it is possible to heat up the end of a piece of all thread rod and shove it up the tube to burn the rubber out of the way.<br />I do not have the chart in front of me, but I think the motor should make 12-25 PSI at 5000 RPM. This is a pretty broad range, so doing a test run to see what the pressure is doing at certain RPM's/MPH might give you some ideas.<br />A good thing to have is a pressure gauge on the dash for troubleshooting or problems that come up while underway. If you get a plastic bag wrapped around your water intake, the pressure gauge will tell you right away. By the time the temp gauge reads high, the pump is already shot. But, if you are looking up to avoid crashing into things, chances are you would not see it anyway!<br />I am troubleshooting my own overheating problem on my 1987 150 Merc, after changing the thermostats, replacing some pressure relief valve parts, temp gauge, sending unit, water pump, head gaskets, exhaust manifold cover gasket, adding a dash pressure gauge....I went back to the beginning to the pressure relief valve and it looks guilty.... pending a test in the bay. <br />Well, maybe I gave you some ideas......good luck

 

[9675hpforce]

Re: Hot Merc 200hp

Change out the thermostate asap with the small small venting hole up. Also try and play around with the tstate out blowing and running water through.

 

[trumanlake]

Re: Hot Merc 200hp

Hey aquasport, I have a 1985 200hp ser 6625329 just 30 units older. Just wondering if you were still having some trouble. I can give you all the particulars on water pressure if you still need them. email me kaywilli@iland.net