1988 Mercury Blackmax 200 HP Cooling System Problem

[pressnutt]

Hello , everyone and thanks in advance. I have a 1988 200 HP Mercury Blackmax engine. Last year it would crank it up and after a few minutes of running the water temperature gauge would creep up to the second bar and then it would start to pee water like crazy out the back. This year the first time I took it out on the lake it heated up and it pee'd like normal. The next time I took it out as soon as I crank the motor it starts to pee immediatley with no bars on the temp gauge. I thought bad impeller and it needed to be changed anyway. I changed the impeller and oil in the foot and go back to the lake. Same thing. As soon as it is cranked, it starts peeing. The strange thing is that the water stream is weaker than normal and at ilde is sputters the water out not a hard steady stream. When I idle it up with a litte gas on the hot foot the stream gets harder, but when I let off the gas it sputters the water out. The water stream when at higher idle is not hot and lukewarm at best. I tried driving it down the lake and the stream is hard and normal but at times it starts to sputter the water out and keeps doing this as I go down the lake. The psi gauge reads about 5-7 psi at idle and around 15 psi at about 4000 rpm's so the water pressure seams normal to me. I know that at 135-140 degrees water temp it is supposed to start peeing like crazy. I have a seloc manual and it is kind of hard to follow on the water system. I was wondering if this could be caused by a stuck poppet valve or a stuck thermostat that could could be causing it to pee at first start up and no initial warm up. How do I check the poppet valves and clean them and could thermostats that are bad cause this? The lake water around where I live in North Carolina is starting to warm a little and I want to keep this motor running cool and calm once higher water temperatures arrive nearer the summer. Any ideas or suggestions would be greatly appreciated, I have a bass tournament on Saturday and would love to have this fixed by then. Thanks in advance and sorry the post was so long. Josh

 

[rentprop1]

Re: 1988 Mercury Blackmax 200 HP Cooling System Problem

I'm having a similar issue, and will continue to watch this thread, but I have a question...when the pee stream starts to sputter or dribble, if you shut the engine off ( wait about 20-30 sec ) and re-start does the pee stream start flowing well again....this is what happens to mine ??

best of luck

 

[pressnutt]

Re: 1988 Mercury Blackmax 200 HP Cooling System Problem

Rentprop, it does what yours does sometimes. I can turn it off and wait and then start it again and 95% of the time it starts peeing a weak stream out and then about 10-15 seconds of running it begins to sputter the water out the back. I have been reading all over the net and haven't found a clear solution. I was hoping this morning there would be many responses to my question. I am calling a local marine here where I live today and see if they have ever heard of this happening and I will keep a check here on iboats today at work and see if I get any more responses. What baffles me is that the motor runs fine like a sewing machine, I just know it isn't supposed to pee water until around 135-140 degrees and it pees all the time now with varying pressure. Thanks guys. Josh

 

[j_martin]

Re: 1988 Mercury Blackmax 200 HP Cooling System Problem

You have more than one problem

One is t-stats stuck open. They usually get that way with an extreme overheat At any rate, they need changing.

Thus, water pump is suspect. Impeller, housing, base plate, and gaskets could all cause problems.

The unsteady tattletale stream at running speed could be anything from a bug nest in the hose (common) to a bad head gasket.

If you've been into a gob of mossy algae, or as I did one time have sawed a rotton log in two at speed, you might have debris in the cooling system. You can usually get at most of it by removing the exhaust chest cover.

hope it helps
John

 

[rentprop1]

Re: 1988 Mercury Blackmax 200 HP Cooling System Problem

I removed my pee tube today and found some small pieces of sand / shell, but nothing that would seem it would inhibit the flow of water ?? mine has always pee'd at startup....I 'm not sure I have a thermostat it's a 60 HP Merc Bigfoot

where is this exhaust chest cover ??? got a pic

 

[pressnutt]

Re: 1988 Mercury Blackmax 200 HP Cooling System Problem

sorry accidentally copied original post. Question below. Thanks Josh

 

[pressnutt]

Re: 1988 Mercury Blackmax 200 HP Cooling System Problem

sorry about last post it was a copy of original. Just got back from working on the motor. Found what looked like wood chips stuck in the poppet valve. I went ahead and changed the thermostats. I cranked the motor after the thermostat change but before taking out the wood chips. LOL It stilled pee'd when cranked immediatley. I didn't get a chance to crank it afterwards. Too late in the neighborhood I was working in. Going to the lake tomorrow and try and see what it does with the wood chips removed. I have a quick question, under the poppet valve cover there is a rubber disk, followed by a rubber diaphram, then a plastic cylinder. Is that plastic cylinder supposed to come out of the engine block or is it supposed to be held in by a spring. It would not come out but it would spin. I removed the wood chips, and replaced it back the way it was. Hopefully the wood chips where holding it open and letting water flow all the time thus explaining the peeing all the time. Thanks in advance and sorry about the last post copy. Josh

 

[big_b16]

Re: 1988 Mercury Blackmax 200 HP Cooling System Problem

When your engine is running, the water pump is spinning. The driveshaft is mated to the crankshaft. When you put it in gear, the lower unit starts spinning the prop shaft. In other words, when you first start your engine...prior to putting it in gear...you should have a stream of water. The higher the engine RPMs, the faster the impeller is spinning. The poppet valve is a pressure control valve, affecting the water volume in the engine (a given volume with the t-stat open, and another with the t-stat closed). When the t-stats are closed (engine cold) the higher rpms will try to force more water into the engine, the pressure control valve (poppet valve) will open letting the extra water bypass. If you have crap on your poppet valve, the t-stats have likely had crap pushed up to them too (you changed them so they should now be OK). You've also got some stuff in your waterjacket most likely. If you're getting constant overheats, it might be time to order some new gaskets and pull your waterjacket covers (heads and exhaust sides) and make sure all the passageways are clear. It's the only real way to make sure you're getting proper coolant flow.

 

[boatman 57]

Re: 1988 Mercury Blackmax 200 HP Cooling System Problem

for the one with overheating things,,,,,,,,,,,,there is also a water tube at bottom left side that will let water out on the spot 10 second about if anyone still have-n promblem with the mer.