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Old 07-23-11, 08:15 PM   #1
champman
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Default really need help with my merc.

Hey folks, I could really use some help from anyone with a working knowledge of a 1989 175hp merc. outboard. I have had some over heating problems for a month or two. It will run cool enough at idle but wants to heat up at full throttle. I have changed out the water pump,stats, water lines and today I replaced the poppet valve but she still wants to run very warm to almost hot. I ran a compression test on the cylinders, all had 130 psi. I called the local merc. dealer and he seems to think it is the temp. sending unit after all I have done to it. The one big question I have is about the poppet valve. When I put the ear muffs on and start her up a small amount of water is coming out of the weep hole on the poppet valve housing.Is that "ok" or is somthing wrong there? The dealer thinks it shouldn't be leaking but he didn't sound too sure. If anybody has any thoughts on this it will be greatly appreciated. If you want talk one on one about this, post a reply and I will give you my number.thanks, Bill
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Old 07-23-11, 10:27 PM   #2
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i am NOT a mechanic, but if the "pee" stream is weak, something is either clogged up or pump is not working right.
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Old 07-23-11, 10:39 PM   #3
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Thanks for replying bama, the pee stream is great that's what has me beleaving it's the temp. sender itself. I'll figure it out sooner or later. Any other ideas are welcome. thanks, Bill
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Old 07-24-11, 09:46 AM   #4
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I had a similiar problem on a 150 (XR6) merc and it was the thermostats. I'm not 100% on the "weeping" poppet valve, but I don't think it should be leaking any water under normal circumstances.
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Old 07-24-11, 11:04 AM   #5
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is it noticably getting hot or just the hot alarm sounding?
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Old 07-24-11, 02:00 PM   #6
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Hey Embrey, Yes it shows hot on the guage , about 3/4 hot anyway. Sometimes the alarm goes off also. The weird the is that it cools down when I throttle down and runs at normal temps.
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Old 07-24-11, 02:54 PM   #7
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well, if its really getting hot,the sending unit isnt causing it.being on the muffs is hard to figure these problems out since the hose is pressurizing the system. its probably leaking by due to the pressure and may not do that on the lake. are you sure the water pump was done right? sounds like a possible gasket blown out down there. do you have a water press guage?
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Old 07-24-11, 03:36 PM   #8
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I'm sure the pump is good. I put a new kit in this spring then replaced it when all this started but I still had the same problem. I also agree with you about the muffs, I don't thinks the poppet valve would leak under normal operating conditions. I don't have a pressure gauge on the motor but the water flows very well through out the motor. I put her on the water saturday and the water peed out fine at idle and at full throttle. What has me puzzled is the fact that it was fine one weekend then the next weekend I put it in the water started it up and when I ran it out the over heating problem popped up like something was working... then it wasn't. I'm going to try the temp. sender eather way, just another $30.00 to the boat monkey!
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Old 07-24-11, 04:04 PM   #9
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Sounds like a water pressure problem. I wouldn't worry about the poppet leaking when you have the muffs on. My dad's boat does the same thing, but like you said doesn't leak while on the water. The only explanation other than the thermastats not working properly is the water not circulating. So it is either the pump or there is something blocking the ports for the cooling system.
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Old 07-24-11, 04:36 PM   #10
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Thanks for the poppet info. Z. I have put the muffs on and taken the water lines off and fired it up and the water flows good through the lines. I think the guy who said " it's not the kill, but the thrill of the chase " never shot anything!
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Old 07-24-11, 05:26 PM   #11
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Bahahaha... He was the fisherman that never caught the fish. I would have the pressure tested. Im betting that is where your problem is! Just out of curiosity how long at full throttle does it take for this mama jama to start overheating?
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Old 07-24-11, 06:47 PM   #12
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Right out of the box. I push the throttle over and the temp. just keeps going up untill I throttle back then it goes down, if I push it back up the temp. goes up.
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Old 07-24-11, 08:22 PM   #13
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This may be a dumb ?, but are you sure the temp gauge and alarm aren't FUBAR'd?
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Old 07-24-11, 10:01 PM   #14
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That's my next move and if my luck holds true, it should have been my first! Are we having fun yet?
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Old 07-25-11, 09:41 AM   #15
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I talked to a friend that has been through pretty much every boat motor problem known to man and his ideas were the gauge being messed up or the thermastats not being adjusted correctly. He said there is an adjustment screw and more than likely the thermastats aren't cutting it, as far as cooling, at full throttle. Maybe all that is needed is a little adjustment? Good luck my man. Hopefully you will be out on the water in no time
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Old 07-25-11, 11:19 AM   #16
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never seen adjustments on thermostats...lol. they are bypassed at full throttle anyway.
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Old 07-25-11, 11:37 AM   #17
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Nevermind then. lol Just passing along what I was told. Although I may have misunderstood. Good possibility there too.
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Old 07-25-11, 05:27 PM   #18
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Going to set up an external water pressure guage then test run it again. I don't think it has low water pressure but if the water pressure is too high I may be looking at an internal engine problem. At this point I'm hoping it is just the temp. sender. I've never heard of adjustments on stats but I intend to look anyway. thanks again fellas.
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Old 07-25-11, 06:55 PM   #19
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Is this a saltwater series 175 ?

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Old 07-25-11, 07:09 PM   #20
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Quote:
they are bypassed at full throttle anyway.
You lost me - how are they bypassed? A thermostat is a part of the cooling channel inside the outboard. It's purpose is to restrict the flow of water (coolant) while the engine heats up to operating temp then open to allow a greater flow of water to cool the heated engine. As far as I know there is NOT a seperate channel, piping or hose to bypass the t-stat - if that were so you'd need another set of valves to restrict the flow of water through the bypass during warm up. It's a supposed feature of a defective t-stat to fail in the open position rather than closed, but that isn't fool proof. The t-stats may also be not operating properly due to grit, or sand that has made it into the cooling system and they may need cleaned or replaced.
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Old 07-25-11, 08:35 PM   #21
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Sorry guys, didn't mean to start cooling system war here. I do know that on this 175 merc. the poppet valve restricts the water flow up to about 3000 rpm so the t- stats can warm up quicker ,143 degrees, then the water flows through out the motor when the poppet valve is forced open. Once again, my problem is I have put new Quicksilver OEM water pump, t- stats, poppet valve, hoses and preformed a compression check( 135 psi ) on all cylinders since the over heating problem started and nothing has improved . I am replacing the temp. sendor hooking up a pressure guage( this boat doesn't have one) this week and lake testing it again. I believe the guage on the dash to be good. I'll keep you all posted. thanks everyone, Bill
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Old 07-25-11, 11:26 PM   #22
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Psi gauge is handy,at idle will show about 6-8,and always keep it above 15 psi when running on plane,mercs can go down to 12 but if healthy and set below pad 3-4 in inches should actually read 20 or more.
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Old 07-26-11, 06:08 AM   #23
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Thanks for that info. llimule, I was wondering what pressure I should be looking for. I don't understand the below the pad part. Doesn't the supply line for the guage go on the motor?
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Old 07-26-11, 08:12 AM   #24
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The pad is the lowest part of running surface,it sticks down from the boat in the center,yes it goes into a plug in the block in powerhead,remove plug insert psi fitting.
Relationship to pad is important when running low water nose cone or a stock unit when on a jackplate or as in height of motor under water when running.
Stock normally 3 1/2-4 in with most motors.
With a 200 venom with lwp I was getting close to 30 psi at 1 in under,wot,stock on others about 22 psi at 4 in under.
If it is over heating and not false reading take it easy on it to many times melt something,or damage to point of rebuild.
Ive had even a one year old water pump lose part of its rubber,and thats all it takes part of it its like a lil rubber wheel.Should be replaced about every two -three max years if used much religiously.Doesnt cost much,so have it done,dont attempt yourself.
If wondering how deep you are take a straight edge,3 ft yardstick,broom stick etc. place in front of lower unit even with prop shaft and see where it comes to in relation to lowest part of boat,to high be low water pressure,and would cause it to overheat .Did you by chance mount it yourself? Set about 4 in under
Some boat hulls have a lip at that edge and like it a tad deeper than that,hefty boats like older rangers.
Almost willing to bet your set to high and starving it of water.Simple solution would be to move it lower.
Example I am running a stock unit now and if set say 2 1/2-3 in under or higher would go about 50 -100 yards on plane and set off alarms,but would run fine at idle as boat is lower in the water.
If no pad on bottom just use lowest part to measure from.Water inlet holes on motor will then be below the boat,not sucking air.

Last edited by lilmule; 07-26-11 at 08:49 AM.
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Old 07-26-11, 12:14 PM   #25
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Lil' mule could be right but wouldn't that only be right if the motor was moved just before the problem started?
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