Mercury classic 50 overheating

I am completely new to this so be gentle.
I just got this great little boat with the classic 50. I think it is a 1988. The motor is exceptionally clean and corrosion free. The guy I got it from has been fighting a problem with it overheating.
When I crank it up ittakes several seconds to build up a stream. At that time it looks pretty good. When I rev the motor the stream does not seem to increase. I watched a video that made it look like this was not normal. My buddy had changed the pump and housing chasing this problem and felt like it went away for a couple of weeks.
When you put the boat in the water and start running it you can idles and putt around with no problems. When you romp down on it after about 20 or 30 seconds the stream stops and you see some steam in the general area of the back. Of course I have been dropping it back to idle and letting it cool back down. Neither of us have gotten any alarms so we are not even certain that the alarm circuit is functional. I talked to a mechanic about it and he asked about the proper spark plugs. Thoe have been cahnged and they are the correct expensive ones. He asked about mixture and the boat seems to run okay. It has plenty of power. He was leaning toward a cracked exhaust plate and suggested pulling the power head. He discouraged us from pulling and of the plates on the power head. He thinks there is too big of a risk of breaking the bolts. Yesterday out of boredom I rrmoved the plug from the head and poured some vinegar in. I was surprised that the only place I saw it coming out was a slow drip wround the impeller. I did that a couple of times and then cranked it briefly with the plug removed. I got a reasonable stream out of the port but it wasn't exactly blasting out. This afternoon I put a pressure guage on that cylinder head port and could not get a reading of any pressure. The stream was unchanged. My buddy has had the foot off several times checking the pump and is confident that it is in right and sealed well in the shaft.
This is a really nice motor that is worth working on. The mechanic gets a hundred dollars an hour. He really wasn't encouraging us to put it in his shop. I'm sure he was doing us a favor.
Any suggestion will be appreciated. I really hate to pull that power head unless we have tried everything else. It would be nice to have a few more people say that is the next step.

Re: Mercury classic 50 overheating

I recently put a pressure gage on the rear jacket of my 70hp merc (1978 model year with a 1988 powerhead) to see if I'm better off measuring temp or pressure, and it barely moves the needle. There is not a lot of pressure in the jackets, no worries.

Your motor probably doesn't even have an alarm.

Lots of possibilities causing your issue. The most likely is a piece of old impeller floating around and stopping you up, either in the exhaust plate under the powerhead or (much more likely) behind the rear cover. It will rest at the bottom, then shoot up and stop the tell-tale outlet under high revs.

If you had a cracked exhaust baffle as suggested, you would likely have crappy power and a host of other symptoms.

If the motor is really so corrosion free, it may not be hard to remove the rear cover. Hit one of the bolts with some PB Blaster or Aerokroil, tap it a few times with a small hammer, then gently try to loosen it. They should only be torqued something like 15 ft lbs anyway. If that goes OK, get ready to take it off and look for impeller bits.

Re: Mercury classic 50 overheating

Okay, now the stupid question. We don't have a book. We have been looking at that cover but cant figure out how to get to it. Does the lower cowling ring come off easily. Is that the trick? I saw another thread where they talked about the plate that the spark plugs mount in. That would be the head right? Should we pull the head? Is there a gasket? Do we know where an online book can be found?
Sorry about all the questions. I'd really like to go fishing Friday.

Re: Mercury classic 50 overheating

1988 Merc 50hp should have a rear cover support bracket like #9 in diagram:
http://www.**********/parts/search/Merc/Mercury/1988/1050312BC/COWL SUPPORT BRACKETS/parts.html

Remove that bracket by removing the some of the 7/16" rubber mount nuts #13 in above diagram, then the 10 (IIRC) bolts holding on rear cover #11 in this diagram:
http://www.**********/parts/search/...0312BC/EXHAUST AND MANIFOLD COVERS/parts.html

Then you're lookng for rubber impeller bits, or other debris inside the water passage area. Use a flashlight and a long this screwdriver or somesuch, sometimes stuff can get wedged in there.

While you're at it, look at the tell-tale hose outlet from the inside, there could be something wedged in there, too.

You would need to replace gasket #12 in second diagram.

There is no cylinder head on your motor, the cylinders are "closed off" (aka "blind") via the block casting, with only the spark plug hole at the one end.

I was wrong earlier, Torque spec for the 10 rear cover bolts is a mere 70 in-lb.

BTW, here's your condensed service manual:
http://ebookbrowse.com/3-cylinder-models-pdf-d164588108

EDIT: looks like I can't link to the diagrams, but the manual should give you what you need.

Re: Mercury classic 50 overheating

This motor is actually a 1988 Marinier 45 HP 4 cylinder 2 cycle engine. I was told that it was the same as a Mercury classic 50. I noticed that the link to the manual in this thread was to a three cylinder. I ordered a manual that covers just about every boat motor ever made. I can just imagine how helpful that will be. I found a good site that has parts breakdown diagrams

Re: Mercury classic 50 overheating

Your hundred dollar an hour mechanic should know that sparkplugs do not control the temperature of combustion. It's quite the other way around: the exisiting temperature of combustion dictates the choice of plugs.

You won't measure any pressure in the cooling path cuz it relies on lots o' volume and the pressure that causes the flow is not measurable by conventional means. A normal system would show a fraction of a psi.

Do you have any other symptoms of overheating? Steam is quite normal, and were it I, I too would be concerned about the interuption of the stream, but before I broke out the wrenches, I'd be sure I actually had an overheating problem. There is a ho-ho-ho whole lot more of cooling water that circulates through the engine than what that little pee hole shows. It's a bypass and it's not uncommon for it to be clogged, or partly clogged. You'll find that it's fed by a 5/16" hose that eminates from the top of the head, runs down to a restriction just inside the lower engine cover. In my neck of the woods, it's not uncommon for dirt wasps/ dirt dobbers, to homestead that area. And that little easily removed restriction is a good place to look.

I'm surprised that your engine doesn't have an alarm, cuz my '84 merc 50 hp does. You can easily check the alarm (if you have one) by removing it and treating it to a powerful hair drier. Make sure it's energized (and grounded) and when it gets to about 205 degrees F, it should howl. If you don't have one, I'd get one.

Bottom line, and don't take offence, please, I'm suspicious that you're chasing a problem that doesn't exist. But I'd urge you to determine for sure that the engine is actually overheating before you start turning wrenches. Three times that if your fasteners have been treated to three decades of exposure to salt water.

Good luck. Go fishing Friday, but bring your cell phone. Don't call anybody until you smell hot paint. Yo, and BTW, one little seize never hurt nobody.

Re: Mercury classic 50 overheating

Looking at the impeller is not a gauge of its condition. Replace it. Also make sure the water tubes and connectors mate properly when reassembling the leg. Don't know if this engine is supposed to have a thermostat in it but if it does, make sure it is installed and functioning. A thermostat stuck shut will cause an overheat at idle. One that is stuck open can cause poor engine performance. A bypass valve stuck shut or inoperative causes an overheat at higher speeds.

Re: Mercury classic 50 overheating

Your engine does not have a thermostat or popit (bypass) valve so you can probably rule them both out of the problem. You can inspect the impeller and wear plate and they are servicable check under the w/pump housing in the water pickup for pieces of a old impeller or other debrie, if there is none there, you will need to remove the exhaust plates to inspect the water passages and especialy the one between the exhaust plates and the lower powerhead water jacket they seldom plug up but I have seen a couple dozen do it over the years. You must use care in removing the waterjacket bolts as the will break if you try to force them, tap them, lube them, turn them back and forth till they come loose. Well placed heat is great also.

Re: Mercury classic 50 overheating

Before you do anything remove the Tell Tale then run the engine and the water should be luke warm. The Tell tale restricts the water making it stay in the chamber longer and it heats up when compressed through the reducer at the Tell tale. If it is hot after removing the tell tale you have a problem and the search is on use all info above to guide you in the best course of action starting with the least to the most expensive route. If the stream is luke warm but weak i would replace the impellor first. An exploded impellor will shoot up into the base plate, and the exhaust port plate, and lodge in there as indicated above. Try the new impellor first. You are going to have to change it anyway. I would rather remove the LU twice as opposed to riping off the powerhead for no good reason. The gaskets are not cheap.

Re: Mercury classic 50 overheating

The tell tale has nothing to do with the operating temperature of the engine or water temperature, 90% of the cooling water goes out the exhaust tube so the reduction on the fitting at the end of the tube has nothing to do with water temperature. When a engine cools at idle as you said in the orginal post that it does that is a good sign that the pump is OK (a bad impeller won't pump at idle) so you must have a restiction that is causeing overheating at higher RPM when water flow stops as the RPM increases it normal is the water pressure from the pump compacting the debrie in the smaller cooling passages of the engine. The impeller pieces don't explode up the water tube to the engine, they were not cleaned out after the original impeller went bad and water flow from the repaired pump pushed them up the tube into the cooling system.

Re: Mercury classic 50 overheating

I really apreciate all of the information and suggestions. I have a question.
Are there any places that I can apply a backpressure to dislodge debris? I still dont have a good feel for all of the paths this water takes between the pump and the hot water discharges. It would seem to me like you could take the pump out and push water from a water hose into that port on the head, or perhaps even the the hose that goes to the tell tale. I'm sure this is a bad idea. I just don't know why.

Re: Mercury classic 50 overheating

If you remove the powerhead and invert it, then flush it from the telltale outlet, then "maybe, but I doubt it."

Once debris gets into (for example) that rear cylinder cover area, it isn't coming out easily unless you remove the rear cover.

Re: Mercury classic 50 overheating

Just had the pleasure after feeling my engine seemingly running hotter thatn it should, I found two broken fins gone off the impellor which lodged in the lower intake screen. I had the impellor showed yesterday and new gaskets put it all together a while ago and is running correct now.

Re: Mercury classic 50 overheating

Not true I hade 2 fins missing off my impellor this morning and it was pumping alot of water at idle. Hot water. I replaced the gaskets on the plate removed the fins and put in a new impellor and it runs warm but not hot. Removing the tell tale will allow more water flow and if it,s hot then there is a bad impellor or a blockage somewhere. If a thermometer isn,t handy Then to be sure you have an over heating problem you can removing the tell tale it will be easier to determine how hot the water is actually getting in a diagnosis mode. I never ever said the impellor pieces explode up into the exhaust plate. After the fins break off for whatever reason the can go 1 of two ways up by force through the presure sent by the remaining fins or down into the base under the metal plate restricting the intake. Replacing the impellor without checking this for the fins will reduce water flow to the impellor and cup. My reasoning behind disconnecting the TT was the impellor fin was altimately restricting the intake water flow. At times it would restrict some and others it would restrict more.Sometimes felt luke warm. Being it was above normal operating temp it was hard to determine the amount of tempature. from slightly hot to very hot. By removing the TT I could feel a tremendous difference in the amount of heat and was able to determine that it was in fact running hot at one start and hotter on another start with the increased water flow.

Re: Mercury classic 50 overheating

Max, In your mind you know your right and it serves no purpose to argue with the likes of you. It is people that go on and on about things that they know an minimal amount about, that confuse people that are looking for help, hell a couple like you would confuse someone that was experienced at marine repair. So I wish you and yours luck with your blabbing, I am done with all of the crap you spread, have a nice day. You may have my place here, I have better things to do. Bob

Re: Mercury classic 50 overheating

Sorry you feel that way and that you scrutinize every word someone eles has to say when first of all you in your mind read it the way you want to interpret it. There was NOTHING I stated in this thread that cannot be tryed and considered to confirm overheating BEFORE removing the covers on the engine. As stated by the poster that he inspected the impellor only and did not remove or replce it. He did not inspect the entire LU for remnats of a broken (EXPLODED) impellor. Therefore removing covers before doing a proper job of assesing the unit with the proper inspections of all parts associated in accordance with but not limited to the water pump in it,s entierty and removal of and replacement of all nessecary items would be a totally uncalled for action that he would take as a result of your information. Moving on from my information to your information would be considered the proper proceedure And by the way thanks for the insult. I respect you as an educated man and marine machanic. Hell even the pros are wrong alot of the time right ? But don,t you dare judge my inteligence or machanical abilities based on your assumption. Have a nice vacation

Re: Mercury classic 50 overheating

I didn't mean to cause an arguement. I appreciate all of the suggestions here. I like to get a lot of opinions and average them out. I took the boat fishing yesterday. It was a blast. I'm not sure that even the idle stream is what it should be. At just a little pas idle the stream will stop for 3 or 4 seconds about every 20 or 30 seconds. Something is just not right. I taslked to the guy that did the water pump again and he is sure that he cleaned the input. He actually changed the pump twice. The first time was the impeller and the second was the whole kit. He is also sure it is seated properly.
For now I am going to keep fishing till it turns cold. Then I have a buddy with a great shop that is going to tear into it with me. He is one of those guys that can do anything (machinest/welder/mechanic, and general smart guy). It sounds like we ought to start with the covers and keep cleaning till we find a blockage. Of course the pump will be checked in the process. I'll be sure to report results as we find them. Even if it is not running hot I want to see water coming out of that tube. I could never be comfortable till I am confident that the motor is right.

Re: Mercury classic 50 overheating

Not to worry fastbullet just was having a bad day I guess and i,m not intitled to one but thats par for the course. It aint my first rodeo. Be careful and keep that eye on the stream. It is absolutely posible that there is a piece of impellor up in the covers but to jump the gun and assume that would be a detrimental and unnessecary mistake. The word explode musta jared a nerve and he went out of his way to assume the meaning of it was that when it shoots up the tube into the base followed by the covers that it was an act of an explosion not mentioned anywhere in this thread. Non the less take care of the issue ASAP to avoid screwing up your engine. Welcome to iboats and hope to here good news from you in the future

Re: Mercury classic 50 overheating

Come on Guys be nice. Maxz, That was Laddies and not Fastbullit so slow down allitle. As for Sjoefl1 problem, Being that the LU has been worked on a couple times and has not helped much using a air blow gun and blowing from the tell tail backwards thru the motor might help with removing any obstructions with the LU removed. A water pressure gauge should show near 5 LBs. at idle with a new pump and up to 18 at WOT. Any diffrance below or above those pressures will show that there is a blockage. There are several other things that will cause the simptens being seen, Laddies and Max have stated a few that will cause them, and both are correct and trying to help.Alway start with the easy and cheap fixes first then go to the more $$$ ones. Having done the pump and being sure it is good then try the air and or backflushing next. Then report back as to your progress please. A water temp gauge should run around 145 at idle and higher at WOT. Any temp over 190 is realy running hot. I use both on my motors that are consol control as I and most all others cannot run a boat and watch the tell tail at the same time. The cost of the gauges is alot less than a burnt up motor. JMO
Oldman570

Re: Mercury classic 50 overheating

Yes thank you oldman My appologies to fastbullet for the mistake.