'86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

[Shadetreeboatmechanic]

Hi, I too am new to posting on this forum, but I have been a reader for sometime now. I have learned so much and found so many answers just by searching the old posts. Thank you to all who post on this board.

Now for my problem. First of all my husband & I are shadetree mechanics. He has a very general knowledge of mechanics as he worked as an auto mechanic for a few years. I do all the reseach and reading to give him the directions. We have a '86 140 Mercruiser with Alpha I outdrive. Standard cooling system. I do have an orginal shop manual I think I almost have memorized. We have an overheating problem and an idle problem. Here's what we have done and what the boat is doing.

We took it out a couple weekends ago (1st time this year). Ran it for quiet some time at around 3000 RPMs just cruising. No problems except for a miss going from idle to accelerating.

We took it out a few days ago, Still had slight miss but if you feather the shifter through that point it runs great. We ran it for about 10 minutes at Full throttle. It overheated BIG TIME. We sat let it cool off then slowly cruised back to dock. It did not overheat at low speed but still had the miss.

We brought it home took entire upper cooling system apart. We found the thermostat was broke, the exhaust manifold and riser were clogged. We cleaned them both throughly replaced all gaskets & thermostat. Changed Oil and filter. Checked the water lines going through the transome. All clear. Lower Unit impeller was changed last season) Started it in the drive with muffs. No overheating at all and she was throwing more water than ever.

Took the boat out yesterday morning. Other than the miss going from idle to to accelerating it ran great, no overheating problems at all. We ran it for 30-40 minutes at Full throttle and it never got above 160.

So when we got it home we decided to tackle the idle problem. We removed the carborator cleaned it throughly. Cleaned all the fuel lines. Checked all the plugs and wires, both still look brand new (replaced last season) Checked all the wires for corrosion. Hubby lightly sanded the points. Did NOT adjust timing. Started it in the drive with muffs. Great water output. Ran great no miss. Soooo we decided to go for another test run.

Put the boat back in the water. Started great. Ran Great after hubby adjusted the idle a little. Idled out of the no wake zone hit the throttle she took off and ran beautiful Until it OVERHEATED again!! We let it cool while watching the storm clouds roll in. We idled back into the dock still overheating but it was a nasty storm coming and we had to get off the water. Loaded it up, came home, parked it in the garage and came in the house. We are stumped!!

We don't have a clue why. Can someone please help us figure this out. We have talked to a couple real mechanics and they don't have a clue either. Said possibly the timing but if that was the case why did it not over heat on our first run out yesterday?

All help is greatly appreciated. This is driving us nuts!!

 

[Fishermark]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

Welcome!

I think you've identified your problem:

We found the thermostat was broke, the exhaust manifold and riser were clogged. We cleaned them both throughly replaced all gaskets & thermostat.

If the manifold and riser were clogged - with rust I presume? - they need to be replaced, not cleaned. That would be my first thought. Impossible to get all the rust out of the passages - and even if you do, more can flake off and plug things back up again. Not to mention hydrolocking the engine when they get too thin and begin to leak internally. I know it's a lot of money, but it is money well spent in the long run. Just my thoughts.

 

[Shadetreeboatmechanic]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

Thanks for the reply. We thought about that but figured they would last a little while longer, maybe through the summer so we could replace them during the winter months.

But what I don't understand is it did great as far as cooling yesterday morning and in our drive, but as soon as we put it back in the water yesterday it overheated in less than 5 minutes and not even at full throttle (the water was rough due to the storm)

You could be right. Maybe something did flake off between running it in drive and the 15 minutes it took us to drive to the water launch it and start it. It just irritates me that it's doing this. I ran so great until hubby said Oh NO. Its bumfluzzling us why it's just started this.

Thanks for your help.

 

[rodbolt]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

forget everything you know about automobiles, trust me.
now you need to do a leak down test on the cylinders.
you only get so many overheats before a head gasket leaks.
if the cylinder sealing is intact I would replace the manifold and riser. dont try the boil them out trick.
it always leads to problems.
that rust your boiling out? that used to be the metal in the castings.
if your in saltwater I would also pull the circulating water pump for a look.
that engine should never see above about 150* if everything is correct.
granted on an automobile severly retarded timing can cause an overheat, we just dont see it on raw water cooled engines as there is always cool water coming in.
on your 140 the cooling water exists the block,then flows to the manifold up fwd and exits the exhaust aft via the riser. clog a manifold or a riser and water simply cant escape fast enough and the engine overheats.
normal symtom of a failing pump is low speed overheating and with a bump in RPM it cools down again, clogged riser is about the opposite, will flow enough water for idle cooling and the harder you load the engine the faster it overheats.

 

[Shadetreeboatmechanic]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

forget everything you know about automobiles, trust me.

LOL we figured that out when I started reading the shop manual insturctions to hubby!!

if your in saltwater I would also pull the circulating water pump for a look

Yes were are in saltwater. We did take it off. I took it to a local shop because the guy is really good to look at things for me to help us out. I buy all my parts there. He said it looked fine and he would not replace it if he was me.

on your 140 the cooling water exists the block,then flows to the manifold up fwd and exits the exhaust aft via the riser. clog a manifold or a riser and water simply cant escape fast enough and the engine overheats.
normal symtom of a failing pump is low speed overheating and with a bump in RPM it cools down again, clogged riser is about the opposite, will flow enough water for idle cooling and the harder you load the engine the faster it overheats.

But what I don't understand is why it cooled fine yesterday morning but then yesterday evening when we took it back for another run it overheated QUICK. I am taking within less than 5 minutes at a slow cruise and kept going up when we tried to raise the rpms hoping it might cool it down.

you need to do a leak down test on the cylinders.
you only get so many overheats before a head gasket leaks

We will do this one day this week. We are taking a break from it today.

dont try the boil them out trick.it always leads to problems.

We were told it wouldn't hurt to do it one time. They have never been off the boat until we took them off. We didn't boil them out we just used scrappers, rods, wire brushes ( and even hubby's gun cleaning kit) We flushed and flushed with water then blew them out with the air hose.

One more question. Where is the cheapest place to purchase a manifold and riser and what brands should I avoid?

 

[EricR]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

The Osco and Barr aftermarket manifolds I have always had good luck with. I worked briefly at a place that did stern drive stuff in the early 90's, and in salt water use even changing the zinc anodes regularly replacing the elbows and manifolds on a sea water cooled engine was just an accepted maintanence item every few years.

Sounds like you are pretty adept with these things. Keep at it, and you'll find the problem.

 

[chiefalen]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

twenty years on the riser and manifold you did good getting to here take them off again see any holes where it rusted thru the engine mounted water pump hows that look.there was a problem with impellers in the outdrive that were defective right from the factory check that make it the first thing than the engine mounted water pump second risers and manifold third and than the t-stat boil the t-stat with a thermometer see if its opening up at 140.good luck

 

[Shadetreeboatmechanic]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

First thank you all for the help you are giving us. We greatly appreciate you sharing your knowledge with us.

twenty years on the riser and manifold you did good getting to here take them off again see any holes where it rusted thr

They weren't hard to get off. Heavy to move but not hard to get off lol
No there wasn't anywhere that was rusted through. They actually didn't look that bad once we cleaned everything out. Theyboth were corroded some but we cleaned them out as good as we could. We flushed them with water really good and then blew them out with air hose.

the engine mounted water pump hows that look

Looked good. Took it to local boat shop. Mechanic there said it was fine.

there was a problem with impellers in the outdrive that were defective right from the factory check that make it the first thing

We ran that impeller a couple times last year. And a couple weeks ago. No problem with heating either time until this week. It's only been ran about 5 hours of running since it was replaced.

than the t-stat boil the t-stat with a thermometer see if its opening up at 140.good luck

Did that a little while ago. Worked fine.

Guess we're going to pull the manifold and riser and take them to a local machine shop and have that guy look at them. He has done a lot of work for us and is very good. He will be honest and tell us what he thinks. We are beginning to think that maybe where we cleaned them out maybe something else has came loose in there that we didn't flush or blow out. He may acid dip them so he can look them over good. He don't cut corners when it comes to stuff like that.
Thank you again

 

[Shadetreeboatmechanic]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

I forgot to add that after the first overheat we changed the oil and filter even though the oil looked fine. (changed last season and only ran it a couple more times) We again used the Mercruiser oil and filter purchased at the boat shop. We didn't want to chance the oil breaking down since it had gotten hot.

We checked the oil several times yesterday just be on the safe side. The oil looks great so we know there isn't a leak or blown headgasket. All the other gaskets have been replaced this week. My local boat shop loves me

I am anxious to see what the machinist tells us. He will be very blunt and honest about the condition of the manifold and riser. He tells you what is best even if it's not what you want to hear. I'm pretty sure he's gonna tell us to replace them as all of you have said but I just want to make sure we aren't missing something somewhere else. If he says they are fine then we know we are looking at one of the water pumps or something along that line.

I will keep you posted as we figure things out. Any more advice will be greatly appreciated. You guys are great!!!!

 

[Shadetreeboatmechanic]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

I forgot to add that after the first overheat we changed the oil and filter even though the oil looked fine. (changed last season and only ran it a couple more times) We again used the Mercruiser oil and filter purchased at the boat shop. We didn't want to chance the oil breaking down since it had gotten hot.

We checked the oil several times yesterday just be on the safe side. The oil looks great so we know there isn't a leak or blown headgasket. All the other gaskets have been replaced this week. My local boat shop loves me

I am anxious to see what the machinist tells us. He will be very blunt and honest about the condition of the manifold and riser. He tells you what is best even if it's not what you want to hear. I'm pretty sure he's gonna tell us to replace them as all of you have said but I just want to make sure we aren't missing something somewhere else. If he says they are fine then we know we are looking at one of the water pumps or something along that line.

I will keep you posted as we figure things out. Any more advice will be greatly appreciated. You guys are great!!!!

BTW if we do have to replace the manifold and riser I win the bet. I bet hubby that they are the problem and we should get new ones, but no he didn't think so. So we will see. If I win I get a full day of fishing from daylight til dark. I like to fish better than he does. If he's right I have to clean the garage.

 

[Shadetreeboatmechanic]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

UPDATE:
We are pulling the manifold and riser this evening and taking them to machine shop tomorrow to be checked. I will let you know when we find out something. Thanks again for the help.

 

[Shadetreeboatmechanic]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

Ok we got the manifold and riser back from the machine shop today. The guy said they looked great. He said they should last for another 4-5 years. He said they were thick and in good shape. He checked them inside and out. He said they only thing he found was a few loose pieces where we had tried to clean them out. He's really good at what he does and he really knows his stuff. I am confident he knows what he is talking about. He has been in this business for many years. He said he had seen some really bad manifolds but that ours looked good. He soaked them for a day, sandblasted the inside, flushed them really well then put some type of scope inside so he could look at what you can't see from the outside. He said they were good.

We reinstalled them this evening and will be taking the boat out either tomorrow evening or Sat morning. I will let you know when we get back how it does.
Thanks again for everything.

 

[RJLeuwen]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

When was the last time the water hose from the bell housing (the part the outdrive is bolted too) to the gimbal housing was changed?

Raise the Drive all the way up and inspect the hose for cracks and kinks (it's ont the port side of the housing) may have cracked thru the last time trailered the drive before your last test run!

RJ

 

[oops!]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

this is a simple impellar problem......

(im not a mechanic)

but the reason it works on the muffs and not on the water is cause the water pressure in the hose !

change your impellar

 

[wca_tim]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

this is a simple impellar problem......

(im not a mechanic)

but the reason it works on the muffs and not on the water is cause the water pressure in the hose !

change your impellar

not a mechanic either... but this was what I was thinking as soon as I read cooled on muffs (has external water pressure supplied to get water to the circulating pump), doesn't cool in the water (impeller / drive pump suplies the water flow / pressure to the circulating pump).

Note that it only takes turning one the wrong direction (don't ask how I know this from personal experience) or without water, some crap in there to chew it up, etc... I also had the pleasure of learning that you can get somewhat similar symptoms if you kink the water hose that goes from the out drive to the transom assembly...

Some of what was clogging things above didn't happen to be what looked like pieces of black rubber did it? Hope it works out for you...

 

[Dakota47]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

May want to check the power steering cooler (if you have one) the water goes thru it before the engine gets it.. coolers can clog easy.

 

[jerryjerry05]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

Put the boat in the water and remove the water feed from the rear of the motor. Start it upo and see ghow much water is comming thru. Then rev it up you should have a LOT of water.Enough to put out a fire.
Or if your not sure just change the impeller.Jerry

 

[obezag]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

If you're judging the overheat by the temp gauge are you sure it and or the temp sending unit are functioning correctly?

 

[Shadetreeboatmechanic]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

wca_tim I also had the pleasure of learning that you can get somewhat similar symptoms if you kink the water hose that goes from the out drive to the transom assembly...

RJLeuwen Raise the Drive all the way up and inspect the hose for cracks and kinks (it's ont the port side of the housing) may have cracked thru the last time trailered the drive before your last test run!

BINGO You both win the prize!!! How could we have missed something so simple? We changed it last year but it's just a little to long. That was the problem!! I read what you guys sent last night to hubby. He just happened to think to check it this morning before we went out for another test run. Man would we have been mad if we had went out and it over heated again.

Now the fun part comes. Trying to change it without removing the gimble housing. I think with my small hands we might be able to do it.

I'll let you know when we get back later if we can get the hose changed before the storms come.

 

[Shadetreeboatmechanic]

Re: '86 Mercruiser 140 with AlphaI outdrive is Driving us CRAZY

Ok we got the hose changed. It wasn't easy but thankfully we did get it without removing the housing. I read somewhere that the watertube is a 50 cent piece that will make you loose your religion. I would have to agree.

Hopefully we can take it out in the morning before the storms in the afternoon again. We didn't make it in time this evening before the storms.

I will let you know.