[SOLVED!] used Mercruiser 140 engine - overheating?

[Neutron68]

Quick history: 
Last summer I was trying to diagnose an oil usage problem with the Mercruiser 120 engine that was in the used SSV-177 I bought used.  After trying some upper engine cleaner in the oil, it was still using about 1/2 quart of oil per hour and leaving an oil slick in the lake.  I'm not an experienced mechanic so it looked like my options were have the engine rebuilt or swap the engine.  I ended up having the engine swapped out for a used known-working Mercruiser 140 (serial number 3247890, 1972?). 
Details of engine swap:  New starter, rebuilt/adjusted carb, new fuel filter in carb, new fuel filter in fuel pump, new fuel hoses, new spark plugs, my previous red spark plug wires, my previous distributor with electronic ignition, new temperature sender, new oil, new oil filter, winterized with RV anti-freeze...
During this same period, I also had the lower unit replaced by a private stern drive specialist, due to a crack that was letting gear oil out of the lower unit and water in.   During the lower unit swap, all the lower unit seals were redone and a new impeller was installed, etc.   
After the engine swap, the engine was winterized and put into the cabin garage.  The exhaust manifold's drain plug has been covered over with a hard, tan substance (epoxy?), so it can't be drained and purged of sand as you would like to each fall.  Since the manifold was to be filled with antifreeze, I was advised not to worry about the lack of a working drain plug.

Today:
I rolled the SSV-177 out of the cabin garage, put water muffs on the lower unit and started it up.  It started with some difficulty, but did start.  We ended up dribbling a little gasoline into the carburetor and also needing to push the throttle lever open to a position higher than idle.  Then, it started and ran smoothly.  We then put the boat into the lake and drove it from the boat launch to my dock where it sat for about 4 hours.  In mid-afternoon I wanted to take the boat out for a shakedown cruise to see how it ran, etc..  It started with some difficulty again.  I ended up pushing the throttle lever (neutral button pressed in) to a higher throttle position.  After a few tries at cranking it with the higher throttle position, it started.
I ran for about 5 minutes around 1200 RPM and all was fine.  The temp gauge as showing about 150 degrees.  Then I pushed the throttle up in increments to see what speed we could get out of this 140 engine with the new 23 pitch prop.  At the throttle lever's WOT position, I was getting 4000 RPM and 37.5 MPH measured by the GPS.  At that point, I noted that the temp gauge was showing 240 degrees!!  I throttled back immediately and opened the engine cover to let things cool off.  The temperature finally fell back down to 150 degrees.  If I cruised around 1200 RPM the temp stayed around 150 degrees.  At 1800 RPM the temperature was up at 160 degrees. 

Given that the engine will run at normal temperatures at slower RPMs, I'm thinking I have a water flow problem.  Does that sound right?

If you agree this is a water flow problem, what are the likely suspects?  Bad thermostat valve?  Rust-constricted exhaust elbow?  Rust constricted exhaust manifold?  Dirt/plugged exhaust manifold?

When I feel the water hoses, the water intake hose is cold, the big water pump hose is hot and the hose from the thermostat housing to the exhaust manifold is warm.  I think the hose temperature details indicate that the thermostat is opening and letting warm water go into the exhaust manifold.

Photos, if helpful...
http://i870.photobucket.com/albums/ab264/neutron68/Glastron/20141101_135727_zpsdi3tbkjl.jpg
http://i870.photobucket.com/albums/ab264/neutron68/Glastron/20141101_135749_zpsztsdiotc.jpg
http://i870.photobucket.com/albums/ab264/neutron68/Glastron/20141101_135939_zpsf3xkycny.jpg
http://i870.photobucket.com/albums/ab264/neutron68/Glastron/20141101_140132_zpsgtjwlv4l.jpg

Eric

[Plugcheck]

I would try the easy stuff first.  Change the thermostat, then clean out the exhaust manifold next.  Several well seasoned marine mechanics on this board may also comment.  Is it possible the gauge is wrong?  240 would have felt like on fire to me, my 140 in a 80 16ss would run all day and never hit 190.

[Rich_V174SS]

Either a clogged up exhaust elbow or manifold restricting water flow or an aftermarket water pump impeller was used. Your starting issue sounds like an improper cold-start procedure. You are supposed to press the throttle-only button and pump the throttle a couple times and start the engine with a slightly increased throttle setting. Then, as it warms up the choke opens and rpm increases you back off the throttle until it will run at idle on its own. Your engine's top rpm of 4000 is not enough, should be closer to 4500. I would try a 21p prop.

[Neutron68]

Thanks for the input.

I'm pretty sure the engine was hot when the temp gauge was showing 240.  When I opened the engine cover, I saw a wisp of smoke coming from somewhere between the exhaust manifold and valve cover.

Temp gauge:  I trust it.  It was working fine with the 120 engine I had in the boat last summer.  I never saw the gauge read higher than 160 degrees with the 120 engine, even after full throttle runs.  I had cleaned all the rust out of the 120's exhaust elbow so I know it had, good water flow.

Water pump, lower unit:  It was replaced in fall 2014 during the lower unit replacement.  I trust the installer.  He is a Mercury-trained tech, with a main focus on stern drives.  He is very particular and through with his work.  He found and fixed the mistakes of another shop that had worked on the drive in 2013.

Starting difficulty:  I'll try your cold-start procedure, Rich.  Does the repeated throttle lever pumping prime the system with fuel?
With the previous 120 engine, a previous owner put a fuel primer bulb in the fuel line, so I always gave the primer bulb a few squeezes before attempting to start it.  The 120 almost always started within 5 seconds of starter cranking, after the choke was set, with no throttle pumping and with the throttle in the idle position.

Rust constriction:  This is my fear.  I have experience taking the exhaust elbow off the 120 engine and cleaning it out.  It took me several weekends of work, with the rust-eating acid, the sanding of the mating surfaces so they were flat/true, and the final re-installation.
The the exhaust manifold is a new story.  It looks more scary/complicated, with the crab attached to the top and a solenoid attached to the bottom, etc.

Thermostat valve:  it would be nice if this turns out to be the problem.

Engine RPMs:  Given that I will have to change from a 23 pitch prop to a 21 pitch prop to attain 4500 RPM, do you expect the new top speed to be lower than 37 MPH, the same, or higher?

Exhaust manifold drain plug:  Any thought on this?  IF the exhaust manifold is ok, should I try and remove the (epoxy?) plug and fix the drain hole correctly?  I've read that one should retap the hole with a tapered 1/4 inch NTP tap and then "insert a brass 1/4 inch NPT nipple with sealant, then a brass coupling, then a brass plug."
see http://forums.iboats.com/forum/engine-repair-and-maintenance/mercruiser-i-o-inboard-engines-ouldrives/417263-mercruiser-3-0-drain-plug

Eric

[Rich_V174SS]

Water pump, lower unit:  It was replaced in fall 2014 during the lower unit replacement.  I trust the installer.  He is a Mercury-trained tech, with a main focus on stern drives.  He is very particular and through with his work.  He found and fixed the mistakes of another shop that had worked on the drive in 2013.

Doesn't mean he didn't use a genuine Mercury Impeller. Could have been a lower cost Sierra for all I know. I would inquire

Starting difficulty:  I'll try your cold-start procedure, Rich.  Does the repeated throttle lever pumping prime the system with fuel?
With the previous 120 engine, a previous owner put a fuel primer bulb in the fuel line, so I always gave the primer bulb a few squeezes before attempting to start it.  The 120 almost always started within 5 seconds of starter cranking, after the choke was set, with no throttle pumping and with the throttle in the idle position.

Yes, pumping the throttle one or two times squirts in extra fuel for cold starts and closes the choke at the same time.

Engine RPMs:  Given that I will have to change from a 23 pitch prop to a 21 pitch prop to attain 4500 RPM, do you expect the new top speed to be lower than 37 MPH, the same, or higher?

You might gain some speed along with the rpm, only way to tell is to try it. What size is the boat we're talking about again? In an 18 foot boat with a Mercruiser 140 and 21p stainless prop I would expect about 45mph on average assuming the engine is in top condition.

[Neutron68]

Starting difficulty:  I'll try your cold-start procedure, Rich.  Does the repeated throttle lever pumping prime the system with fuel?
With the previous 120 engine, a previous owner put a fuel primer bulb in the fuel line, so I always gave the primer bulb a few squeezes before attempting to start it.  The 120 almost always started within 5 seconds of starter cranking, after the choke was set, with no throttle pumping and with the throttle in the idle position.

Yes, pumping the throttle one or two times squirts in extra fuel for cold starts and closes the choke at the same time.

I tried the cold-start procedure on Sunday afternoon.  I gave it about 4 pumps.  It started sluggishly and ran really out of balance, like 1 or 2 cylinders weren't firing.  It needed a fairly high throttle position to remain running in that state.  After about 30-60 seconds of running out of balance it smoothed out and all cylinders seemed to be firing. 
What happened there?  Did one or more cylinders get flooded with gas and eventually cleared out?

Exhaust manifold drain plug:  Any thought on this?  If the exhaust manifold is ok, should I try and remove the (epoxy?) plug and fix the drain hole?  I've read that one should retap the hole with a tapered 1/4 inch NTP tap and then "insert a brass 1/4 inch NPT nipple with sealant, then a brass coupling, then a brass plug."
see http://forums.iboats.com/forum/engine-repair-and-maintenance/mercruiser-i-o-inboard-engines-ouldrives/417263-mercruiser-3-0-drain-plug

[Jason]

Sounds like it was flooded. 4 squirts is quite a bit. One should be enough. I'd check the choke and make sure it's working properly. Really, we don't even need a choke as we don't start them in real cold weather. I'd make sure it's open while starting.

[Neutron68]

Sounds like it was flooded. 4 squirts is quite a bit. One should be enough. I'd check the choke and make sure it's working properly. Really, we don't even need a choke as we don't start them in real cold weather. I'd make sure it's open while starting.

I did take the spark arrester off and watched the choke flapper when I started it cold.  The choke does close when you set it with the throttle, and it does open and stay open after it starts and warms.

[Rich_V174SS]

You most likely flooded it with too many pumps, and it will run rough until the choke opens as the engine temperature comes up. I generally give it half a pump and leave the throttle set slightly high. Don't start it with the throttle set in neutral, just slightly advanced.

[Neutron68]

I got a new thermostat yesterday to eliminate that as a possible cause of the overheating.
The thermostat housing gasket is expected to arrive in Friday's mail.

Are any special solvents/tools recommended to remove the old thermostat gasket, if it's fused in place? 

[75starflight]

Are any special solvents/tools recommended to remove the old thermostat gasket, if it's fused in place?

A SCRAPER RAZOR

[Neutron68]

To eliminate one of the possibilities, I just changed out the thermostat valve with a Mercury 59078, and a new gasket.

I tried the old thermostat in a pan of water.  It opened before the water boiled, but I don't know what temperature it was when it opened.

The guy who rebuilt the lower unit asked me to see how much water was being pumped by the impeller.  He said to pull the hose from the engine's water intake and start it up.  I did that and shot a movie to show. 
Note:  The test I ran in the movie was with the boat floating in the lake, so the flow was being generated solely by the impeller's action.
see:
https://www.youtube.com/watch?v=Ol7Gx_IDvnA

To me, it looks like plenty of water being delivered.  Agreed?

I plan to take the boat out in the lake this afternoon and see if it still hits the 240 degree reading on the temp guage.

When the engine was swapped-in this past fall, I was told a new temperature sender was put in. 
Is it possible the wrong temperature sender was put in (causing a mismatch to the 1970s temp guage in the dash?) and it is thus giving me a false reading?

edit:  in looking closely at the temp sender...it's got black paint on it, as if it were original equipment or moved from another engine.  All the pictures of new temp senders I see are non-painted brass.  So, now I'm thinking this isn't a new sender...and I need to prove to myself it's good before I go any farther!

Eric

[Neutron68]

Results of Saturday's test run:

On Saturday, I saw what I consider wide fluctuations in temperature readings.  After starting the engine in the lake, at the dock and running at idle (about 1000 RPM), the temperature reading slowly rose to about 160 degrees.  Once I set out into the lake, I was running at 1200 RPM (barely above idle) and the temperatures rose from 160 to 200 in about 1 minute.  If I shifted into neutral and sat at idle (1000 RPM) the temperature would come back down to around 160 in 1-2 minutes. 
The temperature reading appears really non-linear, the way to quickly rises up to 200 once 160 is reached.
At this point, I don't trust the temperature sensor.

I've ordered a new temperature sensor and I'll see if the new one behaves any differently.
I'll also bring my infrared thermometer gun out to the boat and see what temperature reading I get with it.

Eric

[Plugcheck]

Not an outboard expert by any means, but the sensor readings all over, miss fires, and hard starts has me thinking the ground connection to the engine is not as good as it should be.  If the temp sender is one wire, then a loose chassis ground could cause erroneous readings.  I d give a good once over on the harness.

[Rich_V174SS]

I've seen this before and wild swings of temperature readings usually means one of a few things - 1) clogged exhaust elbow, 2) bad water circulator on the engine, 3) defective water pump impeller (aftermarket). I'm willing to bet it's number 3, and I don't care how good the guy is who installed it. I had a boat drive me crazy with the same problem and after replacing the impeller the 3rd time within a week with an OEM part it was fine.

[Neutron68]

The problem was a screwed-up lower unit impeller.

This past weekend, I towed the whole boat to Dan Luke in Excelsior and he took apart the drive unit to get to the water impeller.
Upon getting the drive off and opened up, Dan saw that the water impeller was screwed up.
At least one of the impeller fins was not pointing in the correct swept-back direction, likely from backwards rotation of the impeller.
Dan rebuilt the water pump with a new Quicksilver impeller and reassembled the drive on the boat. 

Dan said this backwards rotation of the impeller is prevented while the drive unit is attached to the engine and it can only occur when the drive is off the boat and the propeller is turned backwards. 
The opportunity for backwards rotation occurred 2 times this past fall:
1. when I transported the disattached drive unit from Dan's house up to the cabin, and
2. when the boat engine was removed and replaced a couple of weeks later
So, the backwards rotation could have been done by me or by the guy who swapped the engine.  I can't be sure.

This weekend, I tested the boat in the lake, and I can declare that the overheating problem is solved.
Both the temp gauge in the dash and the infrared thermometer showed that temperatures were in the expected ranges.

The previous Sunday, the exhaust elbow got up to 180 F after running the engine at 1500 RPM for 5 minutes in the lake. 
This weekend, the exhaust elbow, only got up to about 85 F, after running the engine for an hour, in the lake!
The previous Sunday, the exhaust manifold got up to 200 F. 
This weekend, the exhaust manifold was around 150 F.
The previous Sunday, the engine block got up to 180 F. 
This weekend, the engine block was around 140 F.

I think I've finally got all the major malfunctions fixed!
Now, I can relax and start enjoying the Glastron!

Eric