Potential Mercury 135 hp overheat. Help!

Joined
Nov 24, 2009
Messages
19
Hi there.

I'm new to the whole boating thing and recently purchased a 1996 fletcher 18ft boat with a 1996 Mercury 135hp 2.0 litre V6 outboard.

I decided, that as the engine hadn't been run for a while, I'd start it with the flushing muffs. I connected it all up and started and ran the engine at idle (and revved up slightly twice) for no longer than 2 minutes, when I realised there was no tell tail.

Water was coming from around the prop etc, as expected, but as I said, no tell tail.

I immediately shut down the engine after a couple of minutes, when I realised no tell tail.

My main worry now is, have I damaged the engine? There was no overheat alarm, but then again I'm not sure if it has one.

I'm booked in for a powerboat course to learn stuff like this next month, but in the meantime, would you recommend me getting the engine checked or not for over heating damage?

Thanks again for your time. It's very much appreciated!!
 

sullmate

Petty Officer 3rd Class
Joined
Dec 23, 2008
Messages
93
Re: Potential Mercury 135 hp overheat. Help!

I have the same engine 1997 vintage. First of all, your motor has an overheat alarm. It would be a steady beeping noise.
Since the engine has not been started in some time, you may want to replace the water pump impeller before restarting..
The pee hole might be blocked with crud. You may try to clean out the pee with a pipe cleaner.
Was steam coming out of the pee hole?
I would not restart until you have the cooling problem corrected
Sullmate
 

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: Potential Mercury 135 hp overheat. Help!

Many of the V-6's telltell comes from the T-stat housing and will not show flow until the stats open. We don't like it, but that is Merc's design.

Follow your P tube back to the stat housings and it becomes clear. Some have removed the stat and drilled an 1/8 inch hole thru one side of each stat to provide a small stream to indicate flow, the small increase in cooling flow will only slow warm up time a minute but it can relieve a lot of worries.

Test your overheat alarm by grounding the tan wire on the temp sensor with the key ON, if the alarm is working correctly it should sound off.
 
Joined
Nov 24, 2009
Messages
19
Re: Potential Mercury 135 hp overheat. Help!

There was no steam coming out the tell tail. There was no indication of over heating with an alarm etc, or cracking, steam etc. It's more that I know little about outboards and thought there may have been some damage done that I wouldn't automatically know about.

Is there any indication that damage has been done, or am I getting myself worried about nothing?

I will be getting the cooling system checked asap. How much do impellers generally cost anyway?

Thanks again for your time!
 

flotsam35

Cadet
Joined
Nov 23, 2009
Messages
11
Re: Potential Mercury 135 hp overheat. Help!

I have 2 1989 150 HP 2.0's and you should never rev those motors above 1100 rpms when on a flush muff!
That's what the books say. I 've done it..... how can you resist when you hear that rumble.....anyway you prolly didn't cause any damage, The temp of your hose water and out side temp may take 2 mins for T-stats (143degrees ) to open. Idle your motor with cover off and either melt stick the 2 heads or place your hand on top cylinders(hotest). Should be hot but not untouchable. Tell tale starts out very slowy then steady and can vary. Can u see the temp gauge? Also the overheat alarms are very accurate. If you don't know history of the motor change waterpump, t-stats, and popett valve before running again. You'll know how it was run by the look of tstats and WaterPump impeller. All easy jobs if you can turn a wrench. There is great info on this site how to..... and here is a decent video http://www.youtube.com/watch?v=E-uzQi7IgwU ohh I've heard of spiders clogging tell-tales that have been stored awhile....run a thin wire through there.
 
Joined
Nov 24, 2009
Messages
19
Re: Potential Mercury 135 hp overheat. Help!

Thanks for that! I'm going to give a mechanic I know a call tomorrow. Hope much does a new impeller generally cost? I've searched online and I'm guessing they're fairly cheap right?
 

flotsam35

Cadet
Joined
Nov 23, 2009
Messages
11
Re: Potential Mercury 135 hp overheat. Help!

Sorry did't get back to sooner. Yeah the impeller part is cheap, less than 20 dollars and shouldn't be more than 1 hour labor charge. I would recommend you do complete lower unit service for good measure. Good Luck
 

sschefer

Rear Admiral
Joined
Nov 13, 2008
Messages
4,530
Re: Potential Mercury 135 hp overheat. Help!

Replacing thermostats on these is like the impeller and lower unit ritual. You just do it. The current stats that Merc is selling have a bypass hole in them that will give you a tell tale the minute the block fills. The tell tale will increase in volume when the stats open and the engine is running at idle. At speed the poppet valve controls water flow through and out of the engine.

If your tell tale is not showing water, change your thermostats and replace the 3/8 and 5/16 tubing that connects them to the exhaust plate and tell tale outlet. The stats are about 12.00 each if you buy them from Merc and the tubing will run you about 5 bucks. Pretty cheap to do it right.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
Re: Potential Mercury 135 hp overheat. Help!

Sitting engines usually mean impeller problems; possible thermostat sticking problems too.

The rubber gear in the water pump takes (can take, but doesn't always) a "set" (tips folded back) and it doesn't pump as it should. I think this would be less of a noticeable problem on muffs as you have the pressure of the water hose to push water through the pump and into the engine if you have blades with a set.

In the tell tale. yes you could have it clogged by a dirt dobber, but there is more to it than that. Like CharlieB says, your plumbing can determine if you get a tell tale after a minute or so....allowing time for the water to fill the block then overflow and squirt out.

I don't have the engine in front of me but we replumbed my son's 150 of that vintage because we didn't want to wait for the stats to open to get the tell tale.

The way you can tell is to look at the rear of the engine. Both cylinder banks have a little bulge at the top with 3/8" rubber hose connected to these covers. These covers are over the stats and to get water out these hoses the stats have to open.

If your hoses tee together and then go off to the lower unit AND that hose has a tee that goes to the tell tale, you have the type that requires the stats to be open to get pee.

If not, you have the other type which gives you water as soon as the powerhead fills. Trying to remember. On this design, there is a single hose coming out of the top of the block between the cylinder banks. it goes down below the block but also tees off to the tell tale. This type DOES NOT require the stats to be open and pee should start in a minute or two.

What I did to get the latter, was to just move the pee hose from it's original position to the latter position just swapping available plastic adapters. Then he had pee within a minute or so.

Finally,as sull mate said, you have OT sensors and an alarm. Stats open at 143F. The OT alarm comes on at 190F. Also you can feel the top of the block. If you can keep your hand on it for 5 seconds, it is not overheating. Also, if you have water coming from the prop you have water to the powerhead.

Point to remember. You have a stat for each cylinder bank. The water jackets (around the spark plugs) should feel about the same temp. If one is hotter than the other (noticeably hotter) then that stat could be lazy or frozen shut. Changing stats is easy, just pay attention to what comes out and put the new one back the same way.

On changing the impeller, the speedometer tube is a pain to deal with. When you put it back together you need to insure the shift shaft is in the proper position and that the copper water tube properly engages the engine block. Either get a service manual or get a marine dealer to do it for you. While you are there, you might as well change your lower unit oil.

HTH

Mark
 
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