40 HP pees but still overheat alarm at speed

[trackerpro91]

Hello! I bought a "new to me" '91 Bass Tracker Pro 17 a few weeks ago.
QUESTION: Can anything other than a blown head gasket cause the overheat alarm to go off when the throttle is increased past "neutral +" speed?
BACKGROUND: Please bear with me, the background will help. It is a '91 Johnson 40 HP (OMC). The boat was kept in a garage and unused by a widow for over 25 years. Very little use on the motor, but it is over 30 years old (that plastic tip on the manual motor assist also broke). The first use, I took it to the river, warmed it up at slow speed for a bit and opened it up slowly. No problems. Next week, took it to Joe Wheeler with the kids. AM ride no problem. PM ride pulled my son on a tube (He is 130 wet). During the constant throttle changes, it eventually cut off for a minute. Started back fine. Would cut off if throttled too high. Next day, the overheat alarm started sounding when motor put on higher load. No alarm at slow, slow speed. Saturday hooked up motor to hose with attachment. Boat pees fine. Did not throttle high. Sunday went fishing and alarms at any speed past slow, slow. I have the SELOC manual, and it says this situation may be a blown head gasket. So, before I break this down, does anyone have any other thoughts?
Thanks in advance!

 

[DaleH]

GULP ... ouch, it it were mine ... the impeller would have been replaced BEFORE it was even started up after 25-years of sitting! Regardless of what else may be going on ... you need a new one. Use OMC gasket sealer on all bolts.

Sure, she might pump @ idle speeds, but those vanes take a fixed set after a few years (I replace them every 3 seasons) and they no longer move or expand out against the housing and no longer 'SLING' the water. The waterpump is an eccentric centrifugal pump, where pliable vanes on the impeller is a must!

If running ethanol fuels, replace all fuel lines, as lines that old cannot survive today's fuels. The cut out was likely caused by the carb bowl not filling up correctly, probably needs a good carb cleaning. Or if pumping the primer bulb, which actually functions as a check valve, prevents it from cutting out, then the fuel pump diaphragm could be weak or damaged.

It is also not uncommon for older OBs, especially those that have been sitting, to run OK on 1st start, then slowly start to experience more and more issues as the time goes on.

 

[airshot]

Agree with DaleH.....hooking up to a hose means nothing as the pressure from the hose will circulate the water, not the water pump !! Absolutely replace that pump before running again...check for any missing pieces in the cooling system !! Get yourself an actual factory manual and use the Sealok as toilet paper !!

 

[trackerpro91]

Some additional facts: I actually bought it from a friend's husband, who bought it from the widow last year. He ran it about 20 hours last year, said he had no problems (which totally tracks with it showing problems, now). He replaced the plugs and had the carburetor cleaned. He just sold the bait business he had here forever, and he is no stranger to boats.

I only put 100% gas in it, no ethanol blends. Also, I ran it in the water Sunday, and confirmed it was peeing, and it wasn't a dribble- it was a strong stream.

So, so far I am definitely replacing the impeller and looking for some OMC gasket sealer (and hopefully its in all one piece so I don't have any pieces in the cooling system). Also looking for a factory manual and plan on tracing the cooling system for all its pieces. Any lead on a factory manual for the motor would be greatly appreciated.

Anymore info is always appreciated!

 

[trackerpro91]

Where is BRP/OMC Gasket Sealant Compound?​

The above link is about OMC gasket compound no longer being sold. I guess I'll get the loctite.

 

[JL8Jeff]

How hot is the power head when the alarm goes off? Is the pee water warm, hot or cold? My Mercury had the overheat alarm go off and it was not even close to hot. I tried replacing the sensor but the alarm still goes off. It turned out the overheat module went bad. I also get bugs clogging my pee stream from time to time so I'm always looking at it when I first fire the engine up.

 

[trackerpro91]

Don't know. But I can definitely state that the alarm only goes off when I push the throttle forward. It does its beeping. I pull back on the throttle, and the beeping stops (the beep pattern is the overheat alarm for this motor). I can tool around forever at low speed. I read where, in this situation, it may be a head gasket issue - the faster/more load burden on the engine, the more the exhaust gases displace the water in the cooling system, leading to the alarm at higher speeds.

 

[airshot]

A simple compression test would/ should show a bad head gasket. E10 fuel will be no problem but the fuel hoses are probably cracked and mabey leaking from age, you don't want loose pieces in your fuel lines and carbs.
I have found most of my factory manuals on Ebay or orderedvthem from the mfgr.

 

[David Atkins]

Thank you airshot, this guy is very insistent on it being a blown head gasket; the compression test will answer that question for trackerpro91 but chill out - trackerpro91 and take each system one at a time and diagnose them, 1st replace the water pump, bottom line that needs to be replaced after sitting for so long, I used to have boaters bring their boats into my shop all the time and try to tell me what the problem is or was, some right but many wrong, you have to test and replace what needs replacing first and foremost. DO NOT jump to conclusions before you check things out first. WE are here to help you but many of us have years of boating experience to guide us (Hands on) I built and serviced boats for many years along with boating, fishing, family fun outings so I also have experience. The boat sitting for 25 years is going to have issues so just be patient with her, she'll let you know what she needs (Parts replaced), treat her nice and she will give you much joy. a 40 horse on a 17 foot boat is minimal horsepower at best so please keep that in mind as well. Let us know we are here for you!

 

[trackerpro91]

This guy is not insistent on anything; my question was is there anything OTHER than a blown head gasket to cause the problem, under the circumstances in my first post. I've gotten a lot of great advice from much more experienced boaters, and I am greatly appreciative of it.
So, you think I need to replace the whole water pump assembly?

 

[David Atkins]

This guy is not insistent on anything; my question was is there anything OTHER than a blown head gasket to cause the problem, under the circumstances in my first post. I've gotten a lot of great advice from much more experienced boaters, and I am greatly appreciative of it.
So, you think I need to replace the whole water pump assembly?

I always replace the whole water pump assembly, best practice in boat service is to replace entire assembly. A blown head gasket would be the last thing on the list for me or my marine techs; does it happen of course but other things needs to be checked, 1st the water pump, sitting for that many years the impeller is deformed and will not pump full flow, seen that too many times over the last 40+ years, I've also been boating since I was 5 yrs old and owned a boat since I was 12 years old, so been around a bit. Engines sitting for that long also have issues with electrical components so that would be my next check after the after the pump replacement, could also be build up in the water system partially blocking the water flow (Just thought of that)! Let us know! Pictures would help us, too!

 

[airshot]

This guy is not insistent on anything; my question was is there anything OTHER than a blown head gasket to cause the problem, under the circumstances in my first post. I've gotten a lot of great advice from much more experienced boaters, and I am greatly appreciative of it.
So, you think I need to replace the whole water pump assembly?

Always best to do the whole job, especially on older motors !! These engines are made to be used, and when they just sit...weird things happen !! The ability to be out, miles offshore with no one around, knowing you cut corners to save a little time and a few bucks, is not a comfortable feeling !!

 

[RaisedByWolves]

As mentioned start with the pump.

If the pump “looks” ok it needs replaced. If it’s chunked there’s your overheating issue, pieces of the impeller clogging your cooling passages.

This will let it run ok at low speed, but block sufficient flow to cool properly under power.

Hope it’s not that, otherwise you have to find all the rubber boogers to correct this.

 

[jethro]

Not sure your motor service interval but mine is a new water pump and both thermostats every 2 years. It's cheap to do and piece of mind!

 

[airshot]

Thank you airshot, this guy is very insistent on it being a blown head gasket; the compression test will answer that question for trackerpro91 but chill out - trackerpro91 and take each system one at a time and diagnose them, 1st replace the water pump, bottom line that needs to be replaced after sitting for so long, I used to have boaters bring their boats into my shop all the time and try to tell me what the problem is or was, some right but many wrong, you have to test and replace what needs replacing first and foremost. DO NOT jump to conclusions before you check things out first. WE are here to help you but many of us have years of boating experience to guide us (Hands on) I built and serviced boats for many years along with boating, fishing, family fun outings so I also have experience. The boat sitting for 25 years is going to have issues so just be patient with her, she'll let you know what she needs (Parts replaced), treat her nice and she will give you much joy. a 40 horse on a 17 foot boat is minimal horsepower at best so please keep that in mind as well. Let us know we are here for you!

Not sure that 40hp is minimal power, guess it depends on how much speed you really want.. I have a 16' Sylvan side console that weighs over 900 lbs loaded with a 40hp Merc classic, she does 31mph by gps, with me and 29 with two adults and gear. I wouldn't call that being minimal power... Years back we had a 14' mirror with an 18hp Evinrude that we skied with....todays folks must think they need the speed of light to get by....

 

[GYPSY400]

Just to rule out the head gasket quick: compression test.. but test with the other plug in, and then out. If the number changes, you know compression is leaking across the cylinders. I found this when I did my 9.9.

I'm not saying this is the issue - my first thought would be water pump as mentioned above, then maybe seized thermostat causing a flow restriction ( because it's been sitting).. then check the electrical side of the system. The head gasket, if blown, would be a byproduct of overheating.

 

[trackerpro91]

Thanks, all. Ordering parts today for pump/impeller and will be doing compression testing today/tomorrow.

 

[trackerpro91]

AND thermos....

 

[Pappy]

Just to clarify. This engine does not depend on the thermostat much past idle. The engine is heated by the thermostat at idle to promote good idle running characteristics and keep the engine dry internally while running in colder water. The engine is not thermostatically controlled throughout the RPM range. The thermostat cannnot flow anywhere near the amount of water needeed to cool the engine on plane to WOT.

 

[trackerpro91]

Cold comp test, several times, yielded compression of 125 and 120 for the top and bottom cylinders, respectively. Not bad for an engine that age.