Moderated Discussion Areas
  ContinuousWave: The Whaler GAM or General Area
  Overheating an

Post New Topic  Post Reply
search | FAQ | profile | register | author help

Author Topic:   Overheating an
Bigshot posted 01-16-2003 11:24 AM ET (US)   Profile for Bigshot   Send Email to Bigshot  
Interesting topic on another thread sparked my interest(along with others). I began to think what do most people do when they hear that shrieking alarm go off?

Now there are many alarms that sound but most common is the overheat alarm followed by the low oil or fuel restriction alarms. Now when I hear that alarm I instantly pull the throttle back and turn off the engine. I tilt the engine to see if I grabbed a bag or something. If clear I immediately lower the engine and restart it. My theory is that the alarm sounded due to water intake blockage, now that the blockage has been cleared and water pump has resumed normal operation, it is better to have fresh water cooling off the hot engine than steam or air that is left in the water passages. Water dissipates temperature 25 times faster than air(hence why you can get hypothermia in 85 degree water), so what faster way to cool an engine than to run water through it. I came to this conclusion many years ago when my age was in the single digits. If I let the engine sit it would take maybe a 1/2 hour before the alarm would stop sounding. If I started it and the telltale was working, etc it takes a matter of seconds, therfore less chance of doing damage being engine is hot for a shorter period of time. This may not be appropriate if engine is REAL hot as the cool water may crack or warp something, but I would do it anyway.

There are many degrees of overheating. The first is the alarm. Although this is being debated, I have been told that the alarm sounds at the 180-190 degree range which is still relatively cool and nowhere near the temp it takes to warp anything or affect head gasket integrity. Most overheats are at this point and nothing to be concerned about in my opinion. As a child, it was a daily occurance with the amount of seaweed we had in barnegat bay. 2nd degree is when the slow feature is activated. This is a 2 stage process though. The first is that you hear the alarm and do the proper shutdown. Upon restart the slow has now been activated and once the alarnm goes off you can shut down again and reset the slow feature. I would not be concerned at this point either. The other slow is when you don't get the audible alarm for some reason or ignore it, etc and the slow feature engages while running. This is a second failsafe that is saying...."hey moron! you are lucky you have me or your engine would be toast in another 30 seconds!". This is more extreme and I would therefore maybe retorque the heads if I felt the engine temp had reached a high like steam was coming out from water outlets and engine block was sizzling, etc. 3rd degree is when all fails or you had no failsafes to begin with and she gets real hot. Hot like steam is coming out the peehole and you can fry an egg on the powerhead. Hot where the white paint discolors or even peels from the extreme heat. Hot to maybe she even seized but freed up once cooled. The latter being when I think pulling the heads and replacing head gaskets and checking the head for warpage is not out of the question. This does not however mean the engine is toast and should be considered unreliable, just that you may want to take precautions and assess internal damage(if any).

In my years of boating I have done all of the above. I remember running at night when I was like 12 and I could not see the telltale. When I came into my canal I saw the steam and shut it down. That poor 25 Johnson was red hot and making crackling noises. It may have even seized temporarily but I do not think so. It discolored the head slightly and from that day on I am very sensitive to my telltale and guages. My sister also got my 35 Johnson very hot from inexperience but alarm was the savior in that case. Just becaus ethe alarm is sounding and water coming from telltale is not too hot does not mean that it is not overheating. On most engines it does mean she is cool but some have the telltale just to show the waterpump is working, but a clog or stuck thermostat could be overheating the left side of the engine only, so feel around before you think the alarm is just cooky. Basically what I am saying is these engines are pretty tough and are designed to overheat occasionally to a degree. What overheat stories or remedies do you have?

FLUKEDUKE posted 01-16-2003 01:32 PM ET (US)     Profile for FLUKEDUKE  Send Email to FLUKEDUKE     
Glad to say after many years running outboards (mostly OMC), I don't have an overheating story. What I've learned doing my own maintenence is that your maintenance schedule depends on how you use the motor.
Some may consider it overkill, but every spring I replace thermostats and the pump impeller, not due to wear issues, but fishing shallow water tends to suck up a lot of bottom into the cooling system, have seen
thermostats stuck open from assorted sea shells. The boat never gets put away after a day in the ocean without a fresh water flush,
preferred method being, back into a freshwater lake and run to operating temp.
The 2 weekend a year boater can actually have more overheat problems than the every weekend user, corrosion build up if not stored properly, dried out hoses and impellers. Some of the guys I fish with say
I'm paranoid about this stuff but the fact is
if I'm going fishing, all I want to do is fish, yes, and maby have a beer.
Bthom posted 01-16-2003 02:14 PM ET (US)     Profile for Bthom  Send Email to Bthom     
I've kept my boat in the water for the last two seasons,but when it comes out the engine flushing is done in a huge garbage can,bought specifically for that purpose.

My reasoning was that the water in the can gets recirculated through the engine until it gets nice and warm,and warm water would work better at dissolving deposits in the cooling jacket.
Two side benefits are that it is much quieter for the neighbors sake,and the I think the little bit of oil in the cooling water may lube the thermostat and coat the passages a little for the off season,perhaps providing some corrosion protection.

When I bought my boat the service manager at the dealership told me to change head gaskets every two years if I was going to use it only in salt water,and do water pumps every season.I've got twin 150 black max's.I adhered to this schedule for the first 8 years, and did the work myself so cost wasn't a huge factor.Now the head gaskets are a little overdue and I'm wondering if anyone else has gotten this advice.
It did give me the opportunity to inspect the cylinders regularly,but I don't know anyone else who has done it.

That's my tale,Brian

Bigshot posted 01-16-2003 03:34 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Good ideas!

It never hurts to over maintain a boat, especially when it consists of 1 saturday and a 6pack ;)

I usually go about every 2-3 years on the waterpumps but i also run a waterpressure guage so I know if I am not up to par or if some blockage has occured. Wish I would have had that guage as a kid. Removing the water jackets on some engines is a great way to inspect the internals and maybe catch that stuck ring before it stuffs the engine etc. On some Mercs though they do not have heads per say so by removing the rear plate you are just removing a water jacket so don't bother.

Keep them coming...lots of good ideas out there.

TightPenny posted 01-16-2003 03:47 PM ET (US)     Profile for TightPenny  Send Email to TightPenny     
Bigshot, you must be pretty young.

When I was back in the single digits running on the Barnegat Bay, the engines didn't have alarms, didn't have a side spurting tell tale, and the paint color on my Johnsons was green on the 10 and maroonish brown on the 35.

We did have the eel grass, but that generally resulted in a roar of overrev when the grass built up on the protruding nose of the lower unit, causing the propeller to spin in a vacuum. Kicked it in reverse and got going, cause the engine never had the time to overheat.

As to water pumps, I only replaced the impeller once on my 1974 Evinrude, or rather I had Ralph (really Stan)at Red Top Boats replace it. I ran that engine until 1998 when I replaced it with a 1997 leftover 60hp Johnson. The engine still ran, but the darn tilt was so tight that I couldn't lift it unless I was in the driveway and the boat was on the trailer.

NEVER SCARED posted 01-16-2003 04:03 PM ET (US)     Profile for NEVER SCARED    
TightPenny, Are you saying that you ran that Evinrude for 24 years with the same waterpump? You gotta wonder if this "every 2 years" is a dealer scam! I personally ran an Evinrude 15 hp HARD for 6 years and never had a waterpump problem. Im at 3 years on my used 150 Ocean Pros water pump. Darn thing pees so hard, it hurts your palm if you hold it there too long.

Never scared

Knockerjoe posted 01-16-2003 04:16 PM ET (US)     Profile for Knockerjoe  Send Email to Knockerjoe     
I agree the best solution for overheating is performing routine maintenance. Thankfully modern motors do have alarms. But it is important you test these alarms at least once a year. On my 200 Johnson that means grounding out a beige wire on my motor to test the overheat alarm. OMC warning horns are notorious for failures. Another good backup is a water temp indicator or water pressure indicator. The most likely cause of overheating is a stuck thermostat or a failed water pump. Make sure you have tools in your boat to remove your thermostat in case it gets stuck in the closed position. This will save you a tow or worse. And don't forget to change out those thermostats and water pumps periodically. With the price of a powerhead these days spending a few hours on maintenance goes a long way!
Bigshot posted 01-16-2003 04:43 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Early 30's. My 1st engine was a 4.5hp Eska on my 9' squall. It fell off and sank. I then got a 4hp Merc circa 1972 which actually had a telltale. In 1982 we got a new 13' w/35 Johnson elec start which had the alarm. So yes I was 13 when I got my 1st alarm but had done enough damage by then. You know that rev and exhaust sound you were talking that point the alarm would already be sounding so that was the point I was trying to make. The alarm is there to sound early. By the time the engine cavitates from grass you would be in the slow mode. No biggie sounding alarms.

I know a guy in upstate NY that has a 1982 wellcraft with the original water pump in it. He drops it every year to lube u-joints and such but it keeps going and looks good supposably. So yes again...every year or 2 is a scam if you drive normal. My 99 evinrude has original pump.

TightPenny posted 01-17-2003 01:42 PM ET (US)     Profile for TightPenny  Send Email to TightPenny     
Never Scared: I replaced the pump once in the twenty four years that I ran that engine. It was still pumping when I pulled it off the transom of my Sport 15 and gave it to my Uncle, who probably left it in his backyard when he sold his house and moved to New York.

Bigshot: And here I thought that you were a contemporary.

lakeman posted 01-17-2003 01:53 PM ET (US)     Profile for lakeman  Send Email to lakeman     
I have started using a product called salt free or Salt x it comes as a kit you put on the flushing attachment, initial cost was about $30. I have had frieds us this product and who do nothing but salt and they claim that it will go in and breake the salt deposits up in the water jacket. There mechanics say it will/does work. On a TV show SHIP SHAPE or someting like that they were talking about some of these devices and the comment came that 4S outboard need to desalted in the water jacket often because they are supposidly running hotter than 2S motors.

My 2 sense hope it's not another scam

fester posted 01-17-2003 03:36 PM ET (US)     Profile for fester  Send Email to fester     
Make sure you have a overheat alarm that is working and located in a postion that you can hear it while underway. The alarm on my old boat was such that it was difficult to hear unless boat was operating at an idle. A water temperature and possible a water pressure guage are helpful. The problem with guages is that I do not think most people, including myself, look at the guages often enough to catch a overheat situation immediately after it happens.

I think the best prevention is to be aware of situations where your lower unit could pick up kelp or trash that could impede the flow of water into the engine. For instance, a dirty harbor or an area with a lot of kelp. In these situations, you should keep an eye on your temp guage and deal with any overheat situations quickly.

hooter posted 01-17-2003 04:16 PM ET (US)     Profile for hooter    
Here's a few more sticks for the fire: 1) Like religion, replace the wp impeller every 24 months, without fail. 2) Keep a three foot length of weed-whacker string on board t'run up the p-hole (the engine’s) and into all the openings you can get to, if cleaning the screens doesn't do the trick right away.3) Yeah, the alarm should quiet after only a few seconds if you've restored circulation, so cool it with water at idle. 4) Especially on older salt engines, if these steps don't woik, limp back home and pull the heads t'check for lots of scale. A bead blast of the heads(inside and out) and re-paint (outside only) may save you a world of headaches for another very long time. Cost me about $300 last time and the heads were almost concrete with scale (a souvenir from the previous owner of that rig).
STEPHEN posted 01-17-2003 04:53 PM ET (US)     Profile for STEPHEN  Send Email to STEPHEN     
I figured you for at least 50.
whalersailer posted 01-17-2003 06:29 PM ET (US)     Profile for whalersailer  Send Email to whalersailer     
Good topic!

I have a question:

Bigshot says "On most engines it [peeing out the inspection jet] does mean she is cool but some have the telltale just to show the waterpump is working..."

Does anyone know if the inspection jet on the OMC mid 70's-90's triples (70 hp) simply shows that the pump is working or if it is cooling?

I guess a real simple way to check this would be to see if the water coming out is warm or cold. Unfortunately, I won't be able to make this observation until mid April (optimistic), and I have honestly not checked it on this motor yet.



ducktwin posted 01-17-2003 07:32 PM ET (US)     Profile for ducktwin  Send Email to ducktwin     

The "telltale" is simply a water pump indicator. It does not mean the engine is cooling properly.

You can have a closed thermostat and the telltale will look the same.

newt posted 01-17-2003 09:39 PM ET (US)     Profile for newt  Send Email to newt     
All this talk of overheating has me wondering if I even have a temp alarm. Would the new Merc I put on have one if I didn't specificaly ask for it? Or would the engine come with the sensor, and the buzzer or guage is installed by yours truly?
simonmeridew posted 01-17-2003 10:08 PM ET (US)     Profile for simonmeridew  Send Email to simonmeridew     
I understand what you're saying, but howcomes the water coming out of the pisser is warm(or hot)after the engine warms up. Not just on my OMC 70 but on my OMC 6 also.? And it's the same temperature(to my hand at least) as the water coming out of the main water outlet(on my 6 hp?)

BTW I have a water pressure guage on my OMC 70, high recommendation.

Clark Roberts posted 01-18-2003 08:34 AM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
The "tattle tale" stream only indicates water pump operation and on some engines it exits before passing through cooling circuit and may feel cool but on some it is the exit from cooling circuit and will be hot to the touch... may burn if over 130 degrees! The 20/25 Mercs only discharge when thermostat opens so there is a delay of discharge on cold start-up and the cycling of the thermostat can actually be observed. All current model outboards (except the manual start -non electric models) have over temp audible alarms (think I'm right on this) if factory harness and controls are used. Good idea to have temp guage backed up with a press guage but min... temp guage! The temp guage will give you some warning of impending heat-up problems when it deviates from observed normal readings. Happy Whalin'... Clark.. Spurce Creek Navy
ducktwin posted 01-18-2003 09:19 AM ET (US)     Profile for ducktwin  Send Email to ducktwin     
Hello Simon,

The OMC's telltale is consistant. It is typically routed off of the cylinder head drain.

Water will bypass the thermostat, at a reduced rate, even though it is closed.

diamondjj posted 01-18-2003 09:44 AM ET (US)     Profile for diamondjj    
I change the water pump impeller every two or three years on my Yamaha and while I am at it, I also change the anodes that are attached to the cooling water passages in the cylinder block whether they need it or not.
Gene in NC posted 07-04-2003 09:32 PM ET (US)     Profile for Gene in NC  Send Email to Gene in NC     
My advice is, never change impeller. Read on for the whole story, as Paul Harvey says.

'66 100 johnson on '66 Sakonnet bought in '67 was run hard and often. Much of it skiing double in fresh water but plenty wave jumping off the NC coast. Finally after about 10 years, on a Friday after Thanksgiving, returning from sea wide open w all canvas up, did I mention that it was a bit of a wet boat off shore, when we throttled back to come in to the marina the engine dieseled and wouldn't shut off. Tow in. Sat for winter.

Next spring the shop had no idea of problem but willing to replace stuff until final solution. So, back to water skiing. In July dieseling came up again and engine would not stop until fuel disconnected. Old guy, like many of us, pulled impeller and we discovered that rubber slipped on the core until rubber melted and eng over heated. The rubber then cooled and vulcanized itself back to the core.

About ten years ago decided to do it right, some carb work and oh by the way, replace the impeller. It's the, "Oh by the ways", that get you every time.

Another old guy, trying to get the lower leg bolts out, melted some of the leg and damaged the connecting flange that on test let fresh water into the lower case. On the way back to the shop for correction the coupler came off the hitch ball, the safety chain hooks straightened and the boat wound up, badly damaged, in a bean field.

So the moral is never replace the impeller, it can rejuvenate itself, or at least use Permatex #2 gasket seal on the bolts so that you can get them back out.

Must admit benefit of regular impeler service in that bolts more likely to come out w/o major problem or even worse, your boat winding up in a bean field.

That's my story and I'm sticking to it.

Son now uses skeg of OMC on Montauk as a depth finder and dredge for working over bars into shallows which suggests regular impeller changes are advised.

No one will ever read this but I enjoyed sharing it anyway.

Post New Topic  Post Reply
Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.