Blown head gasket / overheat

[woodycooper]

I'm getting overheat horns in the following way:
Let idle for 10 minutes -- temp readings within spec
Run 4K RPM for 15 minutes -- overheat warning horn. Stop the boat, turn off the motor for about 1-2 minutes, restart and go on my way. 4K RPM for 5 more minutes, same overheat. Start again, run 3500RPM until destination, no warnings. Took off cowl after second overheat and took IF readings on the head and all readings fell within spec although higher than idle, 150-154F
Run 25 minutes at 3500RPM -- no overheat warning.

So all I've got so far is running at higher RPM seems to eventually trigger an alarm. The book says that high speed overheats indicate a leaking head gasket. Having already removed them before, there isn't really a gasket but an o-ring for each cylinder. Unlike the heads in other varieties of Evinrude 2-stroke, these have one entrance and one exit for cooling water. The gasketed ones will allow cooling water to leak in or exhaust gasses to be leaked into the cooling passages which would block water flow. But mine uses o-rings so a leaky o-ring would allow exhaust gasses to escape from between the head and block, and that is all.

Here's the data in case anyone is interested.
Model : E150EXERV '94
Parts replaced or rebuilt and verified working: overheat sensors, thermostats, thermostat seals, cylinder head o-rings, raw water pump, fuel pump, fuel tank check valve, carbs rebuilt (last year). About the only thing I haven't replaced (in this load of the parts cannon) is the fuel hose and filter.

 

[Scott Danforth]

Start with your water pump and the impeller that should be replaced every few years

 

[woodycooper]

Start with your water pump and the impeller that should be replaced every few years

I'll note the passage from my original post where I replaced the "raw water pump" otherwise known as a "water pump" but I deal in bigger boats too where there is a distinction.

Here's the data in case anyone is interested.
Model : E150EXERV '94
Parts replaced or rebuilt and verified working: overheat sensors, thermostats, thermostat seals, cylinder head o-rings, raw water pump, fuel pump, fuel tank check valve, carbs rebuilt (last year). About the only thing I haven't replaced (in this load of the parts cannon) is the fuel hose and filter.

 

[racerone]

Defective temperature switch ?.-----Time to test it.

 

[ONERCBOATER!]

I like the defective temp switch.
If that not it.

Maybe partially plugged intake screen?
Block water passages filled with corrosion or sand...?
Thermostat failure...?

How is pee stream even with "new raw water pump" at idle and at speed.
Do you have a water pressure gauge?

I Usually check temp via temp gun or hand see if it really as hot as it thinks it is.

For sure follow other more experienced folks advise before mine heck... my outboard is down right now too.

Sean

 

[woodycooper]

I like the defective temp switch.
If that not it.

Maybe partially plugged intake screen?
Block water passages filled with corrosion or sand...?
Thermostat failure...?

How is pee stream even with "new raw water pump" at idle and at speed.
Do you have a water pressure gauge?

I Usually check temp via temp gun or hand see if it really as hot as it thinks it is.

For sure follow other more experienced folks advise before mine heck... my outboard is down right now too.

Sean

Raw water pump is fine. I have a gauge and it reads maybe 5PSI at idle and 25-28PSI @ 4000RPM, 30 PSI wide open. Pee stream is fine.

I'm looking hard at the temp switch and here's why:

I took the boat out today with a driver so I could take readings underway. I used a temp gun to take readings from the hottest part of the block/head.

Idle was right around 145 which is perfect. At 3700RPM I read 145-155 (it's difficult to get an accurate reading while speeding and leaning out over a running motor). At 4500RPM it got cooler, like 130 or so.

During this testing I got a warning horn once. It came on as I was decelerating from 4500RPM slowly to idle, and at about 3500 the horn went off. By the time I could take readings they were all in spec and the horn was still sounding, so I just unplugged it and went home. This is the second time this has happened during my various testing. The other times the horn has sounded I was cruising along happily at 4000RPM. It's seemingly random.

Therefore, does anybody know if there is a part (power pack perhaps) that controls the alarm circuits? A short or bad component could be the answer. I do also hear a short beep out of nowhere, less than a half second, on occasion, only at idle. With that said, does it sound like a good idea to unplug the overheat sensors to see if the warning horn will sound that way. I've tested the overheat sensor in hot oil and it is within spec, but I did not test for a short or some other issue with the sensor.

 

[ONERCBOATER!]

I have had small leaks that caused a grounded condition due to a cracked wire and drove me nuts. The worst shut me down offshore and I got to self rescue via kicker motor from 20 miles offshore...was slow and unfun.

Found the issue finely by adding salt to my test barrel....and pouring this in different areas until it caused issue...
Oh issue was salt water only and freshwater caused no issues. It was also speed and time dependent due to water slowly leaking only at speed from a cracked fitting.

This probably of no use but if temp switch proves good maybe an angle to explore.

Respectfully
Sean

 

[saltchuckmatt]

Raw water pump is fine. I have a gauge and it reads maybe 5PSI at idle and 25-28PSI @ 4000RPM, 30 PSI wide open. Pee stream is fine.

I'm looking hard at the temp switch and here's why:

I took the boat out today with a driver so I could take readings underway. I used a temp gun to take readings from the hottest part of the block/head.

Idle was right around 145 which is perfect. At 3700RPM I read 145-155 (it's difficult to get an accurate reading while speeding and leaning out over a running motor). At 4500RPM it got cooler, like 130 or so.

During this testing I got a warning horn once. It came on as I was decelerating from 4500RPM slowly to idle, and at about 3500 the horn went off. By the time I could take readings they were all in spec and the horn was still sounding, so I just unplugged it and went home. This is the second time this has happened during my various testing. The other times the horn has sounded I was cruising along happily at 4000RPM. It's seemingly random.

Therefore, does anybody know if there is a part (power pack perhaps) that controls the alarm circuits? A short or bad component could be the answer. I do also hear a short beep out of nowhere, less than a half second, on occasion, only at idle. With that said, does it sound like a good idea to unplug the overheat sensors to see if the warning horn will sound that way. I've tested the overheat sensor in hot oil and it is within spec, but I did not test for a short or some other issue with the sensor.

Sounds like it could be a bad wire somewhere but maybe some gunk moving around....definitely a head scratcher.

When you had the heads off did you true them up?

 

[woodycooper]

Sounds like it could be a bad wire somewhere but maybe some gunk moving around....definitely a head scratcher.

When you had the heads off did you true them up?

There's no gunk in the heads although there's no way to verify this. Unlike earlier models, the heads are self contained -- one inlet and one outlet. I checked to be sure they weren't warped and I cleaned them up well but I didn't true them to a high degree of precision.

 

[woodycooper]

I have had small leaks that caused a grounded condition due to a cracked wire and drove me nuts. The worst shut me down offshore and I got to self rescue via kicker motor from 20 miles offshore...was slow and unfun.

Found the issue finely by adding salt to my test barrel....and pouring this in different areas until it caused issue...
Oh issue was salt water only and freshwater caused no issues. It was also speed and time dependent due to water slowly leaking only at speed from a cracked fitting.

This probably of no use but if temp switch proves good maybe an angle to explore.

Respectfully
Sean

Sean, this description you've given is helpful. It would seem several of us including me think there's some sort of frayed wire or short.

 

[woodycooper]

I have one more question. When I repaired a frayed wire leading to the overheat sensor the wire was shortened a bit so it is just able to plug in. When installed the wire runs very close and possibly parallel to a spark plug wire. Is it possible for induction from the wire at high speed trips the sensor? My understanding is that for this to occur the target of the induction needs to be a complete circuit, and since in its default state it is not then I'd think no induction to occur. In my research I've come across spark plug wires forcing another to fire via induction (causing a misfire), but not through other circuits. thanks all.

 

[Scott Danforth]

Sensor is on a switch that connects to ground

 

[ONERCBOATER!]

Usually Spark plug wire induction issues are from wires that are linear/parallel...if the line crossed/perpendicular much less chance.
However keep in mind there's a few thousand volts in spark system hi tension side. Could easily jump a 12v switch. That said....i dont think this is your issue. It would happen much more instantly and constantly.

I'm going with wire fault or sensor fault ....

One other way to chase it...get a testing prop and a tank or drum depending on engine size. Run it in the drum until you find the fault...could easily monitor the engine and the sensor while running at your desired rpms and load then.

Course that's a couple bucks....but you can buy the test props on ebay.....

Hoping you find issue.
Sean

 

[QBhoy]

Hi. Not normally one for commenting on these engines. Never had one or even anything close to it. But thought I’d ask..does she show specifically that it’s an overheat alarm or are we assuming that the beeping means an overheat ?
I may have missed it mentioned, but what kind of boat is it on ? What’s the height set up like on the transom? At the problematic 4000 rpm…is the engine maybe loosing pick up ability ?
I realise you have mentioned it has water pressure, but please forgive me for questioning this…just that you mention that you are seeing over 30 psi indicated ? That’s over 2 bar. I’m not totally sure you would genuinely see that kind of water pressure on that engine. Could be wrong. What you think ? Where is the sender plumbed in for the gauge showing that ?
I’m rattling on here, I realise..on an engine I don’t know…but thought I’d ask mainly if you are sure it’s an overheat alarm and not anything else like battery voltage, oil level, guardian rpm limiter etc etc
Best of luck

 

[woodycooper]

Usually Spark plug wire induction issues are from wires that are linear/parallel...if the line crossed/perpendicular much less chance.
However keep in mind there's a few thousand volts in spark system hi tension side. Could easily jump a 12v switch. That said....i dont think this is your issue. It would happen much more instantly and constantly.

I'm going with wire fault or sensor fault ....

One other way to chase it...get a testing prop and a tank or drum depending on engine size. Run it in the drum until you find the fault...could easily monitor the engine and the sensor while running at your desired rpms and load then.

Course that's a couple bucks....but you can buy the test props on ebay.....

Hoping you find issue.
Sean

I have done similar. I had my wife drive while I hung over the transom with a IR gun. I only spot tested but temps were all good on the heads. Then a continuous beep, we drop to idle and immediately shoot with the gun and we're running normal temp while the horn was going off. After about a minute the horn goes turns off and I know this was overheat and not fuel restriction because the boat is now in SLOW mode.

So I can reproduce it, but it can take a while. The odd thing is that the whole process behaves like an actual overheat. The horn is seemingly random but the duration is always predictable (in idle it will go away in one minute.)

 

[woodycooper]

Hi. Not normally one for commenting on these engines. Never had one or even anything close to it. But thought I’d ask..does she show specifically that it’s an overheat alarm or are we assuming that the beeping means an overheat ?
I may have missed it mentioned, but what kind of boat is it on ? What’s the height set up like on the transom? At the problematic 4000 rpm…is the engine maybe loosing pick up ability ?
I realise you have mentioned it has water pressure, but please forgive me for questioning this…just that you mention that you are seeing over 30 psi indicated ? That’s over 2 bar. I’m not totally sure you would genuinely see that kind of water pressure on that engine. Could be wrong. What you think ? Where is the sender plumbed in for the gauge showing that ?
I’m rattling on here, I realise..on an engine I don’t know…but thought I’d ask mainly if you are sure it’s an overheat alarm and not anything else like battery voltage, oil level, guardian rpm limiter etc etc
Best of luck

I'll address your message in each point:
The overheat alarm is confirmed by unplugging it while the horn is going off. Plug it back in the horn returns. It will work like this for about 1 minute at idle at which point the horn will turn off and you're free to go on your way.
The boat is a Grady White. I've had it for years and the engine is set correctly (some might even like it higher). Long shaft (EX) Evinrude. I see this as the least likely cause of any issues.
As for water pressure, I could have read the units incorrectly. I need to look closer at the gauge, but it did read 30 <some unit of pressure>... I don't know if it's in the shop manual but I've been told 30 is good, and I do know that it's good enough to pop off the thermostats as during my testing it actually runs cooler than idle temp.
I think I've crossed out all the stupid stuff. 2-stroke, so no oil level, "guardian" is some other version of SLOW and that happens upon overheat. So yeah the problem boils down to the overheat alarm is going off, SLOW (or guardian) is engaged, temp readings are taken, and everything is normal. The electrical diagram of my engine has both sensors going straight into the power pack, and if the wires are OK then that must be the false alarm.

 

[ONERCBOATER!]

It looks like your chasing the problem down sometimes it is a long road.
2 stroke definitely eliminates the low oil level alarm....but is it oil injected, VRO, or premix. If oil injected or VRO it may be not getting right flow or that signal failing which may trip a limp mode.....just a guess I don't know I just know when the probable causes are removed...then the possible causes are next to check...then finally the impossible causes checked.

Sean

 

[flyingscott]

are you sure its the overheat alarm and not the VRO?

 

[woodycooper]

are you sure its the overheat alarm and not the VRO?

Alarm goes off, drop off a plane to idle, remove cowl and pull starboard sensor lead out, horn goes out. VRO has been unplugged (no warnnings) , and gas pre-mixed 50:1.

 

[woodycooper]

It looks like your chasing the problem down sometimes it is a long road.
2 stroke definitely eliminates the low oil level alarm....but is it oil injected, VRO, or premix. If oil injected or VRO it may be not getting right flow or that signal failing which may trip a limp mode.....just a guess I don't know I just know when the probable causes are removed...then the possible causes are next to check...then finally the impossible causes checked.

Sean

It's premixed. VRO is unplugged (no alarms possible from that). When I get the alarm I can make it stop by unplugging the overheat sensor on the starboard side. I'm buying two new ones. This will be the second set I've purchased. They've been bad out of the box (I used OEM). Same for thermostats. I'm on my third set. Started with Sierra, then bought OEM and neither one worked right. Third set works. I've begun testing every component out of the box before installing it because I've received more bad parts than good.