Overheat alarm early and continuous

[nesdonfoye]

We have a 2008 F50TLR that very quickly begins to sound the overheat alarm and go into limp mode. The tell tale is very strong and I replaced the thermostat. I thought it might be a false alarm due to a defective sensor, so pulled that and mapped the resistance/temp. Anyone know where I can find the spec for this? I get about 2150 ohms at 60 deg F going to 200 ohms at 200 deg F, and starting at a rate of about 25 ohms/deg and getting down to about 2.5 ohm/deg at the highest temps.

The background is that I have been assigned to the watercraft committee at the co-op boat club I belong to. We own various race patrol and workboats with about half a dozen 15 hp and the same of 40-60 hp outboards. All Yamahas and all 4 stroke. I was assigned to this work service position (the club is operated by member volunteers) because I was a professional auto mechanic for many years, and still have nicely stocked Snap-On roll cab. But I'm not as familiar with outboards, and clearly can't use my OBD scanners to look at the ECU.

I've searched and read many posts here and did see the spec mentioned but not specified. The only manual we have is for an earlier model with an open/closed temp switch spec. Since we have 40s 50s and 60s some carbureted, some FI bought over 10 years, I hesitate to buy a manual for each motor especially since I'm not sure this sec would be included, and because they get aged out periodically and we may have a new one or two in the fleet next year if we find the repairs on the couple that are down right now are going to be prohibitively expensive.

I see a lot YDS software and cabling on Ebay but hesitate not knowing what versions or cabling I may need for these motors. I think only 4 of our motors have ECUs and two of them are brand new so off my radar, and which may need some different versions.

Thanks in advance for your help. Very happy to have found such an active forum!

[boscoe99]

How do you know that the alarm is over temperature related? As opposed to oil pressure related?

The sensor over temperature alarm set point is 194* F. Near the 200 ohms value you mention.

If the alarm is sounding quickly upon first start of the day, when the motor is cool, I would be suspicious thinking that the motor is actually over heating. There is a 75 second delay built into the system.

[nesdonfoye]

I had hypothesized that it was the actually the oil alarm, despite being reported to me as an overheat alarm, because I found it with the oil off the bottom of the dipstick. But was told by another member that the oil alarm sounded different and would not put it in limp mode. The motor was on another damaged boat, and had not been run in a year, being retired due to what was reported as an overheat.

We had the starter on another engine fail, a carbureted 60, which is one of our oldest motors. With a new starter being $600 and just the Bendix and rebuild parts at close to $200, we took a chance on a third party starter for $170. But it was faulty, so we just opted to put the much newer 50 on the boat and deal with the alarm. One of our instructors tested it after we got it installed, and said the alarm came on about 5 minutes, which seemed short to me.

I haven't launched it and run it since I added oil. I think I'll reinstall the sensor and take it for a ride.

[nesdonfoye]

Bizarre and unrelated, after I reinstalled the sensor and was slinging the boat into the water, the starter solenoid literally exploded, like gunshot loud exploded, so I never got to run it.

In all my decades of working on engines, I've seen a few batteries explode, but never a starter. Someone may have tried to run it with the sender out, which would pump water right onto the starter, which could have been a factor as I also discovered that the key had been left on. But still. I should have pulled the battery terminal so nobody could try to start it when the sensor was out.

[99yam40]

I have never heard of anything like that happening.
with no one even trying to energize it even.

I am guessing you meant to say water was possible getting onto the solenoid not into the starter,
and both should be sealed up some what, so I do not understand this exploding thing at all

[nesdonfoye]

Yes, this starter has the solenoid mounted to it with a pinion actuating lever rather than a Bendix, so I tend to think of the motor and solenoid as the starter. I expect the separate solenoid relays are probably better sealed than the starter mounted ones. We're on the Hudson Estuary, so the water is brackish. I wonder if water had leaked into the solenoid, and shorted out the terminals generating heat while also somehow electrolyzing the water and creating H2 and O2. Maybe once the water was consumed it started to spark, maybe it was hot surface ignition, maybe it was grease that got vaporized by the heat likely the key being on is a red herring.

As I was installing the sensor I did not notice it seeming wet, but was surprised to see the boat dripping with a puddle under it when I arrived as it had been out of the water since yesterday when I pulled the sensor. Lots of people are allowed to use these boats, and I should have realized that on a Sunday someone might have tried to launch it, tho no one has come forward.

[TownsendsFJR1300]

Sounds like someone tried running it and pumped water under the cowl and into the solenoid.

Water dripping and key left on tells the story.. I'd guess water got in there and shorted the terminals..

As for the explosion, internally, something expanded very quickly.. Very odd..

[zenoahphobic]

Yes, the hidden bomb, electrolysis; hydrogen being made by an electric current through conductive water. Not in the front of many boating people's minds. Have heard of batteries exploding in poorly ventilated bilges; why not in a wet "starter" but be pretty rare indeed.
When there are lots of people involved, the chances that strange things happen increase dramatically.

[nesdonfoye]

I just dropped it off to be rebuilt at a place that does nothing but alternators and starters. They've been around for decades and so have probably seen million of starters, and they said they'd never seen this before either. I think it must have been a perfect storm of just the right conditions. I wonder if a little less/more water, salinity, time etc might have shifted the parameters enough to prevent this, wonder if somehow swinging and vibrating on the hoist may have somehow triggered it. Probably never know for sure as I doubt I could duplicate the conditions.

As I said, I've seen a number of lead-acid batteries explode, all were during or after charging when the jumper or charger terminals were being clipped on, removed or disturbed. This is the reason why, when jump-starting, you should make your last connection by clipping the negative cable to grounded metal away from the battery. All lead-acid batteries generate hydrogen, most prolifically when being overcharged, and the spark of a transitional connection can ignite the gas inside the battery via the vents. Interesting analysis of outgassing in batteries:
http://mathscinotes.com/2013/02/batt...tgassing-math/

[panasonic]

Post the engine data plate information on the transom bracket...model, serial number.

I may have the manual for that engine and i can give you the information on the oil pressure and overheat tests.