Yes me again...Therm alarm this time

[ifish4tuna]

Un-bah-lievable....new problem
OK for those that don't remember 3 postings ago... 1999 ox66 250hp

Cold engine
Alarm sounding & thermal indicator flashing with key in on position with engine off.
Thermal indicator on the instrument panel flashing next to the 3 oil indicators.

Turn engine on, water pumps out of the spicket. So not a water pump issue.

My assumptions :

test engine coolingwater temperature sensor
test thermo switches

Question - which one of these would cause the alarm to sound? Both?

Any other advice/options for possible cause?

Really what I think I need for advice is how to hook up the winky blinky. I have it but have never used it, not clear how to hook up. It has several connectors. I've heard it should be connected to the oil harness, but there is also a wire with a plug in it hanging on the harness.

Thanks in advance, Ed

 

[ifish4tuna]

I guess I could swap them to the other engine one by one and see if the problem follows the parts.

I have twin 250s. Problem only occurs on one engine.

Ed

 

[Megabyte]

When were the t-stats and poppit valve last replaced?

Is the alarm sounding right away, or only after idling awhile?
Big block Yamahas do not pump enough water through themselves under 800 rpm in gear and will alarm even when idling after about 10 to 15 minutes of operation.
Ask me how I know this...

 

[ifish4tuna]

alarm sounds when cold, without engine running.
tstat & poppit ok/new

 

[TomS]

Ed,

Winky-Blinky is easy.

It has three connectors, two of them can plug together - these are the ones you need. Ignore the third connector which only has 2 wires going to it.

It connects in series to a similar set of male/female connectors that are in the area of the VST tank and LP fuel pumps.

There is also a single blue wire with a bullet connector on it. If you look around the wires in the same vicinity or possibly at the bottom of the engine block near the oil control rod, you will find a single blue wire with a rubber cap over the end of it. Just remove the rubber cap (mine was originally clear plastic but had turned brown/black) and plug the two blue wires together.


I haven't had the need to play with thermo-switch, but service manual lists a continuity check test - let me know if you need details.

Looks like below a certain temperature, there should be no continuity between the two wires on the thermo switch. Then as the temp increases beyond ~190*F there should be continuity.

So if I read this right, a simple check would be to see if there is continuity on either thermo switch with the engine cold.. which you could do without removing the thermo switches from the engine.


Just to double check, only the temperature indicator is blinking, correct?

-- Tom

 

[ifish4tuna]

Hi - Tom. Thanks.

So are you saying the winky gets inserted in line into one of those connections, so both connections of the winky are used connecting to 2 pieces that would otherwise be connected to each other? In any case I don't think it provides much value in this case, since its an engine off situation (although alarm keeps buzzing even w/ engine on).

I had intermitent results this morning as I swapped parts & put things back together. At one point the alarms stopped and I thought it was due to parts swap, then I put the black cover back on, and thought OK I'll try it again before declaring victory and boom, alarm on again. So I cursed a few dozen times, and scratched my head. Disconnected the black cover again disconnected one of the thermals, and tested again. No alarm. Plugged the thermal back in, No alarm. More head scratching and swearing.

Went home with 2 of the thermals. I did mix up which was in which engine to begin with, but it seems irrelavant since the problem was coming & going with or without devices connected.

I have the manual, and did the hot water test this morning. One of the thermal switch devices (that I pulled out) does not register, but by it not registering it just means it's open (no continuity) The alarm would only sound if closed. That part would have gotten me into trouble if the engine really was overheating (no alarm), but would not have been the cause for the false alarm.

The other one tested OK.

I went to Baert to pick up the new thermal devices that connect to the thermostat covers. Clydes thought was that it's likely a short in one of the pink wires. This theory seems to be consistent with my cover on/off issues. I picked up 2 parts anyway just to experiment further.

Guess I'll look for knicks in the wires tonight if I get out early enough, or tomorrow AM. Unless anyone has any better ideas. I have a feeling this one is only going to be solved with prayers....

 

[DaleH]

I went to Baert to pick up the new thermal devices that connect to the thermostat covers. Clydes thought was that it's likely a short in one of the pink wires. This theory seems to be consistent with my cover on/off issues.

Here's some Merc info, which sounds ALMOST identical, as the owner of an Optimax was getting a phantom overheat light and alarm with the ignition ON but motor OFF. Turns out the ECM is trying to indicate a problem.

”The ECM provides throttle position and engine temperature sensor failure warning to the boat operator. Sensor failure is indicated by alternately illuminating the low-oil and overheat lamps (on some rigs this is a combined light) as well as activating the warning horn. This warning will occur 15-seconds after a sensor failure has been detected by the ECM. The warning will continue until the key switch is turned off or sensor problem is corrected."

Sounds like you may need to check/test your temp sensor. Merc used to use one with 2 leads, as I first described, but some later models use one with 4 wires on it, as located on top the port-side powerhead ... black ground wire, brown (or tan) wire to temp gage, and two other wires, usually tan with a blue trace, which is the temp switch to the warning horn.

Merc used 2 types sensors, one a snap-cap type that closed to ground when hot, opens when cool or an impedance type where at 77-degrees F = 1,000 ohms impedance and when at > 200 degrees it drops to 79 ohms. If you have a multimeter, check the sensor – if infinite … your sensor could be toast."

For this owner, it was his on-board under the motor cowling oil tank, wasn't full or had air leak, so he needed to fill from the remote tank. Turns out the indicators were tying to WARN him of this issue. But maybe the bold text above might help, i.e., if infinite reading ... maybe the sensor is toast.

Please let us know!

 

[ifish4tuna]

Well I may have found it. Got down there tonight after work just in time to get eaten alive by the midgies.

I have a very very very strong hunch that it was as Clyde said...caused by a short in the wires. I did as he recommended and walked back along the pink wires which quickly be came wrapped in tape at the top of the power head. Just at the top in the port side corner of where the plastic cover bolts in, I found a section of taped wires that had been worn away due to abraison.

I did not force it to short circuit again as a test due to the bug factor and my general mood, but the alarm did re-occur this morning after I put the cover back on, and then off when I took it off, so I think the pressure of the bundle of wires was the key.

Tomorrow I am going to check it again w/ magnifiying glass to see if I see bare wires. It was getting dark tonight. Then I am going to wrap that section with more tape, and inspect other wires on this and the other engine for the same.

Photo attached from my crappy cell phone.

Maybe a better photo tomorrow.

Ed

 

[SBH2OMan]

Sounds like your are visiting Ox66 Hell... I've been living this sort of thing all summer. Boat runs fine, then put the cover on, won't run right. Boat runs fine for two hours, turn it off to add oil to the remote tank, turn it back on, won't run right... etc. It sure is incredibly maddening! At least I don't have 2 of them to deal with, thank God!

Any way, re-reading through this thread, it sounds like that bad thermo sensor you had (the one that wouldn't close when hot) might have been throwing off a "bad sensor" alarm to the ECU, which then gives you the symptoms you describe. Did you just try replacing the sensor and checking again for that alarm? You're probably on to something with a loose/corroded wire, too. These cowls must fit very tight because I have had similar problems (and continue to have them) and still haven't tracked down the cause.

One of the things I find most maddening about these engines is that they are technologically "in between" old school carbureted motors that either run or don't (I yearn for that simplicity!) and the modern ECU-driven engines that actually describe in specific detail what is wrong with on-board systems so you can actually fix them.

These Ox66 motors are just self-aware enough to scream like a baby and refuse to move, but cannot tell you what is wrong. Trying to trace down problems really requires an incredible degree of patience...

I think I just decided on a new nickname for the Ox66 motor - the Angry Baby. :twisted:

 

[ifish4tuna]

It has not happend since adjusting the wiring harness underneath the plastic cover, and applying electrical tape. Pretty sure it was a short.

Did have another interesting problem this weekend though. Topic for another thread.

Ed