I did the dumbest of things... Mercruiser 4.3l MPI Water Temp not registering....

[Slugger11]

I recently de-winterized my Mercruiser 4.3l MPI engine with the water boot in my yard. All worked great and it seemed like the tune-up the shop did last fall helped a bunch. Antsy to test it on the water, I headed to the lake. So far so good... now it goes south..

I get to the lake, and get the boat on the water, start it up, it idles great. I take it out after letting it warm up some and then hit the gas for a few. I get to approx 4400 rpms and 40 mph. I run this way for a while (2 rotations around the lake) and all is going great. I stop, and do some hard take-offs simulating a skier etc..

After the 2nd time doing this, the alarm goes off (just a single loud tone, no beeping or anything like that). The motor starts to hesitate and won't do much past idle.
I scan all gauges, Oil pressure is ok, battery is ok, but Water temp is NOT even registering the 105 deg..

I start limping to the dock, and as I get about 100 yards from dock, the alarm stops and boat returns to normal idle. I scan all gauges again, no difference.

I get the boat on the trailer and as I'm putting on tie-downs, i see it.... a vision that still haunts me..

Yes, the boot was still on the lower unit...

FRIG FLIP FRACK and a few other choices...

I get the boat home and hook everything back up. Idles like a charm, but still nothing registering on temp gauge.

I did the following for troubleshooting:

1) Tan wire at temp sensor grounded to engine - (Should result in pegged gauge -- NOTHING) Visually confined multiple times.
2) I grounded tan wire at gauge (Should result in pegged gauge and IT DOES, GAUGE IS PEGGED) Visually confined multiple times.
3) I ran a test wire from the temp sensor to the gauge and yep... the temp gauge shows about 150 deg at idle.

I know the water temp system was working before my f'up...


Any thoughts on the possibility that the wiring between the sensor and the gauge "just happened" to go bad after this or am I missing something.


Thanks in advance!

 

[alldodge]

Yes, the boot was still on the lower unit...
but Water temp is NOT even registering the 105 deg..

You burned up your impeller and lets hope that is all that happened. The ECM read the motor was hot and went into guardian mode. The gauge is the same for what the ECM gets its readings from. Replace the impeller and maybe the pump depending on the housing

 

[Slugger11]

AllDodge,

During my testing, I ran a completely new wire from the temp sensor on the motor to the gauge (effectively replacing the stock tan wire).

During this testing from cold start to running a while, I can watch the temp gauge seem to work perfectly. IE: moves up to about 150 deg after
about 5-10 minutes of idle.

I can loosen the blue cap at the thermostat housing and watch the water flow out, so its getting there.

Still think an impeller is crapped out?

 

[alldodge]

I can loosen the blue cap at the thermostat housing and watch the water flow out, so its getting there.

I'm only trying to understand from what your telling us. The replaced wire on the gauge gets it working now but don't know what happened prior. Your term "left the boot on" makes me thing you left the garden hose "muffs" on. With that on the impeller was getting very little water.

If you have the boat on a hose, the hose will push water thru the motor. I don't know if your impeller is gone, but from what your saying so far this is my best guess at the moment

 

[Slugger11]

I'll try and explain better.

Post incident, with boots on the following items are noted.

Water temp is not registering in the normal fashion. However, if i jump a wire from the temp sensor post to the guage, the temp is instantly registered. If i remove this jumper wire or disconnect it (and put stock wire back in place) the temp will not register.

This tells me the stock wire is bad. But how would this just suddenly happen.

Where is the code reader connection at, I'm not seeing it anywhere

I see what you are saying about the hose pushing water. I have a horse trough ill test it through as well to validate impellor.

 

[Fun Times]

The sensor on the starboard side of the engine/boat has the Tan wire going into the T/housing (Correct ?) for the temp gauge while the 2 wire sensor on the port side of the T/housing is part of the alarm system and what the ECM looks for. Sometimes one of those two sensors tends to pick up on certain situations when the other one may not.

The two wire sensor most likely put the engine into guardian mode when you thought the engine temp was fine at 105ish degrees at the dash. That or the water pressure sensor saw to low of water psi....Or a combination of both.

To repair the gauge you may want to wiggle the main 10 (or 14?) pin cannon plug connector a round at the engine side and see if you can get the gauge to work. Then remove and inspect the wire pins. If nothing found, start ohms checking the wire between the sensor and gauge including both sides of the cannon plug connector. It's most likely something silly not making a good contact.

While the impeller may seem to be working okay on the garden hose pumping water, the impeller has been compromised by leaving the flushing attachment on the lower unit even if it's just a little bit of potential damage, it would be best to change the impeller before the next trip out because you'll never know the extent of the damage (if any as the Alpha Gen 2 impeller is pretty hardy if you have an Alpha drive?) until you have a look inside.

That mentioned, you probably could have just removed the flushing attachment and finished your boating day as you were still getting some water which is why it took awhile to show up. You wouldn't be the first boater to have left the flushing attachment on the lower gear case housing and you won't be the last either.

 

[tpenfield]

Look at the bright side . . . even though you left the muffs/boot on the outdrive, at least you didn't have the trailer still attached to the boat while you did your laps around the lake

Hopefully you will get the gauge wire sorted out and the engine will be OK.

 

[Slugger11]

The sensor on the starboard side of the engine/boat has the Tan wire going into the T/housing (Correct ?)

Correct, this is the termination that I am referring to at the temp sensor.

To repair the gauge you may want to wiggle the main 10 (or 14?) pin cannon plug connector a round at the engine side and see if you can get the gauge to work. Then remove and inspect the wire pins. If nothing found, start ohms checking the wire between the sensor and gauge including both sides of the cannon plug connector. It's most likely something silly not making a good contact.

I can make the gauge work, just by running a new wire from the above Tan connector to the T/housing. IE: Imaging me running a new wire from the T/Housing to the gauge, effectively replacing the TAN wire, the gauge works and the temperature is registered correctly.

(if any as the Alpha Gen 2 impeller is pretty hardy if you have an Alpha drive?)

Yes I have the Alpha 2 Lower

That mentioned, you probably could have just removed the flushing attachment and finished your boating day as you were still getting some water which is why it took awhile to show up. You wouldn't be the first boater to have left the flushing attachment on the lower gear case housing and you won't be the last either.

After the incident and I saw it on the trailer, luckily the dock was full. Otherwise I may have, but I was a little flustered, so just wanted to get away...

thanks!

 

[Rick Stephens]

Everyone got that your temp sender and gauge works when you swapped in a direct wire. Fun Times gave you very specific instructions on how to find the bad connection between sender and gauge.

 

[Slugger11]

To repair the gauge you may want to wiggle the main 10 (or 14?) pin cannon plug connector a round at the engine side and see if you can get the gauge to work. Then remove and inspect the wire pins. If nothing found, start ohms checking the wire between the sensor and gauge including both sides of the cannon plug connector. It's most likely something silly not making a good contact.

Guys, help.. I have looked all over for this connector and it is probably right there in front of my face.. But can someone expound with the location of this guy? Photo would be great!

Thanks in advance!

 

[Slugger11]

Thanks for all your help on this.. It's going to the mechanic as soon as I can get an appointment.

I did find the connector, removed it and re-seated it. The temp gauge is now working!!!!!! WooHoo...

However, that was short-lived as now there is no water flowing for cooling. This was working earlier today
when I was looking for the connector and had the motor running to get it warm. With my "bypassed wire", the
lower sitting in a tub of water, the temp was a rock solid 160 deg. with pulses of water coming out the bottom of the lower drive.

Now, where water used to be pulsing, its like person spitting, very little and the temp goes to 180 deb before I shut it down.
If I put the flush boot back onto the lower, the temp is rock solid 160 deg and the pulsing is back to where it was previously.

This is getting to be above my pay grade.

Thanks again!

 

[GA_Boater]

Thanks for all your help on this.. It's going to the mechanic as soon as I can get an appointment.

I did find the connector, removed it and re-seated it. The temp gauge is now working!!!!!! WooHoo...

However, that was short-lived as now there is no water flowing for cooling. This was working earlier today
when I was looking for the connector and had the motor running to get it warm. With my "bypassed wire", the
lower sitting in a tub of water, the temp was a rock solid 160 deg. with pulses of water coming out the bottom of the lower drive.

Now, where water used to be pulsing, its like person spitting, very little and the temp goes to 180 deb before I shut it down.
If I put the flush boot back onto the lower, the temp is rock solid 160 deg and the pulsing is back to where it was previously.

This is getting to be above my pay grade.

Thanks again!

As suggested - Replace the burned up impeller from leaving the muffs on while motoring around the lake.

Using the muffs on in the driveway and and not overheating proves you burned up the impeller. The water pressure from the muffs is supplying water to the motor, not the impeller.

 

[Rick Stephens]

You can only safely use a water trough if the water level gets up to the cavitation plate. Sterndrive pumps are not suction prime-able - they must be immersed to fill with water or they will spin dry and never pull a drop of water up. You WILL burn up an impeller running your drive in a water trough that the water level does not fully get over the top of the pump. Always safer to use muffs.

 

[Fun Times]

Glad you found the connector and was able to get the gauge to work again....For some reason I had a feeling the problem would be there. Things like that happening is just one of those things to add one more :faint2: on a already what could go wrong type day.

Good luck with the cooling issue.