DF140 Overheating

I have twin 2003 DF140's. In preparation for spring, and to avoid issues, I have performed the following maintenance.

New fuel filters from tank to engines

New Fuel lines from the tank back to the engine

New Primer bulbs (the heavy duty Yamaha bulbs)

Serviced and cleaned the IAC valve and set the idle per service manual

New zinc's including the rectifier zinc's

Fresh oil change, engine and gear case

Fresh fuel with Startron added

New water pumps/seals

New Thermostats

New spark plugs

The other day I was running at around 4000 rpm, both engines running like a sewing machine, all the sudden the check engine light and rev light with an alarm shows up on the starboard engine, it sags and looses power, I throttle back to idle, turn off the engine and it restarts fine.

This occurred 4 times in a 2 hour period, in-between it ran perfect as always, the temperature gauge never showed any signs of over heating, tale-tail was strong, and each time I would shut the engine off and restart and it would run fine again.

From what the gauges and alarm tell me, it looks like an overheat, but didn't seem hot, and from what I understand there are two conditions that would cause this, #1 cylinder or exhaust reaching maximum temp #2 the temp to rise time

I realize the temperature gauge it self may be slow to respond, but even after restarting the temperature was within normal range and didn't appear to be overheated.

I assume that since I am not getting any self diagnostic codes that all the sensors are working properly

I am not so sure that the source of the problem was an actual overheat situation

At this point I am wondering if I might have a sticky pressure relief valve triggering the temperature/rise alarm or a loose/corroded wire or something?

With all the maintenance that has been done on the engines, from what I could find on-line, I have already eliminated some potential causes.

This even happened once on the water hose, I made sure the water flow was good and the flushing cups were attached, it occurred within 15 minutes of starting the engine, turned off the engine and restarted and ran fine for the rest of the flush out

Has anyone had this sort of issue, or know what might be going on?

Any help or ideas on this issue would be greatly appreciated

Thanks!

I have same engines only 06's with less than 300 hours each. I am having a similar problem with the starboard engine where after running (4000rpm) out to the fishing grounds about 6 miles in the morning; when I come down off plane and start trolling (1200rpm) the temp alarm and light go off and engine shuts down this has happened three days in a row. I don't use the engine again until it is time to go home and she starts right up and runs great and never overheats all the way back to the boat launch.

mainiac2 said:

I have same engines only 06's with less than 300 hours each. I am having a similar problem with the starboard engine where after running (4000rpm) out to the fishing grounds about 6 miles in the morning; when I come down off plane and start trolling (1200rpm) the temp alarm and light go off and engine shuts down this has happened three days in a row. I don't use the engine again until it is time to go home and she starts right up and runs great and never overheats all the way back to the boat launch.

Click to expand...

From you describe sounds like it could possible be a sticky popit valve (Water pressure relief valve). From what I understand, the valve closes at idle to increase water pressure and when running at higher RPM's the valve opens to moderate the pressure so the water pressure does not get too high. That is why i thought maybe the issue with mine is the opposite causing a sudden change in temperature which would trigger the temperature rise alarm. My engines have a little over 2,200 hours each, so yours aren't even broken in yet

I appreciate everyone's input on what might be causing the random overheat problem..

The issue causing the over heat, or rather false over heat, was due to a faulty / erratic exhaust temperature sensor that is located on the rectifier.

I took the suspect sensor on the starboard side and compared it with the sensor on the port side.

Using a volt meter to measure the resistance, I filled two bowls with water, one with ice water at approx. 32° and the other warmed up to approx. 140°

The graphs are not exact, I did not worry to much about being too granular, rather than check to see if both sensors were responding the same.

I switched between cold and hot about 20 times with each sensor.

The port engine sensor, when going from cold to warm, showed a nice linear decrease in resistance every time.

The starboard engine, suspect sensor, when going from cold to warm, was all over the place, showing erratic jumps in resistance, and an overall ending resistance showing about 25%-35% hotter than the port sensor.

The suspect sensor would always show a spike around the mid way mark, jumping drastically from 1.68 Ohms to around 2.4 Ohms, and then drop to around 0.5 - 0.4 Ohms.

Apparently the ECM on the engine will only flag a diagnostic code if the sensor has completely failed, so because the sensor was responding the ECM was interpreting the drastic change as an over heat, triggering the alarm and reducing RPM to 3,000

About 75% of the time, once the suspect sensor would warm up past around 90° it would somewhat smooth out, but still show that the engine was warmer than it actually was.

This behaviour explains why this issue was less frequent in warmer water conditions, and happen more frequently in colder water conditions, usually after about 10 or 15 minutes or running at 4,000 rpm, and why the engine would usually run normal after turning the ignition off back on.

When running in cooler water conditions the temperature would swing across a wider range hitting the erratic spikes around the 90°, and by the time I stopped the boat and restarted the engine the internal temperature was above the erratic spikes and would continue on until it started acting up again.

Also, I noticed that Suzuki changed the sensor installation taking it out of the water stream, I am not sure if this was one of the reasons or not, but sounds plausible.

I am going to replace both exhaust temp sensors, keep the port, good sensor as a spare.

Since both cylinder head and exhaust temperature sensors are the same, I am considering taking the failed sensor, cut the sensor off the pigtail and solider a 1.5 to 4 ohm resistor on the pig tail, to make a "dummy load", which could be used in an emergency should a sensor fail on the water and positive it is not an actual overheat.

mainiac2 said:

I have same engines only 06's with less than 300 hours each. I am having a similar problem with the starboard engine where after running (4000rpm) out to the fishing grounds about 6 miles in the morning; when I come down off plane and start trolling (1200rpm) the temp alarm and light go off and engine shuts down this has happened three days in a row. I don't use the engine again until it is time to go home and she starts right up and runs great and never overheats all the way back to the boat launch.

Click to expand...

I know it has been a while but did you ever resolve your issue? I have a starboard engine after running at 4K rpm for 15-20 min had a temp light come on and water pressure drop. I shut the engine down, restart was fine no issue.

Thanks