DF140 Overheating

[keakar]

well motors with that much age will almost always have areas of blockage that cause hot spots but they dont often trigger alarms even thou the hot spots can and often do shorten the motors life so if the money isnt a big concern i would still pull the heads on both motors to clean them out. to me its like a routine maint. thing even thou its not all that routine to do something once every 5 years or so

[TXFishin]

DF140 Overheat Resolved

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.

[Harper]

Nice job of analyzing the problem....

[TXFishin]

Nice job of analyzing the problem....

Thanks. I thought about what all the possibilities were and what was most likely to cause a random overheat, and thought that there was no issues, that the engine was acting as it thought it was suppose to, so that would mean something is telling it that it is overheating when actually it wasn't.

I had a similar issue that took about a year to figure out, and come to find out it wasn't an issue at all. The engine at times when idling would sound a beep every 1-2 seconds, with no error lights or anything, after restarting the engine it would go away.

What was happening was the idle was set a little too high.

The normal idle should be around 650-750 rpm, and is controlled by the IAC valve.

In order to set/adjust the idle you have to turn the idle air screw, increasing the RPM above 1,000 rpm. Once the RPM is set to above 1,000 the IAC valve is placed in bypass mode and a beep is sounded for 5 minutes to confirm and let you know the IAC valve is in bypass and ready to adjust the idle. Once the idle is adjusted you increase the throttle to which disengages the CTP (Closed Throttle Position) switch, the beep stops and the idle is now set/learned by the ECM. The IAC valve was also a little sticky which would cause the engine to die if you chopped the throttle too quickly, so I cleaned it with MAF sensor cleaner and resolved that issue as well

[keakar]

it would be nice to see how the new sensors read on the chart before you install them, sorta like a base line to compare to

even thou the "good" sensor followed a better line it had some herky jerky to it so im curious if the new ones are like that or will work more smoothly

[TXFishin]

it would be nice to see how the new sensors read on the chart before you install them, sorta like a base line to compare to

even thou the "good" sensor followed a better line it had some herky jerky to it so im curious if the new ones are like that or will work more smoothly

Sorry, I may have miss-typed something, but the "good" sensor actually was nice and linear as it is suppose to be.

I will test the new sensors for future reference, and this time I will check the response time against the old "good" sensor.

I also read somewhere that the later model engines don't have the exhaust sensor, but the part is listed for 2002-2010, so maybe it was only the latest or the John-zuki models, or the information was incorrect

While I was at it I figured it was time anyway so I went ahead and changed out the Water Pressure Valve since it was only $14, but the old one I took out still looked like new.

Not ruling out the possibility of corrosion or scale build up, I checked what I could on water passages, and given the engines 2,200 hours each they are relatively clean and only show signs of what I would consider normal build up for their age and hours.

I have been fishing salt water my entire life, have seen engines that looked like an oyster bed with a prop coming out of it and still running, and others that were new, kept up and still had issues.

I have owned Evinrude and Mercury, and didn't have a lot experience with Suzuki, but before purchasing the engines 2 1/2 years ago, I did quiet a bit of research on Suzuki 4-strokes, and while 2,200 hours may be consider getting up there in engine time, Suzuki has a history of long life. I spoke with a guy from SeaTow who said they use the DF140's on their tow boats, and have a pair with over 10,000 hours without any major mechanical issues. The company my brother works for uses Suzuki 4 strokes on their work boats with over 4,000 hours, he said they had to replace the starters because they run quiet, and with any background noise they would forget they were running and try to 're-start'.

I am the 3rd owner of these engines, and most of the time on them are running offshore, the 2nd owner purchased them from a guide in Florida with around 1,000 hours, the 2nd owner fishes Boomvang regularly and said because they were so quiet, and didn't burn much fuel, he never shut the engines off, so each trip would put around 20+hours.

I can't vouch for how the previous two owners maintained the engines, but from what I have seen myself these engines respond very well to regular maintenance and care. I bet if purchased new and properly maintained and cared for, aside from an unusual catastrophic failure I serious doubt you would ever be able to wear them out.

There is one thing I found out after I purchased them, not Suzuki related, but the previous owner kept the boat in a sling, at high tide the lower units would get dunked underwater, and then at low tide they would dry out. This repetitive dunking and drying out was actually worse than keeping them submerged. What this did was cause carbonate build up between the lower unit housing and the bearing carrier.

This build up is extremely powerful, sort of like the way ice can crack engine blocks when frozen, and the build up caused the lower units to crack, the famous "J" crack, at the rear of the lower unit at the bearing carrier, so I had them rebuilt by Boat Motor Recyclers - New, Used and Rebuilt Parts for Outboards, looks as good as new with a warranty at about 1/3 the cost of a new lower unit.

There is a lot of information on salt / scale build up, and found some interesting information (just one of many articles I read: Corrosion in Salt Water Marine Engines - Part 1)

What I read on corrosion and scale issues, that salt alone was is not necessarily a key factor, and a large percentage of engines that had scale build up all had low hours. There was one post where a guy had scale build up issues on a fresh water only engine that turned to be the result of the marina he kept is boat at had a lot of minerals in fresh water supply and flushing the engines with this is what caused his issue.

Hopefully others will benefit from all this and help them out

[briscoe]

hey txfishin

Did you remove the plastic screens on lower unit water intake? They have a directional curve to the shape ofn the plastic and divert the water upward into the lower unit to assist suction. Just something to look at. If removed and installed upside down it hinders suction pressure to impeller.

[TXFishin]

Did you remove the plastic screens on lower unit water intake? They have a directional curve to the shape ofn the plastic and divert the water upward into the lower unit to assist suction. Just something to look at. If removed and installed upside down it hinders suction pressure to impeller.

Please see page two of this thread for the resolution.

Thank you for the information, I always welcome and appreciate help on issues like this. And thinking along those lines I did actually double check that just to rule it out, but was not the issue. Also, i figured it was not likely to cause a random overheat, since I turned the key off and back on and it worked fine after that, it was less likely that it was actually overheating because the engine would not cool down in the time it takes to just restart.

[MarshMarlowe]

2008 Suzuki DF140 / 270 hours

I'm kinda late to the party here, but I'm having a very similar problem. I've actually had this problem since the outboard was new, but I thought it I was tripping an "over-rev" protection circuit. It's become way more prevalent lately. I can't run WOT for longer than about 20 seconds without the motor going into limp mode, while the "rev" and "temp" light illuminate. It's the same for me, I can shut the outboard off, then start it right up again and the problem is gone.

Do you happen to have the part numbers for the temperature sensors?

Thanks

[TXFishin]

2008 Suzuki DF140 / 270 hours

I'm kinda late to the party here, but I'm having a very similar problem. I've actually had this problem since the outboard was new, but I thought it I was tripping an "over-rev" protection circuit. It's become way more prevalent lately. I can't run WOT for longer than about 20 seconds without the motor going into limp mode, while the "rev" and "temp" light illuminate. It's the same for me, I can shut the outboard off, then start it right up again and the problem is gone.

Do you happen to have the part numbers for the temperature sensors?

Thanks

I believe the part number you are looking for, if you are looking for the exhaust temp sensor, will be item # 9 "34830-87J20 Temp Sensor Assy ", see link below, and verify to be sure.

Suzuki Outboard DF 140 Parts Listings - 2002 to S/N 14002F-11XXXX - 2002 to S/N 14002Z-11XXXX - Fig. 31 - Sensor