Best and easiest "tune up" / performance boost for 240EFI engines...

[WAJetboating]

Short version: Replace your head temperature sensor. (It's the one on the port side.)

Longer version: The port side temperature sensor tells the ECU the engine's temperature. The ECU uses that information to control fuel injector pulse width. (There is also a temperature sensor on the starboard side, but that is used to sense the cooling water's temperature.)

The port side temperature sensor has a reputation for failing after a while. I've never experienced this, but the symptoms are many and varied, and usually pretty dramatic. I have a spare sensor that I picked up "just in case" from a guy who was parting out a 240EFI, but haven't ever noticed any of the dire symptoms reported by most victims of a bad temperature sensor.

This weekend we were running the boat and I realized that I've been seeing a bit more smoke lately, even when the engine is fully warmed. It seemed to smoke at idle more than it should, and definitely more than I remembered. Nothing serious, nothing dramatic, but I noticed it.

If the ECU were being lied to about the temperature, and thought the engine was still cool, it would lengthen the fuel injector pulse widths to richen up the mixture and help the cold engine warm up. On a warmed engine, though, that could cause the smoking I was seeing.

So, having a few spare minutes, I thought what the heck - let's swap out the sensor. So I did. (It takes a 13mm socket and about three minutes.) We then ran the engine for the next two days.

WHAT A DIFFERENCE! The smoke was gone - totally. That alone made it worthwhile. But the engine also ran smoother. The change had been so gradual that I hadn't noticed it, but snapping back to like-new performance was amazing. I couldn't believe what we'd lost.

We also gained 3-4 MPH on the top end. I had attributed that to air resistance from the waketower I installed, but now we're back to 54-55 MPH from the 51-52 we were seeing. That may be due to the ~100-200 RPM we gained at WOT. We had been at 5900-6000 and now we're getting at least 6100.

We also gained efficiency. We used to hold 20 MPH (wakeboarding speed) at exactly 4000 RPM. Now the engine purrs along at ~3600 RPM for that speed, a full ten percent less.

It is now my opinion that these sensors can fail gradually. I haven't plotted curves on the old one, but I bet they don't match the ones in the manual anymore. I now think they should be considered a consumable that should be replaced every few years, particularly since they only cost around $40 IIRC.

I wish I had replaced this sensor at the start of last season. My advice: Don't wait. Buy a replacement and swap it in. If you don't get any improvement, at least you have a spare for a component that is known to fail quite often. If you do see improvement, pat yourself on the back for the fastest and cheapest tune up imaginable.

 

[Dr Honda]

Thanks for the heads up on that one.

We've seen that when the temp sensor goes bad... the Merc engines run poorly. This is a great confirmation on the prob. :cheers:

 

[WAJetboating]

We've seen that when the temp sensor goes bad... the Merc engines run poorly. This is a great confirmation on the prob.

True, and I wouldn't have bothered posting if it were just the same old, well known "failure" issue. But what I've learned is that it appears the sensor can fail gradually, slowly affecting engine operation, but perhaps not enough to attract attention.

My engine was exhibiting none of the usual symptoms associated with a failed sensor. It started instantly, idled and ran fine, reached (close to) WOT RPM's, etc. But the sensor was, indeed, failing gradually because swapping it out returned performance I didn't even realize was gone.

 

[wdd5885]

Do you think that would be true of the Optimax as well? My WOT RPM was consistently 5400-5500 rpm all summer (within the range specified in manual), but smoke issues arose intermittently. At first, I blamed it on an off oil brand. I ran out the cheap stuff, and replaced with Optimax DFI oil. This helped, but did not eliminate the issue completely. Engine still smokes. Also, tope speed is 41042 on a handheld GPS. This seems on par with what I read on the interner for that engine on the Islandia. I am not overly concerned, but I will do just about anything to keep her purring like she did all summer. Engine ran great, so I am all about preventative maintenance. Thanks again to WA Jetboating and the others who unselfishly share their expertise.

Oh, and on the advice of many on this forum, my stator is at IMPROS for reconditioning. Will report with results when finished.

 

[wdd5885]

Do you think that would be true of the Optimax as well (temp sensor)? My WOT RPM was consistently 5400-5500 rpm all summer (within the range specified in manual), but smoke issues arose intermittently. At first, I blamed it on an off oil brand. I ran out the cheap stuff, and replaced with Optimax DFI oil. This helped, but did not eliminate the issue completely. Engine still smokes. Also, top speed is 41-42 mph on a handheld GPS. This seems on par with what I read on the internet for top speed on this boat. I am not overly concerned, but I will do just about anything to keep her purring like she did all summer. Engine ran great, so I am all about preventive maintenance. Thanks again to WA Jetboating and the others who unselfishly share their expertise.

Oh, and on the advice of many on this forum, my stator is at IMPROS for reconditioning. Will report with results when finished.

 

[WAJetboating]

Do you think that would be true of the Optimax as well (temp sensor)?

1) I would imagine that invalid data being fed to ANY engine controller on ANY engine would result in sub-par performance.

2) I don't know if the head temp sensor on the DFI is the same as that on the EFI, but I'd doubt it. Therefore I don't know if the EFI sensor's known mortality issues apply to the DFI sensor.

Check the sensor price... if it's reasonable you could take a chance on it.

 

[seidel1981]

What's the part number for this sensor ?

 

[Racereddie]

What's the part number for this sensor ?

Depends on your engine
858535 SENSOR ASSEMBLY, Temperature - Design I SN# 0E406400 THRU 0E418555

885342001 SENSOR ASSEMBLY, Temperature - Design II SN# 0E418556 & Up

 

[WAJetboating]

What's the part number for this sensor ?

It's Mercury part number 13536A14, list price $34.71.

This is supposedly a photo of part number 858535:

...and this eBay auction supposedly contains a photo of part number 885342001:

http://cgi.ebay.com/ebaymotors/Mercury-Quicksilver-Temp-Sensor-Part-885342001-/250782857271

...and neither of those is the sensor in question. Those are multi-pin connectors in those photos, whereas the sensor in question uses standalone bullet connectors.

 

[Racereddie]

Okay so I am finding that there really are quite a few differences between not only the 200/250 and the 240 but from 2000 to 2002 there are differences between the 240's also. 13536A14 or 13536A12 are not listed in the 2002 240hp EFI manual. As for the 2000 240hp from the manual it states that there is a different sensor for the port and starboard sensors. Looking on the crowley's web page it states that 13536A14 is the Starboard sensor, 13536A12 is the Port side. From Boats.net it list 13536A14 as the Port sensor and 974651 as the Starboard sensor. So since you have replaced it and based on the pictures is it the one with the three wires or the one with a single wire.

Eddie

 

[WAJetboating]

Okay so I am finding that there really are quite a few differences between not only the 200/250 and the 240 but from 2000 to 2002 there are differences between the 240's also.

Indeed. The 210/240 (carb/EFI) and the 200/250 (Optimax DFI) are radically different engines. The latter have quite a few additional sensors, for example. The former went through a design change from model year 2001 to model years 2002+, but in this case the changes were primarily in the ECU (SmartCraft compatible) and the addition of an alternator instead of using a stator for electrical power. Most of the engine mechanical, and sensors, etc. did not change going into 2002+.

The sensor in question is the multi-wire "port" sensor.

Hope this helps!

 

[fleiss75]

I have a 2002 X20 but my serial number is OE397311, will that part number still work for mine? I have tried to research it and I cannot find a part number coordinating with my serial number. My boat goes through a full tank of gas in 4-5 hours, I was so happy to read your post.
Now I am having a hard time getting it to start without turning the steering wheel for an extra jolt, and then it has a really hard time just idling. I ordered new plugs and the sensor...I am hoping that takes care of the problem. I am in Central Florida and NO one will work on this boat.

 

[Double07]

I have tried to research it and I cannot find a part number coordinating with my serial number.

Here is where I go to find specific part numbers by just using my engine serial number: http://www.mercurypartsexpress.com/us/parts-search.html
this is a Mercury's part search site. It lists all the parts for the engine as well as the pump, and all you need is either the engine serial number, or the pump serial number. Once I get a part number, I can either search around for a cheaper price using the part number, or I can order it right there from the mercury's site.
Below is a snapshot of what I found on temp sensor on the cylinder head using your engine serial number.
You can check out the site. Hope it helps.

-Chika

 

[WAJetboating]

I have a 2002 X20 but my serial number is OE397311, will that part number still work for mine?

It should. Your boat may be a 2002 but that serial number appears to be a 2001 engine. Nothing weird about that.

I am in Central Florida and NO one will work on this boat.

If you need a shop, find a certified Mercury shop and tell them you have a 2.5L V6 outboard engine. It's the truth - that's exactly what you have. It's a standard outboard that happens to be mounted on top of a jetdrive instead of a "lower unit". Above the prop/impeller it's the same outboard engine that Mercury has shipped for years and years. What scares some of these shops is the "Seadoo" name on the hull... a lot of them presume there are Rotax engines inside and won't touch them. But any good Mercury shop will understand a 2.5L V6 two-stroke EFI engine... there's thousands of them out there.

However, I doubt you'll need a shop. You can get this baby running on your own. Replace the sensor and the plugs (BTW, the plugs are stocked at NAPA's nationwide, they're a standard NGK part number) and report back.

 

[fleiss75]

Okay, replaced the plugs, installed the new sensor. Same issue, will not start unless I have the wheel turned to the power steering assist, if I sraighten it out, the rpms drop below 1k and it stalls out. Checked the battery which was 12.62 and then once started was around 14.01 or so. Once started and moving it runs fine..I can definately tell that it is running rich...anyone behind the boat trying to get up the ladder has the burning eyes. I am assuming there is no specific way to install that heat temp sensor, put heat sink around the metal part and hooked up the wires and made sure the 2 grounds were connected. It doesnt seem to fit flush... I have made 10 calls today and no one services that boat in my area.. the ones that did, did not have the DDT or the new computer to hook up to the boat to check settings.

 

[Racereddie]

... I have made 10 calls today and no one services that boat in my area.. the ones that did, did not have the DDT or the new computer to hook up to the boat to check settings.

I am not sure where in Orlando you live but here in Lakeland right off of I-4 and SR-98 there is http://www.oldsaltmarine.com/ I have not taken my boat to them but I did stop by to talk and when I said jetboat they paused but then they said well it is just a common Mercury. May be worth a shot

Eddie

 

[WAJetboating]

I can definately tell that it is running rich...anyone behind the boat trying to get up the ladder has the burning eyes.

OK, now remove a couple of your new plugs. Are they oily? Covered in flaky debris? Or nice chocolate brown like they should be?

I'm beginning to think you may have some injectors fouling open, which would cause things to run rich. The reason turning the wheel hard makes a difference is that this opens the throttle body butterfly valves a bit, letting in more air and bringing the fuel/air ratio closer to normal. I had this problem, and pulling the injectors and having them serviced cleaned it right up.

Check your plugs.

 

[fleiss75]

Checked all the plugs and they looked great, no crap on them, not black. I checked spark on all cdis and check compression as well and all checked out. I put a full bottle of the quickclean and will try running that...other than that...I would love to pull the injectors..but I am scared to death to screw em up..

 

[WAJetboating]

OK, clean plugs means you aren't running THAT rich.

That said, download the manual and check that the oil pump control arm is positioned and adjusted properly. It's on the port side of the engine. There's a little mark that you align with the cam on the pump, and sometimes the arm is installed improperly causing the cam to rotate the wrong direction and richening the oil percentage.

 

[atlantis6]

You are right, i chanched the sensor on port and starbord and RPM raised to 4000 when idle

 

[fleiss75]

OK, clean plugs means you aren't running THAT rich.

That said, download the manual and check that the oil pump control arm is positioned and adjusted properly. It's on the port side of the engine. There's a little mark that you align with the cam on the pump, and sometimes the arm is installed improperly causing the cam to rotate the wrong direction and richening the oil percentage.

I took a look at the oil pump and I have 3 lines on the arm... Which should it be lined up with?

 

[wildpiguk]

You guys are so lucky...

Hi
I have a 2001 Speedster with the 240 M2 EFi - want to guess how much Mercury want for the Temperature sensor in England....?


$140.00

Yup - One Hundred and Forty Dollars

Groan

 

[atlantis6]

look @ crowley marine i paid for both sensors 90.23 dollar :coolgleam:


look in section REED BLOCK AND CYLINDER HEAD

 

[wildpiguk]

Thanks - would be excellent if poss...
I can't seem to get onto their UK website - any clues?

Did you get from the US?


Cheers Atlantis6

 

[atlantis6]

yes i orderd it in the States.

I didn't knew there was one in uk