Overheat alarm. Remember the beer offer? Still on!

[coves]

1996, 225EFI Mariner, 350 Hours.<br /><br />Even the dealer has given up and had me call Mercury direct, although they would not give any direct advice which, of course I could understand.<br /><br />Once the engine is warm, over 3000 RPM, overheat alarm goes off, computer retards timing to drop engine back to 3000. If I just let it run, withing 20-30 secs temp drops and engine returns to normal. Go run around the lake at various speeds and will repeat above sequence at any time above 3k. <br /><br />New water pump impellar. New thermostats. New head temp sensor. Healthy telltail. New plugs. Compression normal and equal in all six cyls. I have an infared external thermometer and when the alarm sounds, I pull off the cover and head temps have been around 175-180 after full throttle. The Poppet has been fully rebuilt. Back flushed the engine.<br /><br />The book states that the computer retards the timing when the head hits 200. I am now convinced the engine is not overheating, the computer is reacting at too low a temp. The dealer, to his credit, has tried but now states the next step is to call in a Merc Tech, that the power head will probably have to be pulled to inspect some gasket between the exhaust plate and the head, and maybe replace the ECM for the ignition. He also stated that he has yet to have an ECM go bad on this model engine and that he does not have a "spare" unit in the shop to swap out for testing. I am seeing major dollar signs here. If the exhasut plate gasket was the issue why is the head temp not running high? Do I go ahead and replace the EMC ($650 and non-returnable) or just give it up and let the dealer spend my money until the issue is resolved? ANy ideas where to "borrow" an ECM to test this theory? The dealer also stated there was no way to test my EMC to see if it were malfunctioning. I find that hard to believe. They plug cars into test computers all the time. I am sure this guy is right. He has been very helpful in the past and gives me no reason to mistrust him. He has just run out of ideas as well.<br /><br />You guys are great. Thanks in advance for your help, and I am still ready to send that beer!<br />Chris

 

[WillyBWright]

Re: Overheat alarm. Remember the beer offer? Still on!

Make sure it has supressor sparkplugs. Sometimes radio interference from ignition messes with the warning circuitry triggering a false alarm, especially at fairly specific RPMs.

 

[andy6374]

Re: Overheat alarm. Remember the beer offer? Still on!

Now, I know what it is like to want something to workly properly and be used as the factory saw fit. That being said... (please don't get angry).<br /><br />If then engine isn't overheating, it's spitting water, temp gauge doesn't read overheating, and the overheat alarm isn't going off. I would disengage the warning module, that retards your rpm's if it thinks something is wrong (like overheating).<br /><br />If you can actively monitor your engine temp via the temp gauge, warning horn and/or warning light why not just do that. Like you said, the engine isn't really overheating. Sounds like the module is bad.<br /><br />My mercury used to have what is called a lubalert aka warning module that slowed you down to 2K rpms if it was overheating or running low on oil. But it always did it when nothing was wrong. Considering I could premix my fuel and oil and then monitor my temp by means of the temp gauge and warning horn I was happy. <br /><br />Just something to think about. If not... I hope someone can tell you the answer to your painfull woes.<br /><br />-andy

 

[coves]

Re: Overheat alarm. Remember the beer offer? Still on!

Thanks for the ideas. Problem is with this model, the sensor feeds back to the ECM which then adjusts the timing, fuel mixture, etc. with regards to the specific temp. It actually is a variable resistor. It is not just on/off, too hot, not too hot. Yikes, how complicated can we make this? How do our cars ever get around the block?! I definitely replaced the plugs with suppression models. Funny thing is, when I did that the problem went totally away, for a day. I also added a can of de-carb to the tank and the next day the problem returned and has yet to go away. Oh, the pain of owning a boat! ;-)

 

[kerry38654]

Re: Overheat alarm. Remember the beer offer? Still on!

Check the part number on the heat sensor, then call Merc direct. They have updated several of these because the temp setting is too low and causes alarms and faults.They did not send updates to the dealers in most cases, and the part number the dealers show is not the new number. Maybe yours is one of the changes.<br />GOOD LUCK

 

[coves]

Re: Overheat alarm. Remember the beer offer? Still on!

Hey bmass1<br /><br />This is EXACTLY what I feel the problem is. At least this is how it behaves. So I am really curious here. How in the heck did you know about this? This seems like a rather inportant detail to share with their dealers, don't you think? Anyway, I am off to ck part mumbers and give Merc a call. Thanks for the head up. You may have won the beer!<br />Chris

 

[timmathis]

Re: Overheat alarm. Remember the beer offer? Still on!

I hope he gets that Beer. Tim

 

[kerry38654]

Re: Overheat alarm. Remember the beer offer? Still on!

Mechanic working on my 200 Opti brought a 225EFI with him to the lake, exact same problem you're having.He had replaced the heads,water pump,sensor,alarm ect..got all the numbers from his most recent catalog from Mercury,still didn't work. Mercury factory tech came out with his laptop ran the part numbers, found that his sensor number was different. Problem solved,and Mercury picked up the tab for ALL the work.

 

[KCLOST]

Re: Overheat alarm. Remember the beer offer? Still on!

I want to hear the result on this one!!!!

 

[coves]

Re: Overheat alarm. Remember the beer offer? Still on!

OK guys. I called Merc Tech direct. This time I got someone a bit more cooperative. I gave them the part number on the sensor and they cross referenced and stated I had the right part. They claimed there were no "Tech Serv Bulletins" on this issue and in their system no other reference about this issue. They did state that in the recent past there had been some problems with incorrect values on thermostats, but not for this engine model. Argh! Bmass, can you tell me what lake you were on and better yet, since I can't get my mechanic off dead center, how about the name of yours and I can call him! Thank you!

 

[AndyL]

Re: Overheat alarm. Remember the beer offer? Still on!

Just thinking out loud here and may be well off the mark but can you run this motor with the thermostats out and see if the problem still exists. If that is possible without causing a problem further down the line it may indeed point to the alarm module itself. Please check with someone better informed if you are going to try as I don't know what thermal implications this may have on your motor. <br />On a personal note.., I really symapathise with you.

 

[coves]

Re: Overheat alarm. Remember the beer offer? Still on!

THanks for the sympathy. I read some of the trials and tribulations here and it really is amazing that some of these issues are so hidden and difficult to ferret out. With the story from bmass1 above wouldn't you think Merc would know this? Wouldn't you think they would let the tech staff know? Supposedly the Merc Tech had to come there and look it up on his computer. What a waste of resources and his time. I really hope to get that mech name and phone and solve this annoyance without going bankrupt! Keep the ideas coming, guys. I really want to send a beer to SOMEONE!<br /><br />Chris

 

[kerry38654]

Re: Overheat alarm. Remember the beer offer? Still on!

He met me at Lakeview in Ms. I'm not ****in' for him but here is his info: Southern Marine 662-893-5070 his name is Mike, and he's the most honest mechanic i've dealt with.

 

[Motor Boater Bill]

Re: Overheat alarm. Remember the beer offer? Still on!

I am interested by your mention that changing the plugs fixed it for a day--is it possible that a bad plug wire might be causing interference the same way the non-suppressor plugs would? I know nothing about this engine or this problem, so please don't give my question any more weight than it deserves. <br /><br />I do, however, like beer...<br /><br />Good luck!!

 

[coves]

Re: Overheat alarm. Remember the beer offer? Still on!

Thanks so very much, bmass1. I'm pretty much at the end of the line with this as far as I can take it. I will ck with this guy and see what he says and then I will drop the boat off at the dealer and let him have his way with my bank card!<br /><br />Motor Boater Bill. Thanks for your input. I actually swaped out one of the other CDM's for that cyl just to see. It made no difference. Believe me, I would love to send you the entire beer truck at this point. I hate (love) boats! C

 

[Silvertip]

Re: Overheat alarm. Remember the beer offer? Still on!

Mercury should be able to give you the spec (resistance values for various temperatures from cold to hot) for the temp sensor. After all, they gave the sensor manufacturer the parameters. Remove the sensor and measure its resistance at room temperature. Put a pan of water on the stove and insert a candy thermometer. Don't let the tip of the thermometer touch the bottom of the pan. Connect your ohm meter to the sensor and drop the sensor into the pan of water again not letting it touch the bottom of the pan. SLOWLY turn up the heat and jot down the readings and corresponding temps up to about 200 degrees. If the readings track with what Merc customer service or the service manual tells you, the sensor is good. If the values are out of whack at certain temparatures, the sensor is indeed not tracking properly. A few ohms either way or a few degrees off-track should not bother. You are looking for rather significant differences.

 

[andy6374]

Re: Overheat alarm. Remember the beer offer? Still on!

Tell us what the resistances values are as a function of temp. when you get them

 

[Silvertip]

Re: Overheat alarm. Remember the beer offer? Still on!

I will check one of my auto shop manuals. Although an auto engine runs in colder extremes, the temp sensor readings from about +50 to +200 should be fairly close to those for an outboard. I used to have those numbers in my head but I've been retired too long. Other stuff took its place. Stay tuned.

 

[coves]

Re: Overheat alarm. Remember the beer offer? Still on!

Bmass1. I so wanted to send you the beer but when I talked with mike it was a different engine. It was the wrong temp sensor for sure, but a different and non-compatible part for this engine. He was a really nice guy and very generous with his time, but no futher info, leads, or ideas.<br /><br />Next step is the suggestion above. I wont get back to the boat until this weekend and then I will ck the resistance values and go from there. Thanks for all the support. I may need to move from beer to hard drugs if I can't resolve this soon!!!!!!!!

 

[Silvertip]

Re: Overheat alarm. Remember the beer offer? Still on!

Here are some automotive temp sensor resistance values to ponder. They vary from manufacturer to manufacturer but it should give you an idea of what you are dealing with.<br /><br />FORD GENERAL MOTORS<br />-40F = 269k ohms -40f = 100k ohms<br /> 32f = 95k ohms 40f = 75k ohms<br /> 77f = 29k ohms 100f = 1.8k ohms<br />248f = 1.2k ohms 210f = 185 ohms<br /><br />An import (I forgot which) reads 2.0 - 3.0k ohms at 68f. 300 - 400 ohms at 176. These are close to the GM values. Have fun.