Alarm on 496 MAG HO &power reduced but all temps and levels look good??

B

BillZ

New Member
Aug 10, 2010
17
Long Island South Shore
Boat Info
270 Sundancer 2000
Engines
496 MAG HO 8.1 425 HP
496 MAG HO 425 HP about 2 1/2 years old with approx 70-75 hours total. ran great then out of nowhere alarm one long constant beep and engine power greatly reduced. engine runs fine at low speed but when brought up to around 2000-2500 rpm alarm sounds. temp never passes 170 which isnormal and oil pressure stays a constant 40. OD oil level fine and OD sensor tested while open and jumped.. opened alarm still sounds, jumped alarm is 2 short beeps as it is supposed to be. seems to indicate overheat but temp does not reflect that. research show that there are/were issues with the merc sensors. friend had same issue and it was water pressure sensor (diff engine just smaller and newer merc)any help would be appreciated

I hav eno problem getting my hands dirty by changing the impeller (and housing if neede ) but if that were the problem wouldn't I be seeing an increase in temps.. can anyony point me to where the sensor is located, pics if possible, and the correct way to test it. I did order a scan tool from Rinda which comes tomorrow.

Thanks for any help at all
 
Check your outdrive fluid level in the reservoir in your engine room. Low fluid will create this type of situation.

Dave
 
Dave S said:
Check your outdrive fluid level in the reservoir in your engine room. Low fluid will create this type of situation.

Dave
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OD levels fine as stated below. from users manual it states OD oil alarm would be 2 short beeps not 1 long constant beep which is what I am getting, when jumping the OD sensor wires I do get the 2 short beeps so I assume that means all is well with that sensor?

Thanks
 
Mine did that once last season. I took a short, 5 minute cruise on plane to a local anchorage. When I dropped off of plane, I got the same continuous alarm. I shut her down, checked all of the fluids, etc.. Restarted the engine and a the alarm was still there. Went down below to check out the engine manual and didn't see anything about a continuous alarm. 10 minutes later, I started her up and everything was fine. All gauges were reading the same as yours. I've put about 60 hours on her since with no problems.
 
Had the same problem on our 240. MM had me do a hard reset of the SmartCraft tach, which stopped the alarm. But when they scanned the engine, it turned out that the ECM was bad and that caused the alarm. It's an $1,800 fix, so I hope that is not the issue with yours.
 
Check the strainer for the raw water intake, if that looks clean open the sea cock with the strainer cap off to make sure you have water coming in. The intake may be blocked….. Just ran into this issue myself.
 
Down by your impeller housing is your raw water pressure switch.. Mine went bad 4th of july weekend.. Same deal..
 
First off thanks to all for the input... Please do keep them coming. any help with how to locate and test sensors would be greatly appreciated

@ skibum - neighbor did same as you but no such luck for me. day 3 and still alarm at 2000 or so rpm. thanks for the input.

@ highslice - Yikes! ... scan tool coming tomorrow. I hope its not that... not gonna sleep well tonight now. Thanks for the input... I think...

@ hackfor alivin - I am hoping for something that simple. I have the manual but do not see any mention of a strainer and do not see where it would be. part of sea cock? part of pump? Plus wouldn't this be reflected in my temp readings? thats the part that has me confused... if alarm is over heating than why am I not.. which is why Im thinking bad sensor or would it not show has higher temp on gauges? Thanks for the input

@ wvsundancer - "Down by your impeller housing is your raw water pressure switch" i do see a connection that unplugs from the pump. is that the actual sensor or do those wires lead to the sensor. How would I check that the sensor is good. If I simply unplug it I still get alarm. should I jump it closed to test? if so it looks like 3 connectors in the end so which do I short together?
 
The tech from the marina had to come down and plug in the laptop to my engine.. he then took out the old one and tried to clean it himself.. no good.. went back to the parts dept got a new switch and put it in.. then we went out on the river and while he still had the laptop hooked up to my engine he had me put the boat on plane to make sure the computer "liked" the new pressure sensor. Of the 3 DA's I have owned this was a first for me..
 
BillZ said:
First off thanks to all for the input... Please do keep them coming. any help with how to locate and test sensors would be greatly appreciated

@ skibum - neighbor did same as you but no such luck for me. day 3 and still alarm at 2000 or so rpm. thanks for the input.

@ highslice - Yikes! ... scan tool coming tomorrow. I hope its not that... not gonna sleep well tonight now. Thanks for the input... I think...

@ hackfor alivin - I am hoping for something that simple. I have the manual but do not see any mention of a strainer and do not see where it would be. part of sea cock? part of pump? Plus wouldn't this be reflected in my temp readings? thats the part that has me confused... if alarm is over heating than why am I not.. which is why Im thinking bad sensor or would it not show has higher temp on gauges? Thanks for the input

@ wvsundancer - "Down by your impeller housing is your raw water pressure switch" i do see a connection that unplugs from the pump. is that the actual sensor or do those wires lead to the sensor. How would I check that the sensor is good. If I simply unplug it I still get alarm. should I jump it closed to test? if so it looks like 3 connectors in the end so which do I short together?
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In my case it did not show up in the temperature at all. Still had some flow of water, but the intake was restricted enough to produce a "low flow alarm" and the Smartcraft went into throtle limit, thus keeping the engine temp just fine. Follow the hose from the sea cock and you will find the strainer. Have you run in shallow water lately?
 
yes.. my merc manual says the best way to test sensor is to replace it... seems that there should be a correct way to test without replacing it. most auto mechanics I know today are little more than parts changers and often at the customers expense.... is the part he changed the nut with wires at the sea pump or was it at the other end of those wires?
 
hack4alivin said:
In my case it did not show up in the temperature at all. Still had some flow of water, but the intake was restricted enough to produce a "low flow alarm" and the Smartcraft went into throtle limit, thus keeping the engine temp just fine. Follow the hose from the sea cock and you will find the strainer. Have you run in shallow water lately?
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yes... south shore of long island is mostly shallow. followed a more experianced boat out and he ran aground. i stopped 50 yards from him but was then lead through some real shallow stuff.. was at beach and although I never bottomed out there was a lot of sand (all sand here) kicked up when moving. alarm first went off when I left and got a few hundred yards from beach... had already planed in deeper water (15 feet) then alarm and power loss..

BTW my salt water path goes from sea cock thru air actuator (which connects thru tubes to fresh water canister) then to sea water pump... what would the strainer look like.
 
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BillZ said:
yes... south shore of long island is mostly shallow. followed a more experianced boat out and he ran aground. i stopped 50 yards from him but was then lead through some real shallow stuff.. was at beach and although I never bottomed out there was a lot of sand (all sand here) kicked up when moving. alarm first went off when I left and got a few hundred yards from beach... had already planed in deeper water (15 feet) then alarm and power loss..

BTW my salt water path goes from sea cock thru air actuator (which connects thru tubes to fresh water canister) then to sea water pump... what would the strainer look like.
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There you go, checking the strainer and raw water intake is very easy and may save you some time and money.

The strainer is going to be between the raw water intake sea cock and the pump. it will have a hose in and out along with some type of cap... my is a screw on plastic cap. Close the sea cock and remove the cap, the strainer will be inside. If the strain is clean open the sea cock for a short duration and verify water coming in. Good luck.
 
Is it possible that there is no strainer? Is it possible that the strainer is part of the sea cock. there does appear to be 2 bleeder screws below the shut off lever and 3 possible allen screws holding the top plate with the elbow that connects to the hose leading to pump to the rest of the sea cock..but does not look like any of the seacock/strainer combos found on searches... looks like just a regular sea cock. only thing I can find between the sea cock and pump is the acuator. did not get hose off yet.... real tight in there. do you have the same engine? merc MAG HO 8.1 425 HP?


In there now looking for it... going to just pull the hose from seacock and pump while removing it from acuator. the merc manual mentions strainer about 3 times as a cause yet never shows where it is. thanks for your time... really do appreciate it.
 
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My engine model is different from yours but in my case the strainer is in front of the engine (towards the bow) right by the transmission on a “V Drive”. I believe on the 340 it is in the rear of the boat somewhere close to the water pump itself…. Maybe someone with the 340 with help out here. Either way, there is a strainer somewhere but it is not part of the sea cock.

You need to find this as it is important to check and clean several times during the season... all of them, the engines, A/C unit, and Generator... if you have one.
 
You lost me with the "340" not sure what your referring to. engine is a 496 mag ho 8.1 425 HP and boat is a sundancer 270. sorry I dont understand
 
BillZ said:
You lost me with the "340" not sure what your referring to. engine is a 496 mag ho 8.1 425 HP and boat is a sundancer 270. sorry I dont understand
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My bad, I was thinking a 340 with twin 496's..... So with yours you have the 496 with an outdrive???
 
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yes bravo 3. just pulled the pump and impeller looks fine but I will replace since i have it off. no sign of a strainer yet.. got to be between pump and sea cock but damn if I can find it

Well pulled the pump.. replaced the impeller but still looking for the strainer... hate to put this pump back on till I find it. BTW if i open the seacock i still have the hose from it thru the acuator and then open ended where the pump should be i get a full flow from what I can tell
 
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