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Bruce Arner

5.0 mercruiser alarm and heat issue

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I have a 2003 bayliner with 5.0 Mercruiser, I have replaced impellar, but temp still seems to run a little hot, 180, and I get intermittent alarm, also replace thermostat, any ideas? Is there an impellar on engine, everything I have seen says the impeller is on outdrive only

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What would I look for? When I use infrared temp gun on engine, I get a much lower temp, 170-175, but I still get alarm, could it be a bad gauge? does alarm work off gauge or temp sensor? Thanks for replying, 

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Mine also has 5.0MPI and always runs at 170 - 175.  From what I've read, that's not uncommon.  It never gets over 175, but no alarm.  You sure it's the temp alarm going off?

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Mine gets to 180 , Ive been told 180 is not to hot, but it is setting off alarm, not constant, just a beep every once in awhile, my infrared temp gun gives alot lower temp at thermostat housing where sensors are located. 

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Why do you suspect over temp ? Could be a lot of things. "every once in a while" does not tell us what we need to know. Weekly? Daily? Hourly? Every 2 minutes? What is once in a while? 

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Well, it does fine on hose, does fine at idle, at about 20mph, it beeps, no pattern,  will just go off every once in while when temp is around 180, gear lube reservoir full, oil pressure good,  ????????

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If it is a intermittent alarm. That could mean the thermostat connections are getting a little loose. 15 years old parts. Is your engine the type with electrical pins in the thermostat gasket. If yes ?  Do a excellent cleaning  of the surfaces.  Wingnut went into great detail about doing that set of contacts and surfaces very correctly.

Boat in water does it do the exact same amount of beeps ? 

There is a big electrical connector on the engine that connects all signals to the rest of the boat controls. The connector pins are split pins. They do become intermittent with age. It is a KEYED alignment type of connector. Unscrew the connector. Then look at the male pins with a magnifying glass for any corrosion on the pins. Was the connector screwed together snugly ?    CAUTION !!!!!!!!! TURN OFF the big battery selector  switch .....BEFORE....... separating that big connector   !!!!!

If you do not turn the big switch off ??   You could cause a very damaging short circuit to the ignition system.     Reconnect the big plug completely. THEN TURN ON THE BIG battery disconnect switch.      My 2002 developed a very random starting problem.  My mechanic knew it was the big plug pins loosing tension.  Before we went to the boat. He was right.

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Will try that, the gear oil reservoir connections are oily, I guess that could be it, Thank you for the suggestion 

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25 minutes ago, Bruce Arner said:

Well, it does fine on hose, does fine at idle, at about 20mph, it beeps, no pattern,  will just go off every once in while when temp is around 180, gear lube reservoir full, oil pressure good,  ????????

Someone suggested checking manifolds and risers, but it has always been run in fresh water, and from what I have read, they should be fine

 

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Does the beeping get more frequent as you get very close to WOT for several minutes ?  That would indicate possible exhaust problems coming. 

 

EDIT

 ALL oil levels are O K ?

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Try unplugging the wires to the gear lube reservoir. I don't think the alarm will sound with it unplugged. It will at least eliminate that as the source of the alarm. Is your engine a carb or MPI?

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Everyone, what is good temp for the rises and manifolds, anyway? I finally remembered to take my IR gun on the boat with me today. It's always in my truck so I can check my trailer hubs. My risers were just over 100 degrees and my manifolds were right at 160. My temp gauge always reads 155 so it seems like everything is on the money.

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Alarm for coolant temperature sets at 188. Manifolds have their own individual senders but their values are much higher (212 degrees) are not displayed on the helm gauge. So many things can generate an alarm, and it could be low raw water pressure also. On muffs, your raw water pump gets a boost from your potable water hose feed. Your engine coolant circulation pump has an impeller also, but the pump is of centrifugal design and the impeller is rigid stainless steel and will last forever. The only failure item on that pump is the pump shaft seal and bearing so that is not your issue.

There is always the possibility of there being an issue with wiring, but that would be the last place I would look. Make sure you have proper battery voltage as a weak battery or failing alternator can send the ECM into fits, but usually you notice a problem there while cranking the engine. Look at the table below, and concentrate on the items that show alarm beeps at a prescribed interval, and not constant. AS you can see, the occasional ones are associated with failing sensor in most cases and can be hard to narrow down without a scan tool. Most common are IAC valve, lube oil reservoir float switch, trim indicator sender and raw water pressure sender but I'd shy away from throwing money at a problem until you identify the offender as the other approach can get expensive. W

Warning System

 

The engine warning system incorporates an audio alarm and, if installed, a SC1000 System Monitor. When the key switch is turned to the ON position, the audio alarm will momentarily activate to test the warning system. The alarm should sound once if the system is operable. This table is a guick guide, showing what warning output will accompany a fault.

 

 

Fault

 

SC1000

Audio Alarm

Available Power

 

Description

 

Cam Sensor

 

Yes

 

2 Bp/min

 

90%

Open or short, engine must be cranking to set this fault code.

ECT CKT HI

Yes

2 Bp/min

90%

Open

ECT CKT LO

Yes

2 Bp/min

90%

Short

ECT Coolant Overheat

 

Yes

 

Constant

 

6-100 %

Engine guardian overheat condition

EST 1-8 Open

Yes

2 Bp/min

NA

Coil harness wire open

EST 1-8 Short

Yes

2 Bp/min

NA

Coil harness wire short

Fuel Injector 1-8 Open

 

Yes

 

2 Bp/min

 

NA

 

Fuel injector wire open

Fuel Injector 1-8 Short

 

Yes

 

2 Bp/min

 

NA

 

Fuel injector wire short

IAC Output

Yes

2 Bp/min

90%

Only with rpm

 

Knock Sensor 1

 

Yes

 

2 Bp/min

 

90%

Alarm sounds for 20 seconds in NEUTRAL and indefinitely in gear.

 

Knock Sensor 2

 

Yes

 

2 Bp/min

 

90%

Alarm sounds for 20 seconds in NEUTRAL and indefinitely in gear.

Low Drive Lube Strategy

 

Yes

 

Steady Bp

 

0-100%

 

Low oil in sterndrive

Low Oil Pressure Strategy

 

Yes

 

Constant

 

0-100%

 

Low oil pressure strategy

MAP Sensor 1 Input High

 

No

 

2 Bp/min

 

90%

Short, no visual on SC1000

MAP Sensor 1 Input Low

 

No

 

2 Bp/min

 

90%

Open, no visual on SC1000

 

MAT Sensor

 

Yes

 

2 Bp/min

 

90%

Open or short in MAT circuit

 

NOTE: If any 5v sensor becomes shorted to ground the engine will not start. If the engine is operating when the short occurs the engine may stop operating and will not start.

 

 

 

Fault

 

SC1000

Audio Alarm

Available Power

 

Description

Oil PSI CKT Hi

Yes

2 Bp/min

90%

Short, defaults to 51.7 psi

Oil PSI CKT Lo

Yes

2 Bp/min

90%

Open, zero oil pressure

Overspeed

Yes

Constant

RPM Limit

Engine over rpm limit

 

Port EMCT CKT Hi

 

Yes

 

2 Bp/min

 

90%

Open, defaults to 32 degrees F (0 degree C)

 

Port EMCT CKT Lo

 

Yes

 

2 Bp/min

 

90%

Short, defaults to 32 degrees F (0 degree C)

 

Port EMCT CKT

Overheat

 

Yes

 

Constant

 

6-100%

Overheat condition, 212 degrees F (100 degrees C) limit

 

Sea Pump PSI Lo

 

Yes

 

Constant

 

6-100%

Low water pressure strategy, defaults to

43.4 psi

Sea Pump CKT Hi

Yes

2 Bp/min

90%

Open

Sea Pump CKT Lo

Yes

2 Bp/min

90%

Short

 

STB EMCT CKT Hi

 

Yes

 

2 Bp/min

 

90%

Open, defaults to 32 degrees F (0 degrees C)

 

STB EMCT CKT Lo

 

Yes

 

2 Bp/min

 

90%

Short, defaults to 32 degrees F (0 degrees C)

 

STB EMCT CKT

Overheat

 

Yes

 

Constant

 

6-100%

Overheat condition, 212 degrees (100 degrees C) limit

Steer CKT Hi

Yes

No

No

Open and short

 

TPS1 CKT Hi

 

Yes

 

2 Bp/min

 

90%

Short, signal to 5v+, engine will not start. Refer to data monitor screen.

TPS1 CKT Lo

Yes

2 Bp/min

90%

Open

TPS 1 Range Hi

Yes

2 Bp/min

90%

Above 4.8v, 994 counts

TPS 1 Range Lo

Yes

2 Bp/min

90%

Below 0.5v, 35 counts

 

Trim CKT Hi

 

Yes

 

No

 

No

Short, high range, visual warning on SC1000 only.

 

Trim CKT Lo

 

Yes

 

No

 

No

Open, low range, visual warning on SC1000 only.

5 VDC PWR Low

Yes

2 Bp/min

varies

Short any 5v+ to ground

 

NOTE: If any 5v sensor becomes shorted to ground the engine will not start. If the engine is operating when the short occurs the engine may stop operating and will not start.

 

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12 hours ago, tomnjo said:

Try unplugging the wires to the gear lube reservoir. I don't think the alarm will sound with it unplugged. It will at least eliminate that as the source of the alarm. Is your engine a carb or MPI?

Carb

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My old carbed 5.0 ran 175 to 180 all the time. Never alarmed, though. I ended up putting a cooler tstat in it to try to help with running on issues it had. Brought it down to 160.

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That is super odd to me.  Temp should be higher or lower with no thermostat.  Unless you get super lucky at the rpm.

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Yes seemed odd to me to, I have worked on my cars for years, and they have always run cooler with no thermostat, I this my gauge and sensors are bad, rpm gauge doesnt work, volt meter never moves off 0, but it always starts, I have had it out 5-6 times with the alarm, runs fine, ???????????????

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Bruce

You have to many non working circuits for me to guess if The alternator is slipping at that rpm & tripping a  alarm.

Over & out.

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Okay, took boat out today and took temp gun, as I said in earlier post the RPM gauge hasn't been working, bouncing up an down, ran for a little bit till alarm went off, temp on starboard side manifold was 211, temp on port side manifold was 184,  I could still put hand on risers with no problem, temp on thermostat housing was 150, disconnected alarm sending sensor, no more alarm, and RPM gauge started working???????? Still running around 180, and a little over 175 at slower speeds, otherwise runs great

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