Mercury Engine Alarm Interpretation

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
Karld
Posts: 3
Joined: Sat Sep 25, 2021 9:33 am

Mercury Engine Alarm Interpretation

Postby Karld » Sat Sep 25, 2021 10:00 am

[On a] Mercury 2001 3-liter 250-HP engine model XL EFI and serial number OT512640, there is a continuous alarm about three to five minutes after engine start.

I recently noticed the oil reservoir tank on the engine loses about one to two cups [8 to 16 ounces] of oil after the engine has been tilted up.

[There is ] no evidence of leaking at the cap, Seeping oil is visible in the upper cowling, but [in excess] to the amount lost. Most oil is returning to [the] remote reservoir.

Air is being allowed into system somehow.

Q1: [is the source of air into the oil system caused by] bad hoses from [the remote] reservoir [tank]?

[There is] no evidence of leaking [of oil] from remote tank to a thru-hull; [the] hoses [are] not visible [on the] inside [of a] cable tube from [the] hull to [the] engine.

[The] engine starts normally, idles normally at dock, but then [this] constant alarms sounds, [the alarm] shut off, [I] wait few minutes, [then I] restart [the engine,] and again [there are] alarms,

[The engine] temperature gauge reads normal temperatures.

[I have] verified [the] oil float magnet [is] in place and [the] low oil alarm sensor [is] working properly.

Q2: [Is the cause of the alarm due to a] bad oil pump?

Q3: Where is oil sensor [on a 2001Mercury 250-HP XL EfFI engine].

[I] would like to disconnect to see if [the] alarm comes again [in order] to eliminate or [to] confirm the alarm is for oil—or [to confirm the alarm is caused by] something else.

A voltmeter indicates normal charging; [this suggesrs that low voltage is] not likely [the cause of the alarm].

[Please give me] suggestions on how to troubleshoot this alarm. Thank you.

Karld
Posts: 3
Joined: Sat Sep 25, 2021 9:33 am

Re: Mercury Engine Alarm Interpretation

Postby Karld » Sat Sep 25, 2021 4:35 pm

In troubleshooting [I discovered the 2001 Mercury 250-HP two-stroke-power-cycle engine the] oil reservoir is filled from a remote tank.

I [have] now [decided that the] source of [the] alarm [described above is not] oil.

Using a thermometer [I observed the engine temperature rose] quickly from cold start and the alarm horn sounded as expected [when the observed temperature was] about 200 degrees. [The overboard indicator stream was] spitting water but not strongly.

A new impeller with less than two hours of service was just installed [Both] sides [of the engine V-block cylinder heads] rose to [the same] temperatures [in the] same [amount of] time. Both of these thermostats [are] new in the last year.

While the thermostats were removed the system was flushed and vacuumed after treating with "barnacle buster".

Karld
Posts: 3
Joined: Sat Sep 25, 2021 9:33 am

2001 Mercury 250-HP Overheat Alarm

Postby Karld » Sat Sep 25, 2021 4:47 pm

My outboard engine, a Mercury 2001 two-stroke-power-cycle 250-HP model XL EFI had been running fine.

I [had a] shop [perform the] "100-hour service." I then took the boat for a short spin. [The Mercury 2001 250-HP engine throttle was set to] idle for maybe [the time needed for the boat to travel] a half-mile, [then the engine throttle was advanced to wide-open] for about [the time needed for the boat to travel] a mile. Then [the throttle was set to] Idle [and the boat was piloted] to [a] dock for about 20 minutes.

While docking, [the] throttled [was advanced in order to cause the boat] to spin. The alarm horn sounded at about this same time, and a lot of oil or gasoline appeared on the water. Also, I observed there was water squirting out of the top seam between [the] cowling and [the] upper gear housing.

i think I know the [cause of the overheating]; the pick-up tubes [were] not meshed [and were not] properly aligned. No water [was] reaching the power head. The [overboard confidence stream output pressure was] weak.

Using [a] thermometer [I observed that the engine temperature] rose quickly from cold [at engine start]. The alarm horn sounded as expected [when the thermometer indicated a temperature of] about 200-degrees.

[The overboard confidence stream outlet was] spitting water but not strongly.

The new [engine water pump] impeller has less [been in service for less] than two hours.

Both sides [of the engine V-block rose to [the same] temperature [in the same amount of] time. Both thermostats ertr new within the last year. When the thermostats [were] removed, the [engine cooling] system was flushed and vacuumed after treating with "barnacle buster."

Where [should I begin] troubleshooting [to find the cause] of the problem?

I think I may need to remove the lower unit [from the engine] and [make a visual inspection of the components in the lower unit].

Don SSDD
Posts: 254
Joined: Fri Oct 23, 2015 6:58 am
Location: Nova Scotia

Re: Overheat Alarm - Where to begin now?

Postby Don SSDD » Sun Sep 26, 2021 8:00 am

I’d wonder if that flushing and treatment with barnicle buster you did with the thermostats removed loosened up some particles that came loose. While you said it was flushed and vacuumed at the time, more particles may have now come loose. Check your telltale and see if any small bits stuck in it, also remove thermostats and see if any debris visible there.
1986 Outrage 18 with 2001 Honda 130 HP
Former Owner 1991 Guardian 19 with 1994 Evinrude V4 140HP
Former owner 1987 Montauk with 1998 Mercury 90HP
Nova Scotia

jimh
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Location: Michigan, Lower Peninsula
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Re: 2001 Mercury 250-HP Overheat Alarm

Postby jimh » Sun Sep 26, 2021 7:42 pm

Karld wrote:I [had a] shop [perform the] "100-hour service."


What is the "100-hour service"?

jimh
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Location: Michigan, Lower Peninsula
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Re: 2001 Mercury 250-HP Overheat Alarm

Postby jimh » Sun Sep 26, 2021 8:52 pm

Karld wrote:Where [should I begin] troubleshooting [to find the cause] of the problem?


If by "the problem" you mean the engine overheating, the the usual cause of an outboard engine overheating is due to insufficient flow of cooling water. Because it is difficult to measure the volume of cooling water being produced by the engine water pump, you perhaps can measure the pressure of the water in the engine cooling system. To measure the water pressure you should insert a pressure sensor at the appropriate point in the cooling system as directed by the engine manufacturer. Then you can monitor the cooling water pressure as a function of engine rotation speed. After collecting data on engine cooling water pressure as a function of engine rotation speed, you can compare your measured pressure values against the manufacturer's recommended cooling water pressure. Typically an outboard engine manufacturer will publish a chart or a table that graphs or lists the expected cooling water pressure as a function of engine rotation speed. See if your cooling system is working as the manufacturer specified.

If the cooling water pressure is below the expected level, then you can look into the water pump. The water pump may not be working properly.