Problem with a 3 yr old Mercury 25hp EFI 4 Stroke - Chicago Illinois Fishing Forum, Information & Reports
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Old 05-20-2011, 05:17 PM   #1 (permalink)
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Default Problem with a 3 yr old Mercury 25hp EFI 4 Stroke

Has anyone ever had this problem?

I've got a 3 yr old Mercury 25hp EFI 4-Stroke. Every time I take it out since last fall it does the same thing. When I get under way at full throttle, within almost exactly one minute the motor's warning light/alarm (solid tone) comes on and the motor goes into an idle mode. Ok, first thought is that it's over-heating, or it's not warmed up. It's not. Peeing fine, read on...

I shut down the motor, wait a few minutes (was only a few seconds during cold duck hunting season, longer as it is getting warmer now). Then, I start it back up, and have no further problems. It runs perfectly the rest of the day.

At first it was just an annoyance. Now, since the warranty period is about to expire, I want it fixed. Last thing I want is to have it go into idle mode with a barge coming at me!

If anyone knows what could be the cause, and a fix, please let me know. So far the shop has no clue. Thanks!
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Old 05-21-2011, 11:58 AM   #2 (permalink)
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Default Re: Problem with a 3 yr old Mercury 25hp EFI 4 Stroke

http://www.mercurymarine.com/contact-us-online/

Never heard of that problem before, but I searched the Mercury website and found a contact page... Nothing at iBoats or WestMarine...
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Old 05-21-2011, 02:04 PM   #3 (permalink)
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Default Re: Problem with a 3 yr old Mercury 25hp EFI 4 Stroke

Thanks for looking into the problem for me j-k-s. I appreciate it.

Talked to the shop today. They said a Mercury rep just happened to show up while they were looking at my motor. He contacted some engineers. They now believe it is a bad oil pressure switch, and maybe some other sensor. It will be an involved job, and parts have to be ordered. Warranty should cover it.

I sure hope they got it right this time!
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Old 06-19-2016, 05:46 AM   #4 (permalink)
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Did they figure out the problem. Cause I have a 2013 25 horse merc that does exactly the same as yours. The dealer changed the oil pressure switch and still the same my warranty expires the end of July its been doing this since the first spring after I bought it bit getting worse
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Old 06-19-2016, 09:05 AM   #5 (permalink)
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Quote:
Originally Posted by Shayne View Post
Did they figure out the problem. Cause I have a 2013 25 horse merc that does exactly the same as yours. The dealer changed the oil pressure switch and still the same my warranty expires the end of July its been doing this since the first spring after I bought it bit getting worse
I have the same motor but have not had this problem. However it could be fuel. The fuel line could be deteriorating from the ethanol. causing a lack of fuel at the injectors causing a miss fire. Worth a look.
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Old 07-20-2016, 07:29 AM   #6 (permalink)
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Hi. Did you get closer to find the problem? I have a 2011 25HP Merc that have done exaclty the same as you describe. Problem existed since the motor was approx 1 year old. Alarm goes off 2-5 mins after startup. Have to stop the engine and wait for some minutes, problem is gone the rest of the day. Have turned it in to the dealer now, but they struggle to find the problem.
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Old 08-19-2016, 09:38 AM   #7 (permalink)
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When the alarm is going off unplug the temperature and oil pressure senders and see which one causes the alarm to stop ringing is a trick i used on some older motors, not sure if it will work on the EFI. If that does not work dealer may be able to take it out for a ride with the diagnostic program and see exactly which switch it triggering the alarm or hook up a DVM to the switches and monitor the resistance. Normally you can tell if the engine is getting hot by steam coming out the back of the motor or using an infared thermometer on the block.

If you believe it is oil pressure make sure the oil is at the appropriate level, overfull is just as bad as not enough. You may be able to take the oil pressure switch out, install T fitting that allows you to run a manual gauge at the same time.

I wish i could tell you i havent seen this before but the truth is that i have seen several of those Tohatsu make Mercury have oil pressure problems most likely caused by bad bearings on the crankshaft. I know it cutting into your fishing time but it probably needs to go back to the dealer and tell him you done want it back until hes figured it out. Unfortunately mercury will let just about anyone be a dealer, i believe you can even order some of their engines over the internet. This makes it hard to find out who is really qualified to be working on it.
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Old 06-01-2018, 10:30 AM   #8 (permalink)
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I had the same issue and had the water pump impeller replaced sensor checked thermostat checked all to no help.if it is a heat issue,i was told by a mercury mechanic that they had problems with a water tube grommet under the power head and it had to be replaced to correct the problem.he said it was very costly because it was a four hour job
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Old 06-01-2018, 07:24 PM   #9 (permalink)
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I certainly hope it was repaired sometime in the last 7 years since the post was originally made
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Old 06-02-2018, 12:19 PM   #10 (permalink)
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Prop slip and over RPM ?
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