2008 Mercury 20 HP 4 Stroke Oil Warning Light

naneekeenan

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I have a 2008 mercury 20 hp 4 stroke, the model number is 1f20211hk. The low pressure warning light is on and the engine is in limp mode. The motor has less then 100 hours on it. I have already tried changing the engine oil and filter, new lower unit oil, I've replaced the oil pressure sensor, I changed the spark plugs, I replaced the fuel line and put fresh gas in the tank.

when I unhook the wire from the sensor the light shuts off.

What else could it be that is causing the light to turn on?


I appreciate any and all help to get me back on the water. I'm already getting fishing withdrawls!
 

Star

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Re: 2008 Mercury 20 HP 4 Stroke Oil Warning Light

Did you own this motor during that first 100 hours? What did the oil look like when you drained it. What weight oil did you put back in it. It sounds like low oil preasure to me and that switch closes at 10#. Warenty time, I have seen what happens when the rod caps come loose on 9/15 hp and blow holes in the case. It could be a bad pump or passage blockage. Please let us know what it is, I have thought about pulling mine down just to retourque my rod caps after seeing a distroyed engine.
 

naneekeenan

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Re: 2008 Mercury 20 HP 4 Stroke Oil Warning Light

I bought the motor used about a month ago and have put on around 20 hours. I used 25w-40 mercury oil. The oil that came out was black but other then that I didn't notice anything strange. How would I check for a blockage? I's there another electric component to the oil pressure sensor that could be bad? And also, is there any way to have my motor hooked up to a computer and have diagnostics run on it?
 

Star

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Re: 2008 Mercury 20 HP 4 Stroke Oil Warning Light

Your problem is low oil presure. pump not pumping, internal presure rellif not closeing, or bearing or crank problems. You have to get a good oil presure gage on it to see what the preasure is at idle and 2000 rpm. there isn't any electronic oil presure regulation on that motor. Talk to the seller.. Are you useing a mercury oil filter. BLACK oil is not right at 100 hours... Dark brown is. Buyers aren't always told the truth!!!!
 

naneekeenan

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Re: 2008 Mercury 20 HP 4 Stroke Oil Warning Light

What PSI should I be looking for at idle and 2000 rpms? I'm going go pick up an oil pressure tester from my buddy today.
 

Star

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Re: 2008 Mercury 20 HP 4 Stroke Oil Warning Light

25 to 30# (a guess by me)
 

naneekeenan

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Re: 2008 Mercury 20 HP 4 Stroke Oil Warning Light

Thank you for all of this info, you're helping me out tremendously. One last question, where do I hook the oil pressure testing gauge up at? Do I take out the factory oil pressure sensor and Hook it up there?
 

Star

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Re: 2008 Mercury 20 HP 4 Stroke Oil Warning Light

Yes, just remove the oil preasure switch and short the wire to the case anywhere. Screw the gage line into that port (1/8 NPT thread)
By shorting the wire the 2000 rpm rev limiter will limit top speed. If you see much change in preasure I will be supprised. I do not know if there is an oil preasue relif on the pump or not. The pumps are quite simple and either work or not. They increased the output on the15hp 2001 oil pump due to low oil preasure at idle. Ihate to be mister black cloud but I think that if the pump is turning you have a hole or space somewhere in the system that is passing enough oil to drop your preasure. I have heard that the bearing cap bolts have come loose in the 9.9/15 motors and that may be enough to drop your preasure. If that happend you would hear other noises.. like B
 

naneekeenan

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Re: 2008 Mercury 20 HP 4 Stroke Oil Warning Light

The oil pressure read zero and unfortunately the compression would only read 30 on both cylinders. But I didn't thread seal the connection before I threaded it into the spark plug hole. I doubt it would make much difference though. I'm assuming Its blown up and I just wasted 2k on a dealerships scrap metal with stickers on it.
 

Star

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Re: 2008 Mercury 20 HP 4 Stroke Oil Warning Light

Don't jump off the bridge yet. If that is a manual start there is an unloader that limits that compression to about 40#. Any motor can be fixed and even broken the LU and pump with drive shaft sells for more than $1000. 0 preasure is better than some preasure. If you bought it from a dealer talk him into at least diagnosing 0 preasure. Did you use a mercuy oill filter when you replaced it. The oil pump
is driven at the bottom of the camshaft. It can't be removed without pulling the head. I would call or email mercury tech support, and ask about any known 0 oil preasure problems. They are pretty good, but of course they will say take it to a dealer. Tell him you bought it from a dealer and you just wanted to speed thing up by having some of the possibles... It could be something simple
 

naneekeenan

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Re: 2008 Mercury 20 HP 4 Stroke Oil Warning Light

Well that is quite a relief to know that there is an un-loader to limit starting compression. I thought I was out of luck and needed to do a full rebuild. I just purchased a mercury manual for my motor off of Ebay, and will be buying a new pump and relief valve tomorrow. So it looks like I'll be in my garage over the memorial weekend trying to get this motor back in operating condition. Thanks again for the help!
 

naneekeenan

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Re: 2008 Mercury 20 HP 4 Stroke Oil Warning Light

I contacted the mercury tech line and they confirmed that it does indeed have an unloader, the man I spoke with told me that most likely the pump needs replaced.
 

naneekeenan

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Re: 2008 Mercury 20 HP 4 Stroke Oil Warning Light

The pressure relief valve had somehow un screwed itself from the bottom of the engine block and was stuck to the magnet in the oil pan. I screwed my new one in with a little loctite on the threads, put everything back together and it works perfect.
 

Star

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Re: 2008 Mercury 20 HP 4 Stroke Oil Warning Light

BE CAREFUL!!! There may be more parts to that preasure relief valve like a spring and a plunger.... I don't know where you can get a blowup of it other than mercury support.. It may be fine but I am a cautious old fool here!!! Glad you found the problem though. I am very unhappy with some of the info we all get from high priced dealers and repair shops. I have had to learn about the problems of my motor so I can fix it myself.. but in the end I am better off.
 
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