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#4800360 - 06/29/18 08:16 AM 2008 Mercury 90hp 4-stroke outboard EFI
mrnkc130 Offline


Registered: 03/24/18
Posts: 10
Loc: Texas
I have a pontoon boat with this motor, seems to run fine, has about 200hrs on it, new to me.

After pulling the kids on a tube for a while and getting up to 5500 rpm we slowed down and stopped and swam for a while. When I started the motor to leave I noticed some oil on the water, not much but it was still a little concerning. Before we stopped I think I saw a little bit of smoke that I hadnt noticed before either low to the water.
Engine was serviced by a dealer and i've only run maybe a tank of gas thru this since buying it so far. I took it easy on the way back to the dock and checked the oil once the boat was out of the water (seems to take an hour or 2 for all the oil to drain back down to get an accurate reading) and it was full, didnt notice anything wrong really, the rubber grommet for all the cables going into the motor was broken so maybe some water just got in there due to the higher speeds and drained out while we were sitting and caused the oil slick, that's what i'm hoping anyways. I'm new to outboard motors, seem like anything to be concerned about?

Can anyone recommend a good oil for this motor and lower unit? Don't really want to pay the premium for the mercury oil if not needed. Manual calls for 25-40, I'm in Texas so its quite hot out in the summer.
I was going to change the spark plugs (no idea if its ever been done) and just change the oil and lower unit oil for good measure while I was at it.
Thanks in advance!
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1946 Chevrolet 2-ton
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#4800365 - 06/29/18 08:29 AM Re: 2008 Mercury 90hp 4-stroke outboard EFI [Re: mrnkc130]
TOMJ Offline


Registered: 05/17/12
Posts: 87
Loc: Marietta, GA
Originally Posted By: mrnkc130
I have a pontoon boat with this motor, seems to run fine, has about 200hrs on it, new to me.

After pulling the kids on a tube for a while and getting up to 5500 rpm we slowed down and stopped and swam for a while. When I started the motor to leave I noticed some oil on the water, not much but it was still a little concerning. Before we stopped I think I saw a little bit of smoke that I hadnt noticed before either low to the water.
Engine was serviced by a dealer and i've only run maybe a tank of gas thru this since buying it so far. I took it easy on the way back to the dock and checked the oil once the boat was out of the water (seems to take an hour or 2 for all the oil to drain back down to get an accurate reading) and it was full, didnt notice anything wrong really, the rubber grommet for all the cables going into the motor was broken so maybe some water just got in there due to the higher speeds and drained out while we were sitting and caused the oil slick, that's what i'm hoping anyways. I'm new to outboard motors, seem like anything to be concerned about?

Can anyone recommend a good oil for this motor and lower unit? Don't really want to pay the premium for the mercury oil if not needed. Manual calls for 25-40, I'm in Texas so its quite hot out in the summer.
I was going to change the spark plugs (no idea if its ever been done) and just change the oil and lower unit oil for good measure while I was at it.
Thanks in advance!



I have a Yamaha F115 on a pontoon and have been running HDEO for the past 8 years or so. Any 15-40 HDEO would be a good choice.
I have used Rotella 5-40 in the past. Currently running Mobil Delvac. HDEO oils are cheap and have a more robust add pack than PCMO.

As far as a lube for the lower unit, I used Yamalube in the past but have started using Supertech marine gear lube.
Just make sure that you use marine grade gear oil.
_________________________
1992 GMC C1500 Mobil 1 HM
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2007 Honda VTX1300 R Mobil 1 HM

2006 Sea Doo GTI SE Mobil Delvac
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#4800375 - 06/29/18 08:38 AM Re: 2008 Mercury 90hp 4-stroke outboard EFI [Re: mrnkc130]
mrnkc130 Offline


Registered: 03/24/18
Posts: 10
Loc: Texas
Awesome, I like the idea of using something more reasonably priced and changing it more often in the case of a boat motor. And being new to me I think i'll swing by Walmart and grab some for a quick service before taking it on the lake for the 4th! thanks!
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#4800395 - 06/29/18 09:05 AM Re: 2008 Mercury 90hp 4-stroke outboard EFI [Re: mrnkc130]
Snagglefoot Offline


Registered: 12/31/17
Posts: 1909
Loc: SE British Columbia, Canada
NMMA FC oils offer corrosion resistance for your cylinders if your boat is stored in a high humidity environment.

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#4800423 - 06/29/18 09:24 AM Re: 2008 Mercury 90hp 4-stroke outboard EFI [Re: mrnkc130]
Snagglefoot Offline


Registered: 12/31/17
Posts: 1909
Loc: SE British Columbia, Canada


Edited by Snagglefoot (06/29/18 09:50 AM)

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#4800438 - 06/29/18 09:44 AM Re: 2008 Mercury 90hp 4-stroke outboard EFI [Re: mrnkc130]
Snagglefoot Offline


Registered: 12/31/17
Posts: 1909
Loc: SE British Columbia, Canada
This one goes on sale at various places.


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#4800707 - 06/29/18 03:08 PM Re: 2008 Mercury 90hp 4-stroke outboard EFI [Re: mrnkc130]
irv Offline


Registered: 10/08/06
Posts: 1141
Loc: Oshawa, Ont. Canada
Originally Posted By: mrnkc130
I have a pontoon boat with this motor, seems to run fine, has about 200hrs on it, new to me.

After pulling the kids on a tube for a while and getting up to 5500 rpm we slowed down and stopped and swam for a while. When I started the motor to leave I noticed some oil on the water, not much but it was still a little concerning. Before we stopped I think I saw a little bit of smoke that I hadnt noticed before either low to the water.
Engine was serviced by a dealer and i've only run maybe a tank of gas thru this since buying it so far. I took it easy on the way back to the dock and checked the oil once the boat was out of the water (seems to take an hour or 2 for all the oil to drain back down to get an accurate reading) and it was full, didnt notice anything wrong really, the rubber grommet for all the cables going into the motor was broken so maybe some water just got in there due to the higher speeds and drained out while we were sitting and caused the oil slick, that's what i'm hoping anyways. I'm new to outboard motors, seem like anything to be concerned about?

Can anyone recommend a good oil for this motor and lower unit? Don't really want to pay the premium for the mercury oil if not needed. Manual calls for 25-40, I'm in Texas so its quite hot out in the summer.
I was going to change the spark plugs (no idea if its ever been done) and just change the oil and lower unit oil for good measure while I was at it.
Thanks in advance!


I have the exact same motor, only an 07. In order to check the oil, the motor has to be tilted all the way forward (centered, obviously) and left there for 2-3 minutes. Once that time is up, lower the motor all the way level, not any further. Once there, let sit another 2-3 minutes then check your oil.

As far as the oil slick goes, I will almost guarantee it is oil sitting up in front of the engine that seeps/leaks down after an oil change. My mechanics do a [censored] poor job of cleaning up their mess but it's created with the oil filter change. Every year when I get my boat out of storage, I stuff some paper toweling in there with a long screwdriver and soak up the used/left over oil. You will see it in there when the engine is tilted fully forward looking in from the front right side.
As far as seeing smoke, it could be nothing or a bit of the residual/spilt oil got on something hot? If the motor runs good and starts good, I'd say that's all you have to concern yourself with.
I use Merc semi and have since new and have never had a problem. This motor has a lot of use towing my son and his buds around tubing, (sometimes triple tubing 3 full size teenage boys) kneeboarding and water skiing. I do try to run premium fuel (ethanol free) in it and I also give it a little splash of Seafoam every tank.

Also, your motors max RPM is 6000 and it should be run there. The stock prop, which, I assume you have, will only allow it to your range. I purchased 2 Turning Point props (Hustlers) and couldn't be happier. I mainly use the 17P for water sports and the 19 when I want to play. They are great props and allow the motor to run within it's full RPM range. I also gained 2 mph and get far better holeshots and less cavitation. Great props for cheap money! https://turningpointpropellers.com/

Edit: meant to add my bud runs Merc semi or full syn in this motor. Top speed to date, 107 mph on GPS. It's pricey oil but it's good and made for you motor, and like what Snaggle mentioned, it's designed for you motor as well.










Edited by irv (06/29/18 03:28 PM)
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2013 Ram Hemi Bighorn QC 4x4
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#4800755 - 06/29/18 04:38 PM Re: 2008 Mercury 90hp 4-stroke outboard EFI [Re: mrnkc130]
irv Offline


Registered: 10/08/06
Posts: 1141
Loc: Oshawa, Ont. Canada
Mrnkc 130, I can assume you don't have an owners manual?
Google it. 2008 mercury 90 4 stroke owners manual. I just tried a copy and paste but it's a PDF so it is copied in my documents only.


Edited by irv (06/29/18 04:40 PM)
_________________________
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2013 Ram Hemi Bighorn QC 4x4
PP and/or PUP for both vehicles.

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#4801096 - 06/30/18 05:17 AM Re: 2008 Mercury 90hp 4-stroke outboard EFI [Re: irv]
dlundblad Offline


Registered: 09/30/13
Posts: 10193
Loc: Indiana
Originally Posted By: irv
Mrnkc 130, I can assume you don't have an owners manual?
Google it. 2008 mercury 90 4 stroke owners manual. I just tried a copy and paste but it's a PDF so it is copied in my documents only.


I can take some pics of a manual for a 115 Merc today if needed. This engine also has a data matrix sticker that once scanned with a smart phone, I believe takes you to some how to's on the web.

I thought I had this one on my phone, but apparently not.

*Random piece of info, Ours wants 10w30, but says 25w40 can be used. I can only find quarts of the 10w30 so that alone makes it $$$.


Edited by dlundblad (06/30/18 05:19 AM)
_________________________
03 Jeep WJ 4.0 199k Castrol Edge 10w40 HM Fram XG16
02 Volvo S60 2.4T 177k M1 0w40 Mahle OX149D
97 Chevy Blazer 4.3 149k Rotella T5 10w30 Supertech ST3980


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#4801145 - 06/30/18 07:22 AM Re: 2008 Mercury 90hp 4-stroke outboard EFI [Re: mrnkc130]
mrnkc130 Offline


Registered: 03/24/18
Posts: 10
Loc: Texas
Thank you all for the replies.

I didn't get a manual with the boat but I did look up the manual online with the serial number, I see the recommended oil is the Quicksilver and 10w30 also being acceptable, just looking to see if anyone found a more economical oil that performs as well.

I didn't however see the part about tilting the motor up all the way and then back before checking the oil. I have to remove the cover in order to do that because it hits the back portion of the boat, not a big deal though since i need to take it off to check the oil anyways haha!

Yes the motor starts up instantly, runs quietly and smoothly, there is a certain RPM range where it must harmonically sync with something on the boat and makes a rattling noise but im sure its not a problem with the motor. I was NOT running premium in it, i'll try that next tank and see how it does.

I believe it is the stock Mercury aluminum prop, which i had considered changing just due to the fact that its slightly chewed up on the leading edge.

Its a pontoon boat and the only one I've ever driven so the performance seems acceptable to me, it runs about 22mph at WOT, and at that point the water slapping against the bottom stringers starts to get concerning anyways and loud!
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2016 Hyundai Accent
1946 Chevrolet 2-ton
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#4801157 - 06/30/18 07:39 AM Re: 2008 Mercury 90hp 4-stroke outboard EFI [Re: mrnkc130]
irv Offline


Registered: 10/08/06
Posts: 1141
Loc: Oshawa, Ont. Canada
Originally Posted By: mrnkc130
Thank you all for the replies.

I didn't get a manual with the boat but I did look up the manual online with the serial number, I see the recommended oil is the Quicksilver and 10w30 also being acceptable, just looking to see if anyone found a more economical oil that performs as well.

I didn't however see the part about tilting the motor up all the way and then back before checking the oil. I have to remove the cover in order to do that because it hits the back portion of the boat, not a big deal though since i need to take it off to check the oil anyways haha!

Yes the motor starts up instantly, runs quietly and smoothly, there is a certain RPM range where it must harmonically sync with something on the boat and makes a rattling noise but im sure its not a problem with the motor. I was NOT running premium in it, i'll try that next tank and see how it does.

I believe it is the stock Mercury aluminum prop, which i had considered changing just due to the fact that its slightly chewed up on the leading edge.

Its a pontoon boat and the only one I've ever driven so the performance seems acceptable to me, it runs about 22mph at WOT, and at that point the water slapping against the bottom stringers starts to get concerning anyways and loud!


Being "ethanol free" is more important than running premium fuel. The only way we get ethanol free gas up here is to run premium, but not all premium fuel is ethanol free.
If you can get regular (87 octane) that is ethanol free then go that route but if not, check to make sure the premium you are using is ethanol free.

Try to find where that rattle is coming from and fix it if possible. Running your engine to wide open RPM is not a bad thing. You certainly don't want to lug these engines!
If a new prop is required, I highly recommend a Turning Point prop. They are likely the same price as an OEM, maybe cheaper, but they are far superior, imo.
Follow the info in my link, year, size, gear ratio, etc, and it will take you to the prop(s) that will work/fit on your engine. Trust me, you'll be glad you did.

Also, be sure to check out www.iboats.com forum. Its a huge site and has a ton of info on "everything" boating/engine related and then some!
Good luck. Cheers2
_________________________
2017 Chevy Impala 3.6 Ltr.
2013 Ram Hemi Bighorn QC 4x4
PP and/or PUP for both vehicles.

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#4801163 - 06/30/18 07:48 AM Re: 2008 Mercury 90hp 4-stroke outboard EFI [Re: mrnkc130]
mrnkc130 Offline


Registered: 03/24/18
Posts: 10
Loc: Texas
Ethanol is in all grades around here. The closest place I can get Ethanol free is about 25 mile from where I keep the boat. I normally Just fill everything up with non ethanol fuel at winterize time along with some stabil.
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#4805597 - 07/05/18 09:25 AM Re: 2008 Mercury 90hp 4-stroke outboard EFI [Re: mrnkc130]
FastLane Offline


Registered: 12/10/14
Posts: 458
Loc: MB - Manitoba
I use Mobil 1 10W30 without any issues. Buy it on sale and it’s a pretty cheap oil change. My dealer said use whatever you like. Any 10W30 works just fine.


Edited by FastLane (07/05/18 09:28 AM)
_________________________
2010 Silverado 4.8 4x4 Mobil 1 5W30 ACDelco PF48E
2002 Mustang GT 4.6 Mobil 1 5W30 MC FL-820S
1966 Cessna 150 Phillips 20W50
2013 Mercury 30hp Merc 10W30

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#4805796 - 07/05/18 12:30 PM Re: 2008 Mercury 90hp 4-stroke outboard EFI [Re: FastLane]
irv Offline


Registered: 10/08/06
Posts: 1141
Loc: Oshawa, Ont. Canada
Originally Posted By: FastLane
I use Mobil 1 10W30 without any issues. Buy it on sale and it’s a pretty cheap oil change. My dealer said use whatever you like. Any 10W30 works just fine.


That is some bad information. Car oil is not the same as outboard oil. Will your motor grenade immediately after putting it in? Not likely, but over time your motor will pay the ultimate sacrifice which will be costly!! You need NMMA certified oil for 4 stroke outboards.
https://themarinelab.com/best-4-stroke-outboard-oil/

Marine vs. Auto Oil
The basic standard for four-stroke marine engine oil is the FC-W (four-stroke cycle, water-cooled) certification, which was approved by the National Marine Manufacturers Association Oil Certification Committee in 2004. Compared with regular motor oil, FC-W oil features:

More corrosion inhibitors to deal with the marine environment, long periods of inactivity and long periods of operation at low speeds during which the engine is below its ideal operating temperature.

Greater resistance to shearing, the permanent loss of viscosity that occurs when larger oil molecules are cleaved by mechanical forces. Under shear stress, oil can lose its ability to separate moving parts, leading to greater wear or even catastrophic failure in extreme cases. Compared with an auto engine, a marine engine spends much more time at high rpm and under a heavy load, so its oil is more prone to shearing.

An independent lab certifies that marine oil meets the FC-W spec, a test that takes 30 days and costs more than $55,000. The FC-W certification is sort of a “bare minimum” for oil performance. The FC-CW oil sold by engine OEMs significantly exceeds that minimum standard.
_________________________
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2013 Ram Hemi Bighorn QC 4x4
PP and/or PUP for both vehicles.

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#4807213 - 07/06/18 10:05 PM Re: 2008 Mercury 90hp 4-stroke outboard EFI [Re: mrnkc130]
FastLane Offline


Registered: 12/10/14
Posts: 458
Loc: MB - Manitoba
Just a way for the dealers to make more money
_________________________
2010 Silverado 4.8 4x4 Mobil 1 5W30 ACDelco PF48E
2002 Mustang GT 4.6 Mobil 1 5W30 MC FL-820S
1966 Cessna 150 Phillips 20W50
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