What oil do you recommend?

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Jul 1, 2020
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3
Location
Sandpoint Idaho
Per the manual, it says that I need a LOW PHOSPHOROUS, fully synthetic 20w-40 FC-W rated oil. I think that 10w-40 or 15w40 or 25w40 may be acceptable but it MUST meet the 3 criteria of being low phosphorus, full synthetic and FC-W rated.

This is for a GM 305 2010 Mercruiser 5.0 MPI fuel-injected engine.

Do you know of any oils that meet ALL 3 criteria above that you can recommend?
 
Walmart has Magna 1 10w-30 FWC Cat friendly for about $7 a gallon on clearance.

Perhaps since your running in cool conditions a 30 weight may be acceptable...
 
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Originally Posted by BretBouer
I appreciate the recommendation. The oil appears to be only partially synthetic. I am looking for full synthetic.


I think you will be better then good with the Mecruiser oil. Your manual might be outdated and maybe check the newer models manual.
I think Merc may have found out full syn didnt work out too well in their engines. Semi syn has some advantages in heavy duty applications, possibly due to shock loading.

Anyway, Merc is in the business of making engines and anyone buying their engines cant go wrong by using their engine oil, the 25/40 has been around for decades now, proven and reliable or Merc would be out of business.
 
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SERVICE MANUAL NUMBER 24CA693
Crankcase Oil
To help obtain optimum engine performance and to provide maximum protection, we strongly recommend the use of Quicksilver 4-Cycle 25W-40 Marine Engine Oil. This oil isa special blend of 25-weight and 40-weight oils for marine engines. If not available, a good grade, straight weight, detergent automotive oil of correct viscosity, with an API classification of SH,CF/CF-2, may be used.In those areas where Quicksilver 4-Cycle 25W-40 Marine Engine Oil or a recommended straight weight oil are not available, a multi viscosity 20W-40 (SH, CF/CF-2) or, as a second but less preferable choice, 20W-50, with API service ratings of SH, CF/CF-2 may be used.IMPORTANT: The use of non-detergent oils, multi-viscosity oils (other than Quicksiliver 25W-40 or a good quality 20W-40 or 20W-50), synthetic oils, low quality oils or oilsthat contain solid additives are specifically not recommended.The chart below is a guide to crankcase oil selection.

Here is the link C&P didnt work too well ... https://www.manualslib.com/manual/1201866/Mercruiser-305-Cid-5-0l.html?page=45#manual
 
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Quote
. . If not available, a good grade, straight weight, detergent automotive oil of correct viscosity, with an API classification of SH,CF/CF-2, may be used.


API SH/CF..... Well thats not "low saps"....
smile.gif


I would go with Rotella T6 15W-40.... ACEA E6/E9 is low saps requirement for HDEO

https://online.lubrizol.com/relperftool/hd.html
 
Why chance it? Go with the Mercruiser 25W40 synthetic blend. There is no need for full synthetic in this application or Mercury would have it available and recommend it.
 
Originally Posted by BretBouer
Per the manual, it says that I need a LOW PHOSPHOROUS, fully synthetic 20w-40 FC-W rated oil. I think that 10w-40 or 15w40 or 25w40 may be acceptable but it MUST meet the 3 criteria of being low phosphorus, full synthetic and FC-W rated.

This is for a GM 305 2010 Mercruiser 5.0 MPI fuel-injected engine.

Do you know of any oils that meet ALL 3 criteria above that you can recommend?

go to wally world

https://www.walmart.com/ip/Super-Tech-Synblend-25w40-Outboard-Oil-1-Gallon-Bottle/985423053
 
The recommended Quicksilver 25w40 is only $26.7 at Walmart. Why roll the dice on something else? BTW, I wouldn't use a xW30 no matter what the temps, this engine runs under much greater stress that in an automotive application. (When was the last time your car ran at 4k rpms up a 20% incline for 2 hours???)

Quicksilver 25w40
 
Quicksilver 25W-40 is one of the best oils on the market - period. For any full load or HD application it is superior to many automotive oils. Does not shear down as quick as many automotive oils...

Gets used in race engines, motorcycles, and LOTs of boats, worldwide. It's my go-to oil for flat tappet breakin's and most high output street engines, now that I can no longer get Delo 400 SD (severe duty).

I'd use it in that motor in a heart beat. Unless the rings or the valve seals are bad, the CAT's will never see enough oil to matter. We ran HDEO's in gas trucks with CAT's for decades and as long as the motors are in good shape the CAT's don't fail. Once the rings start to go, the CAT's ash cap before they fail from Phosphorus "poisoning". Just not a real worry.
 
Quicksilver 25W-40 is one of the best oils on the market - period. For any full load or HD application it is superior to many automotive oils. Does not shear down as quick as many automotive oils...

Gets used in race engines, motorcycles, and LOTs of boats, worldwide. It's my go-to oil for flat tappet breakin's and most high output street engines, now that I can no longer get Delo 400 SD (severe duty).

I'd use it in that motor in a heart beat. Unless the rings or the valve seals are bad, the CAT's will never see enough oil to matter. We ran HDEO's in gas trucks with CAT's for decades and as long as the motors are in good shape the CAT's don't fail. Once the rings start to go, the CAT's ash cap before they fail from Phosphorus "poisoning". Just not a real worry.

This +1
 
FYI: Mercury Marine does not 'make' their stern drive/inboard engines. They
buy them from GM/Chevy.
Last I heard, the QuickSilver oil was blended by Gold Seal blenders to Merc specifications.

My 2¢
 
Quicksilver 25W-40 is one of the best oils on the market - period. For any full load or HD application it is superior to many automotive oils. Does not shear down as quick as many automotive oils...

Gets used in race engines, motorcycles, and LOTs of boats, worldwide. It's my go-to oil for flat tappet breakin's and most high output street engines, now that I can no longer get Delo 400 SD (severe duty).

I'd use it in that motor in a heart beat. Unless the rings or the valve seals are bad, the CAT's will never see enough oil to matter. We ran HDEO's in gas trucks with CAT's for decades and as long as the motors are in good shape the CAT's don't fail. Once the rings start to go, the CAT's ash cap before they fail from Phosphorus "poisoning". Just not a real worry.
I’m having no luck finding Zinc content for QuickSilver 20W-40. Does anyone know what the figures are? Just curious as I have an old OMC 4.3 flat tappet. Thanks
 
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