Oil types

Jamiesboat · **Joined:** Mon Apr 16, 2012 5:29 pm **Posts:** 17

Hey all hope every ones boat season gets off to a great start! Does any one know the best oil to use in a 1992 5.8 omc cobra engine and what gear oil would be best for the omc out drive any help would be great thank you ahead of time.

NiagaraChillin · **Posted:** Wed Apr 17, 2013 7:57 am

Ohhhh boy. Like "whats the best stereo" and "what sparkplugs should I use", oil type questions usually illicit the most and varied responses. Not to sound like a Richard-head, but search the forums, there are literally dozens and dozens of "What type oil" threads here.

If ya don't find your answer there, LouC will be along shortly to answer all your OMC questions.

LouC · **Posted:** Wed Apr 17, 2013 7:19 pm

Well if you search you will find that people have used just about everything...but here are good choices out there that are pretty easy to find:
Motor oil, straight 30 was recommended by OMC originally, you can use straight 40 if you are in a hot climate, or 15/40 oils like Chevron Delo 400 that are rated for both gas and diesel engines. Merc makes a good oil for I/Os that is a 25/40 grade, any of these would be fine, if you boat in a cool climate I'd go with the Chevron Delo 15/40 or the Merc 25/40.

I would not use car based 10/30 oils because they will thin out in high rpm use in a marine inboard.

Drive oil, OMC originally recommended OMC Hi Vis oil, now superseded by the Bombardier HPF gear oil (also used in Evinrude gearcases) but I have used the Merc High Performance gear oil which is easily available everywhere and my Cobra has done great with it, 10 years worth, based on my mechanic's recommendation.

Oh and if you are going to change the oil in the Cobra drive yourself, it must be done the right way, do it wrong and the drive will be underfilled and you will burn out the upper gear set.

Tubedragger · **Posted:** Wed Apr 17, 2013 7:27 pm

Please enlighten us with the right way to change the cobra drive oil....PLease

deafwish · **Posted:** Thu Apr 18, 2013 2:29 am

Not trying to contradict what LouC is stating, but for the sake of a couple of HP, always go the thicker viscosity - especially in marine applications.
10w30 is very thin for old school marine applications, regardless whether it is automotive or marine designed!
Oil will shear (viscosity index breaks down from heat cycling and mechanical loading) MUCH faster in a marine environment than an auto'.
Running a boat at WOT is like a car being run at 100% load on a dyno, at max RPM for considerable time periods.
Marine oils generally have a much lower API rating (lower spec'), that the automotive equivelants.
The current API specification is 'SN' and this (generally speaking) determines how well it performs.
Try find an SN spec', full synthetic, high zinc product, or find the best PAO/ Ester based product (also with high zinc) of a 15w50, 20w50 or 20w60.
Your oil pressure & engine will love you for it. :wink:

LouC · **Posted:** Thu Apr 18, 2013 5:55 am

Ok if look at the side of Cobra drive from the starboard side, starting from the bottom of the lower unit, there are 2 plugs, the lower most on the forward edge of the lower unit is the drain. A bit higher up at the joint between the upper and lower unit is the fill plug. Now look at the top cover, the large screw in the center has a dipstick as part of it.

To drain you remove the top screw and bottom most drain. Let it drain a couple of hrs. Then replace the drain plug with a new plastic gasket. Now remove the fill it located near the joint between the upper and lower gear cases. Get 2 qts of gear oil, and hook up a gear oil pump to one. Screw the pump into the fill hole. Put the big screw in the hole in the top cover but don't screw it in yet. Then pump gear oil in till you get 2qts in and check it in the dipstick . When it's full, screw in the big screw( new gasket too). Quickly remove the pump from the fill hole. Replace the fill plug with a new gasket. Let it sit for a bit to allow air bubbles to come to the top. Sometimes the level will drop a bit then you re check with the top cover dipstick , if you need to add you can add small amount through the dipstick hole. Do not fill it from the bottom most drain hole like an Alpha that will trap air and you wont get 2qts in.

psusound · **Joined:** Sat Feb 04, 2012 4:08 pm **Posts:** 69

As far as engine oil goes, Mobile One Synthetic, NASCAR uses it, can't be too bad!

rpengr · **Posted:** Fri Apr 19, 2013 8:48 am

LouC wrote:

Ok if look at the side of Cobra drive from the starboard side, starting from the bottom of the lower unit, there are 2 plugs, the lower most on the forward edge of the lower unit is the drain. A bit higher up at the joint between the upper and lower unit is the fill plug. Now look at the top cover, the large screw in the center has a dipstick as part of it.

To drain you remove the top screw and bottom most drain. Let it drain a couple of hrs. Then replace the drain plug with a new plastic gasket. Now remove the fill it located near the joint between the upper and lower gear cases. Get 2 qts of gear oil, and hook up a gear oil pump to one. Screw the pump into the fill hole. Put the big screw in the hole in the top cover but don't screw it in yet. Then pump gear oil in till you get 2qts in and check it in the dipstick . When it's full, screw in the big screw( new gasket too). Quickly remove the pump from the fill hole. Replace the fill plug with a new gasket. Let it sit for a bit to allow air bubbles to come to the top. Sometimes the level will drop a bit then you re check with the top cover dipstick , if you need to add you can add small amount through the dipstick hole. Do not fill it from the bottom most drain hole like an Alpha that will trap air and you wont get 2qts in.

I had always filled my Cobra from the bottom...pump oil in the drain hole until it comes out the middle screw, then put in the middle screw and continue pumping from the bottom until correct height at the dipstick. No trapped air that way. Recheck level after first use.

LouC · **Posted:** Fri Apr 19, 2013 3:41 pm

That way will work if the fill plug is out so the air escapes, but if you leave the fill plug in and pump it in from the bottom it could trap an air pocket, thats why in all of the OMC manuals it says to fill from that fill (upper) plug.

ric · **Posted:** Fri Apr 19, 2013 4:41 pm

What's the best oil? Whatever the owners manual says to use.

deafwish · **Posted:** Fri Apr 19, 2013 5:07 pm

Do some homework Ric & you'll see how silly that response was.
Oil technology has drastically changed for the better, even in the past 7 years. :wink:

Crap - I'm contributing to yet another oil thread!

ric · **Posted:** Fri Apr 19, 2013 5:20 pm

deafwish wrote:

Do some homework Ric & you'll see how silly that response was.
Oil technology has drastically changed for the better, even in the past 7 years. :wink:

Crap - I'm contributing to yet another oil thread!

eject maverick, eject!

deafwish · **Posted:** Fri Apr 19, 2013 5:41 pm

LouC · **Posted:** Sat Apr 20, 2013 11:17 am

Honestly this is not complicated, straight weights will work, as will Chevron or Shell Rotella or Pennzoil Marine 15/40, or Merc's 25/40. Thats all I'd use. No lower viscosity car oils, period.
And Merc's High Performance gear lube works just fine in a dog clutch Cobra.

hutch9900 · **Joined:** Tue Mar 22, 2011 7:14 pm **Posts:** 456

I don't like that my owners manual says to use "Volvo"(with a part number) brand gear oil for the lower unit. It is annoying that it doesnt just say what to use! Why cant they just suggest the proper vicosity?? Did I do wrong by using the Pennzoil Marine Gear Lube? I think it was 80w something.....

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Oil types

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