Correct way to change gear oil on OMC Cobra?

[Darkhorse1201]

I have searched and read on here that the correct way to change the OMC Cobra gear oil is to drain it all and then fill from the bottom plug until it is full at the dipstick (approx. 64 ozs.) However when I read Stuart Hastings Cobra web page he recommends filling the outdrive from the middle hole as to not get an air bubble? I thought that by filling from the drain hole that would acomplish the same thing. Thanks (PS 1992 OMC Cobra 4.3)

 

[Purduebarry]

Re: Correct way to change gear oil on OMC Cobra?

I don't know where you read to fill from bottom. Every thing I have read says from the middle one. Bottom is for draining only.

Regardless of what you do be carful. Supposedly the dipstick can read full and not be, you must run the engine for a few minutes and get everthing to circulate then shut down and let things settle. Then check the level again. Air bubble is bad, melted gears, search for threads that have experienced this and you'll know what not to do. I'd only trust an expert on this (I'm not one) too much can go wrong. Find out for sure!

 

[Boatin Bob]

Re: Correct way to change gear oil on OMC Cobra?

The info on Stuart's site is correct and I believe it was because when OMC built the Cobra they used an existing outboard lower unit so there are different oil passages, filling from the bottom will not guarantee oil getting all the way to upper gears without air being trapped, filling from the middle covers both ways, I've been doing mine this way since 1990 and never had an issue.

 

[Boatin Bob]

Re: Correct way to change gear oil on OMC Cobra?

Not sure who you are but there's no way any manual will tell you to fill from the dipstick hole...that's just asking for trouble. What some have done is to fill from the bottom until it comes out the middle, then put the bottom screw back in and continue to fill from the middle until it comes to the correct level at the top. But you never fill from the top (dipstick hole).

 

[spartanpele]

Re: Correct way to change gear oil on OMC Cobra?

Boatin Bob... Its me...spartanpele...last time this new forum didn't take my name.

If you reread my post, you should fill from the bottom till the outdrive oil comes out the middle plug hole....then put those plugs back in and finish the filling from the dipstick...which isn't much fluid. Thats straight out of the OMC Cobra owners manual.... Now if people want to go and fill the bottom...then fill from middle to top, thats up to them, however, if you do that, you're likely to overfill as you won't know how much you have in till it comes out the top...not good.

As for me, I'm just going to follow the owners manual, which is what most people should do if they own one.

 

[lakelivin]

Re: Correct way to change gear oil on OMC Cobra?

The Cobra owners manual says you should fill from the bottom using a pump, untill it comes out the middle hole. Then put the bottom and middle plugs back in. Then fill from the dipstick hole (on top) till its completely up to the correct level. Put the dipstick back in. Raise and lower the drive up and down a couple times. Recheck the dipstick level and top off as necessary.

??? Just curious, which Cobra owners manual did that come from?

I've got an '89 4.3L cobra. My owners manual, the OEM 1989 OMC Service Manual, and a Clymers manual covering Cobras from '86-'93 all state the same procedure. You remove 'dip stick' on top, drain oil from bottom hole, replace bottom plug, fill from middle hole with pump until oil reaches appropriate dipstick level with dipstick resting on top of hole but not screwed in. Then tighten dipstick, replace middle screw, wait a bit and recheck. After this point all measurements should be made with the dipstick screwed in . Top off from the top dipstick hole as needed until you've got the appropriate level in the drive.

You should note how much oil your drive takes (64 oz for my 4.3L) and make sure thats pretty close to what you put in when you refill the drive. Then recheck the level several times (after everything settles for a little while, after starting it the first time, etc.)

Several people on here fill from the bottom plug to the middle plug, then from the middle plug to the dipstick, and I have no doubt that works as well, but the OMC Cobra recommendation is as I outlined above.

 

[spartanpele]

Re: Correct way to change gear oil on OMC Cobra?

Its from a 1994.... Therein could lie the difference between one method and another... Although my 1994 says Cobra on the outside, its technically a VP...cone clutch, etc, etc..

Sorry for any confusion:%

 

[Boatin Bob]

Re: Correct way to change gear oil on OMC Cobra?

OK Spartanpele...I think you've nailed it as yours is a 1994 with the cone clutch drive, completely different drive and if you read Stuarts site he is primarily dealing with a dog clutch drive as am I and Lakelivin so I guess we're all correct depending on how you look at it. But for swsidlo who has a 1992 I would still recommend filling from the middle.

 

[Purduebarry]

Re: Correct way to change gear oil on OMC Cobra?

I think the point is to top off, not necessarily "fill" from the dipstick. At this point you are talking about a small amount. Regardless of the method would everyone agree it is still safe to; fill, raise, lower, run it for a minute then recheck. If you are sure about your procedure that's fine, but if not, I'd make darn sure everything is full before WOT. Too many variables here, the year etc. and gears are expensive!