OMC Cobra 5.0 lower unit oil question

[Bsluper]

Good afternoon, I have done some research on this but have a few additional questions. I am trying to drain and replace the lower unit oil on a 1993 OMC Cobra 5.0 Ford EFI (model #50FAPRJVN). People here have referenced a resource on Crowley marine buy that does not say to remove the lower drain plug at any point. So I would like to confirm that I have the complete order of this down. THANK YOU for any feedback or input.

1. remove the top plug/dipstick and replace gasket
2. Remove fill plug and replace gasket
3. Replace bottom plug and replace gasket
4. After oil is done draining begin slowly filling through fill plug (middle)
5. QUESTION Do I already have the bottom plug screwed back in when I begin filling or do I wait for oil to be coming out of it before screwing in?
6. Constantly monitor dip stick levels and stop when oil reaches mark.
7. Screw in top plug/dipstick
8. Remove oil pump
9. Screw in fill plug
10. QUESTION would it be good to then unscrew top plug/dipstick and leave it off for a few minutes to ensure that any air can leave?
11. Run engine for a second then double check oil levels.

THANK YOU again for any and all help and please do not hesitate to correct anything or provide feedback or advice!!

 

[ThomW]

1. Have lower unit in down position.
2. Place oil pan under lower unit
3. remove lower drain plug (very bottom) and make sure you find gasket
4. remove middle vent plug and find gasket.
5. open dip stick on top of lower unit.
6. have a cold beer while all oil drains out.
7. screw lube pump to the very bottom hole and start pumping gear lube in until you see it come out middle vent hole.
8. replace middle screw plug and gasket.
9. continue pumping from the bottom, while checking the dip stick until you see the lube appear on dip stick.
10. replace dip stick plug and gasket.
11. quickly remove gear lube hose from bottom plug hole and re-insert screw and gasket on the bottom hole.
12. run it a few minutes on the hose and check dip stick. Top off in needed.

You always want to pump the gear lube from the bottom up, as it will force all the air out and ensure you have no air bubble trapped.

 

[Bsluper]

1. Have lower unit in down position.
2. Place oil pan under lower unit
3. remove lower drain plug (very bottom) and make sure you find gasket
4. remove middle vent plug and find gasket.
5. open dip stick on top of lower unit.
6. have a cold beer while all oil drains out.
7. screw lube pump to the very bottom hole and start pumping gear lube in until you see it come out middle vent hole.
8. replace middle screw plug and gasket.
9. continue pumping from the bottom, while checking the dip stick until you see the lube appear on dip stick.
10. replace dip stick plug and gasket.
11. quickly remove gear lube hose from bottom plug hole and re-insert screw and gasket on the bottom hole.
12. run it a few minutes on the hose and check dip stick. Top off in needed.

You always want to pump the gear lube from the bottom up, as it will force all the air out and ensure you have no air bubble trapped.

Thom,

Thanks! For some reason I thought I had read to fill from the middle hole, glad I didn't do that, luckily I won't be doing it until tomorrow. Thanks for helping me not trash my lower unit!

 

[Scott Danforth]

read the factory manual........ follow the factory manual.

 

[Bsluper]

read the factory manual........ follow the factory manual.

Scott,

Thanks! I found a manual online and it says to fill through the middle plug, not the bottom plug!

 

[hugh g]

1. Have lower unit in down position.
2. Place oil pan under lower unit
3. remove lower drain plug (very bottom) and make sure you find gasket
4. remove middle vent plug and find gasket.
5. open dip stick on top of lower unit.
6. have a cold beer while all oil drains out.
7. screw lube pump to the very bottom hole and start pumping gear lube in until you see it come out middle vent hole.
8. replace middle screw plug and gasket.
9. continue pumping from the bottom, while checking the dip stick until you see the lube appear on dip stick.
10. replace dip stick plug and gasket.
11. quickly remove gear lube hose from bottom plug hole and re-insert screw and gasket on the bottom hole.
12. run it a few minutes on the hose and check dip stick. Top off in needed.

You always want to pump the gear lube from the bottom up, as it will force all the air out and ensure you have no air bubble trapped.

Yea, a lot of guys fill their Cobra's from the bottom plug, until they grenade their drive because Cobra's are filled from the MIDDLE one.

 

[Bsluper]

Yea, a lot of guys fill their Cobra's from the bottom plug, until they grenade their drive because Cobra's are filled from the MIDDLE one.

Glad I know that now! If you would indulge I do have a question that the manual did not address. When I begin filling from the middle plug do I leave the bottom plug out until oil begins dripping out or do I screw the bottom plug in before beginning to fill?

 

[hugh g]

Glad I know that now! If you would indulge I do have a question that the manual did not address. When I begin filling from the middle plug do I leave the bottom plug out until oil begins dripping out or do I screw the bottom plug in before beginning to fill?

You screw the bottom plug back in then fill from the middle. Once the drive is full have that plug ready once you unscrew the pump because oil will drain back out. When I had my 3.0 Cobra I would screw the dipstick in & not much oil would drain out. Don't overfill it, but if you lose some you can top off the drive thru the dipstick hole. After filling mine I would start the engine, let it run for a few seconds, then wait a while & recheck the level. I owned my Cobra for over 20 years, that's how I did it & never had a problem.

 

[Lou C]

right Hugh has got it, drain from the bottom most hole, replace drain plug, fill from middle hole with the dipstick just resting in the top hole, not screwed in so air can escape. When its full on the dipstick thread it in then remove the pump and replace your fill plug, threading in the dipstick will help reduce how much gear oil you lose when disconnecting the pump. Then recheck with the dipstick you can add any extra needed from the top hole. All 3 fiber washers for the drain/fill plugs and dipstick should be changed each time. Most Cobras take 2 qts of gear oil. I've been using the Merc High Performance Gear lube.

 

[ThomW]

right Hugh has got it, drain from the bottom most hole, replace drain plug, fill from middle hole with the dipstick just resting in the top hole, not screwed in so air can escape. When its full on the dipstick thread it in then remove the pump and replace your fill plug, threading in the dipstick will help reduce how much gear oil you lose when disconnecting the pump. Then recheck with the dipstick you can add any extra needed from the top hole. All 3 fiber washers for the drain/fill plugs and dipstick should be changed each time. Most Cobras take 2 qts of gear oil. I've been using the Merc High Performance Gear lube.

So I see that you guys are correct with filling it from the middle hole. My apologies.
Can I ask why that is on Cobra drives? Why can't it be filled from the bottom hole all the way up like other drives? How would filling it from the bottom hole cause an air bubble? Just trying to learn something new here.

 

[Lou C]

I've read a few things but its apparently related to how the oil flows from the lower unit up into the upper gear housing. Anyway I've had this one almost 20 years and never had a problem doing it by the book.

 

[Bsluper]

right Hugh has got it, drain from the bottom most hole, replace drain plug, fill from middle hole with the dipstick just resting in the top hole, not screwed in so air can escape. When its full on the dipstick thread it in then remove the pump and replace your fill plug, threading in the dipstick will help reduce how much gear oil you lose when disconnecting the pump. Then recheck with the dipstick you can add any extra needed from the top hole. All 3 fiber washers for the drain/fill plugs and dipstick should be changed each time. Most Cobras take 2 qts of gear oil. I've been using the Merc High Performance Gear lube.

So, I’m an idiot. Hahahaha. I did everything right with changing the lower unit gear oil and started the boat which ran for exactly 15seconds before I turned it off. Then realized I had forgotten to screw in the dipstick screw and it had been just resting on the threads. No oil came out of the top. But, did I just trash my entire lower unit? Is there anyway to check to see if I trashed my lower unit? Again, I’m an idiot haha. Thank you all for your help!!!!

 

[Lou C]

Nah should be just fine

 

[Bsluper]

Thank god!!!! I was really worried!

 

[Lou C]

Just re check it with the dipstick if is fine just screw it in if it’s a bit low just top it off from the dipstick hole.

 

[Bsluper]

Just re check it with the dipstick if is fine just screw it in if it’s a bit low just top it off from the dipstick hole.

Lou, Everything seems okay and I realized while cleaning the boat today that I forgot to say thank you. Thanks!

 

[Lou C]

Great and you're welcome! Enjoy and as long as you keep up on the maintenance the Cobra should last. I just re-installed mine yesterday. I pull it off each fall and store it in the garage.

 

[Bsluper]

Great and you're welcome! Enjoy and as long as you keep up on the maintenance the Cobra should last. I just re-installed mine yesterday. I pull it off each fall and store it in the garage.

That’s impressive! I wish I had the room in my garage and the tools to do that!

by the way, do you know the answer to this? https://forums.iboats.com/threads/1993-omc-cobra-flame-arrestor-hose-question.745234/

 

[Lou C]

Here’s the install of my old ‘88 Cobra as you can see it’s been used in salt water a long time, it will get painted with anti fouling paint before it goes in the water.
I think the way you were thinking of connecting that crankcase vent hose is correct...