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mercmastertech, Service Manager, Master technician
Category: Boat
Satisfied Customers: 249
Experience:  Service Manager, Master Mercruiser, Master OMC Cobra and Certified Volvo Penta Technician
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What are the steps for changing the lower unit gear oil on

Resolved Question:

What are the steps for changing the lower unit gear oil on a 1993 Volva Penta Stern Drive? Do you fill from the bottom drain plug? How do you know when to stop filling? I know my manual says capacity is 2.8 quarts and there is a dipstick but I have had friends that service Mercruiser Sterndrives that say the fill until it comes out a top opening. That doesnt' seem logical for this model in that the top opening is the top of the dipstick, which would be too much? Do you simply keep checking the dipstick as you pump from the bottom?
Submitted: 7 years ago.
Category: Boat
Expert:  mercmastertech replied 7 years ago.

Welcome to and thank you for your question.

You can fill your Volvo Penta drive unit by removing the dipstick from the top of the drive unit, remove the front starboard corner fill plug on top of the drive unit (allen headed screw with a small oring underneath it - use caution not to lose the oring, replace the oring if damaged), then use a small funnel to add the drive lube into the fill plug hole (add 2 and half quarts), let the lube in the drive settle for a few minutes, recheck the lube level on the dipstick and top off as needed.

Alternatively, you can refill the drive unit by removing the rear cover of the upper drive housing, once the rear cover is removed, you will see a vent screw (typically an allen headed screw) on the rear starboard side of the upper drive unit, remove the vent screw. Fill from the bottom drain plug until lube runs out of the vent screw, reinstall/secure the vent screw and gasket, let the lube in the drive unit settle for a few minutes, check the lube level on the dipstick and pump more lube into the drive (from the bottom drain plug up) until the correct lube level is reached on the dipstick.

Yes, it is also permissible to remove the dipstick plug from the upper drive unit, then fill from the bottom drain plug hole until the correct level is obtained on the dipstick. This method will require patience as you will have to pump the lube into the drive and continually check the dipstick until the correct level is reached on the dipstick. Its not uncommon to have no lube showing on the dipstick until the lube is allowed to settle inside the drive for several minutes.

After filling the drive unit, be sure to let the lube in the drive settle for a few minutes or longer, recheck the lube level on the dipstick and top off the lube as needed (or remove lube if overfilled).

I hope that you find this information useful, thank you again for your question.
mercmastertech and 3 other Boat Specialists are ready to help you
Customer: replied 7 years ago.

Your advise is helpful and reassuring. I want to check out the vent screw you reference on the rear starboard side of the upper drive unit to make sure I find it and when I do, I'll accept your answer. Alternatively, I have one more related question. In visiting with the local marine shop, they recommend a synthetic gear oil. I had previously purchased on-line (internet purchase) Sierra Premium Gear Oil (non-synthetic) but locally they recommend against using it. What are you recommendations on using synthetic versus standard gear oil on a 1993??

Expert:  mercmastertech replied 7 years ago.
Hello again,

See picture below for the location of the vent screw behind the upper drive rear cover (red arrow pointing to it)...


The earlier Volvo Penta drives recommendation was to use engine oil in the drive unit, then the recommendation was switched to a mineral based gear lube (non synthetic), the later models (including your drive and the current DP and SX drives) recommendation was to use a full synthetic GL-5 drive lube. Our shop uses the full synthetic GL-5 on all of the Volvo Penta drives without any issues. I would recommend using the full synthetic GL-5 gear lube in your drive unit.

I will attach the Volvo Penta drive lube recommendation chart for your reference...


Thanks again for your question.
Customer: replied 7 years ago.
In reviewing your lower gear unit lube specifications you forwarded to me, I see that the drive that SP Drive is supposed to use the same lubrication as the engine, The side of my drive has the letters SP CDTrim. My engine is a 4 cylinder and calls for SAE 20 W/50 engine oil. Are you still advising the use of fully synthetic oil in the lower unit. Also, would you agree with the recommendation of using SAE 20 W/50 in the engine?
Expert:  mercmastertech replied 7 years ago.



Being that you have a SP (single prop) drive unit, you can use the same oil that is recommended for your engine. If your owners manual or sticker/stamping on the engine indicates using 20W-50 in your engine, then yes, I would agree that you can use the same oil in the drive unit as indicated in the lube chart (Volvo recommended different viscosity engine oils for different engine models throughout the years).


If you have an SP-A2 or SP-C drive unit (non 2.15:1 ratio), it is permissible to use full synthetic GL-5 drive lube (see footnote on the lube chart). As stated above, our shop uses full synthetic GL-5 for all of our Volvo Penta drive services and have not had any problems but that is not Volvo Penta's formal recommendation, Volvo Penta's formal recommendation is to use the lubes recommended on their lube chart for the drive unit specified.


Thanks again for your question.

Edited by mercmastertech on 10/2/2009 at 8:21 PM EST
Customer: replied 7 years ago.
Not sure how to determine which SP drive I have. As I stated, the side of it states SP CDTrim. I don't have the owner's manual, I just reference a book I purchased on-line entitled Volvo Penta Stern Drive OHC and DOHC 1992 and 1993 Tune-Up and Repair Manual written by Joan and Clarence Coles "Certified Textbook". I guess what you are saying is it doen't matter either way. Except I thought you referenced that once you do use synthetic, you don't want to go back. Since I bought the boat used, I don't know if it has synthetic in there now or not.
Expert:  mercmastertech replied 7 years ago.


Do you have an engine serial number handy (usually a 10 digit number that starts with a 4)? If so, I can try to find out what engine/drive you have if you wish (it may be next week before I can try to find out for you through Volvo Penta's database).

There's usually a sticker on the engine or a stamping on the oil fill cap that indicates what viscosity oil you should use in your engine (20W-50 was a common viscosity oil used on the older 4 cylinder Volvo Penta engines). Technically, you are correct, you should not switch back and forth from non synthetic to synthetic oils but I will tell you I see all types of fluids used in the Volvo drives (Mercruiser lube, Automotive rear end lube, etc.) as many shops do not have access to the lube recommendation chart and are unsure on which lube to use.

Thanks again.


Customer: replied 7 years ago.

I will look up the serial number and get it to you. I just want to do this right, not cause any problems for the boat down the road. I really appreciate you assistance on this. I'll send it over after I get off work. I won't be storing the boat for a couple weeks.




Doug Larson

Customer: replied 7 years ago.



I found a tag on the engine near the radiator that has a number of different numbers on it. These are the numbers I think you are looking for as best I could make them out. They are hard to read.


Volvo Penta

230A / SP

XXXXXXXXXX (possibly the serial number- it is 10 digit)

Customer: replied 7 years ago.

I went back to look at my message and all the numbers were turned to "X" that I entered. I'll try that again.




two, two, zero, zero, zero, two, five, one, seven, two- in the event the numbers are corrupted again

Expert:  mercmastertech replied 7 years ago.
Hi Doug, will filter out any numbers that it thinks may be a phone number so I suspect that is why the numbers came up as XXXXXXXXXX on your first post.

I just checked Volvo Penta's database, the 22000 25172 number you provided (without the space) is a serial number for a 230A engine but it was never registered with Volvo Penta when the boat was purchased so the database does not show what drive unit is mated to the engine.


That's OK though, the 230A engine model was sufficient information for me to look in our Volvo Penta service manuals for the recommended engine oil viscosity. According to the Volvo Penta factory service manual, the 230A engine oil viscosity recommendation is indeed 20W-50 oil so you can use the same viscosity oil in your drive unit as indicated in the drive lube chart above.

I hope this information helps, thanks again for your question.

Edited by mercmastertech on 10/2/2009 at 10:24 PM EST

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