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??
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.
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.
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.
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.
230A / SP
XXXXXXXXXX (possibly the serial number- it is 10 digit)
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