I’ve had this O’Day 28 boat several years and it has a Universal 5411 2 cylinder diesel with a Hurth HBW-5 or HBW-10 transmission. I finally read the manual and discovered that to measure the transmission oil level you unscrew the dip stick and check the level by just inserting the dip stick without screwing it back down. Therefore my transmission has not lost any oil while I’ve owned it but it has been continuously low. Probably whoever last changed the oil checked the level with the dip stick screwed back down. Anyhow, my question is simply what type of oil do I use? The manual says Type A. I can’t find that anywhere and how do I determine what is in there now?
Transmission oil
- Thread starter wing15601
- Start date
Hurths use Dexron. The Dexron is up to about 9,000,000 now, well past III. 
Drain and refill.
Good luck.
Drain and refill.
Good luck.
You may already know this but do not drain trying to use the drain plug. Use a suction pump in the fill opening to drain out the old. The drain plug is inaccessible and if cross threaded will leak and require major repair to the housing.
Really good practice to change trans oil end of every season.
Really good practice to change trans oil end of every season.
WING 15601..... I have an 1983 O'Day 30 with a Hurth transmission. Note that the Hurth manual recommends that the fluid be changed every year and and the fluid should be filled completely during the off season and drained down to normal level for the the time you are using the boat. Below is the response I received from Mack Boring regarding the fluid for the transmission.
"Most major brands still offer Dextron III. Dextron III is available and is more commonly known as ATF fluid. In regards to Dextron IV this is a synthetic based fluid and is not recommended by ZF as viable fluid to use in their transmissions. ZF DOES NOT recommend the use of a synthetic based fluid in the transmission.
Most major companies are switching to different names for DEX III this is the way AutoZone has it listed DEX/MERC. This is a Dextron Mercon blend and will work fine for your application most DEX III fluids are a multi-blend with Mercon.
I also searched NAPA auto. They have the same DEX/MERC blend and commonly known as ATF fluid for NAPA it’s the same fluid named differently. I hope this helps you"
http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?R=NO_75200_0274140289
"Most major brands still offer Dextron III. Dextron III is available and is more commonly known as ATF fluid. In regards to Dextron IV this is a synthetic based fluid and is not recommended by ZF as viable fluid to use in their transmissions. ZF DOES NOT recommend the use of a synthetic based fluid in the transmission.
Most major companies are switching to different names for DEX III this is the way AutoZone has it listed DEX/MERC. This is a Dextron Mercon blend and will work fine for your application most DEX III fluids are a multi-blend with Mercon.
I also searched NAPA auto. They have the same DEX/MERC blend and commonly known as ATF fluid for NAPA it’s the same fluid named differently. I hope this helps you"
http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?R=NO_75200_0274140289