Hi, I have one of these oil drain kits on my 454, and it makes changing the oil much easier. But not sure what type of drain plug is in the HP 500.

Imperial 1/2" or metric something??

Please let me know,

And if it is metric, who makes on like this? Sierra does not.

Thanks,


https://catalog.sierraparts.com/product/3564Thread Size: 1/2"-20

Note: Does not fit late model oil pan utilizing metric threads

Kit Includes: 42" hose with hose hanger, universal oil pan replacement plug, and end cap

Makes changing your oil a snap and without the mess

Permanently mounts to bottom of oil pan to make changing oil more convenient

Drains 4 quarts of oil in less than 15 minutes without a pump

Fittings on hose machined from corrosion resistant brass

Assembly sized to pass through most common hull drains

If you know it's not a 1/2x thread, you can try a M12 x 1.75 - not saying it's correct as a lot of those engines are only showing a PN on the exploded diagrams, but the M12 was/is popular.

1/2" is 12.7mm

If the thread is correct these are the parts to make the drain lines as per a factory rig (525 EFI has the M12 and the drain line as shown below)...
https://www.mercruiserparts.com/bam/...1345/10127/180

It is the Metric one. The switch over was in the mid 90's.
I added one of the kits to my 1996 Gen V 525SC and it was metric thread.

Out of stock though https://www.cpperformance.com/p-1333...75-thread.aspx

I don't know why every engine doesn't have a drain line kit installed... makes life so much simpler and drains the engine faster/ complete to the plug line.... it takes about as long to tighten down the air tool coupler than it does to drain the engine

Agreed, metric from 1996 on.

I have a couple used ones if interested,

I just bought both of them, and sent the other one back. On my 1999 HP500EFI, it was the metric one.

one other thing, make sure the hose goes through the drain plug hole before you install it. mine needed to be crimped more and didn't know that so it only sticks out just far enough to get the cap off.

I bought one of these kits, but let someone talk me out of installing it. I like to be able to get all the oil out possible, but sucking it out the dipstick doesn't get enough. I think I didn't bend the tube down low enough in the pan. My Mityvac hose isn't a thin enough diameter to go down the dipstick tube either.
Either way I think I'm going to go ahead and install it this weekend. I just rebuilt the engine and wanted to change the oil one last time to Rotella T6.
This should be fun getting to the drain plug...

You have a single boat? No way I'm able to get down and fish those out the drain hole in a twin boat.
I do use the Mity Vac evacuator to draw through the hose kit though.