change out the antifreeze in my Mercruiser MAG 496s

[Tri County Trail]

I need to change out the antifreeze in my Mercruiser MAG 496s (staying with the original Dex-cool antifreeze). New to me boat and want to freshen it up. Is there an easy way to use the extraction pump and pull it out thru one of the lower hoses (which one will get me to the lowest portion of the block)versus draining it into the bilge?

 

[paulswagelock]

Only have done it pulling the block drains. I did it in water, so shut down the bilge pump and used a shop vac to clean up the bilge.

 

[Tri County Trail]

Only have done it pulling the block drains. I did it in water, so shut down the bilge pump and used a shop vac to clean up the bilge.

Did you pull both side of the block drain plugs?
Do you remember what size bolt the drain was?

 

[paulswagelock]

Did you pull both side of the block drain plugs?
Do you remember what size bolt the drain was?

I think they were hex head inset, but don’t remember the size.
They are a bear to get to, lots of other plumbing in the way. I would assume pulling one gets you 70% drained with how low they are.

 

[sejensen737]

I did this a few weeks ago. Disconnected the lowest cooling system hose and drained into a container. Messy. Judging by the amount that came out , removed about 80%. Removing block drain plugs can cause a whole set of other problems.

 

[Tri County Trail]

I did this a few weeks ago. Disconnected the lowest cooling system hose and drained into a container. Messy. Judging by the amount that came out , removed about 80%. Removing block drain plugs can cause a whole set of other problems.

how much antifreeze did you end up adding?

 

[Bill Curtis]

I did this a few weeks ago. Disconnected the lowest cooling system hose and drained into a container. Messy. Judging by the amount that came out , removed about 80%. Removing block drain plugs can cause a whole set of other problems.

Interesting take on removing the block drains. All the boats I had that were raw water cooled, pulling the drain plugs was part of winterizing every year. Never had a problem with them afterwards.

 

[jgoedd99]

Just did both engines and generator a week ago. Not a fun job but it is manageable. I use a "suck bucket" in front of my shop vac. Suck bucket is a 4 gallon pail equipped with a 4 foot section of vac hose and a shop vac inlet connection on the lid. Hook the shop vac to the shop vac hose connection on the lid, and use the hose from the lid to vac out the AF as it drains (catch it before hitting the bilge). I do my best to catch it before it hits the bilge, but some will always end up in the bilge. The AF that reaches the bilge gets vac'd into the suck bucket before the bilge pump comes on. AND yes, you have to drain both sides of the block, one side does not get it all out. I use the same set up to vac AF out of heat exchanger and overflow bottle (first - before draining from block) as these make no mess. After block drains i pulled water pump hose and hoses to cockpit heater (or water heater if you have one) and suck these out using the same set up. I stick a small diameter (~ 3/8") piece of vinyl hose inserted into the suck bucket hose with a crevice tool to get into these smaller areas that will not accommodate a 1 1/4" vac hose.

For generator i use a shallow take out food container placed under the AF drain on the heat exchanger and vac from the container as it empties out of the heat exchanger. This worked extremely well and made very little mess. When generator was done draining i pulled the generator block plug, but i don't think anything additional came out.

Filled all with 50/50 Prestone DexCool and distilled water. Takes about 10 gallons of 50/50 to do all.

Good luck.

 

[sejensen737]

how much antifreeze did you end up adding?

1.5 jugs of Dexcool mixed 50/50 with distilled water/ engine

 

[sejensen737]

Interesting take on removing the block drains. All the boats I had that were raw water cooled, pulling the drain plugs was part of winterizing every year. Never had a problem with them afterwards.

I have experienced siezed/stripped plugs in the past on car engines. I have never actually removed the plugs from a boat engine.