Mercruiser antifreeze?

earl1z19

I need to change the hoses that run from my motor to my hot water tank. Those hoses are filled with antifreeze from the closed cooling system on my Mercruisers. Once I replace the hoses what is the best way to replace the antifreeze that is lost during the change? Does the system require a vacuum to be pulled in order to avoid any air pockets or can I just top off the reservoir after goes through a heat cycle? What antifreeze should be used Dexron or actual Mercruiser antifreeze at $32 a gallon? 

Rich_

Don’t have your answer but age of the engine might help for determining what Merc speced. What color was /is in it? When was it last flushed?

PickleRick

I was purchasing mercruiser coolant for my diesel until I realized it was dexcool.   Now I buy gallons of concentrate dexcool and mix with 50/50 distilled water.  

Not sure on your set up but the coolant cap is the highest point in my cooling system so no real bleeding needed.  Just fill, run for a few minutes. For kicks I'll check it after each of the next few runs.   

I suppose you could pull a vacuum to fill but seems like too much work.  I've not seen a complicated expansion tank on a boat, just simple overflow bottles. 


The dex orangish is really common factory coolant for GM V8 engines.  There were some issues when it first came out and lawsuits tied to it.  In the land Rover world they traded it out to the old school green due to it eating head gaskets.  Said land rover engines were all aluminum engines that were built from buick design 

Those issues have been rectified. 

earl1z19

I figured it was dexcool but wasn't sure about the refill process. With the water heater being lower than the motor its gonna be a mess to swap these hoses but with a few quick changes of the hose i should be able to minimize the amount lost. I am going to do the swap before I go back in the water and then check the refill once i can run it a few times up to temp.

Liberty44140

I wish you luck with this. When I had twin 350's I wanted to change my coolant and no one had ever done it. Given how the anti corrosive properties degrade over time I was shocked that no one here had done it, but I gave up and then sold the boat (boat selling unrelated to the wish to refresh coolant). Currently having my mechanic change all of the coolant on my diesels for that same reason, refresh anti corrosion properties. 

YYZRC

I replaced the engine coolant in my Rinker 330 (twin Merc 350s) as preventative maintenance as @Liberty44140 suggested. I used Prestone Dexcool for GM engines.

earl1z19

Liberty44140 said:

I wish you luck with this. When I had twin 350's I wanted to change my coolant and no one had ever done it. Given how the anti corrosive properties degrade over time I was shocked that no one here had done it, but I gave up and then sold the boat (boat selling unrelated to the wish to refresh coolant). Currently having my mechanic change all of the coolant on my diesels for that same reason, refresh anti corrosion properties. 

I did find it crazy that there are no videos on You tube showing how to change the coolant. My heat exchanger was changed a few years ago so there is newer fluid in the system.  I guess learning as you go is not the worst thing.

YYZRC

Highly recommend pulling the belt off and checking your circulation pump bearings while you are at it. 

Liberty44140

YYZRC is it just as easy as drain and re fill? On my scarab jet all I do is pull a plug to drain, and then re fill and put that plug back in when I get no air pockets, then top off. Same for the Merc's? My worry in this was always air pockets and does it actually need a vacuum to get it all in there. 

That Prestone DexCool would be fine. If it's harder to find in the states, I use Peak Orange Dexcool on my Rotax engine in the scarab as it also calls for GM, same stuff. 

YYZRC

I didn’t overthink it. I removed the hose at the circulation pump and drained what I could. Refilled at the heat exchanger. 

earl1z19

I was able to change the hoses this weekend.  Took less than 20 minutes. Made minimal mess with a bit of planning and a few pairs of locking pliers. The system can be gravity fed. The expansion tank on the 8.2's is the highest point of the closed cooled system as i would expect it to be on all engine sizes. Once I had the hoses replaced I filled the tank with  Dexcool and you could hear and see it draining to the lowest point in the system. Once I do a heat cycle I will check the fluid level and top off as needed.