4.3 LX Gen + Thermostat removal

[chazmean]

I have a 97 Chaparral with a 4.3 LX Gen + that I inherited so I am relatively new to boating on anything other than a canoe . I ran it out on a local lake right before we were expecting to hit freezing temps ( I live in Colorado). The boat ran out fine, but when I decided to freeze-proof it, I realized I was in over my head a bit. I pulled it out of the water, drained the exhaust manifolds and the block via the plugs then took the thermostat housing apart, filled the entire unit with 5 gallons of RV/Marine antifreeze with rust inhibitor ( I replaced all the freeze-plugs) . The entire block was filled as well as the exhaust jackets. The antifreeze ran out the outdrive and I lowered the outdrive to the lowest point possible. Did I miss anything? As for the thermostat - my plan was to remove it so I could cycle the antifreeze through the engine via the "earmuffs", but I could not remove the thermostat. It appears to be in a plastic housing that would break if I forced the thermostat out of the housing. Is there something I am missing? My apologies for the drawn-out description. I will be brief in the future.

 

[Fun Times]

The plastic sleeves do tend to feel stuck inside the thermostat housing but eventually you can usually walk/rock them out side to side, etc...But take note that the sleeve will not "turn" as you try to remove it as there is a groove that keeps it from turning.

If you damage the sleeve at all you'll want to order a new one plus it's not a bad idea to keep a new thermostat kit and sleeve onboard with you incase you ever need to open the T-housing while out on a long boating trip.

The following video and parts guide of your thermostat design you should have without knowing your engine serial number should help guide you through what the insides will look like if you decide to take it all apart.

https://www.mercruiserparts.com/bam/subassembly/31515/1937/130

 

[Lou C]

Not the same issue per se but I keep a spare thermostat housing with a new stat already installed and new gasket in case I have to change it out with the boat on the mooring. In salt water the stats get sticky after a couple of years and then the engine never will reach normal temps unless you run on plane for a while. The problem is a flake of rust or bit of sand/other debris from raw water cooling keeps the stat from closing, then it can't regulate the temperature to what it should be. Another reason why IMHO all inboards should have at least a half closed cooling system.

 

[Scott06]

It seems like you got it but just to verify how many plugs did u pull ? One on each exhaust manifold, one on each side of the oil pan rails and mine has a drain plug in the middle of the big u hose between the thermostat and the block circulation pump to drain the water trapped in the hose. Also believe on vortec 4.3 that there is pipe plug just below and to right of thermostat housing on the front vertical face of the intake that needs to be drained to completely drain the water cross over .

since u back filled with af any minimal residual water will be ok and not dilute the 5 gallons you put in .

Yes the plastic sleeve only comes out with a chisel... I saved an old piece of a radiator hose off my car and I remove the water in from drive hose on the rh side of the thermostat housing, and I use the cut off radiator hose as 90 deg elbow and pour af in through that so I don’t have to take the thermostat apart. Requires some patience but works.

Yes leave drive down especially if you park it outside as leaves and water can pool in prop hub and crack it. Also on I think starboard side of drive there is a 1/4 or 3/8” drain hole for water cavity just make sure this is clear of debris and can drain