Technical question about flushing coolant through engine to winterize?

Question

I guess this is my question. Is it necessary to bring your engine to operating temperature in order to really get coolant throughout your engine block when winterizing? In other words, does your thermostat need to "open" to get winterizing coolant into your water jackets? If the thermostat is closed, say in a cold start, while flushing with coolant, doesn't the coolant just run up the intake and then back out the exhaust, never really going into the block? Or do I have it wrong (I hope), and coolant still flows through the engine block even on "cold" starting? I just want to make sure I get coolant into by whole block, not just the intake and exhaust. Thank you!

350 Mercruiser, V8, raw water pickup

Answer 1

If it works anything like a car, then yes, the thermostat needs to be open to get coolant to the block. When you flush a car you have to refill the radiator, then bring the engine to operating temperature to get coolant in the block, then top off the radiator.

Answer 2

The answer to this is NO. I work as a marine mechanic at a marine dealer in Montana....we have winterized at least 600 boats in the past few months and never have we had to have an engine at "open thermostat temp" to winterize it. The RV antifreeze we use is rated for -50* to _100*F. When mixed into the system with what little water may be left in the system from draining the block , exhaust manifolds, water pump, and other various water systems, the freezing protection you are getting will be more than enough to handle a Montana winter and should be good enough for anywhere else in this country. On the subject of getting the water to flow through the entire block.....it does that before reaching the thermostat anyway. The Mercruiser engines have a pressure relief type valve in the thermostat housing to allow any excess pressure to exit the engine. The thermostat will open at normal operating temp to allow hot water to exit and cooler water from the lake or ocean to enter and keep the engine from overheating. Marine engine cooling systems operate differently than a car system. They are called open systems....you do not have a radiator that cools the antifreeze that runs through your block. The lake water flows through your block prior to reaching your thermostat......so you will not have to bring the temp of your engine up to add RV antifreeze when winterizing it. To prove my point......when you summerize your boat, you have to open the drains again and allow the RV antifreeze to exit the block, exhaust manifolds and other water systems on board, and every time I have opened a block drain in the spring....I get plenty of RV antifreeze out of that block drain.

Answer 3

Very good question.

You're quite correct, until you've got the engine up to running temperature, you cannot be sure that the new coolant has made it completely around your cooling system.

Bring it up to temperature, make sure the thermostat is opening, then test the coolant with a tester to make sure your engine is protected adequately and you can't go wrong.

Good luck with the winter service, it's been a long time since I've done one!

Answer 4

must let the thermostat  open to get it in the complete engine

Answer 5

These have a bypass that sends the coolant through the engine in circles when the thermostat is closed. this is much the same as the heater circuit on your car.

The engine will be half out of water when you pull the boat out.

The coolant/antifreeze mixture should be plenty strong enough to add to the existing water and circulate in the engine with the thermostat closed,

Even with the thermostat closed a fair amount of water is exchanged out of the engine. Because of this, the thermostat will rarely open unless the engine is under load.

Running for a minute or two is all that is needed.

If you are in doubt, pull a plug out of your block and test the coolant that comes out. 0 F is all you need to not break anything in winter.

Answer 6

You are right, the thermostat should  open fully but if you wait for that to happen  you are flushing cold coolant into a  hot engine which is not good.

Answer 7

Put the muffs on the out drive and run the engine to normal operating temp.  This will make sure there is coolant thru the whole block.  Make sure all the fluids are top off the the correct levels.  Have fun and good luck

Answer 8

I'm a service manager at a used boat center and have winterized over three hundred boats. Raw water, fresh water, inboard, outboards, and I/Os.

First buy quality anti-freeze from boat U.S. or West Marine and buy or borrow the correct winterizing kit for an I/O engine.

Make sure you use the water muffs that draw from both sides when placed on the lower unit. Also, purchase a spray can of storage fluid to be sprayed on the engine and in the carb.

Hook up your muffs on the lower unit and attach a freshwater hose, turn on the water and start the engine. Let run 10 to 15 minutes, This will flush out dirt, debris, etc.

Turn off engine and hook up your winterizing kit. You should have at least 4 to 5 gallons of anti-freeze in the tank. Make sure the tank is above the lower unit because it will gravity feed. I usually put tank on the swim platform. Remove the flame arrestor from the carb. and have the storage fluid ready to use.

The person in the boat starts the engine just after you open the valve to the tank. Let the boat run until you have about a gallon of fluid in the tank and the person in the boat starts spraying the fluid in the carb. until the boat dies out. If it doesn't die out shut down before the fluid runs out.

Take a piece of plastic and put over the carb. and replace the flame arrestor. MAKE SURE YOU TAKE THIS PLASTIC OFF BEFORE TRYING TO START IN THE SPRING. I usually put a tag or tape on top to remind the person de-winterizing.

You can spray the engine down with WD-40 or any left of storage fluid. Don't recover the engine when storing, this is to let air circulate.

Hope this helps - Good Luck.

P.S. The thermostat doesn't have to open because the engine has a water bypass.