No harm at all, in fact it's the right way to do it. Drain both the block and manifolds.

 

Whatever method you opt for, just don't run the water pump dry for any length of time or you will fry your impeller.

 

no no i never start the motors without having something on the muffs water or af.

 

When I winterize my friend's out drive, I attach a tee on the muff. I attach a water hose on 1/2 half of the tee and the AF jug on the other the other half. I open the water hose and run the engine up to operating temperature so that the thermostat is open. Without stopping the engine, I open the AF jug tap and close the garden hose tap and run it until there is solid green coming out. Shut engine off, remove muffs and open engine drain plugs and leave them open for the winter.

 

either way just work fast if you're going to drain the block so your t-stat doesn't close. I used to go through the trouble of draining the block but always felt like there was a clock ticking in my head while I would open up plugs and watch the water run out.

 

along with the fact that im fogging the motor at the same time the af is running out!!

 

maybe its me but the muff way sucked!! antifreeze was going somewhere, mostly on the ground and not enough was going to the block. next thing the high temp alarm went off so i fogged it and shut it down and added af through the thermistat hoses. i would say the block was half full and the risers were dry. question i never really looked at the hoses that go to the risers and manifolds, they are really low. i have always heard you will know when they are filled when you hear af coming out the exhaust, but none came out the exhaust only the t stat housing. is this right?

 

maybe its me but the muff way sucked!! antifreeze was going somewhere, mostly on the ground and not enough was going to the block. next thing the high temp alarm went off so i fogged it and shut it down and added af through the thermistat hoses. i would say the block was half full and the risers were dry. question i never really looked at the hoses that go to the risers and manifolds, they are really low. i have always heard you will know when they are filled when you hear af coming out the exhaust, but none came out the exhaust only the t stat housing. is this right?

My risers are high also. I don't get any AF coming out the drive either. So, I drain the blocks and mani's. Pull the big hose off the T-stat housing and pour AF until the liquid coming out of the t-stat housing is really purple (I see clear water for about a 1/3 of a gal. and then it is pure purple). Once it is really purple I put a cup under the t-stat houseing to catch the fluid and then check it with a A/F tester to make sure it is pure A/F.

 

Agreed - drain block and manifolds before adding the AF.
You are correct that using this method always runs the risk of leaving the block dry if the tstat doesn't reopen.
Go online and look up the cooling system for your engine. Analyzing the flow paths will allow you to understand what will get filled, and how.
For instance, on a 350Mag the flow path is from the inlet on the lower unit to the raw water pump, to PS cooler then to cool fuel block, then to distribution block, sending it to manifolds and to water pump housing, then to tstat housing, to risers and IF tstat is open - to block.
So for me, running on muffs will get everything for certain, except maybe the block based on tstat position.
So my safest method if using the muffs - drain everything. Run on muffs with AF and fog (correct way based on fuel system). When finished, pull main hose off tstat housing and check for AF. Pour AF into hose until it comes out the tsat assembly as pure AF.

Many will suggest draining it all at the end - different discussion.

This year I invested $5 in a baby pool, and $29 in a submersible pump. I put 6 gallon AF in the pool and placed it under the lower unit, then put the muffs on the pump and put it in the pool. Plugged in and started (already drained everything first). Ran it until temp was reached (165). I pulled the main hose and everything including the block was pure AF. Better use of the $35 instead of the premade gravity system you buy online. No timing issues this way.

 

So the kiddie pool is just to catch the spilling/ejected antifreeze and pump it back up?
Also, what kind of AF do you use in the engine block?

 

Following my flow path, a closed tstat would prevent water from leaving the block coolant loop. So, if full of water when on muffs, and tstat stays closed, still full of water. If empty first, water pump should push antifreeze in and recirculate it. The rest of the water goes around the water pump to the risers or exhaust manifolds depending on tstat position.

Here is a link to a picture with the flow paths:

http://www.mercruiserparts.com/images/COMMON/10115.png

Animated path:

http://www.boatinghowto.com/content.php?137-Marine-Cooling-System-Flow-Examples

 

The only I felt safe in winerizing the 7.4 was to drain the block and manifolds. Next we removed the
thermostat and ran the antifreeze into the engine. I don't trust the thermostat to stay open and in PA you don't guess on winterization.