Drain plugs on a Mercruiser 160 6cyl

[Jstep]

I have a 1969 Mercruiser 160 that I am trying to drain before I put it into storage. Figure 5 on page 1A-8 of the service manual shows 3 drains; two marked "Sea Water" and one marked "Fresh Water". I was able to easily find the "Fresh Water" drain on the block, which was more like a thumb-turn valve. I opened it, and probably about a gallon came out from here.

I am having trouble locating the "Sea Water" drains on the manifold. First off, my manifold does not look like the one pictured. The four plugs on the side of the manifold with the square hole are actually on the bottom of my manifold, and I do not have a drain plug on the elbow where it is pictured in Figure 5. My manifold actually looks exactly like the Merc 120 manifold in Figure 6.

I removed what I thought was a drain plug from the bottom of the manifold, from the location pictured in Figure 6, but no water came out. The hole also seems quite plugged up, and I was not able to unplug it by probing with a screwdriver. Here is the "plug" I removed from the bottom of the manifold:

Am I missing a drain plug somewhere? Did I remove the right one from the manifold? Did part of it break off inside, or do I just need to be more aggressive with the screwdriver? What about using a drill to poke through it?

 

[zbnutcase]

Re: Drain plugs on a Mercruiser 160 6cyl

Yeah thats the one and doesn't appear broken. I have never had to use a drill, a small punch and hammer should be all you need. 'nutcase

 

[Jstep]

Re: Drain plugs on a Mercruiser 160 6cyl

OK, I'll try a punch and hammer this evening.

So, those are the only two plugs I need to worry about, then? I don't want to miss one.

 

[ziggy]

Re: Drain plugs on a Mercruiser 160 6cyl

1st i'll say i have the normal cast iron manifold like fig. 5. so what i have to say may not apply to you...

for the last 2 or three years, i've been draining my water into a 34.5 oz. folgers coffee can. between the manifold and block, i normally get 3 almost full coffee cans out of the two. one almost full can from the manifold, an 2 almost full cans from the block. 2 years in a row, when filling with anti freeze i have put in roughly 2 1/3 -2 1/2 gallon of anti freeze between the manifold and block. this seems to be a consistent amount, so feel i'm probably getting it to drain fully. while i do pull the plug on the riser, i can't remember ever getting anything out of it and believe that reason is that water in a raw water system normally drains out, if it were freash water cooled, i think i'd get something out of it.

for my manifold, which is a ppt aftermarket but seems a copy of a mercruiser product. i always have to probe it to get water to flow. i always get a small amount of rust out of the hole while draining. my plug is solid compared to your hollow one, but i always have rust slime on the end of the plug. since you think you have an obstruction, i'm surprised that the plug you pulled isn't filled with rust slime too. why, i don't know.

i'd be careful with a punch and hammer or a drill for that matter if it comes to that. maybe have a look in the hole w/ the plug removed w/ a mirror and flashlight. see if you can see any obstruction. ya don't want to be punching away on the back side of the water jacket. do you have end plates on your style of manifold? maybe ya could take one off and see better what's up. if that's a viable thing to do, be sure ya can get a new gasket..

you do want the bow high when draining so all water flows to the back of the block and manifold.

if you really don't have a plug on your riser, yes, there are only the other two plugs, one on the manifold and one on the block. at least on my 165 L6 that's the case..

don't know if that helps, but it's the best i can come up with...

i still would like to see a pic of your aluminum manifold...

 

[Jstep]

Re: Drain plugs on a Mercruiser 160 6cyl

I tried the punch and hammer last night, and had no luck. I could pound harder with the hammer, but I'm at the threshold of comfort right know, without knowing for certain that I won't break anything.

Here are some pics of the manifold:

This is the bottom of the manifold. The right side of this picture is the aft end of the manifold, where the elbow is. The rusty hole and the far right is where I removed the brass plug that I posted the photos of in a previous post.

This is the bottom of the manifold, shooting toward the bow (left side of picture if the fore end of manifold).

 

[ziggy]

Re: Drain plugs on a Mercruiser 160 6cyl

hum, i have no real insight for you. while it don't look like my manifold, i do think you've removed the proper plug to drain it. why no flow. i don't know. can you maybe take a hose off and see if there's really any water in it? i can on mine. on the ft. side where the hose comes from the tstat i believe. maybe the waters already gone. have you tried to look into the drain hole and look for an obstruction. don't know if i'd try it. but maybe take one of them large plugs out and see what's in there. like, rust, sand, who knows what.

looking at that manifold from the outside. it looks very similar to mine right before it failed. mine failed internally with water seeping into the exhaust runner... might be time to R&R it??? prior to failure. which would likely be water intrusion i believe..
have you got any water in the oil?

i'm running out of ideas for ya... short of removing to see what's up..

 

[Jstep]

Re: Drain plugs on a Mercruiser 160 6cyl

Yeah, I'm wondering if there's any reason I can't remove one of those large plugs with the square hole. Seems to me that would be just as good, if not better, than the drain plug.

I do agree that it would be a good idea to remove and inspect them to see what kind of shape they're in, but that will unfortunately have to wait until spring.

 

[ziggy]

Re: Drain plugs on a Mercruiser 160 6cyl

Yeah, I'm wondering if there's any reason I can't remove one of those large plugs with the square hole. Seems to me that would be just as good, if not better, than the drain plug.

my 'guess' as to why it may not be a good idea is that as rusty as your manifold looks, i'd think that plug would be rusted in real good. like may break the manifold prior to the plug coming loose while trying to use a driver to take it out. like i said, that's a guess.

I do agree that it would be a good idea to remove and inspect them to see what kind of shape they're in, but that will unfortunately have to wait until spring.

while that may seem like a good idea. i would want to 'know' that the manifold is empty of water. if it's not. the question may be rendered academic as if it's got water in it, it'll freeze and then ya'll be hosed too.
the reason i suggest taking it off is because of this... this manifold did not leak externally at all.

i pulled this manifold and filled it with water while off the engine. i filled the water jacket full. it started leaking right away and you can see the trickle of water running down the inside of my exhaust runner. by morning. the water jacket was empty, the exhaust runner was full.
my first clue that this was occurring was a hard start (slow cranking) while at the lake one day. next clue was chocolate milk for oil the next day. i assume that the water leaked into the exhaust runner, then entered my combustion chamber via an open valve, then leaked into the engine oil pass my less than sealed old rings... i did save the engine, only because i was right on to it after i discovered the issue. like within 24 hours.. the manifold is not horrible to take off, but is heavy and awkward to manage...

like i said, my manifold looked just like your at the bottom center of the manifold, rusty. but mine didn't look as bad as yours does. i'd be worried... if that's occurring, and you wait till spring, yer engine will be toast i'd think.

 

[Jstep]

Re: Drain plugs on a Mercruiser 160 6cyl

Well, I took it to a heated storage facility last night, so as long as the heat doesn't go out there, I should be OK come next spring.

If the heat does go out, hopefully all I'll lose is a manifold. Seems like it might be at the end of its life anyway. Maybe I'll see if I can find one in better shape and get it ready to swap out in the spring.