1974 merc 1500 cooling system

[chrishayes]

I am obviously going through this engine and trying to find as much info as possible. Laddies has been a great help. I looking at the cooling system now and wondering if everything is in the right place. First, is there a thermostat on this motor? There is a hose coming from the cover of the engine that goes into the head and tees to the pee hole and up towards the #1 cylinder but has a long bolt threaded into the tube itself. There is a hole next to #1 spark plug that is uncapped and looks as though this hose might supposed to go there instead of the bolt. Is this true? Anyone have a picture of this area that I can look at? Would a picture from me help?

 

[Laddies]

Re: 1974 merc 1500 cooling system

Thats not a cyl head is just a water jacket cover, they had at lest 1 pipe plug it them and some had 2, some bocks were tapped on he top for the telltale so there are variations. Here's a link. http://www.mercruiserparts.com/Show...=END+CAPS,+MANIFOLD+AND+EXHAUST+COVERS+(CONT)

 

[chrishayes]

Re: 1974 merc 1500 cooling system

So, after doing as you said hooking up the hose to the water tube and running it with seafoam, I was able to get the compression from the #1 cyl to 120psi from 90psi. But while running it, I got a little surprise, water started leaking out of the base of the spark plug. I assume that the gasket under the water jacket cover is bad? Could it be something else? Thank you Laddies for your help so far! Once this thing is running tip top again, I will post a video of it running and send you a case of your favorite beer! youve earned it already.

 

[Chris1956]

Re: 1974 merc 1500 cooling system

Chris, Since the 1/4-20 bolts that hold on the cylinder head water jacket cover tend to break, we usually use some silicone around the spark plugs to stop the leak, unless it is a really bad leak.

You might look closely at the cylinder head water jscket bolts. Some years used thru bolts and nuts. You can just break these and install new bolts if necessary. Check the ones on the bottom. They may be tapped into the head. You will not want to break those.

 

[chrishayes]

Re: 1974 merc 1500 cooling system

well, I got the jacket cover off and I cant really see any reason that this would have caused a leak. THe gasket looked decent although it was obviously torn up from removing...am I right to beleive that there would be no other way for water to be coming out of the spark plug hole other than this gasket? Shall I open any other section of the block while I have it all tore down?

One other thing, the #1 cyl is where the water was leaking from and once the cover was off the metal surrounding the cylinder was a slight brownish color unlike the other 5. I would assume that this is due to overheating? What would cause only this one cyl to heat up like this?

 

[chrishayes]

Re: 1974 merc 1500 cooling system

bump, any ideas? I want to be sure I am on the right track with the gasket being what caused the leakage at the plug and if that would cause a slight discoloring of the cyl jacket?

 

[chrishayes]

Re: 1974 merc 1500 cooling system

anyone else experience this?

 

[Chris1956]

Re: 1974 merc 1500 cooling system

Overheating causes all other kinds of issues, but is not visible in the cooling system. Check the spark plug color on that cylinder. Clean the carbs to fix any lean running condition

 

[emckelvy]

Re: 1974 merc 1500 cooling system

Just a comment on the water leak; it's very common to see this type of leak; the gaskets get old and dry up. If the sealing surface of the block is clean, and the cover looks good, a new gasket should cure the problem.

If the block is pretty chewed up, you may have to use a small amount of RTV sealer or a gel-type anaerobic sealer such as Loctite/Permatex 518. You can pick up this stuff at most auto parts stores.

Note that if you use RTV, don't get any copper-containing type. The black automotive or red would work well. Use a sparing coat as you don't want any excess to go into the cooling system. If you use anaerobic sealer, only the stuff that gets squished will harden. Any excess remains uncured and will wash away.

And a thin coating of Permatex No. 3 Aviation-type gasket dressing on the cover bolts will prevent them from ever getting seized in the block.

HTH & G'luck with the repairs.............ed

 

[chrishayes]

Re: 1974 merc 1500 cooling system

Thanks, anerobic=without air for anyone who read that and said, huhhhh. Anyhow, my initial question was, would you replace all block gaskets due to the fact that as you said, they get old and hard? This water jacket gasket was REALLY hard to get unstuck! Not to mention is just brittle and hard as a rock. It aint much fun changing gaskets but if it would help I will do it.

Is this a if it aint broke dont fix it area? nothing else is leaking to my knowledge.