Is this the 3.7 litre merc? They had real issues with the exhaust manifold rotting out--I have seen this several times with these motors. Start at the basics before going crazy. Pull the exhaust manifold and riser and inspect them--I will bet they are the source of your problem. Hopefully you did not hydraulic a rod. These are expensive engines to rebuild if it comes to that. A 150hp outboard will out run and out gun that 170ho I/O.

Good luck with the issue and your decision.

Genie Aye....thanks.

I had read that the exhaust manifolds were suspect on these motors and planned on pulling mine this weekend. What should I look for in your opinion? I'm sure it is hard to see inside. Do they need pressure tested and if so, how is that done?

Hi djfam,

I'm probably not much help, but I hope you are able to save your engine without too much cost\time. I am not in the upper "bracketed outboard" club\groupie thing going on here. My previous owner had put in a rebuilt merc 470 a year or two before I bought it from him. Albeit I never had a bracketed outboard, but I am happy with the 470 set up. They sound good, sip gas and troll well. Being that I am not on a smooth lake, it goes plenty fast enough for me.

Good luck!

rkc

So I finally got to check my compression and it is pretty good. 140, 110, 125, 130. I'm a little concerned about the 110, but it is still right around the right margin. I am still diagnosing the issue, but I am not so sure now that I have a cracked block. There may still be a head gasket issue, but I am leaning now towards the exhaust manifold and elbow as culprits. If the water back flowed through the manifold into the engine, through a crack or busted gasket, I think this may have caused my issue. I will check this weekend if time/weather permits.

One problem I will have if it is the manifold is that it is not made anymore and not really able to be purchased anywhere. Mercruiser number is 71527A17. No-one makes them so I guess I will have to buy used on Ebay if anyone ever posts one. Can I take these to a machine shop for repairing?

Djfam, did the water come from the valve cover vent connected to the flame arrester on top of the carb? Check the oil on the dipstick, see if its milky. Also see if theres oil in the coolant reservoir on top of the exhaust manifold, and was there good antifreeze in the cooling system. I'll try ta help you figure out where your trouble is. I completely rebuilt my 170 Mercruiser 3 years ago and helped my buddy rebuild his last summer, both are running strong. I love these old motors. You can still buy parts for these motors, sometimes it takes a little searching. Ive got alot of parts dealers on a list if ya need them! I had ta buy a new Mercruiser reservoir for mine when I rebuilt it. Good luck!

cfelton....

yes, the water came out of the vent hose that goes from the valve cover to the flame arrestor.

the coolant looks OK and I did not see any mixing of oil with it - level seems fine and it is a 50/50 mix.

Compression numbers again were 140, 110, 125, 130

I'll definitely need some parts help, especially if it turns out to be the exhaust manifold. They no longer make the one I need.

And the oil on the dipstick was not milky but I'll check it again since it has sat now for a few days....

http://inetmarine.com/mcm37l4704854881980-1984.aspx

http://www.outdriveshop.com/exhaustmanifolds.html

I found these in a quick search, but they are not giving them away!!
I remember back in 98 when I bought my 165 manifold and it was $700 then, thats why I went outboard

Good luck

Thanks macojoe...

The one I need is the item for $810.50 that is listed as "No Longer Sold". The other one for the MCM 470 is no good for me.

I'll ask the question again....can I go to a machine shop and get these repaired? If not, why?

Cause it is cast iron, it doesn't take to welding all that well, and how thin is the rest of it? I would hate to fix it and have it break again in short order!!
Just my 2 cents