Overheating question

[mercurymang]

I have just bought a 74 ebbtide with a 74 merc 650 (3cyl) on it. Motor looks very clean. Boat was always garage kept and I don't think it was heavily used. I finally took it out last week and it ran well. I ran it at WOT for about 5 minutes and then brought it down to idle for a bit. I noticed a small amount of steam coming from somewhere around the motor. I didn't think too much about it at the time but i've been on here reading different things and have become somewhat concerned. Is a little bit of steam normal/ok? How would I know if I was overheating the motor? I have been advised to move the tell tale up to the top of the block which i intend to do. In the meantime, I just wanted opinions on where I may stand. Should I not run it at all until I do some investigating?

 

[Chris1956]

Re: Overheating question

Rebuild the waterpump with a new impeller, gaskets and wearplate. That motor has no thermostat, so steam is not normal.

 

[mercurymang]

Re: Overheating question

Good news and bad news. Good news is that I ran a compression test and got almost 150 on each cylinder. The bad news is that i found some sort of leak on the port side. I have attached a pic. Any idea what is going on here?

 

[Chris1956]

Re: Overheating question

The picture was too dark to see. However, since it was near the shift cable, it is likely a leaking exhaust cover

 

[mercurymang]

Re: Overheating question

Ya, i guess that's not a very good photo. There is a weephole there and it appears to be leaking from that.

 

[Maxz695]

Re: Overheating question

It,s either a gasket or a crack in the exhaust cover. as long as it isn,t leaking else where it won,t get into the cylinders. I had 3 cracks on mine. the throttle arm and the shifter bracket will have to come off to remove the cover. Order the new gaskets as your going to need them and hopfully you won,t need another cover when it,s inspected. The cracks can be very small so do a good visual on it before reusing it.

 

[mercurymang]

Re: Overheating question

Just realized that i never wrapped this one up. This issue was the cause of a bunch of work. I was finally advised that the issue was likely the poppet valve. This necessitated removing the exhaust cover which led to the breaking off of three bolts in the block. This led to a removal of the powerhead and subsequent trip to the machinist for some heli-coils and an eventual replacement of almost every part that would be subject to wear and tear over the years.

In the end, the issue was a totally disintigrated poppit valve which i replaced along with the thermostat. Along the way, I learned a whole lot about the motors and am still learning. And still, I have only to run this thing one time. I am dying for some good weather here.

 

[Chris1956]

Re: Overheating question

Gee, Who would have thunk that old inline had a thermostat and poppit. Why did that model get those two parts, while the majority of the Merc IL motors had neither?

 

[mercurymang]

Re: Overheating question

I'm not sure. I know that I spoke with quite a few folks and there were several who thought that there was no thermostat. I have to admit that having the tstat worries me. I have heard quite a few people say they burned up there motor due a sticking thermostat. To that end, i installed a temp guage and maybe that will at least give me fighting chance.