Merc 300 Cooling

[timmeraw]

I recently replaced the power head on my Merc 300 after throwing a bearing. I'm pretty proud of myself after completing it and it fired right up and is running like a champ. Only problem is I don't have any water coming out of the tiny little tell tale under the pan. There is quite a bit of water spitting out with the exhaust and it does not seem to be getting very hot(after maybe 5 minutes in a tank btw). The impeller was recently replaced and it was pumping some water with my other power head.

Any comments/suggestions welcomed.

Thanks,
Tim

 

[Fuzzytbay]

Re: Merc 300 Cooling

Check for a blockage. Try and push a wire through. Where did you find the replacment?
So it was a bearing that went.
Ok glad to see you found a new P/H and I guess you have extra parts now too.

 

[timmeraw]

Re: Merc 300 Cooling

I found the Merc 300 from a guy I met a while back who is into old Mark racing engines and he has a couple of race boats. Anyways..he was cleaning out some inventory and he had this 300 that someone had painted black(to make it looker newer I guess) and he said to come over and he'd try to fire it up. He got it started ok but was not peeing. It was running well and only needed the power head so I bought it. It was really bastardized with a bunch of non oem parts( a tiny Radio Shack rectifier, a starter and soleniod out of a Ford I think etc.) So I just put all my extraneous stuff back on that power head and she fired right up. I was hoping to find that his impellar was shot but it wasn't.

I think there may be an internal block but the old wire trick isn't helping. Again.....it seems to be spitting(not misting) a large amount of water out of the exhaust port (back below head and above water line) and has soaked the lawn 8-10 feet behind the tank I have the motor running in. And as I also mentioned ....the head/exhaust covers etc are not getting very hot after running quite a while. I can literally place my fingers on the head (top cyclinder is warmest as usual) and leave it there not feeling anywhere near hot enough to burn. I believe that there is water getting into the head because I hadn't quite tightened a bolt on the water jacket cover after reattaching a ground strap to the cowling....and water was beading up and dripping out of it when the motor was running.

 

[Fuzzytbay]

Re: Merc 300 Cooling

My 1961 800 did the same as yours. No pee, block nice and cool. Top cylinder warm, but I could keep my hand there, even after a good ten mins on high idle. I ran it, for a while, on the trailer, in the lake, (2 hours maybe all toll) I thought it didn't have a tell tale. I looked for it, trust me. I took three runs on the lake before it came out the pee hole. I guess it worked the blockage out. I too had some water coming out the exhaust port, and prop. Been working great since. I don't think the pee hole blockage is harmfull on that water circuit, but I am not 100% sure of that.

 

[timmeraw]

Re: Merc 300 Cooling

You know...I seem to recall when I was first awakening this old girl (before the head went) ...and it wasn't peeing for a bit and then all of a suddenly it started. Maybe I'll put it back on the boat and go for a short lake test?

 

[Fuzzytbay]

Re: Merc 300 Cooling

Yep, just take the wrap off, so you can keep a feel on the heat. Just go slow, when I was doing my test runs, I went 1/3 throtle with a few shots of acceleration up to about 3/4, I never did go WOT. In fact I still don't go WOT, it goes good enough at 3/4 on my 16' 1964 areoliner.

 

[timmeraw]

Re: Merc 300 Cooling

ok I took it out on the Erie Canal for a "lake test". It is still not pumping water from the pee hole but was shooting a ton out of the exhaust. I went for a short run at 1/2 to 3/4 throttle and it was getting hotter than it was idling in the tank but not scortching hot. I am wondering how hot is too hot? I have read about using some kind of heat crayon or something like that but I would assume too hot is too hot to touch for more than a second or two.

Lets look at this logically...if there is quite a bit of water coming out of the exhaust and it does not immediately get too hot to touch can we assume that the water pump is working and something is plugging the tell tale?

Let me know if I am off base here. Also another small issue is that when I went from F to N it was still idling too fast and when I manually turned the Mag a bit it idled fine. Is that an adjustment on the throttle cable cause when it hits the idle stop it is fine...it just isn't getting there?

THanks,
Tim

 

[Fuzzytbay]

Re: Merc 300 Cooling

I'd say the tell tale is pluged, and the pump is good. Like I did, it took three runs, maybe even four, not really sure. All I know is, it was the wife who told me the motor looked like water was shooting out it......
As for the throtle cable, you have to adjust the barrel. I'll dig up the manual procedure, in the am for it.

 

[timmeraw]

Re: Merc 300 Cooling

Fixed....power washer up tell tale and peeing like a champ now. Here she is:

 

[Fuzzytbay]

Re: Merc 300 Cooling

Awsome looking, makes me feel ashamed to post one of mine. I might anyhow, the painting of the boat, and the motor (maybe) I'll get done next spring. I still need to find a few items, like tach, windscreen, mast light, etc. Once I fine those, she'll be back to orginal.

Here is the link for the throtle adjustment, link and sync etc.
http://www.maxrules.com/timingindex.html

 

[timmeraw]

Re: Merc 300 Cooling

Thanks Fuzzy for the info and I will pass it on to the new owner. Sold it today 1 hour after posting locally on Craigslist. Amazing what difference a motor makes to some people.

 

[thefairlaneman]

Re: Merc 300 Cooling

Seen one of these before?