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Old 26 August 2011, 07:05   #1
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Mercury 3.5 Tell Tale 1983

I am new to power boating and outboards but happy with engines/mechanical things.

I have just got this engine off of e-bay as a non-runner. It now runs (blocked float chamber valve) but I am concerned about the cooling. Serial number is 6202276

It does not seem to have any holes near the head for a tell tale. How do I tell if water is being pumped for cooling.

I have run it in a bin but no water seems to be pumped from anywhere but I do get exhaust gases from above the prop.

I have ordered a works manual for Mercury 2.5 to 40 1975 on but won't get it until next week. The parts diagrams on the internet don't seem to have a tell tale.

Is there a tell tale on this old engine?

Is there an easy way to check water flow if not?

Thanks.
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Old 29 August 2011, 09:11   #2
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Les,

Although my main lump is a merc, I'm not totally clued up about the old smaller ones, however a couple of observations from the small / old end of the scale:

Telltales were a bit of a novelty even on larger engines - I have a '72 vintage 25 where you have to be very aware of the difference between steam & "cold start smoke" - there is a pitiful spray out the idle (top) exhaust port, and that is the tell tale. That flavour of engine was in production 'till 1975/6.

If your Merc is one of the later end of a 25 year production run from the 60s, there's a pretty high chance it won't have a telltale. The fact that it hasn't siezed yet might hint that the pump still works and it's one of them! There is a fab site for ancient OMC stuff, (old-OMC.de or something like that) but unfortunately nothing like it for merc / Yam etc)

The exhausts on older engines did tend to literally be a shaped pipe just behind the prop. As all the cooling water went down the exhaust for cooling, there's pretty much no way of knowing its flowing... until either the paint starts peeling form the leg or it siezes! There lies the hazards of small old engines. Simple solution is preventative maintenance & change the impeller annually.

Depending on the height of your transom, if there is no "relief port" and you've perfectly tuned it in a bucket, remember to take a screwdriver with you on the first outing - a couple of inches difference in depth on the exhaust could be enough to stall it at idle, so you may need to up the idle speed.
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Old 29 August 2011, 12:51   #3
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Old 02 September 2011, 16:19   #4
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Old 12 September 2011, 06:53   #5
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Hi Les,
This engine should spray a little water out of the "ilde exhaust". This is a couple of holes halfway the shaft. There should just spray enough water to make your hand wet at idle and you have an indication the cooling system works right.
Good luck with the old one!
Gr. Wouter
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Old 20 September 2011, 09:48   #6
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Good News/Bad News

Guys thanks for all the replies.

I have run the engine in a tub of water and do get a spray of water out of the exhaust holes.

But I had a terrible job getting it to start. Please see new post on difficult starting.

Thanks

Les
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