Relocating telltale on 3 cyl 65 hp...

1

1975 Mercury 65 3Cyl 650

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Apr 18, 2007
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I just got a 75 Merc 65 hp 3 cyl engine and was reading about the potential for overheat. Mine does not have the top mounted telltale. Does anyone have the Merc TSB letter, or detailed instruction, on relocating the telltale to the top of the engine? I would like to make this modification as quickly as possible.

Any other information on keeping this engine happy and cool would be greatly appreciated.

Engine number is 4138844.

Thank you!

Mark
 
S

stompie

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Apr 11, 2007
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Re: Relocating telltale on 3 cyl 65 hp...

I have two 60HP 3 Cyl one tell tale at the top and one at the bottom. Why should it be at the top? What are the advantages? It is quite simple to relocate. The top of the engine near the thermostat cover there is a threaded plug. At the bottom you might have a threaded elbow. You simply need to swap the two around. Make sure to use some thread tape to prevent leaks.

Will try and take a photo tonight and post it tomorrow. Am in South Africa so when I post it, it will be afternoon in US.
 
1

1975 Mercury 65 3Cyl 650

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Re: Relocating telltale on 3 cyl 65 hp...

When I was trying to learn about this engine on this site using the "search" feature, I found several posts saying the earlier 3 cyl engines without top mounted telltales, were prone to getting steam pockets which could cause it to overheat in cyl#1. Also read that there was a Merc Tech Bulletin that told how to put the telltale at the top, which would eliminate steam pockets, and that newer 3 cyl engines had the telltale at the top when manufactured.

Maybe I am reading too much into this, but seems to me that if mine does not have the top mounted telltale, then I should add it, if for nothing else peace of mind. I was hoping that someone with way more experience than me would wade in and give me some direction.

Here's where I found the mention of the heat situation and the Merc TSB:

http://forums.iboats.com/showthread.php?t=184283&highlight=telltale
 
Silvertip

Silvertip

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Re: Relocating telltale on 3 cyl 65 hp...

With the telltale at any location other than the highest point in the water jacket, it is possible for air pockets to form and therefore prevent cooling water from totally filling the block thus increasing the risk of overheating the top cylinder. Here is a picture of how a newer three cylinder is configured. The smaller hose is for a water pressure gauge (not standard). The bigger hose would simple come off an elbow in the water cover.
Thermostat.jpg


If your engine has a threaded plug where the temp sender is located in the following picture, the tell tale can be relocated here -- again using a simple elbow available at any hardward store.
8b915656.jpg
 
1

1975 Mercury 65 3Cyl 650

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Re: Relocating telltale on 3 cyl 65 hp...

Mine does not have anything tapped on the left side at all, does not
appear to have a temp sending unit anywhere that I can see.
On the right side you can see the hose that runs from the top of
the small housing and goes over the top of the engine to the left
side. I guess the plan was that the water level in the engine would
have to be as high as the hose that goes over the top, which would
be the highest point?
IMG_2248.jpg

IMG_2250.jpg

IMG_2249.jpg

Do you have access to the Merc TSB that was mentioned before?
Thank you!
 
1

1975 Mercury 65 3Cyl 650

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Apr 18, 2007
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Rats....Some TSB's missing from list.

Rats....Some TSB's missing from list.

I searched the TSB's on the site and did not find any mention of a modification to move the telltale to the top. There were, however, a lot of TSB's missing that could be the one I'm looking for.

Missing ones: 75-5 and any 75 TSB's over 75-6, 76-3 and any over 76-16, 7-8, 77-15 and anything over 77-16, 78-3, 78-8, 78-11, 78-15, 78-17 and any over 78-18, 79-5 and any over 79-11.

I have narrowed the field of TSB's considerably. If anyone has access to these TSB's listed above and could glance at them to see if there is mention of relocating the drain to the top, I would greatly appreciate it.
 
1

1975 Mercury 65 3Cyl 650

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Joined
Apr 18, 2007
Messages
9
Top mounted telltale on 3cyl 650 from factory...?

Top mounted telltale on 3cyl 650 from factory...?

Does anyone know what year the Merc factory started putting the telltale on the top of the block on the 3 cyl 650's?

Anyone have a picture of a '76 , '77, or '78 with the telltale mounted on top so that I can see the location?

Thank you!
 
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