1974 Johnson 50 hp telltale

[Oldone88]

Finally got around to putting the boat in the water, and I immediately noticed I couldn’t see any telltale hole of water anywhere. I knew when I ran it in the muff that I had seen the stream of water. Most of the lower unit was submerged but there appeared to be water and exhaust coming out of some slots high on the drive, that was the only place I could see any water being pushed out.


Didn’t run it long due to fear of overheating. When I flushed it home there was a solid water stream coming out the leading edge of the lower unit. Is this the only telltale hole in these engines?

 

[Vic.S]

Your '74 engine does not have what we normally regard as a telltale. Older models didn't

OTOH An 84 model' for example has a nipple in the lower cover, #7 is the diagram below, connected by a small hose to an outlet on the exhaust manifold water cooled outer cover.
All the while this engine is running there should be a strong jet of water from this nipple

You should see some water maybe only droplets or a mist being blown from the exhaust back pressure relief ports shown in your first picture

The hole in your second picture is a drain. It merely allows water to drain from the "leg" when it is lifted from the water

You should be able to touch any part of the power head and maintain brief finger contact except perhaps around the spark plugs. If you cannot the engine is probably overheating

You should not see steam issuing from the relief ports. If you do its probably overheating Similarly you should not see any paint discoloration

 

[Oldone88]

Quote; "Your '74 engine does not have what we normally regard as a telltale. Older models didn't".

I was starting to realize this after getting home and doing some more research. But the hole that you said is only a drain "pisses", water pretty hard when run on a hose. Your suggestion makes me wonder if maybe i didn't get the water pump tubes connected correctly when i installed the lower unit. Does that sound like it could be the reason for it pissing water that hard from a drain?

Using a laser pyrometer, the exhaust cover was pretty hot, around 170-180. the rest of the engine was pretty cool, not sure about touching it with your fingers for long..

Thanks for the information..

 

[F_R]

That hole is a drain hole!! That whole housing fills up with water when the engine is running. The water coming out that drain hole was headed back to the sea anyway.

 

[Oldone88]

That hole is a drain hole!! That whole housing fills up with water when the engine is running. The water coming out that drain hole was headed back to the sea anyway.

But should the water in the housing be pressurized when running on a hose? Just trying to figure out why there's pressurized water coming out of a drain hole..

 

[oldboat1]

Yes. Running on muffs sprays out of every opening and gap. Try test running in a barrel (idle or fast idle only), water about half way up the leg. Monitor temp at the top of the head.

 

[Oldone88]

What kind of temp am i looking for at the top of the head?

 

[oldboat1]

Should not exceed 160F. Likely range 120-140F depending on incoming water temp.

 

[Oldone88]

So essentially there is no telltale at all.. the only way to determine if the water pump is functioning is checking water temp on the top of the head? Debating on installing a telltale setup, and plumbing from the exhaust cover. Any issues with coming off of there? I hate the idea of drilling into the block water jacket.

 

[racerone]

They did not need tell tales back in the day !!----But have you tested your overheat warning horn , yes or no ?

 

[oldboat1]

Think I would run the boat a bit before getting out the drill, although drilling into a water passage isn't too scary if you remove the head cover, mark carefully, take your time, etc. If the water pump impeller is fresh, you should see a good spray coming out of the ports at the back of the leg, if that's any comfort. Additionally, you can install a gauge with a sender that requires no drilling.

I'm not a great fan of tell tales -- tend to clog up and cause more concern than they are worth, but just my opinion. I run a number of period motors (just old motors to many!), and have no overheating problems with them.

 

[Oldone88]

[QUOTE They did not need tell tales back in the day !!----But have you tested your overheat warning horn , yes or no ?[/QUOTE]

It appears that the wires have been cut on the sensor, if its the wires that are coming out of the exhaust cover?

The impeller setup is brand new.. I don't recall seeing a lot of water coming out of the leg ports, but i will check again. Working towards getting a barrel of sorts, so it will be easier to see if its pushing water out of there.

 

[Oldone88]

Where do i find a gauge and sender that doesn't require drilling?

 

[oldboat1]

The sender is held down by an engine bolt (normally a head bolt). Gives you surface temp of the head (much like the heel of your hand, but calibrated!). Can't direct you to one offhand, but check here at iBoats. eBay might have one of the old OMCs, maybe NOS.

 

[racerone]

Have you looked at your motor carefully ????-------Is there a THERMO-SWITCH ( purple wires ) on the exhaust manifold to do with the THERMO-ELECTRIC CHOKE.-------Is there an temperature switch ( tan colored wire ) in the cylinder head for an over heat horn.------Best take the time to study your motor , test the overheat horn.------Do that before you start drilling !

 

[Oldone88]

It appears that the purple wires have been previously cut. The temp switch appears to still be in place. I’m assuming you test it by grounding the wire?

 

[jimmbo]

That usually causes the horn to blow. While that verifies the Circuit and Horn are good, it can't verify if the Switch is good, but they don't fail too often.
Best way to ensure Cooling is to make sure the Water Pump is in good condition, and to replace the Impeller every three years or so, and Never run the engine without water, even for a few seconds ..

 

[racerone]

The Thermo-electric choke was not the greatest idea.----Most were disconnected / bypassed.-----But you should test the overheat horn and wires.-----The switch in the head is reliable.

 

[Oldone88]

I tested the horn and it works. I guess I’m assuming the sensor is good. Ran it in a trash can today and now probably ha e more questions, than answers. Running in the barrel it’s still pissing water out the drain hole pretty well. Also I’m losing water out of the middle section of the lower unit. There was water coming out of the discharge area but not as much as I was expecting. Seems to me that I’m losing a majority of the water flow inside the leg. I checked temps after about 10 min and was around 140 at most places. Exhaust cover was closer to 170.

 

[Oldone88]

[No message]