1974 Johnson 70-HP: Cooling Water Path

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
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Dutchman
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1974 Johnson 70-HP: Cooling Water Path

Postby Dutchman » Mon Dec 14, 2015 3:45 pm

My son [may buy] an old tri-hull boat with a 1974 Johnson 70-HP Model 70ESL74M. He was running it on muffs [or hose adaptor] yesterday, and we were wondering where the cooling water should exit. It was coming from many places below where the gear case meets the [mid-section of the] motor. This [joint] would be under water when the boat is running in the water.

As there is no tell-tale [or overboard confidence stream of] water, how would you know if the pump is cooling?

He ran the motor for a long time and shifted it thru F-N-R several times. The head stayed cool but I thought water should come from the propeller hub.

Please advise.
EJO
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dg22
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Re: Help 1974 70HP Johnson

Postby dg22 » Mon Dec 14, 2015 10:48 pm

I have a similar vintage OMC, a 1973 Evinrude 50-HP. There is no water indicator. [Cooling water] just exits out the exhaust.

When on the muffs [cooling water] mostly exits via the water outlet on each side, just above the anti-ventilation plate, and some through the propeller hub. In the lake, more water pumps out the upper exhaust relief, located at the back of the mid section. Therefore, when the motor is running in the lake it is more noticeable that it is pumping water well.

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Re: 1974 Johnson 70-HP: Cooling Water Path

Postby jimh » Tue Dec 15, 2015 10:07 am

To assess the cooling water pump operation you need to monitor the water pressure in the outboard engine cooling system when the outboard engine is operating in the water in its normal position. When an outboard engine is operated off the water and cooling water is supplied by a hose adaptor, the water pressure in the hose can overcome deficiencies in the operation of the cooling water pump and mask problems in the cooling water system. Deficiencies in delivery of cooling water from the pump usually show up at high-throttle engine speeds, not at idle speeds.

With regard to buying any 1974-model year outboard engine, an immediate change of the water pump impeller and associated seals and wear plates is recommended, unless you know for certain that the water pump was just overhauled by a competent technician.

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Re: 1974 Johnson 70-HP: Cooling Water Path

Postby Jake » Tue Dec 15, 2015 11:20 am

My 1973, 65 hp Johnson's only "tell-Tale" comes out just above the [anti-ventilation] plate and shoots directly at the hull.
See: https://www.youtube.com/watch?v=zSG4iFy3diI of a 1974, 70 hp running on muffs.

This one [the engine shown in the recording linked above] has a high tell-tale that I do not think is original, but [the motion picture recording linked above] also shows the [water outlet] I am talking about that is low and on the leading edge of the lower unit.

Jim is correct about running on muffs; mine [i.e., the 1973 Johnson 65-HP engine] will shoot [water] out this hole even before the motor is running if the pressure is high on the hose.

Just for a check, run hose at lower pressure then start and see if the arc of the stream changes.

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Re: 1974 Johnson 70-HP: Cooling Water Path

Postby jimh » Tue Dec 15, 2015 2:07 pm

Thanks for posting the link to the motion picture recording of a 1974 Johnson 70-HP outboard engine that clearly shows the engine has an overboard cooling water discharge or tell-tale or confidence stream. This seems to contradict the earlier comments that the engine lacked such a device.

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Re: 1974 Johnson 70-HP: Cooling Water Path

Postby dg22 » Tue Dec 15, 2015 4:36 pm

My service manual does not show a tell-tale water cooling indicator for my 1973 Evinrude. It was one of the first things I noticed when I got the motor and had the same concern.

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Re: 1974 Johnson 70-HP: Cooling Water Path

Postby jimh » Wed Dec 16, 2015 6:27 am

Perhaps there is a difference in the cooling water path on a 1973 Johnson 70-HP engine compared to the one we are discussing, a 1974 Johnson 70-HP engine.

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Re: 1974 Johnson 70-HP: Cooling Water Path

Postby Dutchman » Wed Dec 16, 2015 11:44 am

Jake and all: thanks for your replies.

Yes, the engine was tuned and checked by a marine technician earlier this year, but the current owner is not a boater and couldn't give any details; he inherited the engine with another deal.

Yes, we are aware of what needs to be done and maintained with an older outboard.

The video is nice but as mentioned does have a upper tell tale stream.

Yes, we did have a stream coming from the leading edge as mentioned by Jake and from the water outlet on each side, just above the anti-ventilation plate like dg22 indicated.

I think we got our answer, and, pending a true sea trial, my son will get [the 1974 Johnson 70-HP engine] off the market, as the price is really right.
EJO
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Re: 1974 Johnson 70-HP: Cooling Water Path

Postby dg22 » Wed Dec 16, 2015 1:37 pm

At the link below there is more information on this and how to add your own tell-tale water cooling indicator to your older OMC motor.

http://forums.iboats.com/forum/engine-repair-and-maintenance/engine-frequently-asked-questions-faq/228380-johnson-evinrude-adding-a-tell-tale

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Re: 1974 Johnson 70-HP: Cooling Water Path

Postby jimh » Thu Dec 17, 2015 10:55 am

Thanks to DG22 for the pointer to the very interesting article that describes adding an overboard cooling system confidence stream to older OMC outboard engines that lacked them, or moving the source of the confidence stream water to a new location on some engines that already had a confidence stream. Based on this new information (contained in another article on another website) it seems reasonable (in this thread on this website) to think the 1974 engine shown in the youTube recording was likely modified to add the overboard cooling system confidence stream, and to surmise that perhaps the 1974 engine that is under discussion in this thread may not have an overboard confidence stream because it has not been modified.

Also interesting to note (as is mentioned in the discussion on another website): the installation of the cooling system overboard indicator serves a dual purpose. It not only provides the operator with an indicator of the flow of water in the cooling system, but it also provides a means for entrapped air to escape from the cooling system. Adding a cooling water overboard indicator would be a good modification to make if one had an older OMC engines that lacked one.

On OMC and later BRP engines, the joint between the gear case and the midsection often has intentional reliefs so that water can enter or exit the interior of the midsection at that point. It is probably inevitable that some water will get into that cavity, and by intentionally making the joint line between the mid-section casting and the gear case casting have a relief, entrapped water can escape.

Several comments (above) mention seeing cooling water flowing out of the mid-section-to-gear-case joint. Where is this water coming from? Is there an intentional outlet in the cooling system that discharges water into this cavity after it has passed through the engine block? Or, is the water just being pushed into the cavity by the use of the hose adaptor and is coming from the water pump, perhaps from a relief to vent the pump? A discussion of the cooling water path of the 1974 Johnson 70-HP engine seems incomplete without clearing this up.

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Re: 1974 Johnson 70-HP: Cooling Water Path

Postby Dutchman » Thu Dec 17, 2015 1:15 pm

jimh wrote:Thanks to DG22 for the pointer to the very interesting article that describes adding an overboard cooling system confidence stream to older OMC outboard engines that lacked them, or moving the source of the confidence stream water to a new location on some engines that already had a confidence stream.
I agree thank you DG22

Several comments (above) mention seeing cooling water flowing out of the mid-section-to-gear-case joint. Where is this water coming from? Is there an intentional outlet in the cooling system that discharges water into this cavity after it has passed through the engine block? Or, is the water just being pushed into the cavity by the use of the hose adapter and is coming from the water pump, perhaps from a relief to vent the pump? A discussion of the cooling water path of the 1974 Johnson 70-HP engine seems incomplete without clearing this up.

Again I agree and we won't find out until it is taken apart next spring unless somebody else can enlighten me(us).
EJO
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Re: 1974 Johnson 70-HP: Cooling Water Path

Postby jimh » Thu Dec 17, 2015 4:00 pm

OMC Service Bulletin No. 2276 Rev.1, April, 1994 is now reproduced in HTML in a separate thread.

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Re: 1974 Johnson 70-HP: Cooling Water Path

Postby dg22 » Thu Dec 17, 2015 4:20 pm

You are welcome. After seeing that video posted by Jake of an 1974 OMC with a tell tale confidence stream located higher up like many outboards, I started searching the web for this. I'm going to add this little modification to my motor in the spring. I re-did my water pump in the fall and it would be nice to a have tell-tale confidence stream higher up to know that things are working well with the water pump. Regarding the mid-section-to-gear-case joint, possibly the seal from the inner exhaust housing to gear case is worn or maybe there is a relief to vent the pump as Jim indicated as a possibility. I guess the worse case scenario would be if the brass water tube was not seated in the water pump housing when the lower unit was last installed. Things to check when you take apart and re-install in the spring.