1979 115 temp gauge

[wavrider]

I have a 115 johnson and the conductor (wire) that connects to the temp sensor is broken. There is enough of the wire left coming out of the sensor to re-attach the wire to it.
I took my volt meter and checked for voltage on the circuit but there was no voltage.
My question is, how does this circuit actually work?
I have a manual but it does not really explain the circuit for gauges to indepth.
Is there supposed to be a voltage going to the sensor? If so what volatge should it be?
Thanks for any replies and Happy New Year.

 

[emdsapmgr]

Re: 1979 115 temp gauge

Your 79 has a temp switch in each head. This is a temp switch, not a sender. The switch closes (goes to ground) when the temp rises to around 212 degrees, signalling the horn in the control box to sound. The horn sender should shut off when the temp goes back down below approx 175 degrees. You should find no voltage at the sender lead. You can test the horn by grounding the harness wire going to the sender. You can test the sender by putting it in hot oil and check for continuity. The factory service manual powerhead section explains this in detail.

 

[HighTrim]

Re: 1979 115 temp gauge

Your heat switches, installed in each cylinder head, are in series with a "HOT" warning horn in the remote control box. Should an irregularity develop in the cooling system and cause abnormal water jacket temperatures, the switches close the warning circuit. A switch may be checked by submerging it in hot oil as stated above. Using a test light to check the contacts and a thermometer to check oil temp., the contacts should close at a temp of 211 F + or - 6 and open at 175 deg F plus or minus 7.

To remove switches for testing, pull back the insulating sleeves and open the knife terminal connections. Remove the cylinder head covers and switches. On installation, clean the gasket surfaces thoroughly. Apply gasket sealing compound lightly to both gasket surfaces. Also apply the same sealing compound to top surface of heat switch grommet and again after cover has been installed. Install the cylinder head cover using a new gasket. Reconnect the heat switch leads and slide insulating sleeves over connections. All done.

 

[wavrider]

Re: 1979 115 temp gauge

Thank you for the replies.
I have a Seloc manual and it does describe the tests and repair.
I have a Gauge for temp monitoring. Most of the gauges I am used to use a resistive value to move the needle of the gauge thus I was looking for an voltage coming into the sensor.
I will try to grab some pics of it tomorrow and post them.
Thanks again for the replis and Happy New Years.

 

[Silvertip]

Re: 1979 115 temp gauge

If you have a gauge to monitor engine temp, then you likely have one sender that's a "thermister" or temperature sensitive resistor that controls the gauge. The other sensor is a snap switch that is open circuit during normal operation. If an overheat occurs the switch closes and sounds the overheat warning. These are two very different senders.

 

[wavrider]

Re: 1979 115 temp gauge

Yes Silvertip two different type of sensors.
I fully understand the circuit description behind the temp sensing over heat horn where the horn alarm sounds above a certain temp.

The gauge if I am not mistaken should work the same as an auto gauge in the sensor and movement of the gauge.

The only sensor I recall seeing is on the starboard head, sort of recessed rubber looking item with a brown wire coming out of it, broken in two of course.

I will dig into the ole 115 today after I get my morning pot of coffee and head up to the garage. thanks for the replies,WAV

 

[wavrider]

Re: 1979 115 temp gauge

Finished the coffee, went to garage, charged battery and went fishing in the 16' with the 1970 33 hp johnson.

Four bass and one speck later finally went to the boat ramp and headed to the house to work on the 115.

Starboard side of the heads has a temp switch, wire is broken and the other part that connects to the alarm? was inside the plastic flexable tube. Port side has no temp switch at all. The brown wire is there just tied off to the rest of the wires in the harness not connected to anything. In order for this wire to sound an alarm there should be a voltage on it correct? For example, 12vdc to a horn on the positive side, the negative side will run to the temp switch, if it gets to hot n shorts to ground the horn will sound. Am I correct in this assumption?

I grounded both wires and no alarm. Started the engine and grounded the wires again same results no alarm. I am beginning to think the temp gauge is not hooked up to anything yet when I remove the panel there is wires running to the gauge? Things that make you say "hmmmm".

I noticed my tell-tale was weak as far as pressure so I removed the fitting at the exhaust cover and there was some type of crud, looked lke old rubber hose that has sat on a ford intake for 20 years, I mean it was hard n brittle.
Maybe part of a deflector tube or hose?

Replaced fitting and connected tell-tale plumbing, started the engine and now my tell-tale stream shoots out 5 feet at idle, really strong not exagerating at all. Did I mention I got 4 bass and a speck today? *(grin).

Starboard side I believe #1 and #3 felt cool to the touch while engine was running, Port side #2 and #4 were warmer than the starboard side. I also noticed that water was coming out of the idle bypass exhaust port (openings mid way up the lower unit? perhaps incorret nomenclature) immediately when the engine started with no warm up period, bad thermostats on starboard side stuck in the open position?

I removed the hose from the Port side head to the t-stat and started the engine for a short period of time, less than a minute, water flowed freely from the port side head so no blockage on the coolant system to cause heat.

Plan of action and please if I am doing something incorrect or not required let me know.

Order two head and associated gaskets, order two temp switches, order two t-stats and associated gaskets, might as well put new waterpump on even though it seems like the one on there now is working fine. I do not know the history behind this engine but from what I am seeing little if any maintenance has been done in a long time. Thanks for the replies. WAV.

 

[HighTrim]

Re: 1979 115 temp gauge

I would at least look at the impeller to ensure that the chunk of rubber wasnt part of it. When was it last changed?

 

[wavrider]

Re: 1979 115 temp gauge

HighTrim I do not know when the impellar was changed last time? I do not know the history of the boat or engine so I am slowly working my way through all the systems to get it up in best possible operating condition.
Thanks for al your information and I will post the results after I have ordered and installed the above mentioned parts. WAV.

 

[DHPMARINE]

Re: 1979 115 temp gauge

Back in 1979 OMC had an optional temp gauge.It came with a sender that mounted in a 'Z' shaped bracket that bolted to one of the water cover bolts on the cylinder head.

It still shows up as a good part #175410.$66.93.

Maybe someone took that sender off your engine.


DHP

 

[emdsapmgr]

Re: 1979 115 temp gauge

Since you don't know the history of the engine, replace the water pump impeller for sure. You don't want the engine to run cold on one side, so the thermostat replacements is a good idea. Both sides should run 143-150 degrees when warm at idle. When you have the thermosat housing apart, check the valve body and be sure those two tiny holes are open... Replace any pressure relief valves that are melted or deformed. Your hot horn in the control box may not be working. It is not unusual for the telltale to plug up. The plastic end is a restrictor, and any crud in the system will lodge there. Blowing compressed air through that cowl outlet will clear it. Or remove the hose at the block and blow outward.

 

[wavrider]

Re: 1979 115 temp gauge

Thanks for the replies and the info, sitting here at the office wanting more vacation time to start tearing into the 115.
I will check on the temp sensor but I did not see any type of Z bracket on the heads so possibly removed on the Port side where there is no sensor or switch at all.

 

[wavrider]

Re: 1979 115 temp gauge

Ordered up the head cover gaskets, head cylinder gaskets and two temp switches today. Should get them first part of next week.

Will I need to wire the switches in series or parallel? The two brown wires are there from the wire harness but I have a gauge and not a warning horn.
Seemed the sending unit was removed previously before I purchased the boat so it will be a new overheat circuit rewire.

The concerns I have is the amount of current the temp switches can handle before burning out. Can I use an automotive 12vdc horn for the alarm and run it to the temp switch, when or if the temp rises enough to "short" the switch the horn will sound.

I need a horn loud enough to hear over the engine and also 22 years of workin on jet aricraft has left me pretty well deaf in one ear and hard to hear out of the other ( at least that is what I tell my other half when she hollers it is time to eat and I am in the garage working on the old johnson ).

Thanks for any input and replies,WAV.

 

[DJ]

Re: 1979 115 temp gauge

Back in 1979 OMC had an optional temp gauge.It came with a sender that mounted in a 'Z' shaped bracket that bolted to one of the water cover bolts on the cylinder head.

It still shows up as a good part #175410.$66.93.

Maybe someone took that sender off your engine.


DHP

I think DHP has it. Someone removed the bracket and tried to wire the guage to one (or both) of the head switches. The ones with the tan wire. That will not work.

If the sender is there, you can make your own bracket to let the sender touch the head.

It is normal for one bank to be a little warmer than the other, on a crossflow.

 

[Lakester]

Re: 1979 115 temp gauge

I need a horn loud enough to hear over the engine and also 22 years of workin on jet aricraft has left me pretty well deaf in one ear and hard to hear out of the other ( at least that is what I tell my other half when she hollers it is time to eat and I am in the garage working on the old johnson ).

Thanks for any input and replies,WAV.

hello,

perhaps a small red light wired in with its GRD tied into horn sys could augment the buzzer's tone?

regards,

lakester

 

[wavrider]

Re: 1979 115 temp gauge

I thought about that lakester, but prefer an audible warning that way if I am not the one behind the wheel Iwill at least know it is warning by beaing able to hear it.
I usually fish with my nephew's or wife, with the nephews I let them man the helm while I work the equipment or the anchoring chore.
I am think9ng of using the door open alarm from an automobile, the ding ding kind that drives you crazy , thanks for the reply,WAV.

 

[DJ]

Re: 1979 115 temp gauge

I thought about that lakester, but prefer an audible warning that way if I am not the one behind the wheel Iwill at least know it is warning by beaing able to hear it.
I usually fish with my nephew's or wife, with the nephews I let them man the helm while I work the equipment or the anchoring chore.
I am think9ng of using the door open alarm from an automobile, the ding ding kind that drives you crazy , thanks for the reply,WAV.

The automobile chime generators are really not that loud. The old OMC buzzers are pretty dang loud and just as annoying. The trick is to put it somewhere where the sound can escape.

A light is a good idea, in conjunction with the buzzer.

 

[HighTrim]

Re: 1979 115 temp gauge

Or some type of cattle prod mounted beneath your seat activated by a piston....... That will get your attention

 

[wavrider]

Re: 1979 115 temp gauge

DJ the old buzzers are prety load that is true, something about the frequency/tone of the auto door open buzzer that just penetrates my hearing capabilities.

Maybe it sounds like the old man over board drills uncle sam used in his canoe club.

Ok I will wire in a light on the console and a buzzer, so have both audio and visual, that really is a good idea. Wire then in parrallel series with both temp sensors connected so if either switch"shorts the alarm n light will activate.

I would like to have the gauge but since I had to replace the tach with a new one I have a suspicion the temp gauge may be faulty also so better to go with the light and alarm.

HighTrim I thought the cattle prod was to be used at the boat ramp to gather bait with, for those of us who can not throw a cast net.

It is a good idea to put one under the seat, I could hit a switch and make my nephew jump his big a## out of the seat (grin).

On the way to look at a 1974 40 hp Johnson this afternon.
I want to upgrade the 1970 33hp I have now with an engine that has a charging system so I can keep the battery charged and use the electronics I am going to install. I will start a new thread on that venture. Taking the compression gauge and spark tester with me. It will probaly take precedence over the 115 as the freshwater speck bite will be on next week ( time to call into the office sick ). Thanks for the replies and enjoy,WAV.