Johnson 175 Seahorse - hot or my imagination?

[texrgd]

I’ve been working on this engine for a bit now. What is the ideal temp for the engine to run at after warm –up? Took it out last week and the temp gage when off the chart after about 15 min. of running medium speed. I shut it down and eased in later with gage still indicating very hot. Replaced the impeller but the old one looked/felt fine. Replaced the gage – needle was swinging wildly and would not go to lowest temp even with a cold engine. Today back at the lake, I put the boat in and kept it on the trailer running the engine for maybe 20 min. The temp gage indicates the temp to be about 200F if I’m reading it correctly. This seems high and by the gage’s tick-marks looks high – not completely to the right but sitting at about 2:00 o-clock. Note: this engine ran great all last season – temp was dead center of the old gage at maybe 110F. This engine does not have a tail tale indicator so I’m not sure how well the impeller is doing – suggestions? There is water coming from the exhaust ports below the engine compartment. Looking for suggestions? All help is appreciated.

 

[emdsapmgr]

Re: Johnson 175 Seahorse - hot or my imagination?

The telltale became standard on 1978 an newer engines, so you must have a 1977. Normal thermostats will open at 143, so the engine may heat up to 150 at idle. You should be able to put your hand on the block or head for 15-20 seconds at 143. If it is too hot to touch, it is too hot. If the water is coming out of the exhaust relief, that is a good sign. You did not mention the warning horn going off--the engine control box has a horn which is connected to sensors in each head. These sensors will trip the (hot warning) horn at about 212, and shut the horn off when it gets back down to around 175. suggest you verify that this system is operating. Possible you have a bad guage temp sender.

 

[Texasmark]

Re: Johnson 175 Seahorse - hot or my imagination?

Normal setting on a household hot water heater is 140F if that gives you any indication what a 143 stat feels like when the stat starts opening.

Mark

 

[texrgd]

Re: Johnson 175 Seahorse - hot or my imagination?

Correct, this is a '77 model - sorry about that. The horn did not go off either time I got an indication that the engine was running hot.
OK, any way to test the esisting tstats when I pull them? And if possible, how to test the warning horn also.
I'll have to do some digging in the manual to locate and test/replace the gage temp sensor/sender.
Thanks emdsapmgr.

 

[texrgd]

Re: Johnson 175 Seahorse - hot or my imagination?

Ok with the water temp and water heater. I'll keep it in mind. Is this a way to test the tstats? Thanks Texasmark.

 

[Theoutdoorsman]

Re: Johnson 175 Seahorse - hot or my imagination?

You should be able to put your hand on the block or head for 15-20 seconds at 143. If it is too hot to touch, it is too hot.

This would be a really good starting point !!! If you can't lay your hand on the heads for any amount of time, I'd say your next move should be to replace the water pump and thermostats. It's advisable to test your temperature sensors, as outlined in the service manual, so you are certain they will function properly. I'm not for sure how to test your warning horn, but on my 1979 E'rude 140, I can pull back the protective rubber sleeve that is covering the wire connections, and ground them to a bolt on the block, and insure my warning horn is opperating correctly. Maybe others can assist you in some testing on your particular model. Good luck............ ALAN

 

[ezeke]

Re: Johnson 175 Seahorse - hot or my imagination?

The warning horn is controlled by the temperature switch at the cylinder head - tan wire. It will close when the temperature reaches 211º F. +/- 6º and sound the horn.

A few inches down the tan wire you should find a sleeve which, when slid away, should reveal a connector. Disconnect the connector and ground the control end of the wire. That will sound the horn if the horn is working and the ignition is on.

You must remove the outer cover on the cylinder head to remove and test the actual switch.

 

[Theoutdoorsman]

Re: Johnson 175 Seahorse - hot or my imagination?

And there you have it. I figured it was probably the same, but I would be doing you an injustice if not 100% sure. Correct me if I'm wrong here, ezeeke, but can't those switches be extracted without removing the "top cap" on the head? If I'm not mistaken, they should slide straight out....... right? If so, it might be a good idea to remove them and make a visually inspection of them for corrosion and whatnot. And while there out, he can test them with an ohm meter and pot of hot water to ensure they are opening at the correct temperature. Just remember to seal them once re-installed so as to prevent moisture from coming into contact with them. We sure don't want them to corrode.

 

[ezeke]

Re: Johnson 175 Seahorse - hot or my imagination?

I'm not sure, but most of the motors at that time had them under the water cover - sells more gaskets that way.:'(

Anyway, the method is correct, but I use cooking oil and a meat thermometer when she isn't watching.

 

[Theoutdoorsman]

Re: Johnson 175 Seahorse - hot or my imagination?

Texrgd....... If/when you decide to remove those water covers to test your temp switches, try not to act too surprised at what you see. You'll likely have a lot of deposits caked underneath. It's really no big deal to remove/replace those water covers. You'll likely be in for a shocker though. Mine was soo packed with crud, I don't see how any water could pass through the water jackets at all........ ........ Your service manual should have all the torque specs and torque sequence outlined within. And follow ezeke's advice.... It be a shame if you got yourself a knot on the head from moma....... ....... The meathod of testing those temp switches is in the manual as well. Good luck............. ALAN

 

[Texasmark]

Re: Johnson 175 Seahorse - hot or my imagination?

No on way to test stats. Put them in a pan of water on the stove with the fire low enough so that the stat has time to follow the heat (temp) of the water. I usually put a candy thermometer in the water to monitor the progress....candy as it reads that hot.

As the water gets to within 5 or so degrees of the stamped value the disc at the top of the stat will start to retract and continue as the water gets hoter. By 155 ish degrees it should be fully opened.

On the temp sensors, sons and my Merc has them under a little retainer held in place with a screw on the head(s). Remove the screw and little plate and by pulling on the wire it slides right out....it's just a little disc thing with the wire coming out of the back of it.....kinda like a little battery......Texas Instruments made millions of them and the trade name was "Klixon" snap action switch.

When I was stationed at Bergstrom (many years ago) I spent many a night fishing for sandies at the marina on the East side of travis. We'd rent a stall and two or three of us would put out 3 or so lines apiece and plug our lights into the marina's 115v (part of the slip rental) and have a big time. About 2-3 am was usually when the run occurred and it was frantic while it lasted.

Mark