1975 MERC 165 (6) TEMP GAUGE PROBLEMS

[sprintin]

Sorry. I just realized I posted this in the wrong thread and can't figure out how to change or delete it...

Hey, guys!

I did it. I went to fix something that wasn't broken in my 1975 Glasply 21'. She was running fine, great actually. I noticed that the temp would run slightly high at about 3/4. It has done this for the 2 years I've owned the boat.

For me, though, it was too much for my OCD to handle seeing the temp run that high and I wanted to make sure something wasn't coming down the pipe.

I bought a Faria 13004 temperature gauge and installed it (only because I couldn't find an original replacement). But when I run the motor, the gauge quickly heats up to 250+ degrees. I have a temperature gun and the temp at the thermostat housing sits at about 160 +/-5. I ended up replacing the temp sending unit with a Faria 18-5897 sending unit.

Same result. Gauge still pegs 250 and the temp at the thermostat is about 160.

Any ideas?

Thank you!

 

[alldodge]

Howdy

Start by looking real close at the terminals on the gauge. It should have
+ 12V
- Ground
S - Sender

If you switched the wires it will be backwards.

If wires are connected correctly, remove sender wire from the gauge and turn key ON. With key ON and the sender disconnected the gauge should read below 100. If this works, then jumper a wire from the sender pin to ground, it should show above 240

 

[sprintin]

Thanks, AllDodge. I'll check it tonight and get back. :rockon:

 

[sprintin]

I think this thing is all over the place.

Took your advice, AllDodge and basically removed the gauge and reinstalled it. This seems to have fixed the issue and I think it was due to a loose ground and/or bad sending wire. Thanks for your help on that.

The gauge seems to be reading more accurately now. She's stilling running warm, though. I replaced the old diagram gauge with a numbered gauge. Now, she runs just north of 175 according to the new gauge, which would be consistent with what the old gauge was reading (although I don't know what the temperature range of the old gauge was because it was a diagram of yellow [cold], green [warm], and red [hot[).

I used my temp gun and I got 140-147 degrees on the top of the thermostat housing (right next to the temp sending unit). I got a reading of 170ish on the bottom of the thermostat housing. But according to the gauge itself, it's probably running at about 190 degrees.

What is the normal operating temp of this motor?

I'm assuming that a 140 degree thermostat would result in the motor running around 140(ish) - 150(ish) degrees. Is that correct?

I've replaced the impeller (last year), the thermostat, and the temp sending wire. She is fresh water cooled.

Thank you!

 

[alldodge]

Your 165 should have a 140 degree thermostat. You should be running in the 140 to 150 range. When was the last time the impeller in the outdrive was changed?

 

[sprintin]

I'll double check the thermostat tomorrow. Maybe I got the wrong one. Still wouldn't explain the fact that it ran warm before I put a new one in last year, but it's easy enough to verify.

The impeller was changed out 07/23/16, but I'll probably do it again this year due to my vibration issue that is resulting in me removing the out drive this weekend (which was also posted on iboats). I don't think the 2 are related because the engine ran warm prior to the vibration issue. But I'm just a backyard mechanic learning as I go.

Thanks again for your help.

 

[sprintin]

An update for anyone remotely interested...

Replaced the gimbal bearing last weekend (for a different issue) and changed out the impeller. Fired the OlGurl back up and still running warm, right at about 210 - according to the gauge. Thermo-toy still reads 140-160 at the thermostat housing.

The heat exchanger and elbow were replaced probably 5 years ago, but the guy that I bought it from rarely used the boat, maybe a couple times a year (and in salt water). I know this as he is close friend of mine.

I guess at this point, I'm looking at the heat exchanger and/or elbow. No problemo, but how do I troubleshoot them? I'm assuming that a bad exchanger = rust = clogged water passage = holes in the exchanger = water in cylinder = bye bye rod/lifter/etc.= boat trailer for sale, includes boat.

Maybe I check with my laser thermo-toy and check for varying temperatures along the exchanger...? Do we know what temp the exchanger is "normal" to run at?

What about the temp for the elbow?

Has anyone ever checked theirs...?

Thank you!

 

[alldodge]

right at about 210 - according to the gauge. Thermo-toy still reads 140-160 at the thermostat housing.

As I see it the only problem you have is your gauge and/or sender. The gauge reads 210 and the IR temp gun reads 140-160. The thermostat housing is where the sender is located, so your HE and everything else appears good.