Temerature gauge not registering properly?

[gss036]

1989 Merc 200 hp. I have been messing w/this for several months and cannot get it to read right, it wants to stay around 100 degrees. I just installed a new temp sensor in the port head. Blk wire to ground, tan wire straight to gauge. Shorted out the brown wire and gauge will peg out to the right, so i know there is a connection. When I run it, I get a good pee stream, heads fells like it at 143 degrees. New thermostats were installed.<br /> Confused as to where to look next? Merc manual doesn't give any troubleshooting in this area. The wires are hooked up properly to the gauge.

 

[KCLOST]

Re: Temerature gauge not registering properly?

What kind of sensor is it.? Part# also...<br /><br />And what is it measuring, metal or water temps...?<br /><br />My temp. sensor only has one wire, a tan w/blue stripe, connected to the brass threads of the sensor and it goes straight to the guage... It measures metal by the way... And it should be in contact with the cylinder head and it is recommended to use a heat sink compound at that point... If you have the same set-up, why would you need a ground wire on the sensor?<br /><br />I'm wondering if you have the correct sensor for that engine....

 

[gss036]

Re: Temerature gauge not registering properly?

Yes I have the correct sensor.14 13536A 7 TEMPERATURE SENSOR 1 $20.76 from Merc parts express. The tan.blu is for the overheat side on the right head and that has only 1 wire because the sender grounds on the head. I have a Merc manual and wiring schematic and checked all that and it is correctly wired. The sensor works on resistance, as it gets warmer the resistance changes and supposedly sends signal to the gauge. That is why I bought a new sensor. Apparently that is not the problem. Maybe the gauge?

 

[andy6374]

Re: Temerature gauge not registering properly?

I would try a new gauge. <br /><br />The tan/blu is usually the overheat switch, but can sometimes, as in KCLOST's case, can be the temp sensor. To test which one is which:<br />The temp sensor will show resistance between it and the powerhead (ground). The overheat switch (for the alarm) will show an open circuit between it and the powerhead.<br /><br />-andy

 

[KCLOST]

Re: Temerature gauge not registering properly?

I looked at the schematic for your year of engine... It does show that the temp. sender wire can be purple, or black, or tan and blue.. And that you have the proper sender for your engine.<br /><br />What it doesn't show is a cylinder head water jacket cover... So I assume you are measuring water temperatures... Is that correct..? Was the sender inserted into the water jacket/passage of the cylinder head so it does not touch metal?<br /><br />It could be the guage as your problem, possibly even the wire from the sender to the guage is faulty...

 

[gss036]

Re: Temerature gauge not registering properly?

KCLOST:The sensor is inserted into a molded hole w/plastic insert to keep it from touching metal. Although the platic only covers part of the sensor. I would think it measures air/metal temp inside the hole. I could put my finger on the metal next to it, but was definately warm,145-150 degrees.

 

[andy6374]

Re: Temerature gauge not registering properly?

Did you have this engine from the get go?<br /><br />I have an 88 V6, and orginally they only had an overheat switch (used a tan wire). But when it got rebuilt a tan/blu was used in place for the tan (formerly the overheat switch) and temp sensor tan wire was added on the port cylinder head.<br /><br />I recently bought a Mercury Factory service manual for my particular motor and this is how I found this out. However, if i type my serial number in at merc parts express, it shows both a temp sender and overheat switch. So either there are some mistakes in the manual, parts express, or something else. I think they started factory installing temp sensor (for temp gauge) in 89'. KCLOST the manual covers yours as well, so if you ever got a question just shoot.<br /><br />I bought mine on ebay for $7, I saw one for V135-V200 89's as well.<br /><br />-andy

 

[gss036]

Re: Temerature gauge not registering properly?

I have a Merc manual covering specific sr#'s which includes mine and others. I bought the engine new in 1989, blew the powerheard in 90, 13 months and 140 hrs out and Merc told me it was my problem. Had a new powerhead done and has been good ever since. My real problem w/the gauge, I can't say for sure when it quit working, just never paid that much attention. It has alway ran great. The overheat works as I spun the impeller once and it worked and then my wife ran thru a kelp bed once and plugged the intakes and it worked so I just never worried about it. I guess now I want things working right since I have time to play with them.<br /> http://www.tflx.com/tech.html teleflex tech page, great info on gauges.<br /> http://www.tflx.com/pdf/GAUWORK.pdf <br />The bottom one shows how to test the gauge, I will have to try is some time this week.

 

[KCLOST]

Re: Temerature gauge not registering properly?

Remove the temp sensor and start up the engine...<br /><br />See if water exits the hole... If that sensor is designed to measure metal temperatures, it has to touch the metal.. It sounds like, it is designed to measure water however...

 

[andy6374]

Re: Temerature gauge not registering properly?

I think water temp sensors are installed on the outer rim of the cylinder head.

 

[gss036]

Re: Temerature gauge not registering properly?

Actually they can be installed either way, depending on the design. This particular model is designed for the cast false hole in the head and water cannot exit. Looking at the teleflex site offers some insight to different designs and ways to install them. I don't know if I will find time today to mess w/it as I am about to take off from here.

 

[KCLOST]

Re: Temerature gauge not registering properly?

Take a look at this link... It shows the type of sensor I have installed on my motor... One wire, and the sensor touches an aluminum plug that sets in the forged hole through the water jacket and rests against the cylinder head, sealed off from water...<br /><br />Part #'s #24 through #28...<br /><br /> Instrumentation

 

[gss036]

Re: Temerature gauge not registering properly?

That is different than mine, that one is also a teleflex product. That is an option when you buy the kit. Look at the Teleflex link and you can see the different sets and senders.<br />I started bidding for a kit on E-Bay, will have to watch myself. Last spring I went after a pump and ended up buying 2 of them, got both for the price of one here at the hardware store. Now I have a spare. That is the bad part of acutions.

 

[KCLOST]

Re: Temerature gauge not registering properly?

I guess my point is, to make sure that you have the correct sensor for the guage... If you are sure of both, then I guess that the guage is the problem... Or the wiring in between....<br /><br />Let us know...

 

[gss036]

Re: Temerature gauge not registering properly?

Thanks KCLOST, that is my next move. I am going to test the gauges, I know the wire in between is good. I will follow the Teleflex test procedures.

 

[gss036]

Re: Temerature gauge not registering properly?

Just ran the test per Teleflex, cannot get the temp gauge to (bottom) peg out on the left side. The right side does peg out with the jumper. Checked the resistance on both senders and they read the same so I wasted $20 on the new sender. Checked my motor tilt gauge at the same time, it does the same so I think I have 2 bad guages. Serveral years ago, the shop blew my TACH while doing something minor and I am thinking the they also blew these gauges also. E-Bay hunting I will go.;-}

 

[andy6374]

Re: Temerature gauge not registering properly?

You should be able to find some on ebay. I saw some last weekend