Is this sending unit installed correctly?

[mtb55]

Hello, I recently purchased a Faria cylinder head temperature gauge with sending unit from iboats for my 1998 2.5 liter black max Mercury. I installed the sending unit according to the instructions but the shape of the head dose not allow the sending unit to be 100% in contact with the head (see picture). Is this installation correct? Thanks for any advice.

 

[Grub54891]

I never installed one of them, but no that does not look right. In order to get full contact, you may have to get a stud type bolt, so you can swing the sensor on to the head.

 

[Faztbullet]

Nope.....

 

[GA_Boater]

Isn't the circled thing a factory temp sensor? The bolt under the circle with the grounds might be a better location. Where it is now is only looking at air temp and won't be doing much.

 

[Silvertip]

Not even close.

 

[mtb55]

No Title

Isn't the circled thing a factory temp sensor? The bolt under the circle with the grounds might be a better location. Where it is now is only looking at air temp and won't be doing much.

I looked at that location by the factory sending unit but the head is slightly elevated at that location so the sending unit wouldn't be touching the head if installed as you suggest. Below is the instructions for the install.

 

[GA_Boater]

Step 2 says the sender must be flat on the head. Time to be inventive. Maybe some type of extension and bending to place it around the top spark plug.

 

[mtb55]

Thanks for all the replies. I'm a little disappointed that something that is advertised as bolt on, one size fits all, is really not. Any suggestions on the best alternate way to mount the sender would be appreciated. Thanks

 

[sam am I]

Sry ya got taken.........Your port head should already be milled out for temp gauge hardware as seen below.



So as perhaps another option than trying to get that thing to fit (probably no big deal but.....), You could go HERE and buy items 28, 29 and 30 and install them as seen above and things might go in a tad bit cleaner for ya.



The senders both should be the same resistance type/slopes, so the Faria gauge you just bought should work with this hardware.

 

[sam am I]

BTW.........Your installation isn't perfect per se BUT, it'll work. Yes, ideally the sensor body should press tightly/directly with xfer grease or the like to the block for NASA grade fastest response times but, I'm willing to bet there will be a at most a slight lag (you'll not even notice) in response time due to the additional thermal gradients of the engine block into the torqued in steel bolt/bar then through the steel bar into the embedded sensor/body (the die's substrate).

The metal all looks thick and short enough with what looks like a pressed in sensor, it should transfer the heat into the embedded sensor/body without much loss. Get a IR gun and check it, shoot the head and watch the gauge, I'd bet they're spot on and track with ea other. If the hood shuts okay with it sticking out.......Run it as is!!!

 

[GA_Boater]

He already has that temp sensor, circled in post #4. Also with the way the Faria sensor is currently mounted it will be so inaccurate to be practically worthless.

mtb55 - Sorry for your disappointment about not being bolt on, but it was a bolt on, wasn't it? Universal mounts usually require customizing.

This is how you customize the install;

1. Loosen the head bolt and rotate the sensor until the bracket is pointing to 3 o'clock.
2. Snug the head bolt. Just snug, not torqued,
3. Bend the bracket down against the side of the head.
4. Remove the bracket and bend it slightly more than 90 degrees. Is is to hold the sensor tightly against the side of the head.
5. Optionally smear some heat sink compound on the sensor for thermal heat transfer. This is not really needed.
6. Bolt the bracket on with the head bolt, ensuring the added bend in step #3 positions the sensor tightly against the side of the head. Bend slightly more if needed.
7. Torque the head bolt. All done.

You now have a belt and suspenders back up temp sender and gauge. The factory sensor is still the primary temperature monitor and will put the motor into limp or shutdown mode if or when the motor overheats.

 

[mtb55]

BTW.........Your installation isn't perfect per se BUT, it'll work. Yes, ideally the sensor body should press tightly/directly with xfer grease or the like to the block for NASA grade fastest response times but, I'm willing to bet there will be a at most a slight lag (you'll not even notice) in response time due to the additional thermal gradients of the engine block into the torqued in steel bolt/bar then through the steel bar into the embedded sensor/body (the die's substrate).

The metal all looks thick and short enough with what looks like a pressed in sensor, it should transfer the heat into the embedded sensor/body without much loss. Get a IR gun and check it, shoot the head and watch the gauge, I'd bet they're spot on and track with ea other. If the hood shuts okay with it sticking out.......Run it as is!!!

Thanks for your help! As it is right now the sender dose scrape the hood, so I'm going to abandon that thing. I'm not sure I understand your previous message when you suggested using the hole that is milled into the port head because there already is some sort of sending unit in there (see picture)????

I wonder if I might be able buy a screw in sender for the threaded hole above the pink dot in the picture???

Thanks again.

 

[mtb55]

He already has that temp sensor, circled in post #4. Also with the way the Faria sensor is currently mounted it will be so inaccurate to be practically worthless.

mtb55 - Sorry for your disappointment about not being bolt on, but it was a bolt on, wasn't it? Universal mounts usually require customizing.

This is how you customize the install;

1. Loosen the head bolt and rotate the sensor until the bracket is pointing to 3 o'clock.
2. Snug the head bolt. Just snug, not torqued,
3. Bend the bracket down against the side of the head.
4. Remove the bracket and bend it slightly more than 90 degrees. Is is to hold the sensor tightly against the side of the head.
5. Optionally smear some heat sink compound on the sensor for thermal heat transfer. This is not really needed.
6. Bolt the bracket on with the head bolt, ensuring the added bend in step #3 positions the sensor tightly against the side of the head. Bend slightly more if needed.
7. Torque the head bolt. All done.

You now have a belt and suspenders back up temp sender and gauge. The factory sensor is still the primary temperature monitor and will put the motor into limp or shutdown mode if or when the motor overheats.

Thanks for the reply, good idea! I wish I had a chance to read your post before I accidentally popped that sender off its plate while removing the hood. Oops!

 

[sam am I]

He already has that temp sensor, circled in post #4.

The motor has two temp devices, a "sender" and a "sensor"

You've circled item 13 from my link, that is his OT "sender". It is just a switch that closes when its too hot, it won't work with a gauge.

He is hooking up a gauge with a and that requires a "sensor" and that's what I lined out for him with item 28 in my link.

Also with the way the Faria sensor is currently mounted it will be so inaccurate to be practically worthless.

Bet it would be very accurate still, just lag 10 seconds in response (think of a pinching a short piece of wire between your thumb and index finger trying to tin it with a soldering iron).........Moot point though, he has a stock one already installed, see below.

 

[sam am I]

Thanks for your help! As it is right now the sender dose scrape the hood, so I'm going to abandon that thing. I'm not sure I understand your previous message when you suggested using the hole that is milled into the port head because there already is some sort of sending unit in there (see picture)????

I wonder if I might be able buy a screw in sender for the threaded hole above the pink dot in the picture???

Thanks again.

That IS your/a temp gauge "sensor" in THAT hole. You have it already installed from the factory. It's item 28. Follow that tan wire and use it!!, It's probably taped off under your dash somewhere. Hook up you Faria temp gauge to it..........Scrap the Faira sensor and mount.

I know you weren't going there but just for brevity sake and future folks crossing this same path/thread...... The temp "sender", item 13 that lives over on the starboard head, is just a OT switch that is either closed or open. It's not made for a gauge, just the OT alarm..See my post #14 to GA above..

 

[mtb55]

That IS your/a temp gauge "sensor" in THAT hole. You have it already installed from the factory. It's item 28. Follow that tan wire and use it!!, It's probably taped off under your dash somewhere. Hook up you Faria temp gauge to it..........Scrap the Faira sensor and mount.

I know you weren't going there but just for brevity sake and future folks crossing this same path/thread...... The temp "sender", item 13 that lives over on the starboard head, is just a OT switch that is either closed or open. It's not made for a gauge, just the OT alarm..See my post #14 to GA above..

Ok, thanks for all your help!

 

[mtb55]

Ok, thanks for all your help!

I tracked that tan wire coming from the port side sender and it goes into a large plug looking thing and then comes out the other side of the large black plug and mounts to a terminal (see picture, terminal is at tip of screw driver). Can I just unplug the tan wire at that little male-female connection by my finger in the picture, then attach that wire to the gauge?

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[mtb55]

Duh, lol...After I got to work I got to thinking; I should of tracked that wire beyond the terminal block, it might lead to the dash board area like you said.

 

[sam am I]

it might lead to the dash board area like you said.

It should be, mine was........Boat manu's (some) pre-wired their dashes and wired into their side of the merc engine plug but, just left out options here and there like temp gauges. These wires were however typically taped off and labeled under the dash.

Merc on the other hand, just wired/built these motors as if the boat manu's did have the gauges and wired their side of the engine plug accordingly.