Suggestions for correcting inaccurate Sierra/Teleflex Gauge Temp readings from block

[sumocomputers]

Recently installed a Sierra/Teleflex Temp Gauge and Sender Unit (68402P), which just has the gauge for COLD-HOT. I have an '89 Johnson 70.

I wanted a gauge with actual degree numbers, so the local shop sold me a 68401 gauge which goes from 120-240F. Turns out this is really meant for an inboard application.

The sender is installed in one of the threaded bosses near the water jacket, but not past the engine block in any way.

Long story short, now that I have installed a new thermostat, things are much better, but the gauge still reads about 20-25F too high if compared to my IR gun where I measured all over the block. When the gauge reads 180, the block reads around 155F in the hottest places.

Called Sierra, and they said that the sender unit is most accurate when measuring liquid, and will be off when just inserted into only the engine block. They even gave me the resistance values for each temp stage, listed down below. Apparently VeeThree actually makes the gauge, and I havent consulted them yet.

So I have 4 options in order to get a more accurate reading:

1. Figure out a way to install this into the water jacket. I am a little nervous about drilling and tapping into the block, but will do it I have to.
2. Install a resistor or rheostat inline (probably around 25-50 ohms), and target that mid-upper range for correction. Turns out the range is not linear, so adding a resistor in one range will make other parts of the range inaccurate.
3. Buy and Install a different gauge (like one from Faria 13009), who say it will be accurate for this application. Will end up losing money on my original purchase.
4. Put a piece of duct tape and write some numbers on it after getting some correlation data between the gauge and IR gun. <--- I HATE THIS OPTION

Most interested in options 1 or 2, and wondered if anyone has ever done either of these?

Thanks,

Chris


RESISTANCE CHART
120 240 ohm
140 155 ohm
160 100 ohm
180 70 ohm
200 50 ohm
220 40 ohm
240 30 ohm

 

[boobie]

I'd call the manufacture of the gauge and see what they have to say.

 

[emdsapmgr]

I'd make sure the sender is the correct one for the gauge. There are different senders-not all are applicable to gauges from other manufacturers. I run all my outboards with the temp sender flat tip tightly resting on the face of the head. (not in the water jacket) and get acceptable readings. I run Teleflex gauges and a Teleflex sender. Agree-call the manufacturer and ask about sender/gauge compatibility for your application.

 

[sumocomputers]

No Title

Hey guys,

I am using both a Sierra/Teleflex Gauge and Sender unit, and have already called them twice, and they have told me 2 things:

1. The sender unit is correct for my gauge
2. The gauge will be off in this application

But apparently VeeThree manufactures the gauge for Sierra/Teleflex, so I am going to give them a call also, but not hopeful their answer will be much different.

Also, I did not use the supplied bracket (thought it was for inboards), but instead threaded the sender unit into the threaded boss on the block (just to the right of the thermostat housing). I just remembered that it did not really go all the way in since it is a tapered NPT thread. Wondering if maybe the tip of the sender is not quite touching the metal block, and measuring air instead?

See Photo. https://dl.dropboxusercontent.com/u/2466418/Uploads/2015-02-23 14.56.51.jpg

emdsapmgr
Are you threading yours into a boss, or using the supplied bracket on your outboards?
I wonder if maybe I need to rethink my mounting?

 

[Faztbullet]

Just go with the original gauge(hot-cold) as you will never see a steady reading except at idle an WOT long run. The reason outboard gauges do not have numbers is the cooling system design that bypasses t-stat at WOT and it causes people to chase non existent cooling problems. The 13009 is a will read the head temp but still temps will vary at rpms Just use what you got and make sure hot horn is workiing

 

[sumocomputers]

Just go with the original gauge(hot-cold) as you will never see a steady reading except at idle an WOT long run. The reason outboard gauges do not have numbers is the cooling system design that bypasses t-stat at WOT and it causes people to chase non existent cooling problems. The 13009 is a will read the head temp but still temps will vary at rpms Just use what you got and make sure hot horn is workiing

Good info. I am numbers guy, so that is why I wanted the numbered gauge instead. I wasn't concerned so much about the steadiness of the reading, as the delta between the displayed temp and the actual block temp. But I see your point, and it makes sense.

At least now I know that when the gauge reads 180, the block is really about 155 (just an example). I might tinker with mounting the sender in a different way, but will probably go back to the hot-cold gauge, and just make some rough tick marks on a white piece of tape to correlate with my IR gun readings.

And yes, my hot horn is working (new buzzer). Still have yet to pull the temp sensor and test it though...

Thanks,

Chris

 

[emdsapmgr]

I use a Z- bracket to mount the sender. I've had ones made for the application, and I've made my own. This sender is fairly long, maybe 1 3/4" . I am aware that some of the later engines have a drilled, tapped hole in the head with a machined flat surface at the bottom of the hole. Just for a temp sender. I am thinking that the sender should bottom out in the hole you describe. It may not read as correctly, or as "responsively" if not bottomed out. These units are much shorter for this application, maybe less than an inch long.

 

[sumocomputers]

The instructions show for Johnsons, exactly the way I have it, but I am going to see if I can get the included Z bracket to work and maybe make better contact to the face of block. I have my doubts the sender is bottoming out currently.

Otherwise the tape and sharpie are coming out.

 

[sumocomputers]

Talked to VeeThree, and they pretty much said what Sierra/Teleflex said. However, based on talking with them, it is important that the "bulb" on the sender touch metal, preferably with thermal compound in between, which I did not use. I am going to try the following:

1. Put some thermal compound in the threaded boss to see if that improves the possible "air gap".
2. If not, try to get the Z bracket to mount the temp sender directly on the block somehow, along with some thermal compound.

They also said I can definitely put a rheostat inline to calibrate a given range more accurately, but that other parts of the range will be inaccurate.

I will post if any of these solutions works.

 

[boobie]

I think the thermal compound may be the answer. Used to use it all the time. OMC called it Heat sink compound.

 

[ssportsmfg]

Just a thought but have you thought about placing a few (how ever many needed) flat washers in the bottom of the hole and then screw it in tight with some thermal grease?

 

[emdsapmgr]

When I mount the sender to the face of the head with the "Z" bracket, I sand a small 1/4" circle of paint/primer off the head, so the tip of the sender is against the bare metal. Probably does not make any difference, bit I keep doing it anyway.

 

[sumocomputers]

End of sender was not bottoming out (probably 1/2" gap). Filled the 1/2" and a little more with thermal compound and as I threaded the sender, I felt it snug up against the thermal compound very well.

Result is the same.

Going to try the Z bracket, and if it is also the same, I am just putting a 30 ohm resistor inline, and be done with it. VeeThree even has a tech article on adding resistors:
http://www.v3instruments.com/trouble_shooting_guides/Lower_Temp_reading.pdf