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Old 16-01-2018, 07:11   #1
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Possible to calibrate engine temp gauge?

We have run into an odd problem. We replaced the control panel for our Westerbeke 58. On the old panel the temperature gauge, one of the few things that worked, worked fine. On the new panel the warmed up temperature is about 160F. An infrared heat gun thingy shows the engine is running at about 180F. Is it possible to calibrate the gauge? Would there be a different sending unit for the new gauge and I need to replace the old sender?

Thanks for your thoughts.
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Old 16-01-2018, 07:38   #2
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Re: Possible to calibrate engine temp gauge?

This is not that odd. The IR temperature probes are not always that accurate. They rely on the emissivity of the material pointed at. The emissivity varies between materials thus the variation. The better ones allow you to pick the value of "e" for calibration.

The other gotcha on these devices is the scan area. They don't measure the laser dot but an area around the dot. Mine (medium priced) has a beam spread diagram on the side to know how big an area it's averaging per standoff distance.

Bottom line, if your new gauge is compatible with the old sending unit (thermocouple type / bulb type) I'd trust the gauge first.

The other variation is that the gauge is measuring internal temperature and the IR is measuring external temperature. Thermocouple would be the most accurate of the 3 mentioned.
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Old 16-01-2018, 07:45   #3
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Re: Possible to calibrate engine temp gauge?

The old gauge would show the operating temperature as around 180F which agrees with the thermal probe. Also we tested the thermostat and it opens at 180 and it is open when the engine gets warmed up. It may be that I need a new sending unit.
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Old 16-01-2018, 13:25   #4
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Re: Possible to calibrate engine temp gauge?

My IR temp gauge was spot on.

Be aware that senders and gauges need to be matched in terms of their resistance vs temp.

When I got my boat the temp gauge was way off. Or rather 1 gauge was off and the other (there were two gauges parallel to the sender).

It turned out that the sender was a dual gauge type. When there was only 1 gauge hooked up to the sender (there was an open circuit to the non-working gauge) the working gauge was in error. Once I fixed the open circuit then both gauges worked correctly.

If I recall (it has been may moons ago) the working gauge read low much like yours.

Check the sender and gauge models for compatibility.
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Old 16-01-2018, 13:53   #5
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Re: Possible to calibrate engine temp gauge?

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Originally Posted by evm1024 View Post
My IR temp gauge was spot on.

Be aware that senders and gauges need to be matched in terms of their resistance vs temp.

When I got my boat the temp gauge was way off. Or rather 1 gauge was off and the other (there were two gauges parallel to the sender).

It turned out that the sender was a dual gauge type. When there was only 1 gauge hooked up to the sender (there was an open circuit to the non-working gauge) the working gauge was in error. Once I fixed the open circuit then both gauges worked correctly.

If I recall (it has been may moons ago) the working gauge read low much like yours.

Check the sender and gauge models for compatibility.
Think this might be the problem even though the new panel is Westerbeke-branded. The new panel came with a new oil pressure sender unit but not a temperature one.
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Old 16-01-2018, 14:39   #6
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Possible to calibrate engine temp gauge?

Now its hard to ignore the numbers, but in truth they are irrelevant. What is relevant is change, if it always runs at 1 O clock and is now running at 2 O clock, then you need to investigate. Many gauges wont have numbers just tick marks for instance.
What is relevant it to be sure that when cold it registers cold and increases until operating temp is reached.
To answer your question, yes it can be calibrated. You start with a known good temp gauge, Id use my Fluke multimeter and a thermocouple, place both in water and start heating the water, then at the temps you want, you Mark the gauge on the outside of the glass. Last step is to put a slippage mark between the glass and the case so that any movement of the two would be known.
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Old 16-01-2018, 21:21   #7
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Re: Possible to calibrate engine temp gauge?

Take the sender out, and hang it in a can of boiling water, if you are at sea level water fairly reliably boils at 212 degrees F.

If you hang a thermometer beside the sender in the water as it heats up you should be able to get calibration points at lower temperatures whilst it is increasing to the boil.
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Old 17-01-2018, 18:10   #8
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Wink Re: Possible to calibrate engine temp gauge?

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Originally Posted by RaymondR View Post
Take the sender out, and hang it in a can of boiling water, if you are at sea level water fairly reliably boils at 212 degrees F.
This is my preferred method and doesn't depend on any assumed accuracy of other equipment. Accurate cal at lower temps not really needed since engine will be OK below 212F and as long as the needle goes down a bit below 200 after you let the water cool a minute, the gauge is working fine. You can run wires from the engine over to your stove top where you put the sensor in the boiling water. You will need a large clamp to make the ground connection on the sensor.

I am amused about why it took a few posts before the most simple and accurate answer showed up. I suppose the world is getting too high tech to remember the basics?
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Old 17-01-2018, 18:36   #9
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Re: Possible to calibrate engine temp gauge?

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you should be able to get calibration points at lower temperatures whilst it is increasing to the boil.

The FAA which uses much higher standards than any boat might, says calibrate and indicator on the "decrease".
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Old 17-01-2018, 20:11   #10
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Re: Possible to calibrate engine temp gauge?

I bought a cheap temp gage on ebay strapped the sensor on to the exhaust hose just before it exits the boat. Raw water in the exhaust chamber keeps temp down to between 35 and 40c in caribbean waters. If raw water reduces due to a blockage or pump failure then exhaust gas temp rises immediately giving a great early warning before engine block temp rises. This works great on my boat. Usually when temp gage alarms engine temp is already in the damage zone.
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