Using Thermo Gun

[Laredo]

I have 1996 Volvo TAMD 61As with 1,200 hours that run great. WOT is 2800 RPM but at 2,300 to 2,400 the port engine analog temperature gauge quickly climbs over the maximum recommended 203 degrees. I always have to back off. I don't know if the engine is really getting that hot or if it is the gauge. This issue came up in the survey when we bought it 18 months ago and the owner said it was the gauge of course. I have a shiny new infrared thermo gun that I want to use while my First Mate drives the boat. I'm embarrassed to ask but where do you point to measure? At the oil pan? Thanks for your help !

 

[oscar]

Coolant side water pump or thermostat housing.

BUT..... the temperature is not measured at the dot. It is averaged over a cone, the diameter of which changes with distance. Read the instructions that came with the thermometer. Or, vary the distance and average out. A good tool when used properly.

 

[rgano]

Use extension wires to crisscross the senders with the port gauge reading the stbd engine and vice versa. If the high temp reading switches gauges, you know the original problem was not a gauge.

 

[Giggitoni]

Use extension wires to crisscross the senders with the port gauge reading the stbd engine and vice versa. If the high temp reading switches gauges, you know the original problem was not a gauge.

This ^

 

[Swfla]

Agreed about switching wires. I'd point the gun at the place the temp sender is located if possible. I find the pointer handy for all sorts of things. At home, water leaks in wall and floor, hot or cold. HVAC uses. Pets like to chase the red dot too.

 

[Lepke]

Not all temp guns are the same. My buddies Harbor Freight gun read 20° high compared to my medical gun and others. Not sayin' HF guns are no good, maybe just this one.
Temp senders can either go bad or develop a corrosion barrier if you don't flush the coolant side.
Point the gun where the thermostat is, just above or below depending on the engine design. Also at individual exhaust ports when under full load to see if the cylinders are running equal. It's worth having a gun.

 

[kchace]

Thermo guns are an excellent tool. To get a reading of a particular spot, put the gun very close to it.

 

[Laredo]

Many Thanks

I sincerely appreciate the rapid and outstanding responses. I will use all of your recommendations this weekend and report back.
THANK YOU !!

 

[High Wire]

Thermo guns are an excellent tool. To get a reading of a particular spot, put the gun very close to it.

Close is the key. Like 1 inch away is good. People incorrectly believe that the laser dot is where the temperature is being monitored. It is much wider. A high quality gun might have a 3:1 ratio and a typical knock off is 12:1. Read the side of the gun!!! The farther away the gun is the more ambient temperature is averaged into the reading making it less accurate.

 

[koliver]

Not all temp guns are the same. My buddies Harbor Freight gun read 20° high compared to my medical gun and others. Not sayin' HF guns are no good, maybe just this one.
Temp senders can either go bad or develop a corrosion barrier if you don't flush the coolant side.
Point the gun where the thermostat is, just above or below depending on the engine design. Also at individual exhaust ports when under full load to see if the cylinders are running equal. It's worth having a gun.

With Covid in mind, I read the forehead temp of my spouse and found that according to the HF gun, she is dead.

 

[C lectric]

The readout can be improved by painting flat black where you intend to measure.
Flat black is the best for good readings.
Do not try to measure hoses as they insulate too much.
Shiny surfaces are less effective than dull.
Expect some difference between the actual coolant and the gun reading. 5 or so degrees.

And yes read the instructions so you understand where the meter measures and how close you must be.

I have included my tome below. Take a look. May not apply but may.

 

[Boat]

Oil temperature is very important in a diesel. Some engine control systems make their calculations based solely on oil temperature and ignore coolant temperature. Moisture must be cooked out of the oil, sufficient temperature critical.

Quick and dirty calibration test is a pot of boiling water.

With Covid in mind, I read the forehead temp of my spouse and found that according to the HF gun, she is dead.

Sounds like a good excuse to play doctor.

 

[AZ2Loop]

One more thought on the gun. Rather than count on it for an exact temperature reading, consider using it as follows. Pick a spot on the port engine and read it, then pick the same spot and same distance on the starboard engine and read. Look for differences engine to engine. I don't count on mine for an exact temperature. I just monitor various spots on each engine looking for a delta of more than a few degrees, which might indicate a lurking problem.

 

[rgano]

With Covid in mind, I read the forehead temp of my spouse and found that according to the HF gun, she is dead.

My condolences.... on your temp gun.

 

[DDW]

Ir guns assume a fixed emissivity for the surface, which is a ballpark figure. In some surfaces, like polished stainless, you will actually be measuring your reflection. They are best used for comparison measurements: Is it hotter now that it was? Is this part hotter than that part? I just stick a piece of blue masking tape on the surface I want to measure, it seems to have around the emissivity the gun assumes (checked by a real thermometer). Easy to do and easy to remove if you don't want it there. Hold it close enough to only be looking at the piece of masking tape.

 

[firehoser75]

Ir guns assume a fixed emissivity for the surface, which is a ballpark figure. In some surfaces, like polished stainless, you will actually be measuring your reflection. They are best used for comparison measurements: Is it hotter now that it was? Is this part hotter than that part? I just stick a piece of blue masking tape on the surface I want to measure, it seems to have around the emissivity the gun assumes (checked by a real thermometer). Easy to do and easy to remove if you don't want it there. Hold it close enough to only be looking at the piece of masking tape.

See the photos for locations to check from Tony Athens, a marine diesel expert. As DDW states, best used for comparison purposes to notice changes or trends. Can also compare one engine (in your ER) to the other. Comparing earlier readings from these locations with changes (usually increases) over time, will give an indication of the pending need for servicing the cooling system.
https://www.sbmar.com/articles/ir-gun-temperature-check/

 

[rgano]

Spray a small dot of flat black paint at all the locations you want to check on your engine and place the IR gun an inch away to measure. Write the numbers you get at what you consider to be an average day and use condition into a readily retrievable document.

 

[oscar]

Some engine control systems make their calculations based solely on oil temperature and ignore coolant temperature.

And where are these systems located on my engines ?

 

[C lectric]

Linked below is a thread I copied from B.D. some years ago written by Ski in NC about the use of temp guns and what he had learned/experienced

 

[RickyD]

My starboard engine always shows higher temp, lower oil pressure, and lower volts. Gauge reads 195 while under way. Temp gun at sensor reads 177. Lower helm gauge reads 180 and proper oil pressure. Every once in a while the gauges blink/quiver. I have some electrical issue but heat is not a problem. So glad I have a heat gun.

 

[richardschmidt2759]

heat gun

Aim at the head, near the thermostat housing .

 

[Slowmo]

Jumping ahead but just assuming that it isn't a gauge problem you might want to check a few simple things. I've been burned in the past assuming a gauge was faulty. I seen the grates on the bottom of the boat get restricted due to various things including what seemed to be just globs of bottom paint. In our area there's a real problem with grass getting caught up.

Another odd thing I had happen was that the sea strainer lid wasn't sealing tightly and it let air in when the pump was pulling on it. I know it sounds impossible but it happened. There was no sign of it since the top of the strainer is above the water line so no leaks when shut down.