How reliable is a laser thermometer?

[funsailthekeys]

I have a Perkins 4-108 that appeared to have an overheat problem. After replacing everything in the cooling system, raw water pump, all hoses, thermostat, acid dip the heat exchanger and acid dip the mixing elbow and doing an engine flush the temperature gauge would still show it over heating above 1800 RPM. So I read on this forum about using a laser thermometer to check the various temperatures around on the engine. Guess what, the thermostat is a 160 and the hottest place on the engine is 167. So when the meter at the helm said 240 the laser meter said 167. I suspect a faulty sending unit for the helm meter. I would appreciate any response as to the accuracy of a laser thermometer. Also the heat exchanger showed almost 30 degrees cooler than the block, I guess that part is working correctly.

[sailingdog]

If you're talking an infrared remote thermometer, they're pretty accurate.

[jnsailing]

What Dog said! We used them a lot at work and they give quite accurate readings at long distances but you do have to be sure you are pointing it at the right spot. It isn't always easy to keep your target aimed correctly over longer distances and on moving platforms.

John N.

[funsailthekeys]

I checked all over the engine block and the temperatures were pretty consistent with exception of the heat exchanger and it was about 30 degrees cooler. So now that things have been affirmed I'll move on to the temperature sending system, Thanks again for your input.

[MoonSailer]

Same problem same results!!!! I have been struggling with overheating for years. Checked everything no improvement. I bought a thermosensor and when the temperature gauge on the boat said 210 degrees I could not find any themperatures above about 174. I checked all over and as you found my heat exchanger seemed to be working with hotter water leaving the boat and cooler water going into the engine. The sender unit is just a resister than changes with temperature. maybe corrosion somewhere in the circuit of a defected sensor???

[chucklesR]

Given the choice of believing a laser and a thermometer and or 20 year old temperature gauge on a boat, go with the laser. Recalibrate or replace the gauge.
You can always check the laser by pointing it at an ice cube, the open air etc..
the cheap one I got as a girt is good for pointing out which soda is colder than the other in the fridge.

[Stillraining]

I have a fairly decent one and is guaranteed to be within 2%

[jrutledge33]

using these many times in autoracing (tires, brakes, radiators, exhaust, shocks)

they are very accurate and extremely useful, but its good to remember that it's taking the surface temperature. in some areas there can be a difference between what the outside is showing and the internal temperature.

[hellosailor]

The accuracy will be stamped on the box.

Now, if you want to CALIBRATE that thermometer...put a pot on the stove, full of water. Boil it. Let it sit for a minute with the flame off, so the heat equalizes through the water and pot. Shoot the side of the pot and see if the thermometer says something like "200F".

With a little creativity you should be able to find other ways to test it for accuracy. Maybe the engine in a car, known to be working, typically 180F.

[sailingdog]

HS-

As Chuckles said...aim at an ice cube, open air, etc... ice cubes, not in the freezer should be at 32˚F until they're water...