An Infrared Thermometer
This is an infrared thermometer and it is what I consider to be a critical tool for any boat owner. As I always say "tools are free!". What I mean by this is the expense of the tool, and doing the job yourself, is always paid for by the labor savings. In 35 years of tool buying I have yet to find one that was not paid off in one or two projects or uses.
There are lots of things an infrared thermometer can be used for on a boat such as refrigeration trouble shooting, stuffing box trouble shooting, electrical trouble shooting and lots of engine trouble shooting. You can also aim it at the ocean before jumping in to avoid "shrinkage".
So just what is engine temp monitoring and why am I reading this? Well, I wanted to pass along my process and pre-planning assessment for potential future overheating events.
This process actually occurs well before you've had an overheating situation and is the whole premise of this article. It is to get a baseline when your engine is running well.
Essentially, you use an infrared thermometer to measure various marked locations on the engine prior to an overheat so that when you have one you can pull out your notebook or computer, compare measurements, and more quickly isolate and locate the problem.
We'll call this our engine temp baseline. Your engine temp baseline should always be derived from a properly running engine with a clean sea-strainer, clean Heat exchanger (HX), clean exhaust elbow and a new or relatively new impeller. Measurements should only be taken after the engine is 100% warmed up from having been run under load long enough to bring the water heater temp as high as the engine.
Measuring My Raw Water Intake Temp
In this photo I am measuring the temperature of the elbow leading to my sea strainer. It tells me the Atlantic Ocean under my boat is 68 degrees and that the temp my raw water pump sees is 68 degrees.
Take this reading an save it to a Word doc. or just write it in a notebook. This is not a critical reading but nice to know each time you check. If the water temp was 32f then I would not expect the same temps elsewhere on the engine but if it's within 5-8 degrees all your other readings should fall in line.
Every spot I measure on my engine gets a number and a "dot" made with a Sharpie marker. I use the "dot" so I can get repeatability every time I aim the thermometer.
Please try to use roughly the same "aiming" distance when taking measurements and this will lead to more accurate readings.
Heat Exchanger Raw Water Outlet toTransmission Cooler
In this photo I am reading the temp of the raw water circuit on it's way out of the HX.
The raw water path on my Westerbeke engine is as follows; Raw water pump to HX intake, HX outlet to transmission cooler inlet, transmission cooler outlet to siphon break, siphon break to exhaust elbow.
Please IGNORE the temp readings on my Raytek Infrared as I did not have the time to properly warm up my engine. I already had these numbers recorded and merely wanted to photograph how to get your engine temp baseline.
Measuring the raw water temp at the end of the HX
In this photo I am measuring the temp in the cavity at the opposite end of the HX where the zinc goes. This is a raw water temp measurement.
Measuring The Wet Side of the Exhaust Elbow
This is the exhaust elbow. The exhaust elbow serves the purpose of cooling the hot exhaust gasses so they can run through the rubber hoses inside your boat without melting them.
In this photo you can easily see my numbering system and the "dot" for repeatability.
The brass elbow coming into the top side of the exhaust elbow is the injection point for the raw water (ocean or lake water) circuit. This is where the water that gets spit out your transom is injected into the exhaust system to keep it cool.
This temp, and the next one, are CRITICAL measurements. Exhaust elbows on short run time sailboat installed diesels tend to load up with rust scale and carbon until they block. A blockage of the exhaust elbow will cause over heating!
Measuring the Dry Side of the Exhaust Manifold
On my Westerbeke and most other diesel engines the exhaust injection elbow is bolted directly to the exhaust manifold. This measurement is how hot the actual dry exhaust gasses are.
As you can see there is about a 100 degree drop in exhaust gas temp after the water injection. This reading is a little low for my engine but again this was for illustrative purposes and the temps on my engine mean nothing for your engine.
If this measurement and differential temperature between the wet and dry side begins to get progressively wider and hotter and hotter it' a good indication you have an injection elbow beginning to clog.
Injection Point and Measurement Dot
This is just a wider angle photo of the injection to the exhaust elbow and the "dot" I aim the infrared at to get repeatability.
Exhaust Manifold and Injection Elbow
Again, just another angle of the manifold feeding into the injection elbow and the raw water hose injection point.
Measuring the Thermostat Housing
In this photo I'm measuring the temperature of the upper thermostat housing.
I know the red laser dot is off slightly from my dot but holding the DSLR camera, with a hot shoe flash, and the infrared while upside down and contorted leaves it up to "close as it gets".
The petcock mounted to the top of this housing is where you would bleed any trapped air off the sealed or anti-freeze side of the system to prevent an air lock. Some engines have this feature & some don't. On some engines this petcock is just in a different location.
*WARNING: Before attempting a bleed a petcock moisten a rag with COLD water so you don't burn your fingers and wear insulated fishing gloves made of rubber. The antifreeze can burn you if you are not careful. I recommend a cold rag over the petcock, rather than pliers because it can spray out at a high force. Trust me, you don't want to use just pliers with no rag to prevent spray while upside down and contorted. Ouch!
Measuring the Low Side of the Thermostat Housing
This should be self explanatory as I'm measuring both sides of the thermostat. Comparing these two numbers will give you an idea of how the t-stat is operating and at what temps it's opening and closing.
With all these measurements it's a good idea to measure them over about a 3-5 minute period and then record a low and high reading for each location so you have a baseline "range".
Measuring the Temp of the Sending Unit
In this photo I am measuring the actual temperature of the sending unit where it threads into the engine block. The t-stat on my Westerbeke is rated at 180 and the Raytek reads 178.5. Keep in mind t-stats are not all that accurate and can have as much as a 5+ degree variance.
Again, monitor this reading for a while to get a low range and a high for your baseline.
Close Up of Temperature Sending Unit
This brass sensor with the wire attached is what I was aiming at in the last photo. This is the unit that sends the temperature to the temperature gauge on your engine panel.
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