Power System Temp Reading 101

Want to set a baseline for engine/transmission temps on my FL SP135's and Westerbeke 8KW. As much for learning as anything else. Exactly where should I shoot temps? I believe, not sure, that taking them it at exactly the same points each time is as if not more important than where. Engine block somewhere? HE and coolers...in the middle, at the RW exit for each? Transmission? Someone help me out with some exacts? Thanks in advance...

Watching for answers.

One tip that was given the last time this came up was to use a sharpie to draw a circular target on the spot you select. It wouldn't hurt to even write the temp next to it. (For folks like me who can't remember something from one moment to the next)

I like to know the temperature right on the sending unit. Then on various places on both the raw water and coolant circuits. Someplace convenient to your specific setup.
For trannys I like to know the oil in and out of the cooler temps.
Same for the engine oil cooler.
Just remember that too much data will drive you nuts.

For engines, a reliable indicator of engine temp is the thermostat housing. It is on the front of the engine above the fresh water pump. If the paint is light colored, then the suggestion above to put a black sharpie spot on a visible place is a good one. IR guns usually read a few degrees lower than coolant temperatures due to the minor insulation of the housing casting.

David

Thanks guys. Any value to shooting the exhaust elbow? Does it give any indication of issues from simple temp tracking long term?

I would like to verify the temp gauges just to see how accurate they are but no reason to doubt them. Should the temp at the sender pretty much match the gauge or would there be some variance?

firstbase said:

I would like to verify the temp gauges just to see how accurate they are but no reason to doubt them. Should the temp at the sender pretty much match the gauge or would there be some variance?

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It should be pretty close, at least at the lower station. I find variation on the flybridge gages, long wire runs/corrosion in the old wires, etc.
I change senders/gages when they start to vary more than about 10 degrees or so (lower station that is)

Sure take a temp reading on the exhaust elbow.

The jacketed part of the exhaust elbow should be 10-20 degrees warmer than sea water temps. Also if you shoot the exhaust hose downstream of the injection elbow, it will vary with rpm and length down the elbow. Mine is warmest at moderate rpms which provides enough load to make the exhaust hot, but not enough raw water flow (which is proportional to rpm) to immediately cool down the exhaust gas.

So mine varies from a peak of about 160 degrees a foot after the injection elbow to about 100 downstream after the raw water has cooled it down.

David

On my 135's I like to shoot the thermostat housing, the alternators, the bottom center of the oil pan, the oil filter, the transmission, the packing glands. I have 2 engines which makes it easy to compare and understand what's good.

When cruising in about 65 degree water, I get these numbers:

Thermostat housing - 178
Oil pan - 185-190
Oil filter - 185-190
Transmission - 140-150
Packing gland - 85-100
Alternators - 125-135

Ken

Obviously, the readings should be done after 30 minutes or more of cruise power to let things stabilize.
I took about 6 key readings on my engines. Don't forget the raw water OUT of the Heat Exchanger. Knowing the RW delta in and out of the HE tells quite a bit indirectly about RW flow and HE effectiveness. As RW flow reduces due to impeller, etc the RW temp input stays the same, but the HE RW output rises. Coolant in/out of the HE might tell something about HE deposit build up.
Note there is some interaction with all these temp readings as to cause/effect. But, its great to at least get a baseline.

Thanks for the comments. Nice coincidence that an email from PassageMaker mag today had the following article on the subject of engine heat and giving a couple of things for the newb to look for.

https://www.passagemaker.com/technical/troubleshooter-engine-temperatures-2017

The article mentions that the raw water pressure is less than the oil pressure in the oil cooler so an indication of an internal cooler issue would be oil in the exhaust. However, I have read many comments about water getting into the transmissions through the tranny fluid cooler. Is the pressure of the water greater in the trans cooler for some reason thereby overpowering the fluid flow? If not what causes the water to get into the tranmission?

I've lost tranny oil out a leaky cooler; yes, a little slick developed. I believe when shutdown occurs, there can be some mixing IN of raw water.
Both are bad news if not catched early. Clutch plates warp when oil is low, and bearings wear out fast with salt water in.
Lived both those miseries...

It's hard to imagine that raw water pressure is higher than even the low pressure side of the transmission oil cooler, but as Diver Dave points out, after shutdown there can easily be mixing in a leaking cooler. In my case it was obvious that the oil coolers were old, so I changed all coolers and oil lines to/from right after I bought the boat.

Ken