Temp Creep

[Steve]

Sirs,
We’ve had our boat for two years now. Single Cummins QSB 5.9 425 hp. The heat exchanger, and coolers were all serviced immediately after purchase. In fact the aftercooler was replaced due to pitting. We fresh water flush fairly regularly and just completed this year’s annual service (but haven’t done the aftercooler yet). In the two years we’ve owned her, the temp has never broke 176 at cruise (2400 rpm) nor 179-180 at WOT (3000 rpm). The last two times out, the temp went to 182-183 when I brought her up to cruise but settled right back to 176-177 and remained there for the duration. When brought to WOT, she climbed to 181-183 then settled back to 179. Is this my “service the aftercooler asap” message? I understand the need to service the coolers every two years but it seems incredible that this would occur exactly on the two year mark.
Thank You

Topic

[Steve]

Solved!

Sirs,

I replaced the thermostat. After a number of test runs she never broke 176 bringing her to 2400rpm cruise and settled at 174-176. WOT never broke 178 and settled at 177 (staying at 2940-2950rpm).

whew….it’s about time I get an easy fix.

I’ll keep a watchful eye on my seawater pump and the aftercooler is scheduled for removal/service in early April.

Thank You for all your input.

Much Appreciated.

[Rob Schepis]

see here re: IR gun use https://www.sbmar.com/articles/ir-gun-temperature-check/
eprmang, yes good numbers. For comparison – On a QSB I inspected I had 71 deg F at the seacock and 109 deg F at the heat exchanger seawater outlet.

[eprmang]

I recently bought an IR temperature gun for my 1998 Nordic Tug with the 6BT5.9 engine. This boat has been operated in fresh water for about the last ten years. I bought it last July and am cruising in the San Juans. I don’t know when the coolers were last serviced so I used my IR to take readings last Sunday. At cruise, 1,400 RPM, I read 55 deg. at the impeller exit and 70 to 80 deg. elsewhere. Temperature of the exhaust elbow was 80 deg. Seems like these are very god numbers but does anyone have a baseline for new coolers and what the danger temperatures would be?

[Steve]

I know the pump was replaced prior to our purchase but not exactly sure when. My guess it’s 3-5 years old. I can hear the impeller buzzing along when the engine is on and there is no high pitch bearing squeal. What else can I be looking for to ensure the pump is working well?

Also, can you please tell me the best place to take IR gun readings on my QSB? I figured I’d do that as well to compare with the display (which is the old smartcraft). I’m sure the display isn’t the problem but it’s a good opportunity for me to learn something new and see if there is any difference in readings.

Would replacing the thermostat be any benefit?

Much Appreciated,
Steve

[Tony Athens]

Steve,

Yes, you have a old 3-pulley v-belt drive. It also means your seawater pump has been in salt water for not less that 10 yrs.. Temp creep could easily be the result of worn/corroded “innards” of your seawater pump.. “Sherwood” metallurgy has left a lot of room for improvement..

Keep an close on your you pulley drive–The middle pulley and bearing has also shown to be problematic on the high RPM versions on this engine.

[Steve]

ESN#46709654

Per the invoice:”Adjusted raw water pump drive belt.”

[Tony Athens]

Seawater pump belt “adjusted” ?? What is the vintage of the engine? Are you talking “v-belt vintage” QSB 5.9? Got a ESN?

Tony

[Steve]

Seawater:
Seacock worked, strainer cleaned, seawater pump impeller and o-ring replaced, seawater pump belt adjusted, replaced zincs in aftercooler and heat exchanger.

The exhaust elbow was replaced last year so the mixer is on the seaward side of the elbow (opposite side from the turbo).

Thermostat hasn’t been replaced since I purchased the boat two years ago.

Coolant:
Replaced coolant

Other:
Engine oil and filter, all fuel filters, gear oil and filter all replaced.

[Rob Schepis]

Please elaborate as to “this year’s annual service” as it relates to the seawater loop, starting from the hull pick up all the way to the exhaust mixing elbow, and everything in between.

[Author]

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