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Old 07-16-2020, 04:41 PM   #1
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What is a reasonable dry exhaust gas temp?

I recently installed an exhaust gas gas gauge which measures my dry exhaust gas temp in the riser elbow right after the turbo outlet. The engine is a JD 4045TFM50 if that matters. I finally got out and measured an exhaust gas temp of 550f while cruising at rpm1800-2000. Engine is running good so am going to assume that is a normal exhaust gas temp. Can anyone with an exhaust gas temp sensor share what sort of temps you are seeing at normal cruising speeds?
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Old 07-16-2020, 05:44 PM   #2
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That reading is fine but you should do full throttle for 3 minutes to see where you stand.
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Old 07-16-2020, 06:23 PM   #3
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That reading is fine but you should do full throttle for 3 minutes to see where you stand.
Ok,thanks, heading out tomorrow and will go WOT for 10 mins to see if my temp increases significantly.
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Old 07-16-2020, 06:37 PM   #4
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Temps depend on engine maker and duty rating. Newer commercial engines have alloys that take high heat with less loss. For older engines and yacht engines, 600įF is a good limit. There still will be some metal loss compared to natural engines.
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Old 07-16-2020, 07:51 PM   #5
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I have a JD 4045TFM75 in my boat. Not exactly the same, but really close. My engine is mechanically injected but electronically controlled. It was available in 3 HP ratings. To change HP you reprogrammed the computer, nothing else. Being OCD, I have all the spec sheets for the 3 different HP ratings and the maximum exhaust gas temperatures.

107 HP @ 2400 RPM 743 degrees F
121 HP @ 2500 RPM 763 degrees F
135 HP @ 2600 RPM 795 degrees F

Hope that's useful.

Ted
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Old 07-16-2020, 08:26 PM   #6
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Originally Posted by O C Diver View Post
I have a JD 4045TFM75 in my boat. Not exactly the same, but really close. My engine is mechanically injected but electronically controlled. It was available in 3 HP ratings. To change HP you reprogrammed the computer, nothing else. Being OCD, I have all the spec sheets for the 3 different HP ratings and the maximum exhaust gas temperatures.

107 HP @ 2400 RPM 743 degrees F
121 HP @ 2500 RPM 763 degrees F
135 HP @ 2600 RPM 795 degrees F

Hope that's useful.

Ted
Thanks, I have spec sheets for my engine but didnít see anything related to exhaust gas temp. You are running considerably hotter than I am showing. My M2 engine is rated for about 120hp so At 1800rpm Iím at about 80hp. Iím heading out tomorrow so will see what sort of temps i get at WOT.
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Old 07-16-2020, 08:45 PM   #7
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Originally Posted by Wdeertz View Post
Thanks, I have spec sheets for my engine but didnít see anything related to exhaust gas temp. You are running considerably hotter than I am showing. My M2 engine is rated for about 120hp so At 1800rpm Iím at about 80hp. Iím heading out tomorrow so will see what sort of temps i get at WOT.
My M2 rating is at 121 HP, so pretty comparable.

I usually run at 1,500 RPM, 7 knots, 40 HP, 2 GPH. So I'm not doing much more than getting the thermostats open. After almost 3,000 hours, I still have all the paint on the exhaust manifold.

Ted
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Old 07-16-2020, 09:17 PM   #8
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I had a boat with J&T 8v92 TI's that ran (on the edge, I suspect) at 950.
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Old 07-17-2020, 01:43 AM   #9
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I had a turbo installed in an F350 years ago. If I remember the max was around 850 degrees. I tried to stay under 750 just to be safe. I could tow 25,000# without going over 750 so that was fine. 550 degrees at those RPMs sounds about right.
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Old 07-17-2020, 09:40 AM   #10
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Quote:
Originally Posted by O C Diver View Post
I have a JD 4045TFM75 in my boat. Not exactly the same, but really close. My engine is mechanically injected but electronically controlled. It was available in 3 HP ratings. To change HP you reprogrammed the computer, nothing else. Being OCD, I have all the spec sheets for the 3 different HP ratings and the maximum exhaust gas temperatures.

107 HP @ 2400 RPM 743 degrees F
121 HP @ 2500 RPM 763 degrees F
135 HP @ 2600 RPM 795 degrees F

Hope that's useful.

Ted
Ok got out on the water today and ran it hard for 5 minutes at WOT 2400rpm and the exhaust gas temp got to 750f and held steady. I guess Iím within spec given your provided numbers. Iím surprised that the last 400-500rpm added 200f but I guess thatís where the HP kicks in.

Thanks for all the replies.
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Old 07-17-2020, 11:17 AM   #11
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Quote:
Originally Posted by Wdeertz View Post
Ok got out on the water today and ran it hard for 5 minutes at WOT 2400rpm and the exhaust gas temp got to 750f and held steady. I guess I’m within spec given your provided numbers. I’m surprised that the last 400-500rpm added 200f but I guess that’s where the HP kicks in.

Thanks for all the replies.
Yes, you could have easily doubled the HP / fuel burn in the last 400 RPM. The propeller HP absorption curve gets very steep at the far end of the graph. Not uncommon to see the HP (and fuel burn) requirement double for the final knot of speed on a hull in displacement mode.

Ted
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