Engine RPMs vs Engine Temp

Marc14857

Marc14857

.
Jun 5, 2004
485
Hunter 44 Mystic, Ct
When motoring on our Hunter 44AC w 4JH4E engine and fixed 3 blade prop, I usually have the RPMs at 1800 - 2000 (3000 max) which feels comfortable and gives us 6 knots +/-. We were traveling home with a group of other boats yesterday (no wind) and had to increase RPMs to ~ 2200 - 2400 to keep up. I noted that engine temp increased significantly but did not overheat. I was wondering at what RPMs others typically motor at and how high does engine temp get. Just want to make sure I'm not pushing engine too hard.

Marc
 
Ralph Johnstone

Ralph Johnstone

.
Jan 4, 2006
7,282
Hunter 310 West Vancouver, B.C.
Marc14857 said:
Just want to make sure I'm not pushing engine too hard.
Click to expand
I'll wait for 4JH4E owners to chime in with specifics, but the last thing you want to do is baby the engine. Normal operation is to load the engine to about 80% of max. or 2400 RPM.

You may be starting to see the effects of not loading the engine sufficiently in the past.
 
B

Benny17441

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May 24, 2004
7,174
CC 30 South Florida
Yes, the higher the RPM the hotter the engine will run, simple physics. These diesel engines run more efficient when hot hence the cruising RPM should be around 80% to 85% of the rated maximum RPM. After a good run, a short "cool down" period of around 5 to 10 minutes at idle speed is recommended before shutting the engine down. Your engine temperature alarm buzzer is designed to warn you well before the engine may reach a critical temperature.
 
Velero49

Velero49

.
Jun 4, 2004
292
Hunter 49 123
What is significantly increased temp? My 4JH4-HTE runs about 165F/2800 rpm with a clean prop and bottom, after 6 month growth it would go to 169F.

Things to check/do:

-Clean prop
-check water coming from exhoust
-Check thru hull intake (seagrass or barnicles)
-Clean hull
-Check engine impeller/replace
-if you have pink/red coolant it should be changed every other year and every 4 years flush and rinse
- Check engine temp with laser


here in FLorida we get a lot of seagrass that plugs the strainers (all of them engine, generator and AC cooling lines).
 
Marc14857

Marc14857

.
Jun 5, 2004
485
Hunter 44 Mystic, Ct
Velero49

All good points. I do need to change out the coolant as it has been awhile even for Extended Protection type. While I understand how to drain the coolant from the petcocks and the water heater, I'm curious how I should go about flushing the cooling system out.
 
R

Rick486

.
Oct 1, 2007
1,865
Boston Whaler Super Sport Pt. Judith
Marc14857 said:
When motoring on our Hunter 44AC w 4JH4E engine and fixed 3 blade prop, I usually have the RPMs at 1800 - 2000 (3000 max) which feels comfortable and gives us 6 knots +/-. We were traveling home with a group of other boats yesterday (no wind) and had to increase RPMs to ~ 2200 - 2400 to keep up. I noted that engine temp increased significantly but did not overheat. I was wondering at what RPMs others typically motor at and how high does engine temp get. Just want to make sure I'm not pushing engine too hard.

Marc
Click to expand
Marc
I run mine at 2350 which with the MaxProp gives me about 7.5 kts. I do occasionally run as high as 2450 which gets me close to 8 with a clean bottom. I change the A-freeze every other year. I have had the mixing elbow removed and inspected by the dealer and it was clean. This spring I had the dealer flush out the heat exchanger and it looked good. I have about 650 hrs or so on the engine, 4JH4E. I don't know what temp it runs at, only that the needle is vertical on the cockpit gauge, and does decrease a lot when I let the engine cool down after motoring. I know Yanmar recommends some running at WOT after running an extended period but I just can't bring myself to do that :)
 
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