R-21 Classic Engine Heat

[tlkenyon]

Nellie May is a 2005 R-21 Classic with the 3YM30. The previous owner installed a water temp gauge, so it is possible to see what is going on in real time. He also installed an oil pressure gauge (50 psi above idle). The water temp usually runs at 160 degrees F, up to about 3,000 RPM, where it starts to climb. Above that, the temp climbs steadily, reaching somewhat of a plateau at 190 @ about 3500. WOT is about 3,850 or so and the within about 2 or 3 minutes at that speed (about 9 mph by GPS) the temp climbs to 205 or so and the high temp alarm goes off.

The closed-loop cooling system is full of anti-freeze. There is no unusual exhaust color, except it gets kinda steamy at WOT. There is a lot of fresh water going thru the system. Upon inspection, the pump impeller shows no wear. I took the screen out of the fresh water strainer and ran without it (in clear, 50 degree springtime water) to see if less restriction in the system would help. Nope. The engine has about 190 hours.

It this normal? Is the cooling system just inadequate to deal with the WOT temp load? Would a bigger pump and bigger hoses assist? We expect to do some river travel and may need WOT for more than just 2-3 minutes at a time.

A search of TugNuts did not reveal info on this topic for the 3YM30 (that I could find). Thanks in advance for the information.

TK

 

[RProffer]

I believe the max throttle rpm for the 3YM30 is supposed to be 3600, and you should run that for no more that 5 minutes in an hour, and you should run it at 3600 for 5 minutes each hour to clean out the carbon. Running at length at a higher RPM can cause over heating and other problems. Check out page 9 of the Operations manual. There is additional info in other sections of the Operations Manual and the Service Manual.

Depending on conditions, I usually get 9 MPH at 3400 or 3500 RPM. If the wind is right, and the water conditions are right, and the moon is in the right phase and I am going down hill - I can get 10 MPH at WOT - sometimes. 😉

 

[SlackwaterJack]

RProffer is right. WOT is to be avoided for anything other than very short bursts. I'll add that the speed differance from 3/4 to WOT is not enough to warrant the huge fuel penalty. The cooling system is sized correctly. I'm fairly certain that the hoses etc.. are sized to allow the heat exchanger to flow to it's rated capacity and if the hoses were increased it wouldn't change anything..you'd need to install a larger heat exchanger.
I operate year-round on the Snake River and the current can get up to 7-8 mph (like today*). I can still make headway in my 21 but I try to start out heading upstream for the day, that way when I want to head home I can be there reeeaally fast. The 21 is a pretty slippery shape in the water and she seems to push through the current well.
If you're not in a hurry, 3/4 throttle should get you there...if the river is too fast for that, you may want to think about running your trip from an upriver start (ain't trailers great)

* in the interest of full disclosure...I wasn't on the river today(I just looked at it), the problem with fast water this time of year...too many trees! 🙂


how to get a 21 to exceed 9 knots

 

[Dave and Genny]

Slackwaterjack!!! I love you last comment and the photo!

 

[captainmike]

It took me a while to figure out what was causing my overheat and steam exhaust at wot.

The answer was where the water was injected into the exhaust manifold was scaled up with salt and crud I removed the small brass 90 degree fitting and cleaned everything out with a coat hanger .

I have a Yanmar 3gm generator in my charter boat the Boston Belle www.bostonbellecharters.com and when I removed the exhaust elbow it was restricted with carbon so I plan on removing and inspecting the exhaust elbow on my Ranger M21 " AURA"

 

[tlkenyon]

Thanks y'all for the great responses. I will stay away from WOT except as needed for the periodic "cleanout." I wonder if anyone has prepared an RPM/Speed graph for the Classic R-21 (displacement hull)? Being a numbers geek, I am going to do that and post the results. Should be interesting. THANKS AGAIN.