WOT?

K

Ken W

Active member
Joined
Jul 2, 2019
Messages
35
Fluid Motion Model
C-302 C
Hull Identification Number
FMLT3123D717
Vessel Name
Tough Guy
New to my Ranger Tug, Tough Guy, an R31S with Volvo Penta D4-300. I usually run at 1500 RPM, 2gph and 6+ knots. I’ve read where some diesels need to be run at WOT periodically. Is this necessary with my boat’s engine?
 
Good question! I've heard this periodically since I have owned a boat and am confused. I run my boat at about 1400 to 1800 rpm for hours, actually about 1900 hours so far. No issues I do on occasion run it up to 75-80% for short runs just because I can't argue this point. I have owned several Dodge trucks with a Cummins engine. If I were to run it at WOT for any period of time I estimate I would be doing over a hundred MPH. Which in Canada gets your vehicle impounded and you get Tarred and Feathered. So ironically the sweet spot on my Cummins at 65MPH is 1800 RPM. If you floor it when accelerating it will rev higher for brief moments while shifting. However as fun as it is I have to back off the throttle and maintain a legal speed or risk sharing a small room with someone. Now to expand on this RPM Sweet Spot concept I have also noticed for years, since my first car, my Dads 69 Plymouth, ran at about 1800 RPM at 65 MPH. (I installed several teenage accessories of which one was a tachometer) Never have I owned a vehicle that the manufacturer recommends running the engine at WOT. Now to debunk this argument further lets add in regular oil changes. I am also a car and motorcycle Nut and have owned several of all over the 42 years I have been driving. I always have done my own regular maintenance as engrained in me by my fore fathers. I have never had an engine failure on anything I have owned. Luck?

I do believe that idling an engine or loading it excessively before it is at running temperature could cause undue stress on the engine. Both scenarios of which brought strong concern and in some cases a firm cranial adjustment by the observing fore father. I have no idea why a boat needs to be run at WOT unless of course you pay for all your maintenance, then the dealer would find this to be imperative and highly recommend doing so as often as possible.

If someone has a better explanation then I would gladly adopt the procedure.

Hope this helps or at least starts a good argument!

Cheers, Leon
 
I don't know anyone who recommends running any engine for an extended period at WOT. Modern diesel engines do need to be able to reach maximum rated rpm. The only way to check for that is to see where the beast runs at WOT. Boats have a way of getting heavier over time as owners load more and more gear and quite often come out of a factory over-propped or suffer prop damage during use. A diesel is basically an air and fuel pump, the two need to mix in the right volumes to burn the fuel efficiently and not coke up the motor through over-fueling. If the engine cannot reach maximum rated rpm the exhaust gas temperature goes to the moon as the engine over fuels while it is off its optimum fuel burn curve, this shortens the life of engines. A pyrometer is often installed in diesel exhaust systems to measure exhaust gas temperatures (EGT). Amazingly, an over propped marine diesel will run much hotter EGT than the same engine propped correctly running at WOT at maximum rated rpm. An incorrectly propped boat running at only slow rpm may, in fact, be running dangerously high EGT. You cannot overspeed a modern diesel as a governor prevents that. You can overload it and shorten its life by having too much prop pitch and not being able to reach maximum rated RPM. I can assure you Dodge and Cummins did lots of work to be sure the maximum EGT was acceptable (probably about 850F) on those trucks through choosing correct gear ratios. Also, the Dodge truck engine from Cummins is greatly derated in HP compared to the marine version of the B series engine to provide a further safety net against over fueling. Leon, your dad's Plymouth didn't have a common rail diesel, great car but not the same type of motor at all. Ken, run your motor at WOT once in a while and make sure it gets to the maximum rated rpm, if it runs a little over that is perfectly ok, if it comes up short and you have a clean bottom consider having your prop tuned.
 
The general advice that has been given here over the years is to periodically run close to WOT but for 5 mins or less.

The idea behind this is to clear out carbon residues that can build up and stick to the valves, cylinders and piston heads due to running the engine at low RPM for long periods.

It's an easy thing to do and I typically do it when some 1 mile out from the marina or anchor spot after a cruise period of several hours.

On my D4-300 the WOT RPM value is at 3650. I will run WOT at around 3500 to 3600 for 5 mins or less as described above.

As an aside, I followed this same procedure on my R-25 Classic with its Yanmar 4BY2 150 HP engine.
 
Hi Ken,

We have the same boat (R31S) that I just bought, it's a 2014. The former owner and my very knowledgeable broker said that this engine is in its happy place at 80% of WOT or 2850 RPM which for us is about 14-15 knots. I am not super psyched at the 10 gph fuel economy at that RPM, but for shorter runs around the sound, it works well. I'm no engine expert, but I heard that it is important for the turbo that the engine occasionally operates at higher RPM to give it some exercise. Would love to hear from anyone that is an actual Volvo-Penta Diesel engine expert on the subject.

John
 
Hey John:

The people/technicians at La Conner Maritime Services are qualified Volvo engine technicians. Give Mark Crandall (the Service Manager) a call at 360-466-3629 and ask your question(s). He may refer you to one of his Volvo certified technicians.

Post back here what answers you get... thanks. 🙂
 
We also have the R-31S. According to Volvo, the rated engine speed is 3500RPM https://www.volvopenta.com/marinecommer ... ation.html
I as well can get to ~3600RPM WOT which has lead me to think (and post once) that the boat is under propped. Even with full fuel, full water, 4 people on board and some growth, I'll still get to about 3600RPM.

So my suggestion is to watch your engine speed and don't blindly hit the stop on the throttle
 
At 3200 rpms, I'm burning 13 gph and traveling 16.5-17knots. WOT is 3500. I've got the 31 command bridge and hard top over the rear cockpit (added weight).
Bobby
 
This is a question with a lot of opinions. I have asked Volvo technicians this question and received answers from "run it hard", "run it at 80% load" "Run it according to the owners manual" "new common rails can be run where ever you want to run them" "run it under 50% and it will last forever" "run it no higher then 80% load, make sure the engine can make and maintain rpm 2% to 3% above the manufactures recommend WOT RPM full fuel, water, passengers and gear, use the manufactures fuel and load curve to compare your results. If you do this run the engine where ever you want for extended period of time". Exception"if the engine is equipped with a VGT turbo periodic WOT and higher rpm operation is desirable to exercise the turbines vane plate.
D4 compare your running results to the graph https://pubs.volvopenta.com/ProdDocs/Ho ... ng=en-USD3

D3. https://pubs.volvopenta.com/ProdDocs/Ho ... lang=en-US


Volvo D3 have a VGT, D4 Volvos I believe use a waste gate.

I asked a Volvo engineer that works with Fluid motion industries what max rpm I can run for extended time. The first question he asked was "what is your max RPM?" answer "4030 rpm", ( 2% to 3% above manufactures recommended is 4080rpm to 4120 rpm) He said " no more than 3400 to 3500 range". If I'm running at a lower rpm cruise 2250 rpm I'm completely comfortable with running there. If I'm running at my high cruise rpm I adjust my max rpm speed based of GPH fuel use.( D3 does not show engine load) In normal sea and wind conditions with fuel and water full and gear onboard I can turn 4030 rpm. At 3380rpm my fuel burn is 8.4 gph. which based on the Volvo graph showing I'm slightly over propped. When I get in a 2' sea with wind I have seen the gph increase to over 9gph and when in a tough climbing out over 10 gph but my rpm has not changed. I'm loading the crap out of that little engine ( way over the recommended fuel curve). I bring engine speed down so I don't go over 9gph which is slightly below 80% load.

If propped correctly run it where ever you want below 80% load. I have used this Volvo technicians advise along with the Volvo engineers advise.
( "run it no higher then 80% load, make sure the engine can make and maintain rpm 2% to 3% above the manufactures recommend WOT RPM, full fuel, water, passengers and gear, use the manufactures fuel and load curve to compare your results. If you do this run the engine where ever you want for extended period of time".)

I need to either evaluate what gear needs to go or re-prop to get the rpm up to 3% to reduce load on the engine.

Engine rpm - GPH first season WOT rpm 4150

2250. 2.2
3250. 6.9
3380. 7.8
3600. 8.7
4000 12

Engine rpm -GPH now. WOT rpm. 4030

2250 2.8
3250. 7.6
3380. 8.4
3600. 9.4
4000. 12

All values clean bottom and good weather conditions. Time to unload or prop change !!
 
As always, great information Brian. How do I get the link to the D3 150 info?
 
Ken W":1kum2joj said:
New to my Ranger Tug, Tough Guy, an R31S with Volvo Penta D4-300. I usually run at 1500 RPM, 2gph and 6+ knots. I’ve read where some diesels need to be run at WOT periodically. Is this necessary with my boat’s engine?
Click to expand...

In short, YES, but not necessary unless you want to have and keep a well running and well performing diesel for a long time.

I recently brought this aspect up with a certified Volvo engine technician with over 30 years of experience under his finger nails (named Scotty).... here's my report of the conversation (taken from another posting I made under Installing Low Speed on D4 300).

"...I quizzed Scotty about running the engine at 700 RPM for extended periods while trolling for fish.... and Scotty additionally replied with some information that addresses another recent post elsewhere here about WOT being used at times and was it necessary ? Scotty said it was very useful to run at high RPM periodically to raise engine temperatures to 'burn off' oily/carbon residues in the Turbo conduit connections and the Turbo vanes as well as the charged air unit (the big finned green box hanging on the upper aft port side of the engine). The charge air unit has many small diameter tubes inside and the moist air mixed with some exhaust oily/smutty fumes will over time build up on the tube's outer surfaces and affect the ability to cool the charged air. Running at high RPM periodically will cause sufficient heat to be built up that will deal with these items and keep the residue build up to a minimum, allow the engine to run smoother, and provide a cleaner exhaust."
 
We attended the Volvo D4 lecture last year at the Ranger Tug Roche Harbor Rendezvous. The Factory Volvo Penta people were there as well as the Volvo Penta techs from Pacific Power Group. They both said that the D4 maximum rpm is 3500. They suggested periodically running it up to that limit for 5-10 minutes as others mention here.

They also said that the D4 will run at 90% of full rpm (3150 rpm) "all day long".
 
Hmmmm... My 2019 R29 CB NW Edition has the D4-300 and at WOT it climbs to 3650 without any issues. I wonder where the 3500 comes from and also wonder if 3500 is supposed to be the max RPM how come mine is 3650 ?
 
baz":10e1nvvy said:
Hmmmm... My 2019 R29 CB NW Edition has the D4-300 and at WOT it climbs to 3650 without any issues. I wonder where the 3500 comes from and also wonder if 3500 is supposed to be the max RPM how come mine is 3650 ?
Click to expand...
3500 rpm is the rated recommended rpm. If properly propped you want the engine to turn 2% to 3% above max. So you are 40 rpm above 3%. Less load on the engine is much better then being on the other side of the curve. I would be comfortable running your engine that turns 3650rpm all day at 3150 rpm. I would not run a engine that turns Max 3500rpm at 3150rpm all day it’s to close to being on the edge. We all have opinions on this. I prefer less load on these small displacement, high speed diesels. Increases longevity.
 
BB marine":1w6vd6cj said:
baz":1w6vd6cj said:
Hmmmm... My 2019 R29 CB NW Edition has the D4-300 and at WOT it climbs to 3650 without any issues. I wonder where the 3500 comes from and also wonder if 3500 is supposed to be the max RPM how come mine is 3650 ?
Click to expand...
3500 rpm is the rated recommended rpm. If properly propped you want the engine to turn 2% to 3% above max. So you are 40 rpm above 3%. Less load on the engine is much better then being on the other side of the curve. I would be comfortable running your engine that turns 3650rpm all day at 3150 rpm. I would not run a engine that turns Max 3500rpm at 3150rpm all day it’s to close to being on the edge. We all have opinions on this. I prefer less load on these small displacement, high speed diesels. Increases longevity.
Click to expand...

Define "small displacement" ... my D4-300 is 3.7 liters in size and that IMO is a BIG 4-banger with each cylinder being close to 1 liter.
 
BB marine":284l2nab said:
Define "small displacement" ... my D4-300 is 3.7 liters in size and that IMO is a BIG 4-banger with each cylinder being close to 1 liter.
Click to expand...

Barry, you are correct 3.7L or 225 cubic inch engine is a big four cylinder engine. It would be a work horse with rated Hp in the range 40 to 50 hp per liter so max around 200hp. When it has an output of 300 hp equalling 81 hp per liter. I consider that a small displacement 300hp Diesel engine. I think it is a good engine with plenty of power available to use but proper propping is very important to maintain longevity. Don't over prop them. Your engine rpm numbers are optimal. ( My opinion)
 
Brian: I really like this D4-300. It has plenty of grunt and it can provide a good sudden felt thrust forward when called for.... Oh and it's nicely and unbelievably quiet IMO with the excellent hatch sound insulation. Apart from the fwd end of the engine's belt location it has plenty of access for maintenance.... Oh, and I like the large oil retrieval pipe/tube on its starboard side for extracting the old oil rather than using the dip stick tube. It's just a very nice performing engine for my size boat.
 
For anyone concerned about your fuel efficiently at higher rpm, th eD4-300 will get about 1.2 NMPM from about 8 knots and up on a R31cb. So the only question is how fast you want to get there.
 
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