Do we ruin our engines if we only run at slow speed

[About Time]

Hi,

I hope someone in the forum can help ... I have discussed with a guy from our yacht club if extended sailing at 1,000-1,500 RPM is actually bad for the engine or not. We both have KAD 44/ 300's and these engines are equipped with kompressor, intercooler and turbo and is good for ard. 3,500 RPMs. I know the answer is more easy if I asked if extended sailing at very high revs is good or bad but what if we are talking extended sailing at low revs ? .... I personally try to do at least 20% of my sailing at high revs and 80% at the 1,500 RPM level. He seems never to go fast and cruises always at 1,300-1,500 RPMs. We cannot find anything in the manual about this ... but we both know that a car that is running around in the city only and never hits the highway may live a tougher life than the car living 'outside' of town.... Thanks for the feed back.

 

[Chris_d]

In my personnel experience there are 1000's of boats with turbos, inter coolers etc.. Running at 5 knots up and down the Thames with no I'll effects, it's generally a complete myth. however having said hat I understand that specifically the volvo Kad44/300 does have a problem with oil supply to the head at constant low revs, Volvo Paul can advise.

 

[Lon nan Gruagach]

The problems that occur at low revs are due to reduced oil flow. Generally this may mean increased wear, it all depends on engine and oil pump design. The problem can be exacerbated by demanding high power at low revs, its an unlikely situation to occur on boat since load is a function of revs (low revs == low power), cars are a different story, flooring it at low speed in a high gear is the worst of everything: low oil flow/pressure, high bearing loads.

 

[About Time]

Chris, - you say the the 44/300's does have a problem with the oil supply to the head at constant low revs..... Should that not be seen on the oil pressure meter ? - my engines show an oil pressure ard. 55-65 no matter I run at low revs (1400) or at WOT.

 

[Nick T]

You might find the following article useful:
http://proboat.com/why-you-shouldn-t-go-easy-on-a-diesel.html
I also understand from a marine engineer I know that providing the engines are correctly 'run-in' with a couple of hundred hours on them, the risk of 'glazing' is minimal providing they are run at around 80% occasionally (as per article above). I run my twin TAMD 61's similar to as stated in the article without problem.
Correct servicing IMHO is essential

 

[Portofino]

It's a complex subject .
1- One issue of low revs is cylinder bore wash -un burnt fuel dissolving the oil film from the rings in the cylinder walls.
Leads to glazing and eventually loss of compression .
Another issue related to above depends on the injector pump /ecu will be the spray pattern .Sub optimal pattern for prolonged periods may lead to piston and or valve pitting. .

2- In the 44/300 series ( -I had one boat with a pair ) the compressor kicks in @ 1400 and drops out -at 2600 -when the turbo takes over .It's only supposed to run for a short ish ? While until turbo kicks in
So really prolonged periods between 14-2600 rpm should be avoided .They are high speed diesels .This range will prematurely kill the compressor only ,not the rest of the engine .
That leaves below 1400 really -which piont 1- above applies .

Or over say 2800 ,3000 to 3100 being optimal Taking into account 10% less than WOT (give or take seasonal fouling issues from 37-3900 ) .
Having said that above for Volvo 44/300 ,s
Some desiel engines will be better suited to low rpm esp larger ones without compressors or even turbos .
Some turbos are better cooled ,some Lub systems and injector systems are better suited to low rpm .

complex subject !

 

[oldgit]

Chum of mine runs a pair on a Brava on the Thames.No known issues.Although boat does have the odd blast when going down to the London tidal marinas.
Shame about the awful deafening ear splitting racket all those belts/blowers create at low revs and the banshee wail at all other speeds..
Nicely compliments the lurchy jerky clunk of those MS4 gearboxes.
Neat combination Fairline.

 

[Momac]

I had a boat with a single kad32's for 6 years and some 600 engine hours . Ran it mostly at river speeds other than the occasional blast when no one was looking and a once a year opportunity for longer fast runs. The engine always performed as it should when asked. When serviced at about 500 hours from new one of the valve clearances needed a very slight adjustment - the first time the valve covers had been off.
My present boat , which I have had for a year and I have added 130 engine hours. It has twin kad32's and is a much more capable sea boat than the last one . It also spends a good deal of its time at river speeds - we did do a much longer sea run this year with no issues. I do have the engines serviced every 100 hours or once a year which for me is about the same thing.
I do use a fuel additive, Marine 16 diesel fuel complete , and I believe this helps keep the engines running sweetly at prolonged river speeds.
So I would say from my experience over several years and above average use , slow running has caused no apparent issues.

I understand the kad300 and kad44 has potential issues with oil not reaching the front end of the valve gear when run at slow speed so potentially causing premature wear.

.

 

[About Time]

Hi all,

Thanks a lot for all your responses. New to me to avoid 1,400 - 2,600 RPM due to the compressor ... Otherwise it sounds like a good idea to go fast occassionally - at least it does not hurt and it is fun
Wish all a good season.

 

[rafiki_]

It's a complex subject .
1- One issue of low revs is cylinder bore wash -un burnt fuel dissolving the oil film from the rings in the cylinder walls.
Leads to glazing and eventually loss of compression .

I'm not sure this is right for a diesel. I'm not an engine expert, but I think this comment applies to petrol engines, where the unburnt petrol acts as a solvent. Diesel is further down the oil chain and I don't think it will clean the bores. Unburnt diesel might generate deposits over a longer period, and I think this is what glazes the bores. Others more expert than me will probably comment.

 

[scubaman]

Regarding the compressor on the volvos mentioned; a volvo engineer once told me that they should be good for around 10000 hours without rebuild/replacing. Based on that there shouldn't be a need to avoid running on the rev range they operate on.

A complex subject indeed. Imho, practical experiences of running engines at lov revs without a problem are a bit meaningles when the engine hours are still on the hundreds. The potential problems would likely manifest themselves a bit further on in the engines life span.

 

[Portofino]

Think it's actually the "clutch " and the electronic bits that operate it , that knacker with constant comp run 1400-2600 rpm .
Comp oil change is somthing like every 100 hrs ,it starts off clear comes out brown ..
Any how they are bolt on -belt driven easy change out .

American sport fishers retro fit a cut off switch to turn the comp off at say 1800 rpm trawl .

Issue here I think is what's going on in the cylinders and oil Lub channels as mentioned -which you can,t really see until it's too late .
Buy really hours wise as you infer we need calibration ,are talking a few 100 or 1000's + ??
Volvo 44 / 300 series
Another variable is oil change frequency and exactly which oil .-multi variable complex subject -engine life .