Possible engine problems ?

[segaerta]

To all engine mechanics amongst you (and I'm not one of them hence this question) :

Recent thread about KAMD300 issues, where Volvopaul commented "engine should be run at cruising speed all the time and was not designed to run at a slow river speed" got me worried a little.

As I typically only spend 20% on the plane and 80% at slow speeds along rivers, canals and estuaries (we're not based at the coast), I'd like to understand if there are any particular risks with VP KAD or Cat 3*** engines when run at slow speeds for most of the day ? If so, what are these issues and can they be easily prevented / remedied ?

Planning to upgrade to two diesels next year w/o changing cruising habits. I'm not looking at the typical river boat either as I still enjoy "travelling at the speed of life" as Princess puts it so nicely in their ads.

Thanks and cheers,
Alain

 

[lewi]

engines of all kinds. diesel or petrol have one common
need.
load. look in any car manual it will say start engine, engage
gear and go.
one thing diesel engines in particular dont like is long
periodes of running off load.
the speed is secondary, hence full bore clear,s the pipes
just have your drive engaged at the time.
the more it works the more reliable a diesel becomes
(i am ##years a diesel mech.)

i know of volvo bus engines that have 1,000,000plus miles.

 

[peterb26]

I agree with Lewi.

Whilst it might be the best possible circumstances to run at planing speeds some 20% below WOT - I dont think it will do massive damage running at displacement speeds as long as its not absolute tickover.

The worst possible use of a diesel engine is to start it up on the pontoon and let it run at idle or fast idle in neutral as there is no load on the engine at all.

Engines are designed for load - once the prop is turning the load is there.

 

[Garryt]

Talking about cruising speed.....many people say that the revs would normally be about 200 to 300rpm below max (taking into account when the boat has a bit of growth on the bottom, maximum achievable revs will be reduced). If an engine on a boat with a clean bottom is capable of 2900rpm, are you saying maximum cruising revs should be around 2300?

Also, what's the thought on how often you should take the engines up to max achievable revs and for what length of time?

 

[Divemaster1]

Agree with previous posts here... but also remember that whilst under load, it is also important to get up to a proper operating temperature for a good and efficient (as designed) combustion and good lubrication of the systems.

Mine (older engines) are reknown for not liking low load for longer periods, so the lowest RPM I'd like is approx 1250 - 1300 (2300 Max) where the turbo's kick in and engines get up to the lower end of the designed operating temperature range. Below this over prolonged periods (read 5-10hrs) I get carbon build up etc., which clears with a nice cloud of black smoke when we are putting more than 25% load on and operating temp is creeping up.

 

[sos247ltd]

Again agree with all posts. Load and heat is vital on diesel engines. On all marine engines we used to run a 'deglazing/bedding' compound in engines while on load test, when supplied for marine propulsion. It helped a bit but loads of engines still had glazed bores because they were never worked. On twin screw boats being used on inland waterways we suggested the owner runs on one engine, not ideal but less embarassing when both engines smoke badly at low rpm.
Expensive to correct if engines are not run correctly /forums/images/graemlins/frown.gif
Regards

 

[bradtarga34]

We have 2 KAD300's on our boat and do quite a lot of crsuing on The Thames which is only about 1000 rpm for the river speed limit. The probelm we had at such low revs was that there was insufficient oil pressure getting up to the top of the engines and I had 3 duff valves that needed replacing on each engine. Apparently, it is a sort of well known problem for some more reliable mechanics on the river here for these engines, and a fix was available. By the sounds of it, this meant boring one of the oil channels a bit to get more oil pressure up, without it afecting things when going flat strap, and I think it affected the valves at the back of the engine from memory. Nothing like a good blast though to blow those carbon build ups out /forums/images/graemlins/smile.gif