Mariner 75hp 2 stroke

Blakeys7 · 17 March 2018, 12:47

Hello

I am just after a little general information regarding my 2004 75hp 2 stroke mariner.

I have it fitted to my 5.2m Rimini rib.

Roughly

1) What would you say its cruising speed would be ?

2) How much oil do they generally use and this is probably linked to my next question

3) How many miles to the gallon/litre would you expect to get ? This would be quite handy to have a rough idea in litres/hour or gallons/hour at river speed and cruising speed. Then I can enter this information on the Nav app.

I know the best thing is to probably go on a longish run to work it all out, however until my experience/confidence gains I would like some sort of idea to start planning short passages.

The engine is current having a service due to old fuel running through it. Ran fine at speed but when ticking over she kept stalling when engaging reverse.

All info greatly appreciated.

B7

Xk59D · 17 March 2018, 13:18

Had one years ago.

Used probably 22-25 litres per hour at 22 knots or so.

Don't know how much oil it used, just kept the on-board oil tank topped up but I guess 40:1 ish

They are thirsty but reliable engines.

Last Tango · 17 March 2018, 16:49

Yeh.

Had one on a Seapro 520. Marginally better than 1ltr/Nautical. I used to calculate it on that basis and it was always pretty close.

WOT four up was about 35kn Cruise about 24kn.

Can't remember exact oil figure but I think it took about a tank full every 120ltr of fuel. This is entirely dependent on the speed though. I think it varies the mix ration from around 100:1 at idle down to about 30:1 at WOT. best to keep an eye on it till you get the feel of it.
The alarm did start to sound quite early, when there was still about quarter of a tank left. Good reliable engine but not the most economical.

uncle al · 17 March 2018, 23:19

I can't help with question one and two, but a guide on fuel consumption is a third of the horse power in litres per hour at wide open throttle. A couple of tips about that engine, the tick over has never been very good, so just bring it down to straight up and down. Set the timing and carburettor setting the idle air setting for all three cars one and a half turns out from lightly seated, ignore the service manual. Regarding car settings, Use only the ngk sparkplugs as per the service manual. It is better to run slightly rich than too weak a mixture. Run a weak mixture the power head goes pop, a major expense.

uncle al · 17 March 2018, 23:20

Car should be carb, damn phone again!

Blakeys7 · 17 March 2018, 23:26

Quote:

Originally Posted by uncle al

I can't help with question one and two, but a guide on fuel consumption is a third of the horse power in litres per hour at wide open throttle. A couple of tips about that engine, the tick over has never been very good, so just bring it down to straight up and down. Set the timing and carburettor setting the idle air setting for all three cars one and a half turns out from lightly seated, ignore the service manual. Regarding car settings, Use only the ngk sparkplugs as per the service manual. It is better to run slightly rich than too weak a mixture. Run a weak mixture the power head goes pop, a major expense.

Thanks for that. I will ring the boat yard Monday and without teaching them to suck eggs, offer your advice 😂

Blakeys7 · 17 March 2018, 23:27

Quote:

Originally Posted by uncle al

Car should be carb, damn phone again!

I knew what you meant 🤔

uncle al · 17 March 2018, 23:33

When I went out and did the annual service on the coast guard boats, all the 75hp that I went to. I put a long bolt through the transom brackets so the OBM would only tilt down to the straight up and down position. They were one of my favourite OBMs. By the way I did customer service/service engineer for barrus the merc mariner distributors for the UK and Ireland.

stul · 18 March 2018, 11:33

why do you do that.Is there a problem with the engine tucking right in ?
Thanks

uncle al · 18 March 2018, 11:45

If you tuck the 75/90hp under because of the design of the cars they have extra fuel going into the cylinders. Keep the OBM up and down stops that happening.

stul · 18 March 2018, 18:42

hi Thanks
Is that at speed or just while just tick over,just trying to learn not questing your knoledge.
I have a humber destroyer 5.5metre with one of these engines been running it around North wales mostlyfor 8 years ,not had many problems.I think 2 times sruggled a little to start and only when we have got the engine warm then cut out for say 5to 10 min that bit when your not sure if you need choke or not but grate engine