Which Oil..?

pyro225

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Oct 1, 2014
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Hi All,

Really struggling - this is a duplicate as wasnt sure if it should be in mercruiser or diesel section... sorry...

So i have the Cummins/Mercruiser 1.7 dti engine.

Time to service it and the manual only gives me a part number for the oil not the oil itself. A quick goole shows its Mercury 15w30. Problem is there is very little detail on there, and the bigger problem is you cant get it in the uk and no one ships...

So i need to know the best alternative and whether it would be synthetic semi synthetic or non synthetic as google doesnt know that either?

Can i use car 15w40 as i can get that easily?

Finally the dip stick extractor pump- is the kind with the ball that collects the oil any worse than the genuine mercury hand pump that screws on top and has a pipe you can put in say a bucket? again the ball kind is 1/3 the price...

​Thanks!
 

oldboat1

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Pyro -- For what it's worth, the Mercedes recommendation for my '80s vintage 5 cyl. turbo diesels was Mobil1 15w50. That was when synthetics became popular ('90s?). I switched over and have been very happy with performance -- still driving them!
 

Scott Danforth

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the 15w40 will be fine.

I personally hate trying to siphon oil out of the dipstick. are you sure there is not a drain hose that can be pulled out of the garboard plug?
 

alldodge

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use the 15w40
as for the suction pump, use any of them that get the job done. I use the electric pump mounted on the 3 gallon bucket. Others use the tall cylinder and really like it. So long as the oil is warm it comes right out without much issue.
 

oldboat1

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Been using a Topsider pump for a number of years, and works OK -- oil temp hot enough to flow easily. (and agree 15w40 would be fine.)
 

pyro225

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Thanks guys - I might be being stupid - but I see 15w40 mineral oil , 15w40 blend , 15w40 semi synthetic and 15w40 fully synthetic which do I need? Also is any motor oil ok it will be changed 1-2 times a season so not like I'm leaving it for years...
 

alldodge

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Use any of them, changing oil has never damaged an engine, only not changing it. There has not been an engine failure due to oil failure in many years, only not changing the stuff. I use regular mineral oil, and while blend and synthetic is better, most will not ever use their motor long enough to see the difference

Just my opinion
 

harleyman1975

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Can you find an oil called Shell Rotella? That is specifically meant for Diesels. A Diesel in a Lorry is the same basic engine a the one in your boat. Heck I use Rotella in my v-8 gas engine.
 

WIMUSKY

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Can you find an oil called Shell Rotella? That is specifically meant for Diesels. A Diesel in a Lorry is the same basic engine a the one in your boat. Heck I use Rotella in my v-8 gas engine.


That would be my first choice too...... I've also used it in gas engines.....
 

rbh

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We also use 15-40 in our diesels -- prefer Rottela if its available.
I consider a marine engine similar to a stationary engine like a generator as they are usually working at a higher RPM than a vehicle with a transmission. So I take into consideration engine load and outside temperatures. If it is -30c out 15-40 may be to thick and at 40c 15-40 may be to thin.
 

HT32BSX115

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If it is -30c out 15-40 may be to thick and at 40c 15-40 may be to thin.

If it's -30c out........don't think the boat is going to float very well......unless it's an icebreaker! 15W40 is fine for all boating conditions.
 

pro-crastinator

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Just a little background, Diesel oils like rotella are better at suspending carbon and keeping things "clean" (er).
Synthetics are even better at this specific task.
That being said, I prefer to use conventional oils on new engines and synthetics in higher mileage power plants.
An automobile mileage example would be 50k miles and up go with synthetic.
Alldodge is absolutely spot on when he says the only real mistake is to not change it.
just my 2cents good luck
 

oldboat1

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rule of thumb used to be you had to stick with a synthetic once you switched (not sure if the rule has changed -- or was true in the first place.) The mechanic I went to for years used regular Quaker State in my old diesels, until I had the idea to switch to synthetic. As above, his rule was pretty much to use what you like, and change it regularly.
 

pyro225

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Sorry to bring this back up - can I use 10-40 instead of 15-40 - the reason I aski A that is what the road version of the engines uses and I have a load of the stuff...
 

Calae 2000

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Just my 2 cents, I have always thought 10w sae is too light an oil for a marine engine especially a diesel. I too would go with 15w40. An idea, if you know where you previously purchased the 10w40 take it back to the store and see if you can swap it for 15w40. Walmart would do this, perhaps not at other retail stores? Worth a try though...
 

ondarvr

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Just my 2 cents, I have always thought 10w sae is too light an oil for a marine engine especially a diesel. I too would go with 15w40. An idea, if you know where you previously purchased the 10w40 take it back to the store and see if you can swap it for 15w40. Walmart would do this, perhaps not at other retail stores? Worth a try though...

Please expand on that idea, I'm just curious.
 

Calae 2000

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Well in the theory the small number is supposed to be the weight of the oil when its cold outside. The higher number for when the motor warms up to temp. I like Shell Rotella to, either straight 30 wt or 15w40.
 
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