What type of oil and lube to use

[Lou C]

I don't think you can go wrong using either Rotella or Delo in the 15/40 viscosity range.

 

[Lou C]

Ah. Didn’t know that. They always said to use Volvo oil like that…but at least had the sense to suggest alternatives on the grade scale. Mercury didn’t and made their own weight and grade up. Presumably for the coin. Whole I’m having a moan…I might as well mention just how bad the quicksilver 25w40 oil is. Terrible stuff. I got analysis done on it after 50 hours. Compared to a U.K. brand called rock oil with 50 hours on it 6 months later. The difference between them was unreal. The quicksilver had totally broken. Down and lost property. Terrible

That's interesting because I did a couple of oil analyses of Chevron Delo straight 40 and and the Merc/Quicksilver 25/40 and the Merc/Quicksilver oil held up just as well, but this was a long time ago, maybe 10 years.
I'd like to see back to back tests of the Merc/Quicksilver and the 15/40 from Rotella and Delo, since those are probably the most commonly used motor oils in inboards if you're not using the Merc/Quicksilver stuff.
There is another option, Lucas oil makes a high zinc 20w/50 marine motor oil, not sure how these perform because they are not used much (expensive) but the specs look good.

 

[QBhoy]

That's interesting because I did a couple of oil analyses of Chevron Delo straight 40 and and the Merc/Quicksilver 25/40 and the Merc/Quicksilver oil held up just as well, but this was a long time ago, maybe 10 years.
I'd like to see back to back tests of the Merc/Quicksilver and the 15/40 from Rotella and Delo, since those are probably the most commonly used motor oils in inboards if you're not using the Merc/Quicksilver stuff.
There is another option, Lucas oil makes a high zinc 20w/50 marine motor oil, not sure how these perform because they are not used much (expensive) but the specs look good.

To be honest. The rock oil I compared it to was a 15w40 and a well known top quality brand here for decades. It may be the case that the Quicksilver oil is just as poor as many others….but certainly in comparison to the rock oil…it was particularly poor in comparison, for degrading. Same boat. Same conditions and use. Just 6 months apart or so.

 

[Lou C]

To be honest. The rock oil I compared it to was a 15w40 and a well known top quality brand here for decades. It may be the case that the Quicksilver oil is just as poor as many others….but certainly in comparison to the rock oil…it was particularly poor in comparison, for degrading. Same boat. Same conditions and use. Just 6 months apart or so.

Ok here are some of my results from quite a while back...

Chevron Delo straight 40 Merc/Quslvr 25/40 should be
SUS vis @ 210*F 67 81.1 68-78
Sst Vis @ 100*C 12.16 15.79 12.4-15.3
Flashpoint in *F 330 420 >365
TBN (didn't test for this) 6.6

Based on this I kept using the Merc/Quicksilver to the present day, the Chevron was tested 11/15/11 and the Merc/Quicksilver was tested 9/23/15

I should probably do another one this coming season, I pulled out a sample last year (2020) if I can find it I'll send it off.

 

[Lou C]

unfortunately that didn't format quite right lol let's try again:
Chevron Delo straight 40
sus vis @ 210*F 67
ssts vis @ 100*C 12.16
flashpoint 330*F

Merc/Quicksilver 25/40
sus vis @ 210*F 81.1
ssts vis @ 100*C 15.79
flashpoint 420*F
TBN 6.6

results should be (from Blackstone Labs)
sus vis @ 210F 68-78
ssts vis @ 100*C 12.4-15.3
flashpoint >365

The other option one would have and it has been recommended by Merc in the past is a 20w/50. While Merc has recommended straight 30 (under 50*F) and straight 40 (over 50*F) as well as 20/40 (impossible to find) and 20w/50 (not common but can be found) they to my knowledge never recommended a 15w/40 which many people use. While Volvo has recommended a 10w/40 it's important to note they were recommending the syn version not dino.

My own backyard mechanic test of oils is this, run the boat up on plane for a while, then let it drop off plane and bring it back to idle, if your hot slow idle oil pressure is 20 psi or higher the oil is not shearing down or thinning out excessively. If you get less than that, maybe it is.
Having said that my hot slow oil pressure with the Merc 25/40 is just as good as it ever was with straight 40 Chevron Delo. So to me that's good enough! I could try the 15w/40 from Chevron or Rotella but I don't mind paying a little extra for the regular version of the Merc oil vs the 15w/40.

Just did an oil change and winterization on my brother's new boat with the Merc 4.5 V6, they say to use the Merc/Quicksilver semi-syn 25/40 so that's what we used. Oil pressure readings are excellent, brand new engine lol.....

 

[QBhoy]

unfortunately that didn't format quite right lol let's try again:
Chevron Delo straight 40
sus vis @ 210*F 67
ssts vis @ 100*C 12.16
flashpoint 330*F

Merc/Quicksilver 25/40
sus vis @ 210*F 81.1
ssts vis @ 100*C 15.79
flashpoint 420*F
TBN 6.6

results should be (from Blackstone Labs)
sus vis @ 210F 68-78
ssts vis @ 100*C 12.4-15.3
flashpoint >365

The other option one would have and it has been recommended by Merc in the past is a 20w/50. While Merc has recommended straight 30 (under 50*F) and straight 40 (over 50*F) as well as 20/40 (impossible to find) and 20w/50 (not common but can be found) they to my knowledge never recommended a 15w/40 which many people use. While Volvo has recommended a 10w/40 it's important to note they were recommending the syn version not dino.

My own backyard mechanic test of oils is this, run the boat up on plane for a while, then let it drop off plane and bring it back to idle, if your hot slow idle oil pressure is 20 psi or higher the oil is not shearing down or thinning out excessively. If you get less than that, maybe it is.
Having said that my hot slow oil pressure with the Merc 25/40 is just as good as it ever was with straight 40 Chevron Delo. So to me that's good enough! I could try the 15w/40 from Chevron or Rotella but I don't mind paying a little extra for the regular version of the Merc oil vs the 15w/40.

Just did an oil change and winterization on my brother's new boat with the Merc 4.5 V6, they say to use the Merc/Quicksilver semi-syn 25/40 so that's what we used. Oil pressure readings are excellent, brand new engine lol.....

That’s great info Lou. Perhaps not too far off what might be expected between the two. One being a straight 40 and the other a 25w40. Suppose it would depend on hours and type of use between them too. Since the 25w40 synthetic blend quicksilver came available and since I’ve owned the boat with the MPi in it…I’ve used that, but only for reasons around the service history file and trying to keep to OEM. That seems to keep its firm and shows better idle oil pressure at the end of the season, compared to previous boats over had using the normal 25w40. But the big difference between these two examples is that the mpi will have very little fuel wastage and washing into the oil, compared to the carbs I’ve had previously. If I was t fussed about OEM service history, I’d be definitely using rock oil again on the Mpi. I use that for the 2016 Merc 115 outboard I have. It’s great stuff for that. Being a little less precious about that boat and engine, I don’t mind so much.
On the synthetic blend quicksilver stuff. To be fair to that…I know of a few guys with carb Mercruiser who have changed over to that instead of the normal quicksilver. They all report better oil pressure at warm idle at the end of the season, than previously did. So it’s clearly better stuff than the normal oil.