Mercruiser engine oil.

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LouDoo

Premium Member
Premium Member
I've been using Mercruiser 20W-40 full synthetic engine oil in my 3.0L (GM) mercruiser engine. Over the weekend I picked up supplies to winterize the boat, and the dealer informed me that mercury is no longer carrying the full synthetic oil, instead they are selling a 25W-40 synthetic blend. The dealer still has some full synthetic in gallon jugs, problem is no quarts.

So my question is: should I continue to use the full synthetic, which means buying 2 gallons, or just use the synthetic blend? Or just switch brands I know a lot of guys use Rotella oil in Mercruiser. [MENTION=65307]Sportster-2001-951C-Stock[/MENTION] can probably answer the question, but I thought I would put it on the public forum in case someone else runs into this.

Lou
 
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Rotella is a great oil, and the price is great. Personally... I'd say it's time to switch over.

That's what I basically did when BRP decied to change supplyers on the 2-stroke oil. Why be the guina pig with a new product?? Just switch to somehting that is proven. (In my case, Quicksilver PWC)
 
So if I made the switch, Rotella doesn't have a multi-weight synthetic oil, my friend at the marina here says to use straight 30wt. Is this sound advice, I don't think I have ever used the boat unless it was at least 60 degrees.

Lou
 
I think the T6 is a multi synth. Let me check.....



****EDIT*****


Yes... the T6 is a 5w-40. Remember... the 5 is for the cold start... but it's a cold flow number. It should protect your engine just fine.
 
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I've been using Mercruiser 20W-40 full synthetic engine oil in my 3.0L (GM) mercruiser engine. Over the weekend I picked up supplies to winterize the boat, and the dealer informed me that mercury is no longer carrying the full synthetic oil, instead they are selling a 25W-40 synthetic blend. The dealer still has some full synthetic in gallon jugs, problem is no quarts.

So my question is: should I continue to use the full synthetic, which means buying 2 gallons, or just use the synthetic blend? Or just switch brands I know a lot of guys use Rotella oil in Mercruiser. [MENTION=65307]Sportster-2001-951C-Stock[/MENTION] can probably answer the question, but I thought I would put it on the public forum in case someone else runs into this.

Lou

I would advise against using a synthetic oil in a flat tappet motor, too much risk of wiping a cam lobe. Something with a cam lube is a better choice, think about a straight 40wt, which is what we use here (NAPA Fleet Oil).
 
I would advise against using a synthetic oil in a flat tappet motor, too much risk of wiping a cam lobe. Something with a cam lube is a better choice, think about a straight 40wt, which is what we use here (NAPA Fleet Oil).

I kind of agree.

Most modern oils have removed most of the sulfur, and zinc. That's what protects the iron/steel parts of the cam/lifters. But, most syth oils have more than enough sheer strength to protect the parts.

Also... Diesel oils are full of additives to protect conventional cam systems. My last Cummins had 265K miles on it... and all I fed it was T5 and T6.
 
I kind of agree.

Most modern oils have removed most of the sulfur, and zinc. That's what protects the iron/steel parts of the cam/lifters. But, most syth oils have more than enough sheer strength to protect the parts.

Also... Diesel oils are full of additives to protect conventional cam systems. My last Cummins had 265K miles on it... and all I fed it was T5 and T6.

I'd agree on dino diesel oil but I've seen what happens to flat tappet cams with synthetic oil on dry starts the lobes get wiped b/c synthetic runs right off the cam while it sets for weeks unused.

Also check the cam manufacturers break in instructions, specifically advises not to use synthetic oil b/c the synthetic is too slippery to cause flat tappet lifter rotation. 2nd fastest way to wipe a lobe is to have a lifter that's not rotating, that's why we don't reuse lifters with a new cam.

Mercruiser cams are very high quality but no cam can take this kind of abuse. You want the best solution I can imagine, stick with merc dino and you will be running that same motor till the day you die.
 
I bought this boat from a friend, and that's the oil he used since new, I changed to full synthetic last year, so I guess in life and politics, change is not always a good thing.

Just my opinion, I think the reason full synthetic oils have become so popular is automobile manufactures have used the synthetics to boost car mileage, but not always the best for engines.

Thanks for the advice guys I'm going back to Mercruiser 25w-40 mineral oil. BTW, it's 26.00 a gallon at the dealer, not too bad.

Lou
 
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Lou... honestly... use what you want. I doubt you will put enough Hr's on the engine to ever cause an issue.

What Sportster and I are talking about is a real issue. BUT... just like any other debate... there are 2 sides.

The facts are:

1) Newer, "Slicker" oils are not protecting iron/steel cams, with flat tappets.

2) It's because of the loss of good high pressure lubes. In most oils it was zinc compounds.

3) SOME older straight weight oils have the old compounds, and protect better. (Beware of non-detergent oils)

Here's where some of the "Gray" comes in.

4) Once you wear the oxide coating off the cam... it wears quickly.

5) Even running proper oils... there are cases of cams wearing out.

Because of that... what % of OLDER engines have been destroyed because of newer oils... and how many would have warn out regardless?



I basically just threw that out there to give you the knowledge of what's going on.

So... with that said... I totally agree with Sportster. BUT... I have personal experience with the Rotella oils in flat tappet engines. AND... with springs that are SIGNIFCANTLY stronger than a typical gas engine. (Since they have to hold back 40 lb of boost pressure)


Anyway... this is the same as any oil debate.
 
Tony, as you probably already know, I'm an OEM guy, my way of thinking is there must be a reason Mercruiser pulled the full synthetic oil after marketing it for only a year. Mercruiser 25w40 mineral oil is what's recommended in the service manual. And after reading your's and sportster's opinions, two of the most respected members of this forum, that's what I have decided to use.

Lou
 
Great.

Take your plan, and run with it !! That engine will probably out live the rest of the boat.


FYI... the new oils are pulling even more of the metal compounds out. So, older engines will be having even more issues.
 
There are some gray areas Tony, all I can offer is what I've seen. I can tell you I've never seen a wiped cam on a mercruiser running mercruiser mineral oil. I've seen the 3.0 with over 6000 hours and still running like a top, on mineral oil this is not uncommon.

Here's a little background on what flat tappet cam manufacturers recommend for cam break in:
http://www.cranecams.com/pdf-tech-tips/cam_failure811.pdf

As far as I know, the Mercruiser synthetic oil was recommended for roller cam motors fitted with catalytic converters, not catless flat tappet motors. I may not be completely correct about that but the reason for removing metals from the oil was to protect cat converters from being contaminated.

I have seen several flat tappet cams lost on seasonal use engines filled with synthetic oil, but can't say I've noticed that for mineral oil. Okay, maybe that's a strange observation I cannot prove but even synthetic oil manufacturers have documented they often recommend their mineral based product in cases where the engine is not regularly run b/c the synthetic oil runs off the cold surfaces faster and they noticed corrosion issues due to this.

So being me, I put two and two together with my experience and conclude that for seasonal use in a flat tappet motor I prefer the old mineral oils that we ran for thousands of hours and never had camshaft issues. This is MY conclusion, the 3.0 is a bulletproof motor when loaded with mineral oil, they just go and go forever. Try and wear one out, I don't think you can unless you run it over 6000 hours maybe and probably more than that. The stern drive will wear out first.

Nothing wrong with the mineral oil in the 3.0, it's proven to work and protect the cam. Run the synthetic if you want, but mineral is MY recommendation for this motor.

You asked my opinion, I gave you my best answer based on what I think I know.

I have no problem with using Rotella oil in this motor either, just that I have not used it in gasoline marine engines before and I have to wonder what's been done to Rotella lately since newer diesels are now running cat converters?

I guess if you really want to be safe you could send your oil off for analysis, they can tell you how much copper/zinc/sulfur and whatever other traces are in the oil before and after being run a season but to me this is pointless for us guys that might rack up 10's of hours between oil changes as long as we're running something made for a flat-tappet motor.

There will always be off-road engine oils available for us hopefully, like the Valvoline racing oil and I'm pretty sure the straight weight 40 oils still contain the additive package just as the mercruiser mineral oil does I'm sure. I don't know about the rotella stuff, wonder if the diesel oils aren't already metal free since the cats are being used on the trucks now those are high in detergent I think and tend to turn black quickly for some reason so I've not used them in gasoline motors.
 
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Here, Blackstone labs (an oil testing specialist) decided to debunk the ZDDP myth themselves since they have first hand experience and apparently felt obliged so loaded their personal vehicle, an 84 flat-tappet chevy, using Aeroshell W65, a straight 30wt ashless engine oil designed for piston aircraft.

According to them this oil supposedly has no zinc or phosphorus component and their results indicate no unusual wear was detected:

http://www.blackstone-labs.com/Newsletters/Gas-Diesel/November-1-2010.php
 
Well, I went to the dealer today and exchanged the full synthetic one gallon, for one gallon of Mercury 25w40 mineral oil and one quart, cost me $2.00 extra.

FYI, here's what the bottle of full synthetic says: "Factory-recommended for Mercruiser gas engines including Emissions Control catalyst engines"

I love oil threads.

Lou
 
Well, I went to the dealer today and exchanged the full synthetic one gallon, for one gallon of Mercury 25w40 mineral oil and one quart, cost me $2.00 extra.

FYI, here's what the bottle of full synthetic says: "Factory-recommended for Mercruiser gas engines including Emissions Control catalyst engines"

I love oil threads.

Lou

They shoulda paid you! :) Yeah we stock the merc and all the OEM oils and will put that in the mercruisers if the customer wants to pay for it but normally just use the NAPA stuff. For Yamahas we use the factory oil.

I dunno if there's any merc synthetic stuffed way back there right now or not, might not be.
 
Attempting to explain my concern about synthetic (engineered) lubricants a little better, I have to ask if these materials are engineered with flat tappet cams in mind, or the more modern roller and follower types of camshaft drive valve rockers? Bottom line, we already have a huge record of successful winter storage periods where spring startups were successful without wiping a cam lobe while using the older non-synthetic detergent motor oils. May the wrath of camshaft failures be forever gone in these vintage design engines!

http://www.machinerylubrication.com/Read/29703/synthetic-esters-perform
 
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