Mercruiser 4.3 MPI - oil - synthetic or regular?

dburne

dburne

New Member
Jun 8, 2012
590
Nashville TN
Boat Info
2013 Sea Ray 190 Sport
Engines
4.3 MPI Mercruiser Alpha One
Hey gang,

I am just curious, regarding engine oil, do you guys run synthetic or regular oil?
The reason I ask - the Mercury manual for my engine recommends only Mercruiser 20w40 I believe, full synthetic. Obviously they recommend Mercruiser oil, as that is their brand and make money off of it. My question is more weight and synthetic or regular.

I took my boat to the dealer a week ago, for it's first oil change - the manual recommends an initial break in period of 20 hours, after which to get the oil changed for the first time. My engine had about 21.5 hours on it, so figured I would go ahead and get that taken care of.

When I got there to get it changed, I mentioned to the service manager that the Mercury manual recommended Mercruiser 20w40 full synthetic, and asked what they use. He said all they use was I think it was Mobile, 10W40 regular oil. I trust him as he has been good to me, and asked if that is what he would suggest, he said absolutely and is all they have used on these boats for years. So he changed my oil using it.

Now I am kind of a by the book type of guy, and would probably have felt better using the 20w40 full synthetic, especially with the warranty it is under, but they have been doing this for many years and figure they must know what they are doing.

So what do you guys do, full synthetic or regular oil?

We have had this new Sport 190 out about a dozen times now, and are absolutely having a blast! It has ran like a top without any issue at all so far.
It saddens me it is already August, and knowing I will have to have it winterized here in a couple of months. Going to try to make the most out of the remaining weekends though. We will have the two oldest grandkids coming up this next weekend ( 8 and 10), and really looking forward to getting them back out there, they really love it.
 
I ran into the same conundrum - manual stating full synthetic yet Mercury going to a synthetic blend. My Mercruiser shop (not the boat dealer) said to stick to marine grade, and that the synthetic blend is good. Just ticked over 74 hours today - the boat's had a busy first Summer - I changed the oil at about 15 hours with the synthetic blend.
 
Thanks Glenn.

Do you change your own oil or have a dealer do it?
 
I use the Mercury synthetic blend as well although Amsoil is great too.
 
Hey Don,

I bought a (manual) extractor pump - the same one I saw in some YouTube "do it yourself videos" that a dealership/service/marina posts. Pretty straightforward and easy, and did it myself.

And that's sayin' something as far as being EASY!

LOL
 
Don't let someone tell you that you need "marine grade" oil, even if that exists your still dealing with a GM engine.
 
As long as you're keeping up with your maintenance and changing oil as needed, you're 99% of the way there in my opinion. Loosing sleep over oil brand, synthetic/dino, ect. is really just trivial. Any good name brand oil will serve you well. Having said that, I use Rotella T 15W-40. I would likely spend the money on the Mercury oil, there's just not a place close to me to purchase it.
 
My Mercruiser guy just feels that automotive grade oils aren't designed for engines that run at high constant RPM, as outdrives run on a singular gear ratio - as opposed to cars with multi-speed and overdrive transmissions. Says he's always used marine oil in his F-350, and believes his high oil pressure at 200K miles is because of it. Not saying he is *the* know-all authority on the subject, but I respect him and am glad to take his advice. Plus, on the warranty end I'm glad to have receipts for Merc's oil.
 
scoflaw said:
Don't let someone tell you that you need "marine grade" oil, even if that exists your still dealing with a GM engine.
Click to expand...

yes, but our 'GM engines' are running in a MUCH harsher and more demanding environment that their GM cousins in cars/trucks.....our engines must perform under constant load for long periods of time and at relatively high rpm's...and they live/work in a wet, moist and corrosive environment....

not really worth getting into another debate about this.....lots of good reading in the archives....there have been numerous debates about this subject that can help you make your own mind up about which oil to use.....

cliff
 
I have a slip at my local marina, as well as an enclosed space up the street from it at a storage facility. I only keep the boat slipped during the weekends, pulling out every Sunday afternoon to clean it - and also open up EVERYTHING (all storage, ski locker, engine cover, etc) just to DRY things out. Friends, family, and slip neighbors think I am NUTS (well, I am).
 
Thanks for all the great feedback gang, I really appreciate it!
I think when the time comes again for an oil change, I may just do it myself as well using the Mercruiser oil.
 
sfergson727 said:
I use synthetic personally, but AMSoil rather than mobile. http://www.amsoil.com/shop/by-produ...ic-formula-4-stroke-marine-oil/?code=WCFQT-EA

Let me put your mind at ease regarding not using the manual's recommendation......Mercury discontinued the full synthetic 20w40. If you stick with Mercury branded oil, your only choice is the semi-synthetic, or straight dino oil. I'd recommend the semi-synthetic blend.

Make sure your service manager is using oil that meets the marine qualities for the engine.
Click to expand...

Scott,

So you are using the 10W-40 Amsoil Synthetic Marine Oil? I want to use the full synthetic but concerned over the 25W-40 vs 10W-40.

Eddie
 
Thanks Scott. I just wanted to get away from the blended oil from Mercruiser. I'll order the Amsoil...
 
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