Which oil to use

"Hi, i have just totally rebui

"Hi, i have just totally rebuilt my 1991 mercruiser 502. can anyone recommend the best oil to use please. thanks Ged"

"Mercs oil is a 25-40 weight.

"Mercs oil is a 25-40 weight. Dino oil.

Ask engine biulder what he reccomends for break in and for how long (how many hours).

After that it is up to you..........


My opinion for what engine oil to run is easy,

I use Mobile 1 100% synthetic exclusively in all my toys...... . In my boat 15-50, 10-30 in my 1996 pick up and 20-50 Vtwin in my HD motorcycle.

Boat and truck get Napa gold oil filters, Bike get Hd oil filter ( they are chrome....bling ya know)

Just my opinion"

"Thanks for the reply Kghost.

"Thanks for the reply Kghost. I have rebuilt the motor myself i,m pretty good on the spanners but not sure on oils. what would you put in ?

Thanks Ged"

"Break-In Procedures for 4-cyc

"Break-In Procedures for 4-cycle MerCruiser Engines

Use Mercruiser HD30 wt. oil

IMPORTANT: The first 20-hours of operation will have a dramatic affect relative to overall engine performance and expected engine life. Proper break-in practices reduce the potential for excessive oil consumption. It also helps to achieve better engine performance levels for a longer period of time.

FIRST 20-HOURS:

1. DO NOT operate the engine below 1500 rpm for extended period$ pf time. Shift into gear as soon as possible after starting the engine. Advance the throttle above 1500rpm if conditions permit safe operation.

2. DO NOT operate at one continuous speed for extended periods of time. Vary the throttle position every ten to fifteen minutes.

3. DO NOT exceed 3/4 throttle during the first 10 hours of operation. During the next 10 hours you may occasionally operate at full throttle for no more than 5-minutes as a time.

4. DO NOT operate at full throttle until the engine reaches normal operating temperatures.

5. Avoid full throttle acceleration from an IDLE speed.


AFTER FIRST 20-HOURS:

To help extend the engine life for a remanufactured MerCruiser engine, consider the following recommendations.

1. Install and maintain the correct propeller for the application. Make sure the prop allows the engine to operate at (or near) the top of its specified Wide-Open-Throttle rpm range. Refer to the Owner's Manual, or consult with your marine dealer to determine the correct prop for the application.

2. Refrain from extended periods of Wide-Open-Throttle. We recommend cruising at 3/4 throttle or below for longer term operation.

3. Change the oil and filter regularly. Refer to the Specifications and Maintenance section of the MerCruiser Owners Guide for recommendations.

Note: It is my preference to change the oil and filter after the first 5 hours of operation. Changing the oil and filter regularly thereafter can only extend engine life."

"Follow the last post as sugge

"Follow the last post as suggested ( my opinion is 30 wieght or 10-40 or a good quality low to medium viscosity) it does not matter that much it is all about the rings and cam breaking in. Typically it takes about 40-50 hours for a good break in and I would also suggest changing the oil and filter after a (on land) heat cycle for aprox 1-2 hours. The motor needs at least 1 hour to break in the cam at aprox 1500-2000 rpms. After that change the oil and filter and then run for ~ 20 hours on a good dino oil following that oil and filter change I would run it another 20 hours on dino oil.

After that I would switch to either 15-50 or 20-50 100% synthetic. Good to go.

Realistically oil is oil and as long as you change it often all should be good.
When was the last time you heard of an oil related failure? If so it was probably due to neglect rather than what oil was used.

One thing you should realize not that it is your situation but.... when a motor is biult by a performance builder, they typically run it on a dynomometer for a short period of time to break it in and tune it then it goes to is final resting spot and it gets used as it was intended from the get go.........They seem to last long and work well..."

"Many thanks guys, excellent,

"Many thanks guys, excellent, will have to read this several times and digest it.
Ged"

"Sorry but "Oil IS NOT OIL

"Sorry but "Oil IS NOT OIL"!
I have a shop full of flat cam's from push rod engines and overhead non roller cam that were using synthitic oils that do not have the pressure additives.
A few years ago, I received a service bullitin stating that the pressure additive was being removed from most grades because the newer engines now use roller cams that do not require that additive.
If you have a push rod engine, use HD oil. Regardless of engine type, use the HD oil for break-in just to play it safe. A new cam can go flat in just a few hours if abused!"

That is why I use MOBILE 1 exc

That is why I use MOBILE 1 exclusively!

"Not sure what the "HD&#34

"Not sure what the "HD" additive referes to. It's not an industry standard, like the API service ratings. Not doubting some manufactures claim to add "HD" additives to their oil and that it means something WRT how they define it. What it acutally gets you seems ellusive and is not the same from one manufacturer to the next.
The API service ratings (http://www.api.org/certifications/engineoil/categories/upload/English_Oil_Guide. pdf) are the industry standards. Get the oil that meets the API standard, and the engine manufacture will back their warranty. Outside of that, it's marketing and sales pitches.

IMO, no need to run a multi-grade oil in an engine you don't intend to operate when it's cold outside.

WRT synthetic oil, I compare it to cold medication that claims if you take their medicine, get plenty of rest, and drink plenty of water, in a week to ten days you'll feel better."

"1. I have a 1979 Merc 470. Th

"1. I have a 1979 Merc 470. The orig owner's book says use 30 wt HD. When that designation first came into use I understood it to refer to High Detergent, ie oil that keeps dirt in suspension so the filter would remove it. I can verify that is does that, having torn down many pre-HD motors and a couple of Post-HD ones. The old motor pans had dirt caked in them. Also some folks said that HD meant Heavy Duty. Can't argue with that assumption. Anyway I have always stayed with the 30 HD.

2. My buddy, a Merc Tech Rep, says Merc oil has an additive that keeps the oil from draining off of the parts, thereby aiding greatly in a cold start. He also claims Merc filters are designed for the increased oil flow from steady 3/4 max rpm of boats, vs cars. Sounds reasonable. Anyone care to comment on these claims?

3. What is "dino" oil? Natural as in dinosaur vs syn?"

"The API service ratings on a

"The API service ratings on a container of Oil are not to be taken lightly. So called modern formulations of Oil do not meet the needs of our older Flat Tappet engines. I even avoid Mobil 1 in my Pre Roller engines. Zinc is an important barrier mineral used in older oils and Diesel Oil. Race engine suppliers even sell it as an additive for extra insurance. Oil with an API of CJ-4 or CI-4 should be used for your break in period and there after. Diesel Oil, Rotella T 10W30 (CJ-4) is easy to find and will be adequate for you. I buy it at Walmart. Be certain to maintain the 1500-2000 RPM on initial start as the Camshaft gets it's lubrication from Crankshaft splash. If you must shut down for any reason, resume breakin RPM for a duration of at least 30 minutes.
Further info. can be had at website "Bob is the Oil Guy". Al W. Good Luck and let us know how it goes."

Cam bearings and lifters are u

Cam bearings and lifters are under pressure

"Al: "resume breakin RPM f

"Al: "resume breakin RPM for a duration of at least 30 minutes"?? Did you perhaps mean 3 mins? Surely it couldn't take 30. I need to know.
And " Diesel Oil, Rotella T 10W30 (CJ-4)". I have thought about that but was thinking 20w50. My motor is old (1979)and I am in the South. What do you think?

Bill: "Cam bearings and lifters are under pressure". Does that apply to my 1979 Merc 470?

Thanks to both of you for your advice. JW in Dixie"

"Warren, It takes a total of 2

"Warren, It takes a total of 20-30 Min to break in a flat Tappet Cam.. Try not to interrupt this time but sometimes it is unavoidable. Static Time the ignition prior to starting as improper Ignition Timing can adversely effect cooling. In service use 20-50W is fine but for breaking in I'd choose the lighter weight for a more thorough splash factor. I'm glad you understand about using Rotella T. Most all open market shelf oils are good. People go wrong when they don't pay attention to API ratings.
Your Camshaft carrier Bearings get oil under pressure as well as the internals of your lifters regardless of year.The Lobes of the Cam only get a coating of Oil produced by the splashing the Crankshaft causes. Keep us informed, please. Al W."