Mercruiser Oil Replacement

[BUBBA0420]

I have been running the Mercruiser Oil (25-40)
in my twin 260 mercs for a couple of years now and have noticed that after a run in warm weather
at say (3000 to 3400) R.P.M. after coming off plane my oil pressure is down to 5 lbs on both
engines so it is obviously breaking dowm. Motors
have 690 hrs on them and there is never any noise
or anything. After getting back to the dock the
oil pressure does come back up some. I am thinking about Delo 400 straight 30 wt or possibly Havoline straight 30 wt. IS the Delo 400
a synthetic oil ??? What do you guys recommend ??

 

[Schmoe]

Boy, oil shouldn't drop down that much, especially a 25-40 weight. I've been using, as a lot of others here, the Pennz. LL 15W-40, which is a dino diesel engine oil, on my 3.0LX. Now that little engine gets worked a lot. After WOT runs or pulling a tube, pressure will drop down to about 35-40 psi, which is about where you want to be. 5 psi just sounds awfully low, almost too low. Maybe your sending unit is on the fritz.

 

[BUBBA0420]

I was thinking the same thing Schmoe but it
happens on both engines (I have twins) I agree
it is low but other than that the engines run great.

 

[Schmoe]

Hmmmm.....odds of both going out at the same time is pretty remote. I will assume you have the two engine guage set up, dual controls for everything....which I think is just too cool. Looks like the cockpit of a F-4 Phantom. Anyway,
I'd drain the oil and try the Pennz. The Delo is pretty good too, it's also a diesel engine oil with some pretty stout additives. Man, I still can't believe the oil pressure would drop that low. Mercruiser just contracts out their oil spec's, they don't make it themselves. I want to lean towards something mechanical, but both engines???? got to be the oil...which is what they have in common. Wouldn't bet on it being both sending units or both oil pumps going out at the same time.

 

[1 FMF]

few years ago, i ran penzzoil synthetic 5w30 during the fall on my 351w engine. when cold and before running 30mph for a length of time, oil pressure was 40-60psi. Running hot, 1500+ rpms I would always have 40-60psi. Idle hot at 1000 it would drop down to 20psi. Idle hot down to 600 rpm I would see about 10psi on the gauge. If I idle up to 1000+ rpms, I immediately see jump to 20+ psi.

Are you running fram oil filters? I've heard that in some instances fram replacements can cause pressure problems. But don't take this the wrong way, this was on a 496 blown engine that was in for warranty. Mechanic, who was a friend, told me about it. Said all they did was junk the ph8a filter and replace it with a mercruiser brand. I believe in that case the correct fram is something like hp2. Oil filters are cheap, try replacing them. AC delco, purolator, k&n if you want to spend the $$.

The 15w40 oils are good. But for your problem I think at minimum a straight 40 oil should be used to verify oil thinning down is the problem. Maybe even mix in some 20w50 or 15w50 oil.

what year engines? fresh or raw water cooled? oil coolers? what's normal operating temp and are you sure? Maybe engines running hotter than should be and the symptom your seeing is low oil pressure at idle because the oil is really hot. Not enough cooling happening at 3000+ rpms, once you slow down cooling can happen and as the oil cools pressure starts to come back. Always a good idea to verify pressure mechanically with gauge on the engine. 5 psi is awful low if that is correct.

 

[BUBBA0420]

Yep Schmoe: 1984 Tiara 27 Continental with dual
Morse Controls throttle and shift. As I say I never hear any noise from motors and both have
around 40 PSI when cold. Put the hammers down and
these baby's just sing in harmony 4400 RPM with
45 MPH running 4 bladed props. It's just makes
me nervous to see the oil pressure that low

 

[terminaldegree]

You could run any good HD 30 weight up there and be just fine; it may even hold up better than the overpriced Merc stuff. Keep in mind that other engine marinizers often recommend the straight-weights for the exact same [gm powertrain-sourced] engines. These mercruiser products often annoy me because they're: 1) more expensive than other parts/accessories , and 2) not necessarily superior in quality.

Having said that, unless you're overheating a little [deferred cooling system maintenance], or your idle speed is too low, I doubt you're getting an accurate reading off your gauges. I don't know if that generation Tiara has the crappy teleflex gauges or something better than that. Hot idle oil psi after a run is always the lowest you'll see compared to other conditions. Lowest I've seen was about 15 psi. [again, using crappy gauges]

 

[terminaldegree]

p.s. I have seen both gauges go bad before at nearly the same time-- both teleflex voltmeters on my parents' '01 Sea Ray 280 sun sport started reading incorrectly almost at the same time, and had to be replaced. Verified incorrect readings by my multimeter and a mechanic...

But hey, it's cheaper to replace 2 gauges/senders than one of those ridiculous Smartcraft electronic gauges. Woe be unto those who have to pay to replace one of those...

 

[BUBBA0420]

Yea Terminaldegree I suppose that is possible.
1 FMF ,,No Fram Filters only the Mercruiser filters and engines run at 155 degrees Raw water
cooled. That why I am thinking straight 30W in either Delo 400 or Havoline. Engines are 1984
with 690 hours

 

[Craig]

I use Amsoil heavy duty diesel engine oil straight 30wt synthetic
in my diesel trawler. It is also rated for gasoline engine use.

My top oil pressure is around 40-45 psi and it usually drops to
25psi when hot and idling.
Craig

 

[Don Stefanik]

You may want to take a look at this replacement product.

PRODUCT DESCRIPTION
AMSOIL 10W-40 Formula 4-Stroke® Marine Synthetic Motor Oil (WCF) is a premium quality synthetic formulation engineered for the harsh operating conditions of marine environments. It withstands the intense mechanical action of continuous, high RPM operation to deliver superior viscosity protection. Formula 4-Stroke® Marine Synthetic Motor Oil is specially fortified with a heavy treatment of advanced additives that protects motors against wear, rust and deposits. It excels in both high horsepower applications and all-day trolling conditions.

4-Stroke Outboard Motor Warranty Certified
Formula 4-Stroke® Marine Synthetic Motor Oil is certified by the National Marine Manufacturers Association (NMMA) for use in four-stroke outboard motors. This high quality oil demonstrates outstanding performance, exceeding the NMMA “FC-W” (Four Cycle-Water) specification requirements. Formula 4-Stroke® Marine Synthetic Motor Oil fulfills the warranty requirements of four-stroke outboard motor manufacturers.

• NMMA Registration #FB-30010B 10W-40
Superior Protection Against Engine Wear
Marine engines operate under high loads and RPMs for extended periods of time, causing traditional automotive oils to break down and lose viscosity. To ensure good protection, the NMMA set minimum shear stability requirements for FC-W. AMSOIL Formula 4-Stroke® Marine Synthetic Motor Oil greatly exceeds the FC-W shear stability requirements, outperforming competitive oils to deliver a superior lubricating film. Formula 4-Stroke® Synthetic Oil also contains robust anti-wear additives that further reduce wear in metal-to-metal contact regions (see Four-Ball Wear Test graph).

Click on graph
to see larger image

While automobile engines normally operate at around 2,500 rpm, outboard motors can run twice as fast, requiring greater levels of wear protection and better bearing durability than automobiles. In addition, prolonged idling and low operating temperatures contribute to fuel dilution, further thinning the oil. To ensure adequate protection for their engines, marine engine manufacturers set minimum high temperature/high shear (HTHS) viscosity limits. AMSOIL Formula 4-Stroke® Marine Synthetic Motor Oils are shear stable and formulated with sophisticated oil additive chemistry, exceeding the HTHS requirements of both the API and NMMA FC-W (see graph).

Excellent Anti-Rust Performance
Marine engines are prone to rust, leading to uncontrolled wear and premature engine failure. However, good rust protection is not natural to engine oil. It comes only by design. Formula 4-Stroke® Marine Synthetic Motor Oil is fortified with a special anti-rust agent, even more than required to pass stringent NMMA FC-W anti-rust testing.

Applications
AMSOIL Formula 4-Stroke® Marine Synthetic 10W-40 Motor Oil (WCF) is recommended for gasoline fueled four-stroke outboard, inboard, inboard/outboard (I/O) and personal watercraft motors. AMSOIL WCF motor oil is recommended for the following applications whenever an SAE 10W-40, 15W-40, 25W-40 or straight SAE 40 oil is called for:

Four-stroke outboard motors: Honda®, Mercury®, Yamaha®, Johnson®/Evinrude®, Bombardier/BRP®, Suzuki®, Nissan®, Tohatsu®

Inboard and I/O: Mercruiser®, Volvo Penta®, OMC®, Chrysler® Marine, Crusader®, Marine Power®, Chevrolet®, Ford®

Personal Watercraft: Honda®, Yamaha®, Bombardier/BRP® (Sea-Doo®), Polaris®

Note: AMSOIL Formula 4-Stroke® Marine Synthetic 10W-40 is recommended for use in place of 25W-40 as specified by Mercury®.

NMMA FC-W • API SL

Service Life

• Four-stroke outboard motors and personal watercraft applications: Due to potential fuel dilution or water contamination, change oil at the engine or watercraft manufacturer recommended interval.

• Inboard and I/O applications: Change oil at two times the engine manufacturer recommended interval or one year, whichever comes first.

Mixing AMSOIL
AMSOIL Formula 4-Stroke® Marine Synthetic Motor Oil is compatible with conventional and synthetic motor oils. Mixing AMSOIL motor oils with other oils will, however, shorten the oil life expectancy and reduce the performance benefits. AMSOIL does not support extended drain intervals where oils have been mixed.

Aftermarket oil additives are not recommended for use with AMSOIL motor oils.

Health & Safety
This product is not expected to cause health concerns when used for the intended application and according to the recommendations in the Material Safety Data Sheet
(MSDS). MSDS’s are available upon request at 715-392-7101 or on our website. Keep Out of Reach of Children. Don’t pollute. Return used oil to collection centers.

TYPICAL TECHNICAL PROPERTIES

AMSOIL FORMULA 4-STROKE® MARINE SYNTHETIC MOTOR OIL (WCF)
SAE 10W-40, API SL, NMMA FC-W

Kinematic Viscosity @ 100°C, cSt (ASTM D-445)
14.1
Kinematic Viscosity @ 40°C, cSt (ASTM D-445)
93.8
Viscosity Index (ASTM D-2270)
154
CCS Viscosity, cP @ (°C) (ASTM D2602)
6871 (-25)
Flash Point °C (°F) (ASTM D 92)
234 (453)
Fire Point °C (°F) (ASTM D 92) 254 (489)
Pour Point °C (°F) (ASTM D 97) -46 (-51)
Noack Volatility, % weight loss (g/100g) (ASTM D-5800)
6.40%
Four Ball Wear Test (ASTM D 4172 @ 40 kgf, 150°C, 1800 rpm, 1 hour, Scar in mm)
0.40
Total Base Number (ASTM D-2896) 10.5
HTHS (cP) 4.6
Humidity Cabinet Rust (ASTM D-1748) Pass

 

[TomJones76]

Are there any UOAs on your WCF product there, Don?
Glad to know Amsoil is competing in this marketplace. The more competition the better the prices and quality of the marketplace.

 

[Don Stefanik]

I have not seen any as this is a new product.
Trust it to be as good as all the other AMSOIL products.

 

[Geoff]

Check your oil levels, perhaps the last time you had it serviced they overfilled the engines and the oil is getting whipped up.

Also, an electrical short can make the guages read a little off. I currently have this problem in my dash, and the tach is about 400 rpm high when it happens.