Suzuki DF 70 Engine Oil

[Tug]

I am just about to winterize my Suzuki DF 70, it calls for SAE 10W-40 engine oil, would it be alright to use SAE 10-30 instead . Thanks Tug

[potter water]

My users guide for my suzy 50's says you can use any weight oil you want, but it should be related to your normal operational days temperatures. 10 40 is better for warmer weather and 10 30 for cooler. So if you use 10 30 for storage it just wouldn't matter. I think the quality of the oil is more important than the weight. (However, if you are operating during the cold of Alaska, thinner oil is pretty important, etc.)

[digger]

From what I have seen, 10-30 is fine, and an option when ouside temp are not extremely high. Make sure it has as good of other specs listed.

[Tug]

Thanks for the reply, that's what I figured but just wanted to be sure.Tug

[starcrafttom]

I have this argument with my car mechanic all the time. His stance is that modern engines are designed to exact tolerances including the oil. So much so that not using the right weight oil can cause damage in the long term. 10-30 does not flow in to a bearing at the same rate and temp as 10-40. Now I am not sure how much it make a difference but if I don't use the right weight oil in my Scion XB then I burn oil faster. You mileage my differ.

[Sunbeam]

I had always had "older" vehicles, and ran oil weight according to ambient temps and usage (hard, easy), as you all mention. Then I got my "modern" tow vehicle (late 90's Ford, Triton engine). I was really surprised to see that 5w30 was originally recommended, and that now, apparently (recommendations changed as years went by) 5w20 is the recommended weight. Wow, that sounds soooo thin to me! I kind of winced when starting the engine after putting that in on the first oil change, but nothing seemed amiss.

If I hadn't checked, I'd have run my usual 10w40 for summer (might have worked fine, who knows, but I went with the recommendation).

[Sea Wolf]

Off the top of my head, it would seem to me that choosing a multiple viscosity engine oil should also take into consideration the differences between automobile and outboard engine temperatures.

Autos run at temperatures well above the normal boiling point of 212 degrees F because of the use of anti-freeze (ethylene glycol @ 50%) and also have 15-18 psi pressure systems, allowing them to run from approximately 230-250 or more degrees.

Outboards have neither the antifreeze nor the pressure systems, and by feeling the cooling water output, we know that they run at much lower temperatures. I would guess the water coming out is 135-175 degrees, though that would be the water jacket temperatures, not the combustion, bearing, or oil sump temperatures. (Time to get out the IR thermometer!)

Without the expertise of an automotive and/or marine engine engineer, we're guessing, of course, but the 10-40 multi-vis that will get your Suburban across the Mojave Desert from LA to Las Vegas in July, may not be necessary in your Suzuki going from Seattle to Friday Harbor. And the water temperature in Florida may well be 30 degrees warmer than that in the PNW, as another factor to consider.

As a further example, the twin V6's in my Sea Ray never get above 150 degrees, which is 100 degrees less than when they're in an automotive application. (The thermostats are selected for 145 degrees operating temperature.)

Your mileage (viscosity) may vary.

Joe.

[journey on]

First, let's look at how bearings work. They hydrodynamicaliy pump oil between the two bearing surfaces as they rotate. That's true for journal bearings, where the viscosity allows the oil to be pulled into the load bearing part of the journal. It's also true for ball and roller bearings. That covers all rolling outboard bearings.

Now, I don't know how the manufactures design bearings, but I think they know how to do so. Therefore, when they recommend a certain weight of oil for a certain temperature range, I think that's their best recommendation and I do my best to follow that. If it starts burning a significant amount of oil, that would be a sign that something is wearing out and should be fixed, such as the rings, valve guides, etc. The bearings still need the right kind of oil. So, if it recommends 10-30, 5-20, 10-40 that's the factory recommended viscosity, and they know way more about their engines than I want to. A thicker oil (higher viscosity) can starve bearings and a thinner oil may allow metal to metal contact in a bearing.

As for running temperatures for outboards, remember they're salt water cooled engines. Salt starts to precipitate out of sea water at about 180 degF, so the thermostats are set to open at a slightly lower temperature. That's the cooling water, not some metal far from the coolant, such as the outside of the head or exhaust manifold. On the other hand, the higher one can run a heat engine, the more efficient it is and car manufactures set the operating temperature as high as they can. Certainly over the boiling point of water. Therefore, in your car 240 degF might be normal since they use a mixture of water and a cooling fluid. Not raw salt water.

So: read the manual and use the motor oil the mfg recommends. This includes both the viscosity range and oil specification. And don't change the thermostat temperature rating. There's a reason for all of that.

And change the oil regularly; oil's cheap, engines aren't.

Boris

[Tug]

The deed is done, I called the nearest Suzuki dealer and spoke to the service department. I asked if I could use Mercury 10W-30 instead of the recommended Suzuki 10W-40 oil. I was told that it was fine and not to worry about it. Tug

[Sea Wolf]

Boris-

Good points!

I'm not trying to disagree with you in the post I made, just point out some differences between marine and automotive applications that could be considered when making engine oil choices.

Apparently, there's a lot of latitude allowed by the factory recommendations, usually.

Regards!

Joe.