[Douglas Alderman]

What engine oil wt. are you using in your boat? I'm using 10-30wt. Quick Silver oil for my Merc.5.0 and have a newer 2005 engine. Will 10-40wt. change the oil pressure? My boat is in warm 90-plus tempatures all the time.

[WetWilly]

Hi Douglas,

As you're already using a 10W-30 weight oil, a 10w-40 won't change your pressure very much at all, I would say at the most maybe 3 - 5 PSI tops. Are you using the Mercruiser brand oil because I thought it's a 25W-40 oil...

First off, here's a little explanation about what the "10W-30" stands for for those of you that would like to know... ( a little synopsis I got from the net)

The viscosity grade (for example, 10W-30) tells you the oil's thickness, or viscosity. A thin oil has a lower number and flows more easily, while thick oils have a higher number and are more resistant to flow. Water has a very low viscosity -- it is thin and flows easily. Honey has a very high viscosity -- it is thick and gooey. Multi-weight oils (such as 10W-30) are a new invention made possible by adding polymers to oil. The polymers allow the oil to have different weights at different temperatures. The first number indicates the viscosity of the oil at a cold temperature, while the second number indicates the viscosity at operating temperature.

In other words, when cold your 10w-30 is as thick (viscosity) as a straight 10 weight oil and at operating temp, no thinner than a straight 30 weight oil would get.

Now whether you need a thicker oil depends on the quality of oil you're using now and the temperature of the water you run in. Air temp doesn't matter as it's the water that's cooling your I/O. Where we run out Talari, the water temp is usually in the 70's near the surface (air temp between 80-100+) and I have never had any problems with Quicksilver 4-Cycle Marine Engine Oil (25W-40 weight oil) in our I/O's.

Well that's my $0.02 on the matter....

Good luck
WetWilly

[dudders]

Originally Posted by WetWilly

Hi Douglas,

As you're already using a 10W-30 weight oil, a 10w-40 won't change your pressure very much at all, I would say at the most maybe 3 - 5 PSI tops. Are you using the Mercruiser brand oil because I thought it's a 25W-40 oil...

First off, here's a little explanation about what the "10W-30" stands for for those of you that would like to know... ( a little synopsis I got from the net)

The viscosity grade (for example, 10W-30) tells you the oil's thickness, or viscosity. A thin oil has a lower number and flows more easily, while thick oils have a higher number and are more resistant to flow. Water has a very low viscosity -- it is thin and flows easily. Honey has a very high viscosity -- it is thick and gooey. Multi-weight oils (such as 10W-30) are a new invention made possible by adding polymers to oil. The polymers allow the oil to have different weights at different temperatures. The first number indicates the viscosity of the oil at a cold temperature, while the second number indicates the viscosity at operating temperature.

In other words, when cold your 10w-30 is as thick (viscosity) as a straight 10 weight oil and at operating temp, no thinner than a straight 30 weight oil would get.

Now whether you need a thicker oil depends on the quality of oil you're using now and the temperature of the water you run in. Air temp doesn't matter as it's the water that's cooling your I/O. Where we run out Talari, the water temp is usually in the 70's near the surface (air temp between 80-100+) and I have never had any problems with Quicksilver 4-Cycle Marine Engine Oil (25W-40 weight oil) in our I/O's.

Well that's my $0.02 on the matter....

Good luck
WetWilly

You (as usual) are absolutely right WetWilly with your synopsis.
One thing - With a 10W/?? oil, you have a better start up lubrication rate. Which means, when you turn your motor on, the oil will be just a little quicker to lubricate your bearings etc at the top end of your motor than a 25W/?? oil.
The 25W/?? still do a great job and the oil still gets there pretty quick, just the 10W/?? types are just that little bit quicker.
My 2cents as well.

[scubydo]

I'm thinking about using synthetic Mobile 1 0w-30, or 0w-40 in my late 90's 4.3 Mercruiser. Any thoughts????

[m&mmariah]

There's a somewhat good discussion forum about engine oil over at www.bobistheoilguy.com.

The even have a sub-forum on boat engines. I'm running mobil delvac 15W40 in my merc 4.3. It's a heavy duty engine oil (HDEO) formulation. Any HDEO should stand up well in marine applications, according to the folks at the other forum. Also, the 15W-40 rating is pretty close to the Quicksilver 25W-40 oil recommendation. Of course, if your engine is still in the warranty period, I'd run the 25W-40.

[garyg]

Scubydo I use Mobil 1 10w-30 in my 2000 Z272 Shabah 7.4 MPI Bravo 111. The previous owner used Mobil 1,so used the same oil.I Have good oil presure and the boat temperature is fine. Gary G

[scubydo]

I had to use the Boat over the weekend, I ended up putting a straight 30 Valvoline in it. I didn't like the oil pressure when the boat was cold, it was 40 psi at an idle, and kicked up just above 60 when cruising around 3300 rpm's. This seems high to me after reading on the bobistheoilguy.com site. I'm thinking I'll try the synthetic mobil 1 0w-30 next. Anybody think that is a bad idea???

[scubydo]

Come on anybody??? Has anybody used the Synthetic Mobil 1 0w-30 in a boat? It's not cheap so I'd really like to hear from someone????

[garyg]

Scubydo Yea I do in my 2000 Z 272 Shabah Open Bow 7.4MPI Bravo 111 I buy it Wal-Mart in the 5 quart jug for $ 21.00. If you look at your post you will see my other reply above yours. I like the Mobil 1,it wontn't break down like regular oil. Gary G

[scubydo]

Thanks. I'll try it on the next oil change.