Shell Rotella T 5W40

Thoughts on using this in a boat engine?

I think it is primarily used in diesels. Truckers swear by the stuff. If you are doing your own service now I would switch to full synthetic. I like Mobil1 but there are many good ones on the market. You do not change the oil in a boat often enough for the extra cost to make a difference, so use the best you can.

If you are still under warranty then use the OEM stuff. I like to do mineat the end of the season and again about a month or two into the season. I don't wait until the hours reach the next interval, cheap insurance IMO.

Not to turn this into an oil debate, but why not use an oil that's meant for our harsh marine environment ?

I use Amsoil 10w-40 Marine Oil. It's a straight 40 wt. that also has the cold flow properties of a 10w. Sure beats Mercs 25w-40 for cold flow and also doesn't have VI improvers (Merc's doesn't either)...

I would bet that the Rotella does have VI Improvers, but know that it's a great oil, but wouldn't want it in a marine engine.

How many synthetics actually use VI improvers or use such small amounts it's basically neglectible?

I vote for Mobile 1. 5 quarts is only about $20.

It's either multi-viscosity or it's not, can't be both. Good stuff though.

Depends on how long you want to keep your boat, but I personally would not put Mobil 1 in a boat engine.

Amsoil has told me that because of the synthetic properties of the oil, it is a straight 40w that also has the cold flow of a 10w. The label shows 10w-40, but it is not a multi-viscosity oil.

Take a look at Chevron Delo 400 40wt and then compare it to the Amsoil Marine 10w-40.

Up here in the northern part of the US, I like to have the cold flow during the fall months and help out considerably over a straight wt oil....

Everyone has their opinion on oils, so to each their own on the oils. But I would not put an oil in the engine that isn't rated for marine use or HD Diesel use.

Amsoil does make the oil for Volvo Penta which is a 10w-30, but they label it as 30wt. It's the Amsoil ACD oil.

Mercury oil is a typical dino oil that is contracted to the lowest bidder, but I'm sure does provide adequate warranty protection.

I put in Amsoil for first oil change this summer. Their application guide recommended the WCT 10W-30.


http://www.amsoil.com/storefront/wct.aspx

Great oil. I used that in my Volvo Pentas. Excellent protection !!

I have been running Amsoil in the car, SUV, and ATV for just over a year and am pleased with the extended drain intervals and cold start properties. I have not noticed any imporvement in gas milage.

I asked the Amsoil rep about running Amsoil in the boat and he said that if it was his boat he would use the HD Marine/Diesel oil since it has more things added to it and has the best corrosion protection. I decided to stick with Penziol HD 40 which is what I have always run in the engine but I did buy 3 quarts of marine drive lube to try this year.

Amsoil's drive lube looks superior to many others from what I've read and it is cheaper and easier to obtain than Merc oil- at least for me.

Here is another related question. If diesel oil is superior to standard "SG/SJ" grade car oil then why doesn't everyone run it in their car? It is usually cheaper too.

Because it's harder to find. I'd love to run Delvac 1 in all my engines, but I can't run out to Walmart and buy a quart or 10.

You want to use a low viscosity spread oil, hence the 25W40 that Merc puts out. The VI enhancers in multi-weight get trashed by the fuel loading that marine engines put on the oil.

Based on sheer numbers from more than you ever wanted to know about motor oil, Amsoil looks to be far superior to just about everything out there, while the old standby's like Castrol and Pennzoil are some of the worst...

However, if you believe this from consumer reports (which I do by the way), then as long as you change your oil regularly, your engine will never know the difference...

I change it once a season.

Nothing wrong with using it.