Diesel oil bad for marine engine?

[Gillsy]

Originally Posted By: AzFireGuy79
Originally Posted By: Donald
I run Rotella T 15W40 in my Mercruiser 5.7L. The marine engine runs more like a constant RPM engine (unlike a car) and a gas and diesel rated oil would be a good choice.


Same here. Just threw in some AutoRX for a little cleanup. Then switching to Redline 5w-30 which is on the thick side for a 30wt and doenst shear very much if at all. Tons of ZDDP to boot. There is of course a point where too much ZDDP can be detrimental to an engines health. People overthink this stuff. The only reason I give a rip about ZDDP is that I have a 87 Mercruiser 5.7 with flat tappet lifters.


Chevron Delo 15w40 or Mobil Delvac 1300 Super. Awesome oils!

 

[Rob_Roy]

We have Merc 25w40 in the 7.4's in the Formula, but I am considering Brad Penn SAE 40 for the next change. Mercruiser is very clear that they don't want an oil with viscosity improvers. I'm fine with that, and want plenty of ZDDP for the flat tappet cam in the big blocks.

Originally Posted By: Donald
I run Rotella T 15W40 in my Mercruiser 5.7L. The marine engine runs more like a constant RPM engine (unlike a car) and a gas and diesel rated oil would be a good choice.


No shock loads (assuming you go around the reefs

), but some boats can get the oil temperature pretty high on a long run.

 

[Gillsy]

Originally Posted By: Rob_Roy
We have Merc 25w40 in the 7.4's in the Formula, but I am considering Brad Penn SAE 40 for the next change. Mercruiser is very clear that they don't want an oil with viscosity improvers. I'm fine with that, and want plenty of ZDDP for the flat tappet cam in the big blocks.

Originally Posted By: Donald
I run Rotella T 15W40 in my Mercruiser 5.7L. The marine engine runs more like a constant RPM engine (unlike a car) and a gas and diesel rated oil would be a good choice.


No shock loads (assuming you go around the reefs

), but some boats can get the oil temperature pretty high on a long run.

Perhaps I'm missing something here.I do believe that ANY multi vis oil has viscosity improvers. 25w40 is 25w oil with viscosity improvers in it.I run 15w40 Delvac 1300 Super, or Delo 400 15w40.

 

[lars11]

Gilsy: No not so.
AutoRX in marine inboard: I would be *extremely* surprised to se any sludgy stuff to clean in an marine inboard. Save that $.

 

[SteveSRT8]

Originally Posted By: italian68
i run a high performance engine in my speed boat. 700hp n/a 510ci bbc hand built by a marine speed shop. the only engine oil they use in their custom builds and mercury racing engines is PENNZOIL GT HIGH PERFORMANCE 25W-50 RACING OIL. 2000+ ppm zinc. ive heard as high as 2800ppm on bitog.

in a stock mercruiser application i would use a 15w-40 HDEO and change at 50hr intervals.


I have a blown stroker big block (572 based) in a go-fast boat and run Amsoil Dominator in it. 3 UOA's proved it to be a great oil.

IME fuel dilution is the number one enemy in my boats. Get a UOA and see how yours is set up, they should be RICH!!!

 

[Rob_Roy]

Originally Posted By: Gillsy
Originally Posted By: Rob_Roy
We have Merc 25w40 in the 7.4's in the Formula, but I am considering Brad Penn SAE 40 for the next change. Mercruiser is very clear that they don't want an oil with viscosity improvers. I'm fine with that, and want plenty of ZDDP for the flat tappet cam in the big blocks.

Originally Posted By: Donald
I run Rotella T 15W40 in my Mercruiser 5.7L. The marine engine runs more like a constant RPM engine (unlike a car) and a gas and diesel rated oil would be a good choice.


No shock loads (assuming you go around the reefs

), but some boats can get the oil temperature pretty high on a long run.

Perhaps I'm missing something here.I do believe that ANY multi vis oil has viscosity improvers. 25w40 is 25w oil with viscosity improvers in it.I run 15w40 Delvac 1300 Super, or Delo 400 15w40.


You can have a monograde oil that meets the cold weather pumping requirements of a multi-viscosity oil. AMSOIL's ACD is a good example: http://www.amsoil.com/storefront/acd.aspx