Remember it's no longer Mobil SHC 75w90 the gods have now changed it to "Delvac Synthetic Gear Oil 75w90" Once the SHC 75w90 is gone, it's GONE!!!

There is a little bit of formulation dif. that Hydro mentioned... The Mobil 1 is more for street use. It's been Mobilube SHC 75w90 till they recently changed the name to the Delvac series is more of a heavy duty application..

How do I know. We've been a Mobil distributor for over 28 years.

So how is Vandy 021 doing these days?

A GL-5 from company A should be the same as a GL-5 from company B. The difference comes in the treat rate of th LS (limitted slip) additive. The major difference between a GL-4 and a GL-5 is the percentage of the gear additive in the formula. 3.5% by weight (of the additive) for a GL-4, twice as much for G-5. Ken

Any idea of what is added for a limited slip set-up?

I have a stock 1992, 454 in a 23 ft boat. Most all of my running is around 3 to 4000 rpm,just up nice and cruising, getting on the throttle ocasionaly. The engine only has about 60 hrs on it [ original engine]. The 1992 factory book calls for straight 30 wt oil and that is what I have been running without any problems. Would there be a benefit to switching to a synthetic oil. If there would be a beneifit what oil and wt should I use? Thanks for any replies.

Just had surgery so I've been down. Anyway, the oil business is good. We have started out strong this year.. We are also awaiting a price increase on all finished lubes. I feel something coming........

I would imagine it is a sort of friction modifier to prevent the cluth pack from chattering when going around corners. The L/S additive is in the GL-5 is at a very low percent, enough to get the finished lubricant to pass a "top off" spec. For "service and factory" spec you need to uptreat the L/S portion of the blend. Thats why a lot of oil companies sell the L/S additive seperatly. Ken

This thread seems to be stuck on mototcycle specfic oils for your boat........................the sad truth is, the motorcycle specfic product, ( not relabeled PCMO's (passenger car motor oils)) are probally the best lubricants you can use in your application. A good petroleum 20w50 motorcycle oil (Spectro 4 20w50) would work excellent in your application. At operating temps(210F oil temp) the 20w50 would offer more film strength than a straight 30, and give you the added benifit of easier engine cranking when cold as well as faster oil pressure when cold. If you start to run you big block harder, I honestly don't know how much harder, or for piece of mind you may want to go to a syn/pet blend or perhaps a full synthetic. Both of the lattter are more money. More than worth the higher price if you leave the oil in for long periods of time. Once again I don,t know what is considered a long time with todays modern synthetics. Only an oil analysis can tell when the oil is "spent".
Find a product and a change interval that you and only you feel comfortable with. As I have stated before I use Spectro Golden 4 20w50, (a syn/pet blend) and change at 25 hours or every fall. At my next oil change I will change to Spectro's new viscosity 15w50 for reasons stated above. Ken

A lot of ppl have been hating on the Mobil 1 EP 15w50. It's still a good oil for boaters who aren't out beating the sh!t out of their engines...