What engine oil to use

Just completely rebuilt a 3.7

Just completely rebuilt a 3.7 mercruiser with all new parts and complete engine components checked and fixed at machine shop. what engine oil is recommended for this application before i start the motor the first time. thanks

"merc recommends 15/40. I pref

"merc recommends 15/40. I prefer straight weight oil 30w here, but depends on climate."

"I use synthetic in all my veh

"I use synthetic in all my vehicles, it's great for cold starts because it leaves a film on the cylinders, BMW uses it and recommends 15000 miles between oil changes under warranty. It's a good idea to fill the filter with oil befor installation."

"Rings need to "seat"

"Rings need to "seat" in a new or rebuilt motor and if synthetic is used immediately, they won't. ask the machine shop what they recommend for the break-in oil and then go to whatever you decide to use afterward. Merc recommends their 25W40 oil (or 15W40, depending on the motor) but as long as it has the same codes applied to it (they're on the bottle label), you should be OK.

Always fill the filter with as much as you can without spilling when the filter goes on, which is hard to do on the Ford motors. If the motor is being filled for the first time after the reassembly, remove the distributor and manually spin the oil pump shaft to get oil to the top end before starting."

"Jim you said something about

"Jim you said something about codes... what codes apply to my marine application and also i hear about the diesel oil the rotella 15-40, would this be ok to run or is the mercruiser 25-40 oil better??"

"If you look on a bottle of mo

"If you look on a bottle of motor oil, there are some two letter codes on the label and they refer to oil specs for additives and other things. You can't use oil for a car on a lawnmower and expect it to last a long time, nor can you use oil for something that sees light duty and low RPM on something that gets the crap beaten out of it at high RPM and temperature extremes.

Rotella is good oil and IIRC, meets all of the specs. Look at Wallyworld for Pennzoil Marine oil and make note of the codes. You should get a manual of you're new to this kind of thing. I have no experience with aftermarket manuals but have only used the ones from manyfacturers (Merc, OMC, Volvo-Penta, etc). The Merc I/O oil bottles have these codes on them, too. If you write them down, you can look for oil that meets them. 30W will work fine if you want to use that but will be a bit thick on cold starts.

If you posted the thread about which filter to use, the manual has the OEM part number and you can cross reference to that. I don't use or recommend Fram or any of the private label filters they make. I use AC filters in my truck but NAPA Gold and WIX are good ones. If you want to spend a lot for a filter, you can use Mobil 1 or Amzoil filters but in light of the fact that the oil should be changed every 50 hours of use, I think it's just better to keep the oil fresh and the motor cool, meaning at normal operating temperature with no overheats. If it does overheat, change the oil and filter immediately and check or replace the impeller/get rid of whatever is clogging the raw water inlet."

"Diesel crankcase oil is rated

"Diesel crankcase oil is rated for diesel but is fine for use in gasoline engines. Most motor oil is rated ONLY for gasoline engine and if so is not to be used in diesel engines. In this case, being a gasoline engine, you do not have a problem either way."

"Diesel oil is a great option

"Diesel oil is a great option for gas engines when new after the running in period to ensure the rings bed in, however, because there is detergent in this oil it does tend to clean the internal components which can in older engines cause more ware noises such as rattles. All the best Trev"

"Trevor, I never understood it

"Trevor, I never understood it that way. Here in the States there are popular myths about automotive mechanics. So there are many things like that to check out. Modern oils contain additive packages that incude detergents in both gasoline engine and diesel engine crankcase oil. The way I understood the difference is that diesel rated crankcase oil withstands the higher force between mechanical components in a diesel engine, but is satisfactory in a gasoline engine."