OMS Oil Raitio

[Salmonseeker]

Hi guys,

Does anyone know if the newest OMS pump varies the oil ratio or if it is constant?

I have heard that it is constant at 50:1 and also that it varies from 50:1 at full throttle down to 80:1 at idle. I don't know what is accurate.

Can anyone confirm the ratios?

Thanks

 

[kenmyfam]

Re: OMS Oil Raitio

As far as I know it mixes at a constant 50 to 1
Any special reason you need to know this ???

 

[wilde1j]

Re: OMS Oil Raitio

It's always 50:1. The older VRO and VRO2 pumps did vary the ratio.

 

[Salmonseeker]

Re: OMS Oil Raitio

As far as I know it mixes at a constant 50 to 1
Any special reason you need to know this ???

I am considering going to premix since the pump has a very small leak that I think is coming from the electronics portion of the pump. It had the leak for a few years now and still runs great.

Most of my boating is done trolling so I am just above idle rpm most of the time with full throttle runs to my fishing grounds. Since I do troll most of the time, a leaner oil ratio would be beneficial to me. So if the OMS pump does vary the oil ratio from idle to full throttle, I might consider keeping the OMS pump. If it is definitely a constant 50:1, I might switch over to premix over the Winter.

From my own experience it seems like the motor uses less oil than 50:1 so I was wondering if it does lean out the ratio at idle.

 

[kenmyfam]

Re: OMS Oil Raitio

Even if it was variable I would never premix leaner than 50 to 1 trolling or not.
When you said "newest OMS pump" I thought there may be something brand new I had not heard about.

Stick with 50 to 1 if you start to premix. Your motor will love you for it !!!!

 

[Faztbullet]

Re: OMS Oil Raitio

Heres some info I had saved on this:
Since 1993, the VRO is actually called an oil metering system (OMS). The ratio averages about 60:1, slightly leaner at idle and slightly richer at full throttle. The older pumps idled between 150:1 (prior to 1990) and 100:1 (1990-1992), then richened up to 50:1 as the engine load increased. These are recognized by the brown fuel outlet fitting and/or a wiring harness attached to the alarm module. Even better, there's a new VRO (OMS) pump that can be used to upgrade all the previous years and model outboards. The new pump (P/N 5004558) contains various fittings for different outboards, and each internal part is replaceable for easier and less expensive servicing. Part number 5004559 updates all early three-wire VRO's except those found on the two-cylinders.

 

[Salmonseeker]

Re: OMS Oil Raitio

Even if it was variable I would never premix leaner than 50 to 1 trolling or not.
When you said "newest OMS pump" I thought there may be something brand new I had not heard about.

Stick with 50 to 1 if you start to premix. Your motor will love you for it !!!!

When I said "Newest", its because the motor is a 2004, so as far as I know its the newest.

I did a bit a searching on Google and keep finding conflicting information, some people claim the OMS pump does vary the ratio, but not as much as the original VRO pumps and others claim the ratio is constant.

 

[Chris1956]

Re: OMS Oil Raitio

Gee, I thought Faztbullet said that very thing. I tested my '98 OMS pump and found it averaged 60::1. I only did one test however, since that was the ratio I was expecting.

 

[rickdb1boat]

Re: OMS Oil Raitio

The OMS system does vary the ratio slightly, but not nearly as much as the old school pump. IMO, this makes it a better pump and gives the engine better longevity.