OMS / VRO Pump Verifying Oil Pump Delivery

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
VKR
Posts: 25
Joined: Sat Oct 17, 2015 8:39 am

OMS / VRO Pump Verifying Oil Pump Delivery

Postby VKR » Fri Aug 19, 2022 11:47 am

I recently installed a new OMS Pump Kit (OEM BRP P/N 5007423) on my 1986 Johnson 150 (J150TXCDC).

INSTALLATION AND TESTING
In addition to a new pump, I installed a new oil tank, inline pulse limiter, and hoses with proper BRP Ratchet Clamps. During the install, I tested the new oil tank and confirmed the low oil alarm will be functional. In addition, with 50:1 premix gasoline (XD100) in tank and flushed through my fuel lines, I installed a 20” clear hose to the oil inlet of the OMS Pump and filled the hose with oil to confirm pump operation at approximately 1,000 RPM. I did not test pumping at the higher RPMs given the related speed and considering safety around the powerhead. The pump drew in oil. The pump pulsed out oil through the clear hose, and I confirmed the no oil alarm worked after oil was exhausted from the clear line. I then removed the clear hose and attached the flushed-out purged inlet hose from the oil tank to the OMS pump. The no oil alarm stopped sounding confirming the pumps ability to self-prime.

VERIFYING OIL DELIVERY
Over a seven day period I ran a total of 63.6 gallons of pre-mixed fuel (gasoline and XD100) through the engine.
I verified the engine was consuming oil.

I tracked the fuel usage using my Garmin GFS 10 Fuel Sensor, which I find to be very accurate. Approximately three-quarters of the total run hours were low speed trolling at about 800-RPM, and one-quarter of the total hours were running at 2,800-RPM or above. Prior to starting this oil consumption test I made sure the oil tank was filled to the rim and made sure no air pockets were in the oil tank. After running a total of 63.6 gallons of premix through the engine, I topped off the oil in the oil tank again releasing any air pockets and filling to the rim. To my surprise, I only added 104 ounces of XD100, suggesting only 104-ounces were consumed. This results in an average fuel to oil ratio of 78:1.

I was confident the OMS oil pump was pumping oil. However, I expected a fuel to oil ratio closer to 60:1. Any thoughts on whether oil consumption is appropriate for my estimated running time at the above speeds? I understand the OMS oil output is "somewhat leaner at idle. Would this account for my 78:1 average fuel to oil ratio?

jimh
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Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
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Re: OMS / VRO Pump Verifying Oil Pump Delivery

Postby jimh » Fri Aug 19, 2022 3:26 pm

I am impressed with the precision of your data and your diligent testing of the system before reverting to reliance on the VRO to provide oil to the engine. It sounds "textbook."

Regarding the ratio of oil-to-gasoline from a properly working VRO, I believe the V part of VRO was for variable. The inference is for engine operation at idle speeds the oil mixing ratio will be leaner; your outcome seems to indicative of that concept.

To have an overall oil-to-gasoline mixing ratio of 1:78 seems higher than expected, which I think is why you are asking about it.

Let's check the math.

Gasoline consumed was 63.6-gallons. Converting to ounces gives 8,141-ounces.

Oil consumed was 104-ounces. This gives a ratio of 104:8141 or = 78.2:1. The math looks good.

I think the measured oil quantity was probably quite accurate as you used the refill-to-same-mark method.

The fuel quantity could be a bit more variable in accuracy. If the fuel sensor was an in-line turbine spin sensor, they are not always accurate a low fuel flow rates. But in my experience they tend to undercount the fuel volume used at low speeds. However, that would suggest even more than 63.6 gallons were used, which would make the ratio number even higher for fuel.

I don't have any data to share from my experience with my Evinrude VRO engine; I just recall that is seemed to use oil in what was an appropriate amount. I never really worked out the ratio (as I can recall) with much precision.

The one perhaps cogent comment that I can offer is in regard to the basis for determining the ratio of high-speed to low-speed operation. Using TIME as the comparison is not appropriate. Let me explain.

Suppose your engine was extraordinarily fuel efficient at idle, to the point that practically no fuel was consumed. Then almost ALL the fuel consumed would have occurred at the higher engine speed. Then, instead of using the 1/4 and 3/4 comparisons of engine operation and rate of oil flow, you would need to use something more like 1/10 and 9/10 comparison, as 9/10 of the fuel was consumed at the higher throttle setting. But this again works against the overall ratio being so lean on oil.

One comment I can make based on experience is that older two-stroke-power-cycle engines tend to be miserable in terms of fuel economy at engine idle speeds. They are using more fuel than you would think. This approach might affect how you apportion the oil consumption rates, so instead of 1/4 and 3/4 as based only on time, on actual fuel volume it might be more like 1/2 to 1/2, that is you may have burned just as much fuel at low speed as at high speed.

If you follow that analysis, then the 78:1 figure looks more reasonable. Let us assume that the VRO mixes 50:1 during high speed engine operation and 100:1 at low speed engine operation. Now we must assess on the basis of an EQUAL volume of fuel was consumed at each operating speed. In that case the average mixing ratio would be 75:1, which is very close to what you measured.

VKR
Posts: 25
Joined: Sat Oct 17, 2015 8:39 am

Re: OMS / VRO Pump Verifying Oil Pump Delivery

Postby VKR » Sun Aug 21, 2022 5:57 pm

Yes, my major concern was the 78:1 Average Fuel to Oil ratio calculated for the 63.6 gallons consumed.

I appreciate your detailed reply. I agree with your point about using Time as the comparison. It isn’t appropriate given it is not the most significant input factor to the fuel to oil ratio (output of concern). For example, checking yesterday, at 1,000 RPM my flow meter displays approximately 2.5 gallons/hour. At 3,000 RPM (cruising up on plane), my flow meter displays 8.5 gallons/hour. Running the math using the 75% trolling vs 25% at 2800 RPM or above, over a 100 hour period I would burn 187.5 gallons trolling and 212.5 gallons at 3,000 RPM. Therefore, your point is well taken regarding oil consumption rates at the two speeds.

In hindsight, I should have performed calculations daily instead of over the seven-day period or, for example, after trolling for three hours to validate the OMS pump's ability to provide variable oil rates. Yesterday, I consumed 8.2 gallons of fuel running up on plane and mainly at 2800 to 3600 RPM. There was limited trolling in and out of two “No Wake” zones. Using the same methodology, I added 17 ounces of oil to top up and burp the bubbles out of the VRO oil tank ensuring full oil to the rim. This yields a 61.7 Fuel to Oil Ratio which I was at peace with from a psychological standpoint. I am gaining confidence in my new OMS Pump install but will continue to take a few more readings prior to going pure gasoline and no pre-mix in the fuel tank.