Constant or Variable ratio oil pump?

[saumon]

Hi,

i currently have a 1993 Merc. 60hp inline 3 cyl that i teared down to rebore it (w/p goes bad, it overheated and piston #1 is badly scored, #2 a bit too and #3 look good: pretty typical of an overheating problem).

A year ago, i bought an almost identical engine (same year) with a blown powerhead for 400$, wich was a deal considering the lower unit was good, the power trim, the starter motor, the switchbox and so on with all theses costly parts.

To make a long story short, my current engine had a red stator, rectifier and fixed ratio while the "parts" engine had the black stator, a voltage regulator and a variable ratio oil pump. I already change my rectifier (i usually got around 16 volts at WOT and it make my battery "boil" so the electrolyte evaporate) for the voltage regulator and i'm wondering what's the deal with the variable ratio oil pump vs the constant ratio one. I assume the fixed ratio always put a 50:1 mix while the variable one range from 100:1 at idle to 50:1 at WOT. Is it right? And is it an improvement, or is it a "test" they made? Is this a good design and should i swap the carbs and this fuel pump on my engine?

Am i better to stick with my fixed 50:1 or is the variable system more efficient?

I really tought about swaping them, so please let me know if i made a mistake or not.

What will be the effects: less smoke at idle and maybe less carbon buildup behind the ring, but also less protection in case of water intrusion or overheating i guess?

Thanks for your input guys!

(sorry for the double post but i first ask in the Merury/Mariner section and didn't get any response...)

 

[rolmops]

Re: Constant or Variable ratio oil pump?

OMC used to have the variable VRO.It was discontinued and they went back to constant 1:50. To many outboards blew up.
I guess you can take it from there.

 

[rodbolt]

Re: Constant or Variable ratio oil pump?

omc/brp has used a variable ratio oil pump since the early 80's. even a bit older if you want to discuss the econo-mixer setup from the late 70's.
mecr tried a stand alone method but it failed.
now, to get back to your merc.
if the oil pump is crankshaft driven with no linkage to the throttle it is constant. if it has a link arm its variable and that goes for all two stroke with crank driven oil pumps for the us market.
the omc VRO got blamed for a lot of failures but since the introduction of the 4 wire vro pump it was very very rare.
most oil related failures from all brands are customer induced due to a simple lack of maint.

happens even today
same with cooling systems.
if you NEED a water pump odds are high you now NEED a piston.
the guys mixing 6 gallons at a time have few issues, most my customers have fuel tanks in the above 150 gallon capacity and then there are issues.
most all modern oil injection systems work very very well but only if maintained.
you CANNOT wait till it fails to fix it or the odds are high the engine was damaged.

 

[saumon]

Re: Constant or Variable ratio oil pump?

The 2 that i have were crankshaft driven. It's only that the one currently on my engine is a 50:1 fixed ratio while the one on my "parts" engine (almost identical) was a variable ratio one linked to the bottom carb, and i'm asking if one is better than the other...cause i'm considering swapping them, thinking that the variable system will be less prone to plugs fouling at slow speed, but i fear to loose the extra protection that the fixed ratio give...