Oil ?

[tx_swordguy]

I know this will bring out the flame throwers but will do it anyway. I am about ready for an oil change in my solid lifter jab 3300. I recently found Mike Bucshes webinar about engine oils. First I respect him and agree with a lot of what he has to say (but take all things with a grain of salt) That said he is a proponent of single grade oils. I have always gone on the idea of oil getting to all the bearings faster with the mult grade to be of benefit, he seems to think the single grade sticks to the parts after shutdown better than multigrade. I have been using phillips xc 20w50 for the last yr in my sonex. I have just recently noticed something with my oil pressure. I cruise at 2650-2700rpm and tx temps thus far have been below 80 and giving me an oil temp of usually less than 165. At these numbers my oil psi is 48-51psi and pretty steady at those numbers. I have just noticed if the oil temp gets closer to 180 and/ or my rpms go up I see the oil psi jumping back and forth between 35-47psi at a fairly fast rate. I am thinking it may be my sender going south so I bought a new VDO sender from jab (have not put it on yet). I always try to keep my oil level 1/2 on the dip stick which is measured full on my engine. Tx temps can easily get into the lower 100s with temps ranging from 87-110 in 24hrs from mid july to mid sept. I am considering either going with the phillips xc25w60 or the 100w single grade. I was wondering if the heavier oil might be of benefit, since jabs run hot usually anyway I am looking for comments/ideas about this. You tx jab drivers can give me your insight as well. fire away
Mark

[lutorm]

As a general principle, the big advantages of multigrade oil is when it's cold outside. If it's 100+F outside the oil won't be very thick anyway. At operating temperature, a 20W-50 and a straight 50 oil would have the same viscosity.

Also, I don't know about the Jabiru specifically but oil temps < 165F sound too cold to me. You want the oil temp to come up high enough to evaporate all the moisture and I think people generally say at least 180F for that.

[sonex1374]

Although Mike Busch does tend to like single weight oils, he routinely recommends Phillips XC 20W-50 for a lot of engines. It's what Jabiru recommends, and I use it as well. The conventional oil component in the XC helps suspend the lead sludge, and Ben at Jabiru USA swore by it.

A fluctuating oil pressure reading can occur with a failing pressure sender, with an over-filled sump (causes the oil to froth up and surge thru the pump, plus run hot), or a weakening oil pressure relief plunger spring. If the sender is failing it will happen at a variety of rpms, sort of randomly. If the sump is over-filled the temps will be high at higher power, but cool off with just a bit lower rpm. If the pressure relief spring is too weak the piston will move off the seat at the higher pressure pulses generated by high rpm (but not the lower cruise rpms).

With warm summer temps there is little practical value in multi-grade, but it's just more convenient to not have to store multiple types of oil for different seasons. Multi-grade is still fine if you fly weekly or so (let it sit for weeks, and then maybe single weight is better). In any case, camguard helps stick to the cam lobes and seems to be a good addition (3-4 oz per oil change means you'll only use a single bottle per year).

This should give you a couple things to mull over as you dig into things.

Jeff

[N190YX]

The Phillips tent at Oshkosh had a graph of viscosity of different oils at different temperatures and I was surprised to see that Phillips XC20W50 both is thinner at low temperatures, and thicker at high temperatures than single weight oils. So I asked them how that can be? They explained that the agents in the oil that make it thicker at higher temperatures actually make it hold up better (stay thicker) at higher temperatures than single weight oils. I had used single weight oils for decades (it rarely freezes here) but had switched to Phillips 20W50 on the advice of the owner of PowerMasters from whom I had bought a fancy Millennium overhauled engine, and have had great results, good pressure and low oil consumption. Interestingly, you can use Phillips XC20W50 to break in a new or newly overhauled engine as well as for the life of the engine, you do not need a non-detergent break in oil, the cylinders (piston rings against cylinder walls) will break in rapidly with XC20W50. You know the engine is broken in when the temperatures stabilize. Has only taken a couple hours flying at high power settings to break in my last two engines, the millennium engine and a factory remanufactured engine, using Phillips XC20W50. (no financial interest, just my experience)