20W50 Oil in a Franklin
- Thread starter vh2q
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lwford
New member
I serviced and inspected a couple Stinsons with Franklin engines. I told the owners that engine was designed and made for 80 oct fuel and back then 50 wt mineral oil. Today you must use 100 oct fuel and the oil requirements have a wider choice i.e. mineral oil, AD oil and synthetic oil. I always used the mineral oil as rarely did these planes do 25 hrs. a year. They since been sold and I had my hand on them for 15 yrs with no major engine problems. So that has been my experience and opinion on the Franklins. Synthetic oil is much thinner when it gets hot and you will find that engine will have leaks that wouldn't happen with 50 wt. I wanted to reply to your inquiry as all too often nobody does, so what good is a forum without input. Lynn
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Robert Szego
New member
Thanks, Lynn.
This is a much-debated issue. There were many die-hards that insisted on straight weight oil (100W or 45W) and this includes me since 1975. However within the last two years I had been persuaded to use non-synthetic 20W50. Both oils served well and without problems, but the multi-weight sure helped winter starting. With pre-heat, of course.
PS: ~ 1980, the engine overhauler (small guy near Bridgeport CT told me the warrantee was void if I use a multi-viscosity oil.
This is a much-debated issue. There were many die-hards that insisted on straight weight oil (100W or 45W) and this includes me since 1975. However within the last two years I had been persuaded to use non-synthetic 20W50. Both oils served well and without problems, but the multi-weight sure helped winter starting. With pre-heat, of course.
PS: ~ 1980, the engine overhauler (small guy near Bridgeport CT told me the warrantee was void if I use a multi-viscosity oil.
Well my question arises from the perspective of the bypass valve, the operation of which is predicated upon a certain viscosity of oil. The spring is calibrated for the original 40 weight recommended oil as I understand it. The multigrades are supposed to maintain a slightly thicker viscosity at higher operating temp, which might confuse the bypass valve. I have also read the Franklins run at lower pressure because they have wider bearing shells. All of this may be folklore but I am new to this so trying to learn. I had an oil temp excursion after I added 20W50, at the same time I had an oil cooler leak.
I do appreciate the input, seems there are not too many participants of this forum.
I do appreciate the input, seems there are not too many participants of this forum.
Adding some history and maybe some smoke abatement on the subject.
I go way back to the late '40's beginning my aircraft mechanic'ing at Aero Mechanics High School in Detroit. Straight aircraft oil was all there was in that era. Stuck and broken rings with scored cylinders was about a 50-50 proposition at 500 hours on an engine. Twenty percent of the planes were flying with stuck rings and burning a quart every 2 hours or so. I remember airplanes trailing blue smoke as they passed the school overhhead at the north end of City airport. When detergent ( compounded, AD) oil came in later, all that went away. It was like the fog had lifted. The change was dramatic.
Some aircraft owners continued to use straight mineral oil and many paid the price. I had my hand in repairing or rescuing many engines in the '60s and '70s. I remember pulling jugs and laughing along with an assistant as pieces of ring hit the floor. Not funny, actually.
Would I ever use a straight oil? No. Maybe not even for break-in, though any straight oil deposits that occur should be gone in a while after changing to AD oil. I could be talked into a lower viscosity, for break-in, though. Oil is the internal engine coolant, and more flow to cool bearings and pistons would seem to be good as the break-in process more quickly polishes high spots to a good fit.
At any rate, all oils are likely better than when these old engines were certified. What was available then should not justify today's choices for aircraft oil.
To directly address the OP's topic: the FAA TCDS for the 220 Franklin shows 15-50 and 20-15 approved, with the required specs for oils at note 13.
Ron
I go way back to the late '40's beginning my aircraft mechanic'ing at Aero Mechanics High School in Detroit. Straight aircraft oil was all there was in that era. Stuck and broken rings with scored cylinders was about a 50-50 proposition at 500 hours on an engine. Twenty percent of the planes were flying with stuck rings and burning a quart every 2 hours or so. I remember airplanes trailing blue smoke as they passed the school overhhead at the north end of City airport. When detergent ( compounded, AD) oil came in later, all that went away. It was like the fog had lifted. The change was dramatic.
Some aircraft owners continued to use straight mineral oil and many paid the price. I had my hand in repairing or rescuing many engines in the '60s and '70s. I remember pulling jugs and laughing along with an assistant as pieces of ring hit the floor. Not funny, actually.
Would I ever use a straight oil? No. Maybe not even for break-in, though any straight oil deposits that occur should be gone in a while after changing to AD oil. I could be talked into a lower viscosity, for break-in, though. Oil is the internal engine coolant, and more flow to cool bearings and pistons would seem to be good as the break-in process more quickly polishes high spots to a good fit.
At any rate, all oils are likely better than when these old engines were certified. What was available then should not justify today's choices for aircraft oil.
To directly address the OP's topic: the FAA TCDS for the 220 Franklin shows 15-50 and 20-15 approved, with the required specs for oils at note 13.
Ron
Apologies for being mislead by an "oil wars" diversion near the top of the thread. The OP's question was:
Some possibles:
If the cooler has a thermostat valve as mine does, it could be the culprit, fails open and bypasses.
There are 2 springs and balls in the engine oil control assembly. One is the oil pressure regulator. The other is the oil cooler bypass. If failed or improperly assembled, a bypassed oil cooler could result.
Oil Cooler clogged?
You may have an oil filter. Should be in series with the oil cooler or if in parallel, it must have a restrictor, otherwise, it is bypassing the cooler. If the filter is in series, "full flow", ideally, the bypass spring should be a little stronger to compensate for the filter restriction pressure so that the it does not bypass unnecessarily.
As i recall, oil cooler and filter restriction and bypassing will show up as reduced oil pressure - not sure.
Ron
Very unlikely, no.vh2q said:
Some possibles:
If the cooler has a thermostat valve as mine does, it could be the culprit, fails open and bypasses.
There are 2 springs and balls in the engine oil control assembly. One is the oil pressure regulator. The other is the oil cooler bypass. If failed or improperly assembled, a bypassed oil cooler could result.
Oil Cooler clogged?
You may have an oil filter. Should be in series with the oil cooler or if in parallel, it must have a restrictor, otherwise, it is bypassing the cooler. If the filter is in series, "full flow", ideally, the bypass spring should be a little stronger to compensate for the filter restriction pressure so that the it does not bypass unnecessarily.
As i recall, oil cooler and filter restriction and bypassing will show up as reduced oil pressure - not sure.
Ron
Good discussion and thanks to those who contributed. All good food for thought.
I found a reference on the Velocity forum to this same issue (oil cooler bypass circuit leading to high oil temps in a Franklin). Due to the layout of that aircraft, owners who use Franklin engines resort to a stiffer spring in the oil cooler bypass circuit. This overcomes the higher pressure drop due to the longer runs and the oil filter. There is an outfit in Poland that sells the stiffer spring.
On the other hand, I spoke with a knowledgeable person I was referred to by Susan at Franklin. He said he had never encountered an overheating problem due to the oil cooler bypass spring not being stiff enough. He has encountered several instances where people installed a spin-on oil filter and plumbed it backwards, which effectively blocks the oil cooler circuit. He did say that a lot of owners put one or two washers under the springs (one or both sides) to up the oil pressure, or just for peace of mind. Apparently, these springs lose tension over time.
Susan cannot supply a stiffer spring. They have only the stock spring(s) in inventory. The manual calls for 2.1 to 2.4 lbs of force to compress the spring to a length of 1 1/16". My springs were both replaced in Feb this year. Out of curiosity, I checked the oil cooler bypass spring that was removed in Feb by this method and it registered at 2lbs. So it was a bit weak. I have no idea how stiff the new spring supplied by Susan is. I asked her to find out.
Having said that, the guys who have been working on my plane were convinced the oil temp excursion was a function of the gauge. We rebuilt the gauge. Same issue. They then rewired the gauge with new wire, said the old wires had a couple butt joints that introduced additional resistance. Apparently higher resistance imitates higher oil temps on the gauge. I would have thought it would be the other way round, since the gauge is effectively a voltmeter. But in their favor, the problem then resolved. At least it did for a 25 min "stress test" flight. Hopefully it will not reappear. I will put a couple washers under that spring though, when we next have the cowling off.
I found a reference on the Velocity forum to this same issue (oil cooler bypass circuit leading to high oil temps in a Franklin). Due to the layout of that aircraft, owners who use Franklin engines resort to a stiffer spring in the oil cooler bypass circuit. This overcomes the higher pressure drop due to the longer runs and the oil filter. There is an outfit in Poland that sells the stiffer spring.
On the other hand, I spoke with a knowledgeable person I was referred to by Susan at Franklin. He said he had never encountered an overheating problem due to the oil cooler bypass spring not being stiff enough. He has encountered several instances where people installed a spin-on oil filter and plumbed it backwards, which effectively blocks the oil cooler circuit. He did say that a lot of owners put one or two washers under the springs (one or both sides) to up the oil pressure, or just for peace of mind. Apparently, these springs lose tension over time.
Susan cannot supply a stiffer spring. They have only the stock spring(s) in inventory. The manual calls for 2.1 to 2.4 lbs of force to compress the spring to a length of 1 1/16". My springs were both replaced in Feb this year. Out of curiosity, I checked the oil cooler bypass spring that was removed in Feb by this method and it registered at 2lbs. So it was a bit weak. I have no idea how stiff the new spring supplied by Susan is. I asked her to find out.
Having said that, the guys who have been working on my plane were convinced the oil temp excursion was a function of the gauge. We rebuilt the gauge. Same issue. They then rewired the gauge with new wire, said the old wires had a couple butt joints that introduced additional resistance. Apparently higher resistance imitates higher oil temps on the gauge. I would have thought it would be the other way round, since the gauge is effectively a voltmeter. But in their favor, the problem then resolved. At least it did for a 25 min "stress test" flight. Hopefully it will not reappear. I will put a couple washers under that spring though, when we next have the cowling off.