I just want to summarise my day with Clive at Ludham Norfolk, his home airfield working on oil pressure (OP) and oil temperature (OT) problems on my engine (serial number 1157 solid lifters large fins). It may of some interest to others out there experiencing low oil pressure issues or normal OP's with a cooler fix (head in the sand approach).
OP's have always been around 3-4 at tick over and cruising a 2900 with an earls oil cooler, braided ¼" pipes and OCA with a relief hole (around 3/32"). OT's hardly ever reached the optimal upper 80's, normally settling at around late 70's.
I was shocked to find OP dropped significantly at cruise to around 2.5 bar max when i removed the OCA and oil cooler. Tick over OP's were at 0.4 bar or less. I moved the OP sensor to the galley and pressures seen were alarmingly low. I did a lot of experimenting and eventually resorted to paying Clive a visit as I had plenty of conversations about OP's and OT's with possible solutions.
Here is Clive summary of our days trouble shooting jabiru's OP and OT's
problems:
Well we had an interesting day with Dean's engine, I hazard to say a completely successful one as the situation at the end is still not ideal. Dean does now have more than a bar oil pressure on tick over.
The `relief valve' was undoubtedly leaking precious oil which we proved by blanking it off with shim. However the significant oil loss isn't highlighted unless flying with the engine up to temperature. The lack of damage to the engine suggests there has been sufficient oil available at all times to feed the critical parts but the 0 psi on tick over on finals was a worry.
Incidentally we dropped off a rocker cover and got oil on our boots.
So after replacing the relief valve with my brass one and a new seat and getting reasonable readings on the ground the flight test showed the problem was still there, generally the pressure reflected the revs and was between 3.8 and zero depending on what the engine was running at. Zero on idle on final (wince).
After confirming with Roger it was OK to do a swap we fitted my Esqual's 3300 oil pump. Interestingly it looked like the relief valve was now in the game as the pressure never went above 4.1 bar, though I suppose that could have been all that was produced. The pressure did look as if it was held at that maximum though.
After flight test and flying home Dean has confirmed his has a readable pressure of 1.8 bar (?) on tick over. When flying, His oil temperatures were high however, higher than before the big pump was fitted (120 degrees Celsius +). I have suggested that now there is oil available to spray about then maybe that oil is picking up heat that it wasn't before.
One other thought Dean, the `leakage' in the engine is increased when the engine is at running temperature so there may be better pressure developed when the cooler gets the temperature down.
Roger also made a great observation, the new Thermo OCA will be ideal for your engine, to optimise the flow to the engine and keep the engine cool should further enhance the pressure situation for you.
Suggested way forward, fit the cooler loop, ground run and read gallery
pressure, flight test and get some readings. After getting a baseline on the
cooler diff put the sender back in the original position. I think you have a
bypass hole in the OCA already. Fly the plane, when available fit the thermo OCA. Fly the plane some more!
At some point I'd like to check what we are seeing regarding the relief valve and potential pulsing, if we still have a shortage of oil then optimising the relief valve performance (make it a regulator) can only help things.
Good to meet Dean, and a fun (but messy day), still need to do some flying when we next meet as it's many years since I flew in an SK. Thanks for lunch!
It seems that Jabiru has got this one wrong and it would be good to see them address OP issues with their engines. Introducing an oil cooler leads to an increase in pressure (likely to be due to back pressure) but that is definitely not ideal and does not translate to an increase in galley pressure which is essential to keep the journals well oiled and optimal engine (heads, cylinder and any other moving parts lubricated). As Roger mentioned, this is likely to increase wear and result in overheating (secondary role played by oil sloshing around) which could eventually lead to premature engine failure.
I appreciate Clive and Roger taking time to run through the technicalities of engine cooling and lubrication, all very valuable stuff and as clearly given me a better understanding on how my block runs! Happy flying ...
Jabiru 2200A Engine Serial #1157 oil Pressure problems
Moderators: John Dean, Moderator
Jabiru 2200A Engine Serial #1157 oil Pressure problems
Is this a possible explanation?
I have had another thought on this matter that may just explain jabirus au reasoning and motives for insisting on having an oil cooler on later engines.
Oil back pressure has been mentioned as the reason why we get higher OP’s with oil cooler. In order to prove whether OP increase was down to back pressure I mounted my oil cooler at the same height as the OCA. On running engine, I still noticed OP increase. I thought this was a little unexpected as I should not have seen an increase due to back pressure being minimal. I also expected to see pressure rising as I moved the Cooler above the engine but change was unremarkable.
Without an oil cooler, I have noticed that OP’s are acceptable to normal at lower oil temperatures. They are also within acceptable (barely) values in cruise (very close to yellow arc). With OT’s around the early 100 C. Oil viscosity changes with temperatures,. Therefore, is it possible that because oil characteristics are effected by temperatures (high temps make oil thinner) ,maintaining OT within certain parameters guarantees OP remains within acceptable ranges. In order to maintain OP within acceptable ranges, an oil cooler is required! There other factor that thicker oil will also reduce is seepage. Apparently, the rotor pump also looses efficiency as oil becomes thinner. So:
Oil cooler = Lower OT’s = thicker oil = more efficient pumping = Less seepage = Higher OP’s
No cooler = higher OT’s = thinner oil = Less efficient pumping = More seepage = Lower OP’s
I think the standard jabiru 2200A pump may also be undersized as volumes required to improve OP significantly are very small.
I have had another thought on this matter that may just explain jabirus au reasoning and motives for insisting on having an oil cooler on later engines.
Oil back pressure has been mentioned as the reason why we get higher OP’s with oil cooler. In order to prove whether OP increase was down to back pressure I mounted my oil cooler at the same height as the OCA. On running engine, I still noticed OP increase. I thought this was a little unexpected as I should not have seen an increase due to back pressure being minimal. I also expected to see pressure rising as I moved the Cooler above the engine but change was unremarkable.
Without an oil cooler, I have noticed that OP’s are acceptable to normal at lower oil temperatures. They are also within acceptable (barely) values in cruise (very close to yellow arc). With OT’s around the early 100 C. Oil viscosity changes with temperatures,. Therefore, is it possible that because oil characteristics are effected by temperatures (high temps make oil thinner) ,maintaining OT within certain parameters guarantees OP remains within acceptable ranges. In order to maintain OP within acceptable ranges, an oil cooler is required! There other factor that thicker oil will also reduce is seepage. Apparently, the rotor pump also looses efficiency as oil becomes thinner. So:
Oil cooler = Lower OT’s = thicker oil = more efficient pumping = Less seepage = Higher OP’s
No cooler = higher OT’s = thinner oil = Less efficient pumping = More seepage = Lower OP’s
I think the standard jabiru 2200A pump may also be undersized as volumes required to improve OP significantly are very small.
1/4" pipes to and from the cooler? Am I reading that correctly? That's around half the diameter of the pipes to the cooler on a Lycoming, so the overall cross sectional area must be around a quarter of the size.
I've no experience of Jab engines (but some with VWs, Continentals and Lycomings) but to me that sounds an awfully small pipe and could represent the restriction that is raising the oil pressure.
Has anybody investigated the normal solution to low oil pressure in cars - thicker (higher SAE) oil? Are we dealing with a multigrade or a straight grade oil here, and what weight?
I'm assuming these aircraft engines are using the correct oil filter. Some similar looking and fitting filters (for cars at any rate) have an internal bypass, whilst some do not.
Finally, what does OCA stand for?
I've no experience of Jab engines (but some with VWs, Continentals and Lycomings) but to me that sounds an awfully small pipe and could represent the restriction that is raising the oil pressure.
Has anybody investigated the normal solution to low oil pressure in cars - thicker (higher SAE) oil? Are we dealing with a multigrade or a straight grade oil here, and what weight?
I'm assuming these aircraft engines are using the correct oil filter. Some similar looking and fitting filters (for cars at any rate) have an internal bypass, whilst some do not.
Finally, what does OCA stand for?
Rob Swain
If the good Lord had intended man to fly, He would have given him more money.
If the good Lord had intended man to fly, He would have given him more money.
Jabiru 2200A Oil Pressure
Hello again,
did the following which made and enormous difference:
1. fitted the 3300 oil pump
2. changed hoses and fittings to 3/8"
3. fitted a thrmostatic Oil Cooler Adapter (laa mod)
Pressures are good throughout the rev range and temps are now nominal. Total cost of changes was around £400.00.
I am surprised that Jabiru importers are allowed to get away with this as there is an obvious inherent design issue here that needs to be addressed!
regards,
dean
did the following which made and enormous difference:
1. fitted the 3300 oil pump
2. changed hoses and fittings to 3/8"
3. fitted a thrmostatic Oil Cooler Adapter (laa mod)
Pressures are good throughout the rev range and temps are now nominal. Total cost of changes was around £400.00.
I am surprised that Jabiru importers are allowed to get away with this as there is an obvious inherent design issue here that needs to be addressed!
regards,
dean