Low Oil Pressure

[vwglenn]

I'm getting low oil pressure reading out of my 3300 at idle. The book calls for 11psi and I'm getting 7. This was after an extended ground run and a couple taxi tests showed oil pressure in the green. I took off and made a single trip around the pattern. When I landed and pulled the power back to idle I got the warning. This engine had about 6 hours on it since it came out from rebuild from at JAb USA.

Ideas?

[DCASonex]

This may sound odd, but you may have too much oil in there, especially if pressure was okay at start. With engine level, fill no more than to half way mark on the dipstick. Reason for this as explained to me is that with more oil, it will be full to point where it blocks passage under bearings that separate cylinder pairs. Piston pairs move in and out together displacing a lot of air. That air will churn and foam the oil when it passes under the bearing supports. This can also cause high oil temps. CAMit engines come with dipsticks more appropriately calibrated, but only when engine is level. For tail-draggers, must raise tail to get engine level, then after filling to half way point, note level on dipstick after putting tail back on ground. The 3300 engines will be greatly overfilled if not leveled before checking.

Are you using the standard pressure port that is at angle near top of crankcase or the forward facing one just below that. Standard port is pressure before filter and oil cooler, the forward facing one is pressure in galley after those. Galley pressure will always be lower, but 7 PSI is low for either.

Since your pressure is low at idle RPM, hose restrictions to oil cooler are not likely to be your immediate problem, but Sonex recommends replacing the 1/8" NPT hose fittings in the oil cooler adapter (OCA) with 1/4" NPT. Even then, depending on type of hose and fittings used to the oil cooler, the fittings may be too restrictive. If using Aeroquip fittings into braided hose, best to use AN8 (1/2") hose for those as fitting for the AN6 hose are a bit restrictive.

If you are not already a member of the Yahoo Jabiru engine forum, should join that, much more discussion of Jabiru engines there than here.

David A.

[vwglenn]

Thanks for the info. I'll certainly look into the oil level thing. With the tail on the ground the oil comes about 1/2 way up the dipstick now. I intend to do some additional troubleshooting this week.

Thanks again

[DCASonex]

Thanks for the info. I'll certainly look into the oil level thing. With the tail on the ground the oil comes about 1/2 way up the dipstick now. I intend to do some additional troubleshooting this week.

Thanks again

Half way up dipstick with tail on ground is TOO MUCH oil. Place a level on top of engine when making initial calibration. Have custom dipstick in mine now, but as I recall tail on ground just wet the tip of standard dipstick when filled to half way point when level. Will vary a bit with tire and tail wheel sizes.

David A.

[vwglenn]

Maybe I should clarify...it's 1/2 way between the empty and full marks not 1/2 way up the stick. Still, I'll start with an oil change and make sure I fill it appropriately. It certainly would be nice to hope a simple oil change and not overfilling the oil could fix the problem. I assume the "calibration" is somewhere less than the what the Jab book calls for (3.69 quarts)?

[vwglenn]

Update: Engine was significantly over filled. Leveled out (tailwheel raised)and the oil was filled beyond the full mark. Changed the oil and filled appropriately. Added a shim to the relief valve (now there are 2).

Oil pressure is worse. I was getting above 11 when it was cold before. Only had issues when it was hot. Now I'm getting between 3 and 5 psi at idle before the oil even has a chance to get to temp. Going to pick up a new oil sender tomorrow (shooting in the dark) and if that doesn't work I'll believe I only have one other option (oil & cooler lines) before I start getting to engine internals.

[GWMotley]

I might suggest that you check the calibration factor that the instrument is set to to be sure it matches the the proper reading for the oil pressure sender

[vwglenn]

Think my next move is to put a analog gauge right in the pressure port to see what the pressure really is.

[vwglenn]

I might suggest that you check the calibration factor that the instrument is set to to be sure it matches the the proper reading for the oil pressure sender

I did just that and, as near as I can figure, it's wrong. The sender is an ELO but has no part number on it anywhere. If it's original Jab equipment it has a range of 0-150 psi. I'm just not sure its original. It could be an 80 psi unit as well. Either way, the EFIS was set up for a 100 psi sender which would be wrong no matter which unit it is. Plus I have reason to believe the old sender was leaking. I bought a VDO sender on my way home and will install it this afternoon.

Crossing my fingers because I think my next course of action is to pull the engine and send it back to JAb USA. Hopefully they will be kind since it only has 5 hours on it since they rebuilt it.

[gammaxy]

Even knowing which sensor I had, it still wasn't completely clear exactly what settings to use in the EFIS. I connected the pressure sensor to my air compressor to verify that the EFIS was reading the correct pressure.