Zenith Aircraft Builders and Flyers
Is Oil Sump Cooling Necessary Jabiru Gen 4?
Most experience reports for the Jab 3300 Gen 4 indicate no problems with CHT's/cooling. I had a Gen 2 3300 built in the transition to Gen 3 with some, but not all of the Gen 3 improvements. On my 750 STOL, I went from a 7-row to a 10-row oil cooler and still ran marginally high oil temperatures. (I'm in East Tennessee, so it's a temperate climate with no extreme summer heat, etc.) I then ducted bleed air off the left ram-air duct and enclosed the fins over the front of the oil sump and ran the ducted air through this and it remarkably helped the oil temps:
I have a Gen 4 arriving next month and have heard they are much easier to cool with the all-aluminum cylinders and increased fin area, so I'm thinking it's likely the oil temps will be cooler, too. So, for those with a Gen 4 in a 750 airframe, STOL or Cruzer, a few questions:
- How many rows oil cooler are you running?
- Have you made any modifications to cool the finned sump such as create an opening in the top baffling of the oil cooler air inlet to allow air to flow up to the sump, or, cut an additional slot in the cowl feeding a duct to the oil sump (I believe Zenith has a kit for this?), or, have found that no additional oil sump cooling is necessary?
- If additional oil sump cooling is necessary, are you in an extreme heat climate - Arizona, etc?
I likely can re-fit my oil sump duct to the new Gen 4 if necessary, but it sure would be nice if no additional cooling was required!
John
N750A
John Austin
Update: Asked Nick at Arion Aircraft (the Jabiru engine dealer) the questions above and said he personally had installed at least two Gen 4's in 750 STOLs, both having the "old style" lower cowl design (same as I have) before it was changed to a more efficient design several years ago, and that they had no problem with cylinder or oil cooling. He recommended going with the 7-row cooler and not adding any supplemental cooling as it was likely it wouldn't be necessary and could always be added later.
John
Feb 29
John Burns
I have the sump cooling duct on my Gen 4 installed with the rectangular cowling hole to feed the air through the duct and past the sump just like the factory demonstrator, but the only problem I have ever had is with low oil temperature. I have the oil cooler taped over for winter and probably won't pull the tape until 50° or 60° temperatures. If I had it to do over, I would skip the sump cooling until I had a reason to add it.
Mar 2
John Austin
Update, I now have a few hours on the new Gen 4 and initially, the oil temps were running about 210 or so in our cool spring weather. Between the cowl opening and the oil cooler, I cut an approximately 1" x 4" slot in the connecting rubber shroud. The slot is immediately adjacent the top of the oil cooler, allowing air to flow up onto the engine's finned sump. This immediately lowered my oil temps into the 190'sF and no large increases in temps in steep climbs. I'm thinking I might frame this slot with some aluminum to reinforce it and perhaps prevent tearing in the corners, etc, and also to provide something to attach a block-off plate if it's needed in the winter.
John
Apr 25