Going out for my second sortie and while in the climb with full power I got that hot oil smell and a bit of mist in the cabin.  Closed the heat control valve, reduced power and "bee-lined" to the airfield with good oil pressure while venting the cabin. Taxied in with good oil pressure to a shutdown in front of my hangar.

What a mess...I was down to just below the min line on the dipstick.  Luckily I have another oil cooler (AERO-Classics) on the shelf which I've been meaning to put on since this summer.  I've heard bits and pieces regarding the quality of the UL provided oil cooler and wanted to see if a different cooler might help out with cooling (and quality?)  Anyway, something to think about I guess...

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Hi David, thanks for all of the info and pics. Your expertise, ingenuity and get 'er done ability is a great help to the rest of us. and your zenith is all nice and clean again.. Fly on.

Roger, Wilco!!


FWIW I have an AERO-Classic 10-row cooler on my Jab 3300.  The original Jab USA FWF installation instructions used rubber washers/bushings with the original 7-row cooler.  When I went to the 10-row, I deleted the rubber bushings because of clearance issues with the cowl.  Being a 6 cylinder, the Jab is an exceptionally smooth-running engine (my DynaVibe prop balance was below the limits of human perception!), but I have carefully watched the oil cooler mounting and have had no problems in 500+ hrs.



John, thanks for the cooler input!  I likely have the same model cooler - non PMA, and it is indeed a ten row vice a thirteen row I stated in my earlier post.  I feel fairly confident that the lack of isolation mounts will not be a problem in the long term - even with my four cylinder engine!  Compared to helicopters, these 750 airframes and components have a life of leisure regarding stress cracking, etc.  Having said that, I do plan on doing the DynaVibe balance on the prop later this Spring as soon as I fabricate a mount for the sensor pickup.  Just got to get over a couple of my own cracks...


The builder of my plane also had the ULpower supplied oil cooler "blow" on him.  He installed the 10 row AERO Classic; no issues since.  These engines always seem to have real warm oil, and cool CHTs.  I'm sitting at a little under 450 hrs on the 350iS now, and it's been great.  But seems the starter solenoid is starting to act up a bit..  Keep up the fun.


  Just have to ask, how many hours did the oil cooler have on it when it died, and how is the replacement attached? Fixed solid or rubber shock?


Hi, Ralph

I sold the 750 to Coner, but in the first 80 hour I lost two ULP oil cooler. They both had two rubber mounts. I changed to a Aero Classic with four rubber mounts. Conor

bought the plane with around 186 tt, and has 450tt now.

Ron Simonsen 

Dave just curious as to what your oil pressures are averaging with the UL unit vs The new unit? . I’m getting 90+ psi at cold startup and at Temp I’m averaging around 40psi at idle with the ULP .

Phil, those numbers are similar to mine with the ULP cooler. 90 PSI initially dropping to 60 during the 1350 RPM warm up. Cruise at 2500 RPM yields about 42 PSI on the oil pressure.  I've only got one flight in with the new cooler so far and the data is not much different.  87 PSI at 1500 RPM during warm up. 41 PSI at 2500 RPM cruise and about 20 PSI at RPM less than 900.  SavvyAnalysis makes reviewing the data easy!!  Hope this helps.


New oil cooler with rubber edge trim installed...

Add one more data point to the blown oil cooler.  Mine went south on my trip back from Oshkosh.  Small pinhole in the front.  I was down to about a quart and a half when I landed.  Just a faint burning smell.  I had no other drop in oil pressure until I landed.  Fueling up the plane and oil dripping every where.  Looked just like David's picture without the skis.  Roger was able to hook me up with a new cooler to get back to Paris, Texas. Many thanks to him and Joyce at Zenith.   Uneventful flight back.  Will be ordering a 13 row aeroclassic later today.  I was planning on switching it out at my 100 hr oil change.  I had about 70 hrs on the engine.  My temps have been in the 198-203 range.   Wondering if  I should pre weld my muffler pipe before it falls off.   I left the oil cooler back with Roger at Zenith as he wanted to have it tested.  Will post with any results that I get. 

I uploaded a couple videos to my YouTube channel.  1960drfred. 

This should be the link. Oil pressure is 67 at 2600 rpm. Temps 195. I think it dropped my oil temp about ten degrees.  There also is also a video on the channel about the fiberglass repair. Whatever you use as a form, just cover it with clear packing tape so it will release from the epoxy mix.  




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