High Oil Temperatures

Mmspeare's picture

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I have a IO-550-N with a IO-550-G oil cooler (N725EM).  As summer started, I am regularly seeing oil temps at cruise at WOT/2400 RPM @ 7-9k of 220/221.  The engine likes to have 6-6.5 qts.   I have changed the vernatherm and baffling looks good.  Any recommendations on what else I might look at?

Legacyl2k's picture

More info needed:  Screen

More info needed:  Screen shot, EGT, CHT, speed, OAT, how long in cruise, compression ratio.   If I guessed it will be one of these issues unless you have and engine issue.  Baffling, Exit /inlet opening, fuel flow, or restricted air flow into or out of or both to the oil cooler.  But need much more info.  This engine airframe combination has worked well for several of my customers.

Mmspeare's picture

Hopefully this screenshot and

Hopefully this screenshot and pic will work.  Engine performing well, 13 degree OAT, 6k at this point, and FF at 16.5 gph.  The typical scenario is during climb at 130 Kias oil temp will rise to 229, then drop to 220-225 after transition to cruise and stay there.  Baffling looks fine, 6.5” inlets, no airflow restrictions.

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Legacyl2k's picture

One general observation is

One general observation is you climb speed vs FF.  FF is kinda low for a high power climb at that airspeed.  If I was doin a diagnostic test flight I would first look at you OT trend at the end if a 30 minute cruise flight at 8000 ft msl. With EGT's below 380.  Then go from there. For the climb I would add fuel or increase the IAS to aid in cooling.   135 kts is slow and probably not passing enough heat transfer through the oul cooler.  16.5gph is a ROP cruise power setting for an IO-550

Lancairmikees's picture

Matt, I used to see 225-230

Matt, I used to see 225-230 temps in climb on a warm day even running 150 deg ROP. Cruise temps in the 210 range. I removed the oil cooler door and opened up the cowl outlet openings about 8 sq in each. Now I rarely see 215 in climb and cruise at about 195. So much better, I put the oil cooler door back on for winter ops. 

Mmspeare's picture

Thanks for the insight.  I do

Thanks for the insight.  I do not have oil cooler doors on N725EM, but sounds like I should definitely consider.

My plane is like Mike's as I

My plane is like Mike's as I have no oil cooler door and the plane gets above 200 in the climb, but stays right around 195 during cruise. That is in 100 degree wx here in TX. The previous owner removed the door due to high oil temps. 

Matt,

Matt,

My first question is have you done the fuel setup procedure out of the M-0 maintenance manual.  There's two sections you need to reference if you haven't done it.  There's the procedure section and then the fuel adjustments section.  Also, when you make one adjustment you have to go back and check the other two as they are related.  You are adjusting Low bypass unmetered fuel pressure, idle RPM rise (relates to mixture richness), and then High RPM Metered fuel flow.  

Bottom line, keeping the CHTs in check during climb out also relates to the oil temp.  I can maintain about 176˚F on the CHTs during climb out maintaining 7˚ nose up pitch.

As far as Oil temp by itself is to consider removing the oil cooler bypass door.  I have never had one on my plane.  My typical oil temp is around 195˚F during cruise in the summer.

I would also check the baffling; more specifically, the gaps around the oil cooler area between the engine case and oil cooler box.  It's common to see 1/4" gaps.  The best way is go into the hangar when its dark and shine a flashlight around the bottom of the cylinders.  Gaps will show themselves.

George

 

Matt,

Matt,

I finished my ES in April.  On the first many flights in Redmond in the winter/spring, the oil temps were perfect -- maybe even cool, especially running it hard in break-in (170-185 range).  I actually worried that they might be too cool as I never got em up to 200 even in hard climbs, go figure, but it was cool at 7500 + Redmond at that time.  Then I flew coast-to-coast in May in some warm temps, and they would go into the low 200s on climb before settling back to 185 - 190 ish in cruise, adjustable via the oil cooler door, which I have, and which works.  Then my recent trip to Oshkosh.  In that flight, my temps started climbing into the 230s!  Hmmm.  I suspected it was probe or electrical issue because they fluctuated too much to be reasonable, and an A&P agreed when he looked at my data.  Plus oil pressure didn't drop much if at all when oil temp spiked.  Diagnosis on the ground showed two things: (1) fastening and unfastening a Deutsch connector to the probe sometimes made the reading consistent with what made sense; and, (2) later, when readings started to fluctuate too much again in flight, the reading was ~ 50 degrees too high on the ground after sitting overnight and rose to implausible readings given the heat of the engine on touch when taxiing.  I am still debugging the issue -- I ordered a new probe.  I will see what happens when I get my new probe (for the g3x) in a few days and change it out.  All of my other temps, and most importantly my oil pressure, have been normal during these escapades, which I think solidifies the evidence that it's either a probe or elecrtical issue.  But if others know better, please pipe up!  Ironically, I had a GSU 25 failure (ADAHRS for %1 g3x, but the switch to the back-up worked like its supposed to) on the same trip, along with a starter failure.  My last name's O'Brien, and we can just chalk that up to the reverse luck of the Irish.

Happy and safe flying,

Dan

Mmspeare's picture

Dan - When my oil temp rises

Dan - When my oil temp rises to 230-ish, my oil pressure is 46.  I was already coming to the same conclusion that I should order and install a new probe as well.  I'll wait to hear what your results are before I order.  Thank you for the insight.  

Matt,

Matt,

My oil pressure has consistently been in the 47-48 range during cruise.  It sometimes moves a degree when I open or close the oil door and oil temp changes, but I never say any of what seem to be more random escapades well into the 200s do anything to oil pressure.  The A&Ps tell the pressure should be dropping if its getting that hot.  I haven't been able to fly the last 9 days but may try to debug this issue this weekend.  BTW, the probe wasn't real expensive at Spruce -- less than $70.  Never thought I'd say an aircraft part seemed cheap! :)

I was showing my brother-in

I was showing my brother-in-law the plan yesterday in the hangar.  Fired up the g3x and the oil temp on the ground read 153!  Definitely time for a new probe.  Hope it's the ticket.  Will find out this weekend.

Happy & Safe Flying,

Dan