Mailing List Message #49480
From: Rino <>
Subject: Re: [FlyRotary] Re: Oil Cooling
Date: Sun, 20 Dec 2009 21:12:48 -0400
To: Rotary motors in aircraft <>
Same observations here when I dumped my engine oil over the lake.  The O2 stopped working and the oil did not catch fire on the exhaust stack (Mobil 1, 10-30).  The question is does the O2 sensor have to be replaced?
The engine rebuilding is coming along.  Here is a photo of the iron laping technique suggested by Lynn, it worked.
Rino Lacombe
----- Original Message -----
Sent: Sunday, December 20, 2009 8:33 PM
Subject: [FlyRotary] Re: Oil Cooling

Glad no damage to engine, aircraft or pilot – seat cushions are easily replaceable.  I guess it just goes to show that you never get to the point that you have eliminated all possible “gotchas!”  .  Anything different, anything new and you have a new system to deal with and all that entails.


Sounds like you at least got your cooling problem licked.  Good observation about the poor burning quality of the synthetic motor oil and about the O2 sensor.  I had not thought about the O2 sensor needing ambient air to make the comparison of O2 levels, but it makes sense when you think about it.


Ok, Tracy, stop messing around, we want to see you fly that thing someplace where the rest of us can see it {:>)




From: Rotary motors in aircraft [] On Behalf Of Tracy Crook
Sent: Sunday, December 20, 2009 5:58 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Oil Cooling


I was ready to flight test the new oil cooler installation this morning (or thought I was).   OAT was only 41 deg and it took a long idle time to warm up so used that time to check for oil leaks and saw no signs.  The pattern of oil and water temps looked good so I had high hopes.  Watched temps during takeoff run and continued to see good numbers. Climbed out to 500 ft and turned left to downwind and thought I smelled a slight whiff of hot oil.  Looked over my shoulder and saw that I was sky-writing with a dense smoke trail so throttled back to high idle and did a hard 360 to the right to setup for a downwind landing (almost no wind).   The only thing new was the oil cooler so I was scolding myself for installing this cheap POS and monitoring the oil pressure to see if this was going to cost me an engine overhaul.  Pressure stayed at 55 - 60 PSI all through the landing so its OK.   The oil cooking off the exhaust system did not ignite.  Wonder if the poor burning qualities of synthetic oil is another good reason to use it?

On the ground it looked like there was a couple of quarts of Mobile 1 dripping off the bottom of fuselage and left wing trailing edge.   Popped the cowl top and the entire engine compartment is drenched in oil EXCEPT for the oil cooler core itself which is dry.  The cooler turned out to be OK.  The leak was from the bottom fitting on the cooler.  It came equipped with -10 male fittings so I had installed -10 to -8 adapters to match the -8 hoses in the plane.  The tightening procedure needed on these adapters had some pitfalls.  I am always careful to use two wrenches on these fittings so as not to put torque on the cooler and damage it.  These adapters require that the adapter be put on first using the two wrench method followed by the hose fitting to the adapter.  BUT,  one wrench needs to remain on the oil cooler fitting and the other on the hose fitting.  I mistakenly put one on the adapter and one on the hose fitting.  This results in loosening the adapter to cooler mating thread as you tighten the hose fitting.  That's where the oil was coming from.

Although this was a very brief flight on a cool day, I could tell from the trend on the oil & water temps that this cooler was going to work much better than the old one even though it is about 25% smaller in volume.  Size really isn't everything.

I properly installed the adapters and hose fittings and tested for leaks (none found) but didn't have enough daylight left for another flight test.  Will try again tomorrow. 

Noticed one other oddity during this test.  As soon as the O2 sensor got covered in oil, it quit working.  These sensors actually have to 'see' the outside air at the cold end of the sensor.  They compare the O2 in the air to the O2 in the exhaust and stop working when they can't.  


On Sun, Dec 20, 2009 at 4:58 PM, <> wrote:

I've been reading everything I could on cooling after my first attempt flopped. Today I got my new cooling set up complete enough to ground test. I copied (my version) from several of you, notably Dave Leonard's radiator and Tracy's RV-4 oil cooler. Hat's off to Ed Anderson for all the under cowl duct work on his website too.

I did achieve the stable temps at low power that Dave L told me are critical. I just now got done running my RV-8 13B turbo for over 20 minutes and got stabilized temps of 140F water and 170F oil. Once the oil cooler thermostat opened, the temps dropped a few degrees.

Outside air temp 53F, 81% RH. Perhaps I should have run it longer, but worries about leaks, fires etc. always make inspections prudent.

I suppose I have overcooled my plane, and added a big drag bucket on the chin, but hopefully it will be safe to fly, and I can work back from 'too cool' for more speed later.

After reading Tracy's post about adding the oil cooler exit duct, and different flow resistance of the two coolers,  I am glad I devided the two.

What I think lead to any success I might be having, is that I devided the air suppies and outlets. The oil cooler gets 100% of the right cowl cheek air, and the heated air exits the right side of the cowl. The radiator gets air from the highest pressure point on the airframe: under the prop spinner. I left out the upper lip because I believe this area has attached laminar flow. The radiator exit air passes out the cowl bottom in the usual way.

The left cowl cheek is for Engine intake, plus surface cooling air on the engine, turbo, & fuel system. It shares the bottom outlet with the radiator air. I'm still working out the this duct.


-----Original Message-----
From: Tracy Crook <>
To: Rotary motors in aircraft <>
Sent: Sat, Dec 19, 2009 5:46 pm
Subject: [FlyRotary] Re: Oil Cooling

In retrospect it does seem obvious but I had never thought about matching the airflow characteristics of the water and oil heat exchangers before.  I should know by tomorrow if this is just wishful thinking.

Those heat exchanger volume figures you mentioned are at best just a rule of thumb but still useful.  Other details can make a world of difference.  For example, my RV-4 has had the same cooling components since day one but cooling on that first flight looked hopeless.  Now it is fine on even the hottest days.  Heat exchanger size isn't everything.

My 20B has significantly less than 1.5 times the core volume of my 13B installation.  I'm hoping that better diffusers and other details will make up for the relatively smaller heat exchangers.

I can't think of any reason why the 20B would need more than 1.5 times the 13Bs cooling requirement if all other factors are the same.  That's a big if of course. 


On Sat, Dec 19, 2009 at 7:15 PM, George Lendich <> wrote:


All that makes perfect sense and leads me to a question which has more curiosity value than anything else. What actual size did you settle on for the 20B. I'm curious to know if the 20B requires more cooling than 1.5 times a 13B.


Calculating the ( rule of thumb) radiator size of approx 600 cu" for 200hp, giving 3 cu" per HP, the size of the Mazda oil cooler then gives a .8 per cu" per hp. I wondering if this holds true for the 20B and indeed the single rotor.

George ( down under) 

Just an update on my RV-8 / 20B  oil cooling experiments. 

On the theory that airflow patterns inside the cowl were blocking airflow through oil cooler, I installed a partial exit duct behind the radiator directing the airflow downward toward the cowl outlet.  It looked very restrictive but flight tests showed almost no affect on water cooling (which is OK)  but a significant improvement in oil cooling.   I further restricted the airflow through the rad by putting some roof ridge vent material inside the inlet diffuser.  This gave a tiny increase in water temp but a further improvement in oil cooling.   Long story short,  after several more tests it became apparent that back pressure under the cowl was having a major effect on the oil cooling.   I have no idea why my instrument did not read the pressure correctly.  It works fine on the bench and is properly referenced to the static system in the plane.   The temptation is to keep changing the cooling outlet scheme until the internal cowl back pressure is low enough to get the cooling good enough.  My belief is that this would lead to a very high drag solution.  You may remember the experiment I did by flying with the cowl removed.  The cooling was never a problem then (except perhaps too much cooling) but the drag was enormous.  The fuel burn was 60% higher at the test airspeed of 130 mph.

The conclusion I eventually came to was that the rad (because of it's relatively low air flow resistance) is hogging the airflow capability of the cowl cooling outlet.  (cowl flap did not have enough effect to fix the problem).   Keep in mind that the oil cooler is a thick AC evaporator core that is very restrictive.   The current experiment is to replace it with a much less restrictive (to airflow) oil cooler.  I found the largest cooler that would fit in the same location as the AC core and I'm using the same diffuser as before (slightly modified to fit the larger face of the new cooler).  This cooler is only 2" thick and core volume is 30% less than the AC core.  It is slightly larger in volume than an RX-7 cooler.  Without any back pressure (flying with cowl off), the AC core had way more than enough cooling capacity (146 F oil temp on a 93 degree day) so I'm hoping that this smaller cooler will be enough.  Should be ready to flight test it this week.

I should point out another symptom. Power setting (and therefore airspeed) had very little effect on the cooling  (i.e., it didn't get much hotter at high power as long as airspeed went up as well.   Things got hot fast in climb however.  This also indicated to me that cooling was limited by airflow through the system rather than by the oil cooler's ability to transfer the heat to the air.  If the cooler is simply too small, more airflow will not help much. 




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