Oil Cooler Secondary Air

jdsmaule · Post by **jdsmaule** » Wed Apr 18, 2018 7:28 am

Does blocking off the 2" SCAT tube that directs air on the side of the oil cooler help lower oil temps? Or does this air flowing over the side of the unit cause a Venturi effect that helps draw air through the cooler?

And is the wire screen for the oil cooler inlet just to keep birds out? Seems like that would restrict air flow to a certain amount.

Andy Young · Post by **Andy Young** » Wed Apr 18, 2018 8:26 am

Which engine? Injected or carbureted? Oil cooler systems vary.

jdsmaule · Post by **jdsmaule** » Wed Apr 18, 2018 9:01 am

Lycoming IO-540-W1A5D, oil cooler is mounted aft of number 5 cylinder.

Andy Young · Post by **Andy Young** » Wed Apr 18, 2018 1:23 pm

I have that same set-up. My guess is that the 2" hose is supposed to lower oil temps by adding a little cool air flow over the side of the cooler. I doubt blocking it off would help. I'm guessing you're wondering if doing so would increase upper deck pressure, thereby increasing flow out the main tube to the cooler; I think any effect in that realm would be minimal, but that's just my intuition. I'd be curious to know what you learn if you try it out.

What kind of oil temps are you seeing? On mine (M-6-235, with the IO) I have to block off almost all the air to the cooler just to get up to 180* most days. I'm using a digital temp gauge. I built to built a cockpit-adjustable door to do this, and it's nearly fully closed most of the time.

jdsmaule · Post by **jdsmaule** » Wed Apr 18, 2018 3:34 pm

The other day with a OAT of ~80F it was indicating around the 190-200 range. Which I understand is right where it should be. But I've been doing some work to get it to this point. This is a new to me airplane. Started flying it back in January in Phoenix when it was cooler (60-70) and several flights in even cooler temps around freezing or just a little under and at the time CHT and oil temps were well in normal range but seemed high for OAT. CHT around freezing or less in cruise before all the work was about 350 (+10 to 20 ish) and oil temp sometimes would be 190-210, sometimes cooler. Oil temps would vary for same OAT between flights. I'm currently running the factory analog gauges so these numbers are based on my interpolation. And from reading on this forum seem to have a history of not being the most accurate instruments.

There was several things I did/ found and each item did not make huge gains. One of which I tried early on was blocking off that 2" SCAT to the oil cooler. Didn't notice any change. But other things I did such as removing the hidden bird nest remnants lodged between the cylinders and inter cylinder baffles, replacing the thermostatic oil cooler bypass valve (although since replacing this temps are consistent), filling the gap on the oil cooler to duct with RTV, RTV around the valve covers, new forward baffles and some other stuff I can't recall at the moment didn't really produce much change either. The most recent thing I did was glass in the missing inlet vertical walls on the lower cowling that were cut down. That seemed to have made a noticeable difference.

So I've begun to wonder if the analog gauge is just not sensitive enough to detect these changes or there was/ is something that is an underlining issue. I was hoping someone with a digital gauge has had experience with blocking off this 2" SCAT and could say it increases/ decreases oil temps by XYZ amount.

Eventually I'll get around to installing a NACA scoop for the oil cooler and go digital gauges, but until than if sticking a piece of aluminum foil tape over a SCAT hole will help I'm game for it!

Andy Young · Post by **Andy Young** » Wed Apr 18, 2018 7:44 pm

Sounds like you run warmer today in general than I do. My cylinder head temps are rarely above 320, even on a hot summer day.

Hard to really know whatâ€™s going on though without good data, and itâ€™s hard to get good data with the original analog gauges.

Duane · Post by **Duane** » Thu Apr 19, 2018 5:44 am

Jeremy, one of the most common mistakes we've seen is that the front baffle on the lower cowling is not in the up position. If the G-95 is down, air can and will bypass the top of the cylinders and head directly to the bottom of the engine where it has no cooling effect.

jdsmaule · Post by **jdsmaule** » Thu Apr 19, 2018 7:38 am

Hi Duane, yep the front baffles are up. I reached out to you probably a month or so ago via your work email and you gave me dimensions to cut the new baffles.

Andy Young · Post by **Andy Young** » Thu Apr 19, 2018 8:54 am

Iâ€™m guessing youâ€™ve checked this, but if you havenâ€™t, the center baffle on top of the engine is also important.

Hale-Yes · Post by **Hale-Yes** » Thu Apr 19, 2018 9:01 am

Duane, I live in one of the hotter dryer places on the planet, (we hit 100 degrees two days last week). What's your opinion of the feasibility and likelihood of improved cooling performance by changing out the 235HP set up for the NACA duct and larger oil cooler setup used on the 260HP IO 540 ? I think that there was a guy working on an STC for this swap, but I don't know where that has gone. Regards, Ed

jdsmaule · Post by **jdsmaule** » Thu Apr 19, 2018 9:35 am

Center baffle is in place with new baffle seals on top. Actually new baffle seals all around the engine. And I have verified with everything installed that there are no gaps or waves when upper cowl is on. Regarding the center baffle, I have some baffle seal material on the bottom in and around the number 2 cylinder push rod tubes that could be improved on but is not terrible. And there is a gap between center baffle and engine where it makes that bend off center between cyl 4 and 2. Appears to have never had baffle seal material in that area. Is there suppose to be seal material down to the engine case in that area?

Andy Young · Post by **Andy Young** » Thu Apr 19, 2018 10:55 am

No, no baffle seal material typically installed at the bottom of that piece. If it were me, I wouldn't pull my hair out any further until I got accurate instrumentation on it. Or at least test the accuracy of your legacy gauges. Put the sensor in hot water with an accurate thermometer in the water, and compare reading to panel gauge.

Duane · Post by **Duane** » Thu Apr 19, 2018 11:46 am

Ed, I can't see why that would not work. That will give you 1 1/2" taller oil cooler. I have never heard of anyone pursuing a STC for that though. It would require moving the lower brace 1.5" farther down on the engine mount.

jdsmaule · Post by **jdsmaule** » Thu Apr 19, 2018 11:56 am

Good point Andy, I'm trying to keep what remaining hair I have left!

Duane, can you post or email a pic of the 260 oil cooler setup? I've looked on the parts CD and saw the oil cooler install for the 235 and NACA scoops, but no luck finding drawings for the 260. I may have just missed it though. Even if only approved for 260 I can't see getting a field approval for the 235 being an issue.

jdsmaule · Post by **jdsmaule** » Sun Dec 02, 2018 11:41 am

Follow up - I recently installed EI's CGR-30 combo, replacing ALL analog gauges. Well worth the time and expense. The final push was when the oil pressure gauge would wiggle on the low end after being warmed up. Analog CHT and oil temp were indicating high compared to digital. Consistently seeing CHTs between 250 and 280, oil temp around 166 in cruise, if I fly best climb angle for 1,500-2000ft can get temps up around 190 but cool down once in cruise again. This is with OAT on the ground around 75-80F. This is in stark contrast to what I was seeing last winter with analog gauges. Oil pressure has been steady, analog was indicating about 10-15psi on the low side. Analog tach was low about 150RPM. Fuel flow/ totalizer has been spot on without adjusting K-factor. And as a added bonus I was able to calibrate the unit to each individual fuel tank and have reasonably well behaved quantity indications now.

Highly recommend digital gauges!

Oil Cooler Secondary Air

Oil Cooler Secondary Air

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