High oil temps - Page 2

Steve Barnes · #11 04-01-2017, 11:53 AM

I have a 3" scat to cooler. On hot days my oil was getting a little warm (not as hot as yours). On my fiberglass plenum (very similar to yours) I left a flat area big enough to attach a 2" scat in addition to the 3" just in case my temps were a little high. I added a cockpit adjustable butterfly valve to the 3" so in cold weather I am just running the 2" scat. Since I added the 2" scat my oil temp has come down.

If you don't have a rounded shape over the bottom tube of your engine mount, that may help a little to get air smoothly out of the bottom cowl. On mine I bent a piece of .016 alum around a broom pole and attached to the bottom skin, then around the the bottom tube of the engine mount then rivet to the firewall with monel rivets.

Steve

scsmith · #12 04-01-2017, 01:36 PM

First, if you have a missing area of baffling around the front of your engine, you have a huge leak path that will tend to equalize pressure in upper and lower cowl areas while doing no cooling. This will make it really hard to get any flow thru the oil cooler. You have to have EVERY possible place for air to go closed off.

Second, the ramps on the top of the cooling openings help get the highest possible pressure in the upper cowl. They are not Super important, but they do help.

Third, your cooler is angled so that the flow out the exit of the cooler is partly obstructed by the firewall. It is not helping to get good flow thru the cooler, especially up in the corner.

Fourth, you should have 4" scat hose. I used 3.5" and my system cools pretty well now, but when I start making a smaller cooling exit on the bottom of the cowl, that raises the pressure in the lower cowl, so I will need to switch to 4" scat to get enough air to the cooler.

N941WR · #13 04-01-2017, 02:06 PM

Edit: I just went back and looked at your first picture again, it looks like you have an expansion chamber on your scat tubing.

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One other thing, if your 3" scat tubing is run right up against the oil cooler and doesn't have any room to expand and let the air slow down, you in effect only have seven square inches of cooling surface. (Pi*1.5^2 = 7.07 in-sq)

If you upgrade to a 4" scat tube, you go up to 12.6"sq of cooling surface. (Pi*2^2 = 12.566 in-sq)

If you make a fiberglass transition from your 3" scat tubing to the full size of your oil cooler, you might be ok. Changing the orientation of your oil cooler so the exit air points towards the exit rather than towards the firewall will also help.

I helped a buddy make this transition for his O-360 so he could go from a 3" to 4" tubing and it was almost too much, as his oil temps were not hot enough.

(Click to enlarge)

Timberwolf · #14 04-01-2017, 07:58 PM

Lots of great information. Will be ordering 4" scat tube. Got the front baffle fabbed up and in today with zero difference in oil temps. The CHT's may have been helped. I believe once I get in the 7 row behind the #4 cylinder it will help on 2 accounts. During the flight today I scrolled through the EGT/CHT's. EGT's were all at 1310 except #4 which was 1220. CHT's were all 340 except #4 which was 273. By putting the cooler in behind the #4 it should rectify the cool cylinder issues, and hopefully cool the oil...at least enough until I can get back from SNF and put in the 4" scat.

I think I forgot to mention but this is all on a -6 with standard gear.

Bruce · #15 04-02-2017, 02:23 AM

I would verify timing again.

20* does not seem right.
Also do you have EI?? On one side?

Timberwolf · #16 04-02-2017, 07:03 AM

Dual mags, verified by 2 different IA's on separate occasions before I purchased, but doesn't hurt to make sure.

What I don't get is after the flight yesterday I landed and put an IR temp gun on the cooler and it shows that the cooler was at 175 degrees. Now it is my understanding that the oil then goes straight from that cooler into the filter return where the temp is then read by the gauge. I don't have a firm grasp as to the exact path of oil flow. But as I understand it the temp limits are set by lycoming off of the oil coming in from the cooler at it's coolest point. If the cooler shows it's only 175 that tells me it is at least doing something, but the temp gauge doesn't reflect that.

DanH · #17 04-02-2017, 07:27 AM

Can't shoot a bare aluminum oil cooler with an IR gun and get an accurate temperature reading. The exception is a gun with adjustable emissivity. Without adjustment, it's probably preset for 0.95, which is way off for bare metals. If you really want to measure a cooler with an IR gun, paint the surface dull black, or cover the measurement area with masking tape.

Even if accurate, 195F would be pretty close to the ambient temperature of an engine compartment after shutdown. Point is, the measurement made after shutdown may be misleading. Easy to rig a contact measurement if you really want to know inflight temperature.

No way a 3" SCAT with a square-edged intake off the baffle will work on an angle valve with squirters. It's the equivalent of maybe a 2"~2.5" smooth tube.

340F CHT is actually kinda high for an angle valve in cruise with stock exit area. That's roughly where my 390 runs in cruise at 50 OAT and only 30 sq inches of exit. Below I've posted data from a long climb at 125 true, with the cowl door at about 46 sq inches exit area. Overall, I suspect you have limited pressure delta. It's all guesswork without pressure measurement.

N661DJ · #18 04-02-2017, 08:32 AM

Dan,
I have a new IO-390 in my 8 running 3" SCAT to a firewall mounted 9 row cooler'
fed from the rear baffle behind #3 cylinder.
AT 3000', 75* OAT, 2550rpm X25.5" mp. engine not yet broken in 7 hrs.TT,
I am seeing CHT's < 350*F, oil 217*F. do you think it would be worth the effort to
change to 4" SCAT? What about aluminum dryer vent hose? smoother inside surface?
Dick

Carl Froehlich · #19 04-02-2017, 08:42 AM

Quote:

Originally Posted by N661DJ

Dan,
I have a new IO-390 in my 8 running 3" SCAT to a firewall mounted 9 row cooler'
fed from the rear baffle behind #3 cylinder.
AT 3000', 75* OAT, 2550rpm X25.5" mp. engine not yet broken in 7 hrs.TT,
I am seeing CHT's < 350*F, oil 217*F. do you think it would be worth the effort to
change to 4" SCAT? What about aluminum dryer vent hose? smoother inside surface?
Dick

You have great numbers. Don't change a thing (other than balancing your injectors).

Carl

DanH · #20 04-02-2017, 09:46 AM

Quote:

Originally Posted by N661DJ

Dan,
I have a new IO-390 in my 8 running 3" SCAT to a firewall mounted 9 row cooler'
fed from the rear baffle behind #3 cylinder.
AT 3000', 75* OAT, 2550rpm X25.5" mp. engine not yet broken in 7 hrs.TT,
I am seeing CHT's < 350*F, oil 217*F. do you think it would be worth the effort to
change to 4" SCAT? What about aluminum dryer vent hose? smoother inside surface?
Dick

At 7 hours it's a bit early to worry about it. It's also a higher than usual cruise power setting, but it's what you need to do for break-in.

Given the conditions and age, the CHT sounds fine. For me, 217F would be an entirely unacceptable oil temperature in the long term. The Lycoming 390 manual is clear; for maximum life, 180F. So yes, I'd be re-working the oil cooler setup.

I don't know about the durability of dryer duct. I use SCEET hose; it has a liner.