Continuing Problems with Oil Temps

BillL said:

I think toobuilder was referring to radiation from the heads to the cooler face - per the view factor, not preheated secondary air. He seems pretty savvy about these things. I would also think it to be small/irrelevant.

I did put a short wrap over the end of the head fins to prevent flow through to the cooler. Don't know if it works yet.

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Yep. That's it. The baffle is primarily for localized airflow management for the head.

However, as long as there is a differential in temperature between the head fins and the oil cooler there will be radiant transfer. This differential is not nearly as great as the delta between the exhaust pipe and the throttle cable for example, but the little scrap of .020 aluminum used as a radiant barier to keep the throttle alive is just as effective in both instances.

The point is, a high efficiency cooling scheme is a game of inches. Once the big things are covered, we really need to pay attention to the details and take a win whenever we can.

Toobuilder said:

That said, I think there is plenty of benefit to providing a full height baffle against the fins of #4 rather than just leaving a hole for the cooler. .

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I am not sure I understand what you mean by a full length baffle. I would like to experiment with a few things with airflow back there and would like to better understand what you are suggesting.

Thanks,

Larry

What I mean is that there needs to be a solid wall of aluminum to ensure the airflow stays in contact with the head fins from top to bottom. I believe that simply cutting a hole in the rear baffle and installing a "screen door" is sub optimal for localized airflow management. Yep, cutting a big hole in the baffle and hanging the cooler works most of the time and is easy, but it is not the best way to go in my experience.

To accomplish this however, you do need to stand the cooler off the back of the baffle a bit to create a plunum chamber that exposes all of the cooler fins. I recognize that this is well outside the scope for most people with a completed aircraft, but I offer it as food for thought for those building now.

I have linked an earlier post that shows the solid baffle, (last picture) and also the fact that the plenum does not need to be very big to be effective.

Toobuilder said:

What I mean is that there needs to be a solid wall of aluminum to ensure the airflow stays in contact with the head fins from top to bottom. I believe that simply cutting a hole in the rear baffle and installing a "screen door" is sub optimal for localized airflow management. Yep, cutting a big hole in the baffle and hanging the cooler works most of the time and is easy, but it is not the best way to go in my experience.

To accomplish this however, you do need to stand the cooler off the back of the baffle a bit to create a plunum chamber that exposes all of the cooler fins. I recognize that this is well outside the scope for most people with a completed aircraft, but I offer it as food for thought for those building now.

I have linked an earlier post that shows the solid baffle, (last picture) and also the fact that the plenum does not need to be very big to be effective.

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Thanks for this detail and the post. Pls take a look at my pic's on Page 2. My opening is the same size as the cooler and my cutout starts above the cylinder fins. Do you think that a plenum will still help in my case. It wouldn't be too hard to stand the cooler off an inch or more to create a plenum if that would help.

Larry

lr172 said:

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It appears my cooler is rated to reject 7500 BTUs/Hr or 125 BTUs/Min. Does anyone know what an IO-320 (160 HP) requires?

Larry

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Looking at the 7 row Niagara it might be in the 250 btu/min range. But - But - the conditions are very important. The upper/lower plenum pressures, oil flow, and inlet temperature are very important to quantifying the heat rejection.

I looked up the MOCAL OC1107-8 performance charts off their web site. This cooler is made for quite low air pressures - like generated by automotive. The heat rejection saturates/plateaus pretty quickly with higher airflow.

It is also quite sensitive to oil flows (they all are) higher oil flows will generate more turbulence in the oil side and enhances the heat transfer. Higher flow will not go through too fast, it will help.

At risk of being annoying and repetitious, you need to quantify the oil temperatures in and out of that cooler, AND get the upper and lower plenum pressures. It appears that the cooler is undersized, underperforming for the area/volume used, compared to even a Niagara 20002a. The numbers should allow referencing the charts and determine which changes might help.

lr172 said:

Thanks for this detail and the post. Pls take a look at my pic's on Page 2. My opening is the same size as the cooler and my cutout starts above the cylinder fins. Do you think that a plenum will still help in my case. It wouldn't be too hard to stand the cooler off an inch or more to create a plenum if that would help.

Larry

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Larry, my experience tells me you would see a reduction in CHT and a slight reduction in oil temp. I believe your cooler is getting plenty of air today so the plenum adds a slight benefit for airflow management and allows it to hide behind the radiant barrier of the full height baffle. At best these would be incremental gains however; I still think you have a root cause to uncover first. And I still don?t like the #6 lines. I don?t think they are the root cause either, but if it was my airplane I?d probably try rule them out as a variable by upping them to #8.

All that said, it does not look like it would be very hard to add some material to the ?L? extrusion, closeout the ends and stand the cooler off an inch.

There also is an issue of turbulent air flow above the cylinders aft of air flow entry.

Sonja Englert talked about it at OSH some years back. She discovered with tufting and camera recording an easily cured problem of broken air flow with a 6 cylinder engine. She installed an air flow guide of sorts and improved cooling considerably.

This was with a certified aircraft, can not remember which, perhaps the Cirrus.

Anyway there is more than one say to skin a skunk...and smooth air flow is always a good idea.

Temps have been in low 80's and I have been unable to get the oil temps above 200. Seems that I am on the fringe of capacity, but need something more when ambient's are 90+ I now also believe that the advanced timing of the EI is adding more heat to the oil and why I didn't see this last year. I realized that my highest oil temps are in cruise and climbs are cooler. During climb, my MAPs are high and therefore timing is retarded. As I get to cruise, the MAPs come down and the timing goes up more than 10*

I was going to put the second mocal cooler in series and stacked on the other one to increase capacity, but seems that I have interference with the engine mount and this isn't going to work. So, I have decided to have my older SW 8406 cooler flushed with an Ultrasonic cleaning process.

My problem is that it looks like I will have less than a 1/4" clearance with the engine mount with the current baffle mounting setup. If I move it any further to port (away from the mount), I will block one of the rows of fins. I am struggling to see how others make this fit. I am thinking of mounting this on the firewall or hanging it from the engine mount.

My question is can I get away with a 3" scat hose or do I need 4"? I just realized that the 10-20* hotter temps on the Port side are probably due to air taken by the cooler and would like to minimize this.

Thanks again for all the support here.

Larry

Larry,

Is your clearance issue a clearance issue from the cooler flange? If so, you can relieve the flange to avoid the problem.

Kyle Boatright said:

Larry,

Is your clearance issue a clearance issue from the cooler flange? If so, you can relieve the flange to avoid the problem.

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Thanks. I figured I could shave off the the flange material, if necessary. It looks like the cooler body will end up around an 1/8" or closer to the frame tube. I will have to commit to this and tear out the old cooler to tell exactly what I have. If I choose to shift the cooler over to port to increase the clearance, any idea how much clearance I need with the frame tube? It seems pretty close to the mounts (i.e. pivot point), so thinking I don't need too much. However, I'm worried a bad guess could net a cracked cooler and a bad day.

Larry

lr172 said:

Thanks. I figured I could shave off the the flange material, if necessary. It looks like the cooler body will end up around an 1/8" or closer to the frame tube. I will have to commit to this and tear out the old cooler to tell exactly what I have. If I choose to shift the cooler over to port to increase the clearance, any idea how much clearance I need with the frame tube? It seems pretty close to the mounts (i.e. pivot point), so thinking I don't need too much. However, I'm worried a bad guess could net a cracked cooler and a bad day.

Larry

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I'll try and remember to measure mine tomorrow - complete with relieved flange.

Kyle Boatright said:

I'll try and remember to measure mine tomorrow - complete with relieved flange.

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Your comments inspired me. I took a ride to the airport tonight and I forgot that the flange didn't meet up with an oil passage. It goes right into fins, so I can carve out more if it than I thought. Upon re-mearsuring, it looks like I can accommodate 1/4" or so, maybe a bit more.

Curious to hear the wisdom on how much clearance is necessary. Given this is an option, can expect fewer issues with baffle mounting over a firewall mounting?

Larry

lr172 said:

Your comments inspired me. I took a ride to the airport tonight and I forgot that the flange didn't meet up with an oil passage. It goes right into fins, so I can carve out more if it than I thought. Upon re-mearsuring, it looks like I can accommodate 1/4" or so, maybe a bit more.

Curious to hear the wisdom on how much clearance is necessary. Given this is an option, can expect fewer issues with baffle mounting over a firewall mounting?

Larry

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My cooler has a 1/8" to 3/16" clearance from the closest tube on the engine mount. There is no evidence of contact over 15 years and 1000+ hours of flight time.

Baffle mounted cooler installations are crack prone, so make sure to reinforce it well. Mine has a 1/8" x 1.25" x 1.25" angle that ties together the left and back baffles, and also serves as one of the mounting points for the cooler. In addition, I have a doubler around the cooler opening. I've never had any issues with baffle cracks.

Kyle Boatright said:

My cooler has a 1/8" to 3/16" clearance from the closest tube on the engine mount. There is no evidence of contact over 15 years and 1000+ hours of flight time.

Baffle mounted cooler installations are crack prone, so make sure to reinforce it well. Mine has a 1/8" x 1.25" x 1.25" angle that ties together the left and back baffles, and also serves as one of the mounting points for the cooler. In addition, I have a doubler around the cooler opening. I've never had any issues with baffle cracks.

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Thanks for sharing the details Kyle. I appreciate it.

Larry

Thought I would post my progress here.

This week I did a mini-top O/H. I swapped all my piston pins with the ECI integral units. This addressed my imbalance issue and hopefully ends the production of AL or Bronze/AL that I was seeing in my filter. I also learned that the person I bought the core from got choke barrel rings and these jugs were straight barrel. It went back together with a hone and the correct rings. I think this explained my blow-by issues and low 70's compression and was likely causing some of my oil temp issues (ring gap was .030" bigger than it should have been). My oil got brown three hours after the last oil change (this was a new development) :-(

I also put in an SW oil cooler. I did two long break in flights and happy to report that my oil temps were down to 175 in cruise on the second long flight. I still have the viscosity plug in there and this should go up once I pull it and go back to the vernatherm.

Thanks for all of your suggestions.

Larry