Has anyone redirected their oil cooler airflow into the bottom cowl on a C model to improve engine cooling?

[DXB]

The left side of my engine of my C model (#2/#4) cools poorly (#4 is terrible in climb, #2 is bad in climb, both are comparably marginal in cruise), and the right side (#1/#3) cools great.   I've been trying to get this issue sorted for the almost 8 years I've owned the plane!.  I can't get my doghouse any tighter.  Fuel flow is 18gph WOT at takeoff from sea level. #2 and #4 are leaner I believe but not much I can do about that on my C (I know about the cocked throttle plate and carb heat tricks).  No evidence of induction leak.  No runaway temps on the ground. My oil temps are fine - sometimes too cool in the winter.  In desperation, we've recently pulled timing back to 23 from 25 on both mags with limited benefit.

Our hypothesis is that the oil cooler being on the lower left front cowl of the C pressurizes the bottom left cowl and is a major contributor here.  Oil cooler relocation on the C would require moving the battery to the tail from current position behind #4  - I am not interested in this option presently.  I am going to fly briefly in the next few days with my oil cooler partly taped off to test this hypothesis.  

Question: Has anyone ever tried ducting the air coming out the back of their oil cooler on a C using a plenum like the one on the backside, plus some scat hose? I'm not sure where to route the hose.  I realize the plenum shown is designed to route air to the cooler, but I'm sure it could be put on the backside also...

 

 

Edited April 4, 2022 by DXB

[carusoam]

I think the method used for this challenge…. Currently…

Are to move the oil cooler to the back of the dog house…

Three fold improvement…

1) Move the warm air somewhere else…

2) have the airflow, or pressure same on both sides of the engine…

3) Keeps ice, snow, dirt, from collecting in front of the heat exchanger fins….

But, this fancy air direction technique could be helpful…. For at least one aspect… dump the hot air somewhere else…

Probably an STC required for this air duct… (?)

PP thoughts only,

-a-

[47U]

5 hours ago, DXB said:

#4 is terrible in climb, #2 is bad in climb

How terrible is it?  CHT redline on my ‘63C is 450.  In the climb I try to keep CHTs below 400 (as advised by Mike Busch, since revised to 410 I think I read).  #4 cylinder is also my hottest.  I reduce my climb rate and get the speed up to 120-130 to keep CHTs under control.  I have a friend with a G that runs 20-30 degrees hotter (chrome cylinders) than I do in the climb.  He just lives with it.

Have you looked at your inter-cylinder baffles between (underneath) #2 and #4?  Baffle tie-rods are in place?

If your exhaust system is stock, I’m not sure if an exhaust plenum on the oil cooler will fit without interference with the #2 exhaust stack.  Do you have a PowerFlow installed?  More power, more heat?

Are your cowl flaps adjusted per the book?

[N201MKTurbo]

I've always heard that air actually flows out of the oil cooler. Adding the plenum may have unintended consequences. I would suggest doing the Lasar oil cooler relocation. They have already done all the engineering and testing.

[Prior owner]

It could just be the picture, but your oil cooler looks like it’s seen better days….what is the condition of the oil cooler? And what is your oil consumption like? Blow-by puts a lot of heat into the oil.

[DXB]

8 hours ago, 47U said:

How terrible is it?  CHT redline on my ‘63C is 450.  In the climb I try to keep CHTs below 400 (as advised by Mike Busch, since revised to 410 I think I read).  #4 cylinder is also my hottest.  I reduce my climb rate and get the speed up to 120-130 to keep CHTs under control.  I have a friend with a G that runs 20-30 degrees hotter (chrome cylinders) than I do in the climb.  He just lives with it.

Have you looked at your inter-cylinder baffles between (underneath) #2 and #4?  Baffle tie-rods are in place?

If your exhaust system is stock, I’m not sure if an exhaust plenum on the oil cooler will fit without interference with the #2 exhaust stack.  Do you have a PowerFlow installed?  More power, more heat?

 

Are your cowl flaps adjusted per the book?

 

-It's terrible - though I believe red line on these O-360s is actually 500F?  If I'm very attentive to airspeed from the moment I lift off (getting above 120mph as quickly as possible), I can keep #4 in 430s-440s on climb, if not I can see >450.  Occasionally I've seen 470+ on #4, leading me to sweat a little and pull back power.  #2 usually gets to 430s when #4 really gets out of control, otherwise more like 410.  

-Yes I got a Powerflow, and everything got worse - i.e. the temps I describe above  - no surprise in retrospect. But the overall pattern among the cylinders stayed exactly the same - #4 would just see 440s when things went bad pre Powerflow instead of 470 after the new exhaust.  The right side (#1/3) cools well both pre and post Powerflow, so it's not the added power alone that is the issue.

- Yup the 4 tie rods underneath and the inter-cylinder baffles are all there.  I've heard somewhere that there are optimal measurements regarding their position but never really understood what was adjustable here - the baffles seem form fitted to the cylinder heads.

- Yes - it's an important point about the cowl flaps - which are fixed on my '68C.  I've seen that diagram before and my measurements do match up.  I've considered what it would take to retrofit movable cowl flaps buying the parts off a salvage plane - seems like a big project but it may come to that.

Thanks for input

 

[DXB]

1 hour ago, N201MKTurbo said:

I've always heard that air actually flows out of the oil cooler. Adding the plenum may have unintended consequences. I would suggest doing the Lasar oil cooler relocation. They have already done all the engineering and testing.

That's an interesting point - if flow reverses out of the cooler, there must be quite a lot of pressure in the bottom cowl to exceed pressure in flight on the outside.  In principle, the cooler is contributing to the high pressure on one side of the bottom cowl also?   Will report back results of taping off part of the cooler on the front for a quick flight...

On the C there's no space to move the oil cooler behind #4 without also moving the battery to the tail - a much bigger ordeal.  

[DXB]

53 minutes ago, PilotCoyote said:

It could just be the picture, but your oil cooler looks like it’s seen better days….what is the condition of the oil cooler? And what is your oil consumption like? Blow-by puts a lot of heat into the oil.

That's actually not my plane - just for illustration.  My oil cooler doesn't look much better  but cools very well - perhaps too well in the winter.  I do have significant (but stable) oil consumption and evidence of blow by, but again no oil temp issues at all.  And the same problem was there years ago when I had lower oil consumption, and the issue is specific to the left side of the engine, so I gotta think it's predominantly cooling airflow to blame.

[Will.iam]

Could #4 going so high compared to the other cylinders be on the edge of pre-detonation? Maybe #4 not getting enough fuel? Could/would cooler spark plugs help #4? Spit-balling here. 

[DXB]

1 hour ago, Will.iam said:

Could #4 going so high compared to the other cylinders be on the edge of pre-detonation? Maybe #4 not getting enough fuel? Could/would cooler spark plugs help #4? Spit-balling here. 

Not sure what "pre-detonation" is... just detonation and pre-ignition.  #4 is the leanest at some cruise settings, but I don't know at WOT for takeoff because I don't lean then obviously.  I don't think it's pre-ignition because that condition should run rough, produce thermal runaway, and have completely trashed my cylinder long ago.  I think a "colder" plug means it dissipates heat to the cylinder head more effectively, so a colder plug would raise CHTs I would imagine.  "Hotter" plugs are generally recommended for lower HP engines like this one.  Regardless, I run Tempest UREM37BY plugs, which are in the middle of the "heat" range for spark plugs that will fit my engine.

[47U]

2 hours ago, DXB said:

-It's terrible - though I believe red line on these O-360s is actually 500F?

You are correct.  My redline is also 500F.  I have an annunciator on my panel set for 400, and start taking steps to cool down if it illuminates.

To complete these mods, what are you using for approved data?  I don’t see an issue with the battery relocation, but the oil cooler relocation is more problematic (in my mind).  Isn’t the oil cooler mod only applicable to the IO-360 engines?  Does the ‘68C have a doghouse?  If so, you’d have to convert to an open-top baffle system?  (Showing my lack of knowledge on model year evolution…)

Changing to adjustable cowl flaps might not help you because the ‘open’ position is the same 1.1” measurement that the fixed cowl flaps uses.  When I got my C, the cowl flaps were adjusted to be open a lot wider than that, way outside the mx manual spec.    

Maybe a wild thought… remove the left cowl flap altogether, go test fly, and see it the #4 CHT improves.  If it does improve, perhaps the oil cooler plenum could be ducted to a set of louvers in the cheek cowl… like a intercooler setup?  (Just brainstorming here…)  That could probably be done as a minor mod, with concurrence of your A&P/IA, of course.  

 

[DXB]

1 hour ago, 47U said:

You are correct.  My redline is also 500F.  I have an annunciator on my panel set for 400, and start taking steps to cool down if it illuminates.

To complete these mods, what are you using for approved data?  I don’t see an issue with the battery relocation, but the oil cooler relocation is more problematic (in my mind).  Isn’t the oil cooler mod only applicable to the IO-360 engines?  Does the ‘68C have a doghouse?  If so, you’d have to convert to an open-top baffle system?  (Showing my lack of knowledge on model year evolution…)

Changing to adjustable cowl flaps might not help you because the ‘open’ position is the same 1.1” measurement that the fixed cowl flaps uses.  When I got my C, the cowl flaps were adjusted to be open a lot wider than that, way outside the mx manual spec.    

Maybe a wild thought… remove the left cowl flap altogether, go test fly, and see it the #4 CHT improves.  If it does improve, perhaps the oil cooler plenum could be ducted to a set of louvers in the cheek cowl… like a intercooler setup?  (Just brainstorming here…)  That could probably be done as a minor mod, with concurrence of your A&P/IA, of course.  

 

You are correct - the LASAR oil cooler STC is for Es and Fs with the open baffle, not the C - another reason not to attempt it on mine .  I was just considering a "minor mod"  to redirect the air out of the back of the oil cooler so it doesn't increase pressure in the bottom cowl.  

The nonadjustable flap is supposed to be set to 1.1cm max open at the trailing edge (where mine is) vs. 2.0cm full opening minimum for the adjustable ones (see diagram you posted above).  I do think the full open 2.0cm does improve cooling - at least folks with adjustable flaps do report full open does make a difference. I don't think removing flap entirely would mimic effects of a wider cowl flap opening - that would create some ram air pressure into the lower cowl based on the angle.  On newer planes, the sides of the cowl flap are boxed in (as opposed to the gap present on the sides of ours) to further limit this effect.

[47U]

2 hours ago, DXB said:

I don't think removing flap entirely would mimic effects of a wider cowl flap opening - that would create some ram air pressure into the lower cowl based on the angle.  On newer planes, the sides of the cowl flap are boxed in (as opposed to the gap present on the sides of ours) to further limit this effect.

Good point…

Please keep us updated as you progress towards a solution.

[Utah20Gflyer]

Have you verified that the temperature readings are accurate?  Could be a bad sensor or gauge.  

[Skates97]

9 hours ago, PilotCoyote said:

It could just be the picture, but your oil cooler looks like it’s seen better days….what is the condition of the oil cooler? And what is your oil consumption like? Blow-by puts a lot of heat into the oil.

Don't just look at the front of the oil cooler. I was replacing the cooler lines in my plane a couple years back and decided to do the oil cooler while I was at it, it was getting old but still looked ok from the front. The fins on the backside however were falling apart.

[markgrue]

Keep in mind that there is more airflow into the right inlet than the left one during high angle of attack.  Descending blade and all that.  Same reason you need right rudder.

 

Mark

[Hector]

I have a 67 C and can verify that 2 and 4 are the hottest in mine as well with 4 being the worst. However, my temps don’t get as high as your. #4 can get to 425 right after takeoff when I’m climbing Vy but will decrease to 400 at 120 mph which I usually transition to at 1000 AGL. This is all in the hot Florida summer. In the winter I can cruise climb with all temps below 400. Level cruise is never a problem in my C with #2 and 4 in the 360 range and 1 and 3 in the 34 0s. My dog house is tight so I’ve run out of ideas to make 2 and 4 cooler during climb. All that being said, my engine has 1750 hours and it seems to be doing just fine with very little oil consumption and good compressions so temps in the 420s for a short period of time don’t appear to be hurting the engine much.


Sent from my iPad using Tapatalk

[SheryLoewen]

I can tell you--- airflow thru the oil cooler flows forward. Also relocating the cooler (LASAR) with doghouse baffles does not work (TRIED)

 Paul Loewen

[Andy95W]

Paul, your knowledge and experience are astonishing.  Most people here probably don’t realize your decades of work on Mooneys of all types, or the number of STCs you’ve received for your mods.

Thank you.

[carusoam]

It’s always great having Paul’s experience shared here!

And pre-flown parts sold here too…

Go Lasar, Lake Aero Styling, Paul, Shery, Et Al….

Best regards,

-a-

[takair]

Dev

I’m sure you have looked at the following, but figured I would post just in case.  One area that is hard to seal and hard to tell if it is sealed is around the alternator and starter.  This is especially true if you have a cowl closure.  I often find big gaps around the nooks and crannies of these.  This allows air to leak past and not through the cylinders.  This is similar to the theory of the oil cooler. Often when the alternator retrofit occurs or a new starter goes on, the felt around it gets abused or the new baffle is not tight enough.  Another thing to look at is the heat inlet air.  In the original, a duct went into the exhaust muff and then got ducted out.  I don’t know how Powerflow ducts this air….but worthy of consideration.  You don’t want that air uneducated in the lower cowl when heat is off.  One other thought….unlikely, but worth mentioning, be sure you don’t have an exhaust leak blasting your thermocouple.  I’ve had a crooked exhaust flange that would go through even no blow gaskets and blow on the CHT thermocouple.  This will give a false rise in CHT.  It is very obvious though…..grey exhaust makes a mess.  Anyway, good luck.  For what it’s worth I was recently flying a 63 C that seemed to do well…so it is possible.  I was able to keep the hottest CHT to under 400 at about 120mph cruise climb.  It was pretty much stock, but had a cowl closure.  Not sure if he had done anything else special to it. I’ll check with the previous long time owner. Hope you find a way to get the temps down.

[MB65E]

Hi, I’ve looked at doing this. Having it exit through the left cheek panel with its own naca duct would be ideal. I stopped as the space required is limiting. I like the aluminum box you found. Other issue is that the area of the hose is smaller than the oil cooler area itself. Moot point if the air flows backward through the cooler anyway. It would be more efficient for sure. Some of the Lancair 360 cowls could be used as an example. 
-Matt

[Browncbr1]

 

27 minutes ago, MB65E said:

Hi, I’ve looked at doing this. Having it exit through the left cheek panel with its own naca duct would be ideal. I stopped as the space required is limiting. I like the aluminum box you found. Other issue is that the area of the hose is smaller than the oil cooler area itself. Moot point if the air flows backward through the cooler anyway. It would be more efficient for sure. Some of the Lancair 360 cowls could be used as an example. 
-Matt

You could use the blue aluminum box and about 6-8” of SCEET to a NACA or gills out the bottom of the cowl just in front of the left flap.
shoot,  you could just adel clamp some longer sceet to just go out the flap to at least test it.   It could just articulate with the flap.  Smash the tube a little flatter and adjust the flap position to account for the exit area

[Prior owner]

As mentioned above, I would look at exhaust flanges leaking onto the CHT probes, the  intercylinder baffles installation, absolutely confirm that you have no intake leaks by pressurizing intake and bubble testing. In the end,  Climbing out at 125-130 mph will cool things down as well. I tried everything, and when I finally ditched my chrome cylinders, everything got better.

[Chessieretriever]

Maybe your engine is producing a beneficial incremental amount of power due to your power flow exhaust and therefore could benefit from the carburetor main jet change that Mooney proposed (larger main jet with different atomizing hole patterns on the jet). I know of a person with a C that uses this mod and requires 19.2 GPH on take off at sea level (also has to climb at 120MPH) and is able to keep temps on the 2/4 bank below 400F. Obviously he is cooling the cylinders with fuel. If all of this does not help perhaps you can take 1 or 2 degrees of timing out (retard it) to reduce the thermodynamic load on the cylinders and hence reduce your temperatures; this may be great on take off but will produce a slightly lower performance at altitude in cruise power settings. Last but not least maybe a little adjustment on the cowl flaps (trailing more open in the fully closed position to allow for a steeper angle when in the open position) associated with that side of the engine can help (mentioned already); there is a little room on the heim joint threads that could be utilized and still meet the specs.