Oil Temp in a Climb

[Roger Lee]

I looked at Wayne's CT one day about a month ago and couldn't find his problem. I wish I had had more than one day. His may be internal where most others are external. That said his has been like that since day one. Yours came on later so something changed that should be able to be put back. On a hot day I can see 240F when climbing hard and or heavy. I haven't seen over that.

I fly in AZ. And don't have any over heating issues. I do fly early in the morning, but it can still be 85F. I advise everyone not to worry up to 240F. Once you get to 250F it's time to cut back. The yellow starts at 230F and that isn't a worry and just meant to get you to pay attention to a climbing temp.

[Ed Cesnalis]

Jeremy is coming on Tuesday to replace my oil lines, add a 90° fitting and generally rule out a reduced radius.  I'm hopeful but not confident that this is going to be my issue because we have looked here before.

 

Using Google to search for other ideas I noticed that air movement through a tightly fitted cowling is sometimes the issue.  Rans has a fix for their S-6 / S-7 and it is to put spacers at the firewall to keep a gap between the cowling and fuselage. This fix allows hot air to escape the cowling and can reduce temps from 260° to 235°.

 

Thinking about this and what we who have the overheating have in common.  We all have older model CTSWs and at least some of us if not all took delivery without firewall blankets.  The installation of the firewall blanket does correlate to the time period where my overheating started.  If the blanket made the change would it be from containing more heat or disrupting air flow?  Does this seam likely? 

[Ed Cesnalis]

The blanket makes a seam where it terminates at the belly of the fuselage.  On the right side the blanket is too long and restricts the size of the opening by 3/8" and on the left side its too short leaving a rough seam.  Not very aerodynamic but the size of the obstruction is small.

 

 

[sandpiper]

CT - mine came with the firewall blanket in May 2007. Had no problem that summer. The only thing changed since then is pitching the prop for 5500 flat out and level at 4500 ft.

 

Maybe I should pitch it back to how it was delivered?? Which is to say 5300 flat out and level.

[Ed Cesnalis]

CT - mine came with the firewall blanket in May 2007. Had no problem that summer. The only thing changed since then is pitching the prop for 5500 flat out and level at 4500 ft.

 

Maybe I should pitch it back to how it was delivered?? Which is to say 5300 flat out and level.

 

John, seems like flatter should be cooler because of less load or is it hotter because it is developing more power?

 

If it was the pitch I would think you could just throttle back some but that doesn't seem to be very effective.  Must be global warming?

[Roger Lee]

Ed,

 

You can also flush your oil radiator out. Do it backwards so anything forced in, but can't get through will hopefully flush back out. I looked at Wayne's a few months back. His has had an issue since day one. I couldn't find the issue in the day he spent here. I had tried some things so we did not repeat those. Yours came on later so in your case something has changed. Wayne's may truly be an air flow issue.

[Anticept]

This is very tempting.....loose the oil cooler, simplify the system, reduce the weight and I would guess better overall temp control.

 

While this looks neat, I don't know if I would want to use it. If the coolant/oil barrier broke down and coolant got into the oil, it would destroy your engine. It wouldn't be sudden either, as more than likely it would be a slow contamination, scrapping your engine long before you realize there is a problem.

 

Big planes do use oil to fuel exchangers, but those two are compatible. It's one of the reasons kerosene is liked, it's not only a good fuel, but a great lubricant too.

 

Way back in the day with big radials, they would pump some fuel into the oil to thin it out too (called an oil dilution valve). It wasn't really good on the engine, but they had not invented multi-viscosity oils yet either, so starting with thick oil would have been worse.

[sandpiper]

While this looks neat, I don't know if I would want to use it. If the coolant/oil barrier broke down and coolant got into the oil, it would destroy your engine. It wouldn't be sudden either, as more than likely it would be a slow contamination, scrapping your engine long before you realize there is a problem.

 

Big planes do use oil to fuel exchangers, but those two are compatible. It's one of the reasons kerosene is liked, it's not only a good fuel, but a great lubricant too.

 

Way back in the day with big radials, they would pump some fuel into the oil to thin it out too (called an oil dilution valve). It wasn't really good on the engine, but they had not invented multi-viscosity oils yet either, so starting with thick oil would have been worse.

Not just the big radials. The DHC-2 Beavers, which have the R-985, also had oil dilution. Then there were the really big radials like on the B-50's which had water injection, not in the oil, but to keep the combustion temps down? Something like that.

[sandpiper]

Ed,

 

You can also flush your oil radiator out. Do it backwards so anything forced in, but can't get through will hopefully flush back out. I looked at Wayne's a few months back. His has had an issue since day one. I couldn't find the issue in the day he spent here. I had tried some things so we did not repeat those. Yours came on later so in your case something has changed. Wayne's may truly be an air flow issue.

Roger - I have back flushed the radiators at least twice to no avail.

 

CTLSi - the problem with not worrying about it anymore, at least on mine, is as it moves higher into the yellow it starts moving really quick toward red unless I level off and power back. One time it moved so fast I hardly had time to react. And, when solidly into the yellow, it takes a long time after level off and power reduction before it gets back into the green - if it does at all. And, it's not as hot here in western Oregon as it is at your place. For example the OAT might show 85F at take off and maybe 70F at level off.

[Anticept]

Not just the big radials. The DHC-2 Beavers, which have the R-985, also had oil dilution. Then there were the really big radials like on the B-50's which had water injection, not in the oil, but to keep the combustion temps down? Something like that.

 

Water injection was to prevent detonation from heat, by cooling as you said. It was used for War Emergency Power.

 

By the way, R-985 is a big old radial .

[Ed Cesnalis]

CTLSi,

 

Enjoy your cooling system, may it always work well.  My issue has been getting worse in recent years and there is no doubt I have an issue.  I used to find an altitude where OAT was less then 70 and I was fine, now I need less than 40.

 

------------------------------------------

 

Using radiator tape is one way to show that airflow through the cooler is a big factor, so is the fan mounted on the cooler.

 

Oil-flow through the cooler is a big factor as well, that is just obvious.

 

Tuesday we replace oil lines, add a 90 degree fitting and re-route a line.  We will inspect the old hose to see if we can determine a weak radius that is either reduced or prone to reduce at high temps.  We will limit the amount of hose so no extra length encourages an unwanted radius.  We will inspect and back-flush the cooler.

 

If these things do not correct my heating issue I will want to determine if the focus needs to be air-flow, oil-flow, both or a higher capacity cooler.  Chris says above that a fan would be the cheapest test.  Are there any tests or specs for oil-flow rates in the cooling system?  

 

What is the best explanation for my anti-freeze / coolant remaining 40 degrees cooler than my oil?

[FastEddieB]

Ed,

 

This may have come up before in this thread, but...

 

...can one reasonably expect a fan to move more air through the oil cooler than 70k+ ram air?

 

I can imagine scenarios where a fan could actually interfere with desired free flow through the radiators, rather than augment it.

[Ed Cesnalis]

Ed,

 

This may have come up before in this thread, but...

 

...can one reasonably expect a fan to move more air through the oil cooler than 70k+ ram air?

 

I can imagine scenarios where a fan could actually interfere with desired free flow through the radiators, rather than augment it.

 

If I don't find relief from a new and newly routed oil line on Tuesday I want to have a basis for deciding if I should next work on air-flow or oil-flow or a higher capacity cooler.  Chris says the fan is a cheap way to test not that it is a solution.

 

The 70k+ ram air will create high pressure on the front of the coolers but without some reasonably low pressure on the back it may or may not be enough.

 

How much air-flow through the cooler do I have?  How much do I need?

How much oil-flow through the cooler do I have?  How much do I need?

 

Is there any engineering and test methods on these questions?

[sandpiper]

CT - I hope it works for you with the hose modification. Mine did not. If it works I will need to see what you have done differently.

[Tom Baker]

I don't have answers, but I am going to throw some observations out there.

The purpose of oil, besides lubrication is to remove heat from the engine. When there is a change like yours, if it is real can only be one or two things. The oil is not being cooled as good as it once was, or it is absorbing more heat than it once was. If the oil line coming from the sump is restricting flow it would cause the oil to stay in the crankcase longer allowing more time for heat transfer. If this was the case I would think the oil would wind up all in the crankcase and none in the tank causing problems.

 

I don't think you can increase oil flow, because the engine is the biggest restriction in the system. If you had a restriction before the oil pump the indication would be low pressure. If the pressure is normal I don't think you can push any more flow through the engine.

 

If the cooler is plugged or coated on the inside it will not transfer the heat from the oil to the air like it once did. In my past experience with oil coolers on other aircraft flushing the cooler does little good to help increase heat transfer. Only when I have had cooler professionally cleaned or replaced with new did I see a reduction in oil temperature. In one airplane I had issues with needing to step climb in the Summer and temps at red line. After replacing the cooler the highest temp I saw was 20° bellow red line.

The comment about if it is real only goes to make sure that the indicated temperature is really what you are seeing.

[207WF]

Heat exchanger. Interesting. If I could average my high oil temps and my low chts, it might be a lot better, wf

[207WF]

Ed, did you buy that bigger radiator from fd? Wf

[Roger Lee]

You do need to check our oil cooler and here is why. (I just had a case like this o the the Rotax forum). The issue with our oil cooler getting a reduced flow comes from the gearbox.

 

Anyone know why?

[Ed Cesnalis]

I don't have answers, but I am going to throw some observations out there.

The purpose of oil, besides lubrication is to remove heat from the engine. When there is a change like yours, if it is real can only be one or two things. The oil is not being cooled as good as it once was, or it is absorbing more heat than it once was. If the oil line coming from the sump is restricting flow it would cause the oil to stay in the crankcase longer allowing more time for heat transfer. If this was the case I would think the oil would wind up all in the crankcase and none in the tank causing problems.

 

I don't think you can increase oil flow, because the engine is the biggest restriction in the system. If you had a restriction before the oil pump the indication would be low pressure. If the pressure is normal I don't think you can push any more flow through the engine.

 

If the cooler is plugged or coated on the inside it will not transfer the heat from the oil to the air like it once did. In my past experience with oil coolers on other aircraft flushing the cooler does little good to help increase heat transfer. Only when I have had cooler professionally cleaned or replaced with new did I see a reduction in oil temperature. In one airplane I had issues with needing to step climb in the Summer and temps at red line. After replacing the cooler the highest temp I saw was 20° bellow red line.

The comment about if it is real only goes to make sure that the indicated temperature is really what you are seeing.

 

Tom,

 

Thanks,

 

I have confirmed with a digital thermometer that the temps I see on my panel are real.  

 

We only did a cold flush on the oil cooler which apparently does nothing.   "OIL COOLERS HAVE BEEN COMPARED TO A 30 MICRON OR FINER FILTER"  duh, I guess 300 hours could cause this oil cooler/oil filter to become a bit clogged?  Also not knowing that it takes a hot flush to release the contaminants means that a simple flush is a waist of time. 

 

I'm now thinking that a hot-flush or a cooler replacement is going to be the fix.

 

http://www.hotflusher.com/index.cfm

[Anticept]

CT:

 

Out of curiosity, why would a flush change anything? You have no thermostat, so the cooler is in line with your reservoir and engine. If there was a problem with it being clogged, wouldn't the oil pressure drop, and the temperature you see at the sender be COLDER, since it was exposed to the air longer?

 

With a thermostat, I can see a clogged cooler being a problem since it's parallel with the engine at that point.

[Ed Cesnalis]

 

CT:

 

Out of curiosity, why would a flush change anything? 

 

 

I used to be able to climb 9-12,000' in a steep initial climb and my oil remained at 230F.  Now I can't get to pattern altitude without hitting 255F.  I can no longer climb over the terrain in front of me and it takes the fun out of it.

 

From Hot Flush:  "OIL COOLERS HAVE BEEN COMPARED TO A 30 MICRON OR FINER FILTER"

 

"The only way for heat to transfer efficiently out of the oil is for the oil molecules to make as much contact with the metal in the cooler as possible.

Regardless of an oil coolers configuration, they all share the same characteristic; tiny oil-flow channels. These tight spaces put a real squeeze on the engine oil in order to create as much hot-oil to oil-cooler contact as possible, offering liberal opportunity for the transfer of thermal energy from hot oil, to oil cooler.

Newer style "stacked-plate" type oil cooler, the oil passageways are created by hundreds of small corrugations stamped into what's known as the "turbulator plate". The turbulator plate is formed from .020"-thick aluminum sheet, which has been expanded to a thickness of roughly 1/16" by the stamping of the corrugations. Older style oil coolers and even some later model fuel heaters which are of a "tubed" type of construction, share the same problems. Hot engine oil is forced between what precious little space there exists between each of the oil cooler's many hundreds of straw sized air tubes. This close spacing of the tubes, about equal to the thickness of a playing card, will strain most any debris from the engine oil as it passes through the oil cooler's core.

Whether it is a tubed, or stacked-plate cooler 100% removal of the contamination from within is always the most challenging aspect of performing a proper oil cooler overhaul. It is also the most important part of the overhaul since the oil cooler's performance will be a direct reflection of how effective the flushing process was.

Proper cleaning of an aircraft engine oil cooler is definitely not something that can be achieved by simply pumping cleaning solvent through it. There are still facilities that perform this practice and consider it clean. Which is terrible, especially if it is being remounted onto a freshly overhauled engine, and believe that the cooler is "overhauled". The truth is, even with the Hot Flush machines high speed reversing and heated cleaning agent, it can still take hours to clean the cooler."

[Anticept]

But you haven't seen a pressure drop. When a cooler gets clogged up by contaminants, I would expect a pressure drop to occur long before the oil temp goes through the roof. This would especially be true of stacked plate coolers, where contaminant buildup would have next to no effect on the heat transfer due to how thin the buildup would be until it outright blocks the passage.

 

I say you should still look into it, it would be interesting to see the result. In fact, are there any other CTs in your area? Might I suggest talking to them and ask if you can borrow their cooler to see if you can duplicate the problem first?

[Ed Cesnalis]

Oil molecules need to make as much contact with the metal in the cooler as possible to transfer heat.  The tiny oil-flow channels must be coated with contamination preventing contact yet open enough to permit flow.  I don't think 30 micron will restrict flow yet it will reduce oil to metal contact.

 

When we flushed it with solvent there was no contamination released so we assumed there was none there.  The cooler had been acting as a 30 micron filter for 2-300 hours and the performance deteriorated.  Now years later the performance has finally become dismal.

[Anticept]

Then again you have the older smaller cooler right? I can see heat transfer deteriorate if the cooler was sized exactly for the engine, instead of oversized like the newer models with the thermostat (and as commonly done with cooling systems in cars).

[Tom Baker]

The issue with the cooler is not so much restricted flow, but the interior surface of the cooler gets a thin coating of gunk on it. This thin layer retards the heat transfer from the oil to the air.