recent High Oil Temps

My O-320 used to run pretty consistent 190* oil temps, even in 90* ambient weather, with an occassional peak at 200 in a climb. Over the winter, I was lucky to get to 170. During my spring flights, the O/T seemed to track as normal, maybe closer to 200. A few flights ago, I noticed continued oil temps around 200. Second to last flight, they peaked around 215 and the last flight topped out at 225. Clearly a trend that needs to be resolved. It is possible that this has been building all winter, as I would not have known. Pretty hard to get excessive oil temps when the ambient temp is 30*

A couple of flights ago I replaced the oil cooler lines with better quality hose and fittings when I re-did all of fuel lines for the FI installation. I confirmed solid flow through the hoses before installation.

My current thinking is that my problems lies in either the Vernatherm or a partially blocked cooler.

I have been finding small black carbon chunks in my oil filter. Not sure if they are continually being made or remnants from the major carbon problem I had due to the glazed cylinder 70 hours ago. I was thinking that the oil cooler gets oil before the filter and it could be partially blocked from carbon. However, the rapid onset doesn't really support that theory. I suppose that draining cooler to replace the hoses could have upset something to cause the rapid onset of symptoms.

I pulled the Vernatherm. I put it in 200* water and it expands .180". The specs say that a minimum of .160" is a passing grade. I am wondering if expanding further then this increases the cracking pressure of the spring and therefore keeping more oil flowing through the cooler.

Has anyone done this test and kept the measurements of the expanded vernatherm? I hate to spend $270 for another if mine is working properly.

Does anyone have any thoughts or experience that could help here? Any other possible causes that I may have missed. I can't see how this could be airflow related, as it came on over night and I have noticed no increases in CHT's or done anything to change flow. My cooler is a 9 row mounted on the baffling behind #4.

Thanks for your assistance here.

Larry

I would look at the cooler, maybe try flushing it out into a strainer to see what comes out. If you have some chunks of carbon in there, I think that would give you the higher temps.

Can't hurt to get the cooler flushed, but I'd also do a hot leakdown. Blow-by is a big contributor to oil temperature.

Black chunks of carbon in the filter likely coming from the underside of the piston. I forget your configuration, what is your ignition system? Any change of a timing change in that period? Advanced timing will heat pistons more.

BillL said:

Black chunks of carbon in the filter likely coming from the underside of the piston. I forget your configuration, what is your ignition system? Any change of a timing change in that period? Advanced timing will heat pistons more.

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I have one mag and one EI. I am running about 36* on the EI. The EI was installed earlier this spring, but have seen several warm days post installation where temps only hit 200 or so. You've got me thinking though. I will plot out the temps on a chart to see if they correlate with advanced timing. The higher MAPs don't have advanced timing. It is still suspicious that on two flight across two days with similar weather that one hits 210 and the next hits 225. I suppose that the extra heat produced by the timing pushed my cooler beyond it's limit. Have others seen temps rise after EI installation?

Larry

lr172 said:

I have one mag and one EI. I am running about 36* on the EI. The EI was installed earlier this spring, but have seen several warm days post installation where temps only hit 200 or so. You've got me thinking though. I will plot out the temps on a chart to see if they correlate with advanced timing. The higher MAPs don't have advanced timing. It is still suspicious that on two flight across two days with similar weather that one hits 210 and the next hits 225. I suppose that the extra heat produced by the timing pushed my cooler beyond it's limit. Have others seen temps rise after EI installation?

Larry

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Larry, I have read about some events, yes, but don't know the brands etc. the EI may have some quirks about exactly what the point of ignition really is, as the engine sees it. One diagnostic check would be to fly, stabilize the temps, then drop just to the mag for 5 min and see if the temps lower, and back to just the EI to also have a single-plug-firing comparison. As DanH recently pointed out, a single plug will lower the PCP and give a slower combustion event, so it is not a risky test. Unless both are screwy then this should eliminate the EI as a factor.

The absolute temp of the oil will remain relatively flat until max flow is reached through the cooler, then it should be about fixed in the ambient-oil temp (fixed altitude/speed etc). If you could plot that data against ambient it would define when the vernatherm is fully open.

DanH said:

Can't hurt to get the cooler flushed, but I'd also do a hot leakdown. Blow-by is a big contributor to oil temperature.

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I'll do that this weekend. I have noticed recently that my belly has a bit more oil on it than it used to.

Larry

Ground

I had the same symtoms with my -320, and after an embarrassingly long search of issues in front of the firewall (vernatherm, cooler, baffling, etc) the problem was discovered to be a *very* slightly bad ground on the instrument. My continuity tester had showed continuity to ground so I had ruled that out early, but a more thorough examination revealed just a tiny bit of resistance there, enough to bump the indication up about 20 degrees.

-jon

BillL said:

Larry, I have read about some events, yes, but don't know the brands etc. the EI may have some quirks about exactly what the point of ignition really is, as the engine sees it. One diagnostic check would be to fly, stabilize the temps, then drop just to the mag for 5 min and see if the temps lower, and back to just the EI to also have a single-plug-firing comparison. As DanH recently pointed out, a single plug will lower the PCP and give a slower combustion event, so it is not a risky test. Unless both are screwy then this should eliminate the EI as a factor.

The absolute temp of the oil will remain relatively flat until max flow is reached through the cooler, then it should be about fixed in the ambient-oil temp (fixed altitude/speed etc). If you could plot that data against ambient it would define when the vernatherm is fully open.

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I have done a Megasquirt intsatallation and it's reference timing was set via a timing light off the #1 cylinder, using the same flywheel markings used when setting mag timing. I am pretty confident that my EI is configured and timed correctly. I have a switch that adds about 5* of timing for LOP(32->37 at that RPM/MAP setting). When I set up in cruise and fiip that switch, I can see my RPMs increase (FP prop). I have also set the timing at 25* at 1800 and my RPM drops are pretty close across the Mag and EI, as expected. The drops were very different when I was running a lower advance at run-up RPM, as expected.

It would be an easy test to set my advance map to a straight 25 and see if my temps drop and I will try that at some point in the diagnostics. However, I question if that could account for a 25* increase in oil temp.

mosquito said:

I had the same symtoms with my -320, and after an embarrassingly long search of issues in front of the firewall (vernatherm, cooler, baffling, etc) the problem was discovered to be a *very* slightly bad ground on the instrument. My continuity tester had showed continuity to ground so I had ruled that out early, but a more thorough examination revealed just a tiny bit of resistance there, enough to bump the indication up about 20 degrees.

-jon

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Very interesting and thanks for sharing. I pulled the sender last night and tested it on the bench, showing accurate results. However, when I took the wire off the sender, it did not seem as snug as it should be. I planned to re-install and test again today; Maybe that was it. I wouldn't have guessed that an issue like that could make a subtle difference like 20 degree.

Was your sender a single wire unit, getting it's ground via the threads? If so, how did you resolve the ground issue?

EDIT: I just realized your ground issue was at the instrument not the sender. I have an EMS that is behaving properly in all other regards, so don't have a ground issue there. However, the loose sender wire could have been an issue. I have also heard others have issues with grounds on single wire senders. Have others seen ground issues with these single wire senders?

Larry

lr172 said:

Was your sender a single wire unit, getting it's ground via the threads? If so, how did you resolve the ground issue?

Larry

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I always wire a ground to single wire senders. It is not hard to solder a wire to the sender case.

Carl

Carl

What technique do you use to solder a ground to the case of a sender? I have had to replace senders that have been modified like that due to failure, which was blamed on the solder mod. This sounds like a good thing to do, as long as you can keep from harming the sender.

lr172 said:

I have noticed recently that my belly has a bit more oil on it than it used to.

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Napkins (and bibs) work great for that.

longline said:

What technique do you use to solder a ground to the case of a sender? I have had to replace senders that have been modified like that due to failure, which was blamed on the solder mod. This sounds like a good thing to do, as long as you can keep from harming the sender.

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I guess if you really heat the stew out of the sender you could screw up a diaphragm.

Tin the #20 wire then put it on the side of the sender where there appears to be the most metal. Put a soldering gun on the wire just long enough to get the solder to flow.

If you don't want to solder use a hose clamp to clamp a tinned piece of wire onto the side of the sender. Tin the wire so you will have less potential for corrosion.

Carl

I studied the data logs a little more thoroughly. It gradually goes up during the climb (6000') and continues to rise through the 75-80% power phase of my flight. There was no real change in rate to indicate that the Vernatherm was opening or closing. Flight started around 180* O/T, so Vernatherm should have been mostly closed and I see no evidence of it's impact or change. However, it must be mostly closed or my O/T would have gone way past 225.

As I pull back the power for decent, the temp slowly drops to 200*. I am thinking this is a capacity issue. Either the cooler is partially blocked causing reduced capacity, the vernatherm is not seating strong enough causing reduced flow through the cooler or the heat from blowby. I have been working on cleaning out the cooler and see what that does. I also installed my backup vernatherm, but it also extends .180" so I don't expect that to change anything.

I should be able to test flight tonight or tomorrow morning, if the weather holds off.

Larry

I'm glad I'm not alone!

I've had a similar problem over the past two years. Everything ran fine for about four years, then one spring as the outside air temperature rose, so did my oil temps. I have replaced the vernatherm, the oil cooler, the oil lines, and all of the baffle seals. All with no major change - still hot oil. This year I replaced the vernatherm with a plunger and a spring to force all of the oil through the cooler (to verify my new vernatherm was working). Also no change.

Early on I did verify the oil temperature sender was working by noting the oil temp at shutdown and comparing it to a mercury thermometer and got within 5 degrees. But that was two years ago. This discussion about electrical grounds has me thinking I need to do that check again!

So I can't offer you a solution, just sympathy! Please let us know if you find a solution. I'm willing to try almost anything at this point!

Paul

Other things I did in case you are interested:
- verified timing (one EI, one mag)
- replaced OT sender
- compression check
- borescope cylinders
- oil analysis
- verified all baffling was in place and secure
- verified crankcase breather tube was not blocked

n18pf said:

I've had a similar problem over the past two years. Everything ran fine for about four years, then one spring as the outside air temperature rose, so did my oil temps. I have replaced the vernatherm, the oil cooler, the oil lines, and all of the baffle seals. All with no major change - still hot oil. This year I replaced the vernatherm with a plunger and a spring to force all of the oil through the cooler (to verify my new vernatherm was working). Also no change.

Early on I did verify the oil temperature sender was working by noting the oil temp at shutdown and comparing it to a mercury thermometer and got within 5 degrees. But that was two years ago. This discussion about electrical grounds has me thinking I need to do that check again!

So I can't offer you a solution, just sympathy! Please let us know if you find a solution. I'm willing to try almost anything at this point!

Paul

Other things I did in case you are interested:
- verified timing (one EI, one mag)
- replaced OT sender
- compression check
- borescope cylinders
- oil analysis
- verified all baffling was in place and secure
- verified crankcase breather tube was not blocked

Click to expand...

Appreciate the commiseration! I hope that checking grounds solves your issue. My first flush is getting some stuff out, so I hope that addresses my issue. Your's is quite puzzling. Something had to change, but you have replaced a lot of parts.

Good luck,

Larry

My experience with advanced timing is the the CHT's go up noticeably long before any oil temp rise is realized.
I missed what your compression checks were?

Not on an RV, but I had similar oil temp issues on my Twin Comanche and found the ground strap from the engine and airframe didn't have good connection.

Just another data point. My oil temp increases when my air conditioning is running due to current flow from the charging system.

rv6rick said:

My experience with advanced timing is the the CHT's go up noticeably long before any oil temp rise is realized.
I missed what your compression checks were?

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On the timing, that's what I would have expected and my CHT's are around 350, while the O/T is 225. Engine only has 90 hours on it and I haven't done a compression test yet. If my problems persist after the steps mentioned above, my next step will be a compression check.

Larry

Low clouds today, but was able to get a test flight in. O/T peaked around 205* in 85% cruise. Ambient was about 75* Most of the flight was in the 190's. Certainly an improvement. I'll see what happens over the next couple of flights before I claim victory. I will also play around with the timing a bit to see if that is having an impact.

Thanks for the assistance and ideas.

Larry

Got a longer run in today and things are definitely better. By studying the logs, it seems clear that the Vernatherm is working. I hit a peak of 204 during my higher power cruise testing. As I began my slow down for pattern entry, the temp dropped down to and stabilized at 185* I am convinced this is a cooler capacity issue. Given that I had a bit better performance last year, it may still be partially blocked. I was not able to do a professional flushing job. It's also possible it is just not big enough to shed the heat. It is a Mocal 9 row cooler.

Just thought I would post final results for the benefit of others using this thread in the future.

Larry

I bought pop corn..

Ok... you got me on the edge of my seat. What was the final outcome of your hot oil issue?

N363RV said:

Ok... you got me on the edge of my seat. What was the final outcome of your hot oil issue?

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It was the oil cooler. The Mocal 10 row just wasn't enough to do the job. I installed the SW 8604 and I get consistent 185-190 temps now (I put the Vernatherm back in). The additional advance from the EI is driving up the combustion temps (a good thing). At the lower combustion temps with the Mag, the Mocal was enough, but it must have been on the fringe and couldn't handle the higher temps from the extra advance. I say this because my oil temps would rise above normal only as my MAP got low enough to trigger more advance (later stages of a long climb and mostly in cruise). Also, I did not have the problem until I installed the EI.

Larry

lr172 said:

It was the oil cooler. The Mocal 10 row just wasn't enough to do the job. I installed the SW 8604 and I get consistent 185-190 temps now (I put the Vernatherm back in). The additional advance from the EI is driving up the combustion temps (a good thing). At the lower combustion temps with the Mag, the Mocal was enough, but it must have been on the fringe and couldn't handle the higher temps from the extra advance. I say this because my oil temps would rise above normal only as my MAP got low enough to trigger more advance (later stages of a long climb and mostly in cruise). Also, I did not have the problem until I installed the EI.

Larry

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Nice choice Larry, about 30% more heat rejection than the standard vans Niagara 20002A 7 row cooler and smaller than the 9 row. I will keep this in mind if I need more cooling. I think it will fit without baffle mods. That Mocal unit was great for automotive with saturated cooling at a low speeds, but only had about half the capacity of the SW you selected.

BillL said:

Nice choice Larry, about 30% more heat rejection than the standard vans Niagara 20002A 7 row cooler and smaller than the 9 row. I will keep this in mind if I need more cooling. I think it will fit without baffle mods. That Mocal unit was great for automotive with saturated cooling at a low speeds, but only had about half the capacity of the SW you selected.

Click to expand...

Bill,

I agree with your assessment on the Mocal. It just isn't designed for this application. That said, I am thinking the SW might be overkill with my little 320. I am sure the Niagra would have been enough, but I got a good deal on this cooler.

Larry