Timberwolf
Well Known Member
Any and all ideas are welcome as we would like to make it down to sun n fun if I can get this one figured out.
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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
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
....I decided to adjust the oil pressure. Oil temps down to 86c constantly.
Looking at the 2nd photo I see you don't have an inlet screen over the air entrance. This is asking for trouble . Consider what a bird entering that could do to your oil temp if it went in there. Have you checked the cooler for any obstructions ?. This might be the source of your high temp. Put a screen cover over that air entrance ..Hey guys thanks for all of the replies. Back at a computer so I can give a little more detail. Temp probe verified with boiling water, new baffling material and all seems well sealed. Ducting is 3" scat right into the cooler. Ducting all to the cooler and the cooler face is well sealed with no leaks. It attaches to the back of the baffling with a tig welded aluminum tube to a flat plate, not exactly contoured. Engine does have oil jets and timing is verified at 20*. Looking at the chart for the X-series coolers, it looks like they recommend no less than a 13 row for oil squirters. I only have a EI scanning egt/cht gauge so not able to log the temps, but I do believe they all evened out one I powered back at cruise. I haven't had a chance to really get up and check with different temps, but all this was around 80 degress OAT. If I remember correctly I want to say my CHT on my #1 was under 290 with everything else leveling out around 340. I'll try to get a flight in today to verify.
Some observations...
This plane doesn't have the front baffle right behind the ring gear. I just cut one out with the plasma and baffling material will be here Monday. Though some air could be escaping to the lower cowl from here, I have it pretty well sealed up with RTV.
Looking at a buddies RV-7 I see he has the ramps on his top cowl. I suspect to speed the air past the front cylinders and make it all the way to the rear cylinders to prevent this very issue.
I've read where others have had some of the same issues and people have put on a firewall cooler as well as the one behind the #4 cyl. I have the previous owner shipping me the 7 row that went behind #4 in hopes that I could run them in series to get the temps down until I can fix it correctly
https://drive.google.com/open?id=0B_6aLvKRR_V2YjhuYTdHcTFUaWM
https://drive.google.com/open?id=0B_6aLvKRR_V2SUxxNnlRSjMyVmM
Looking at the 2nd photo I see you don't have an inlet screen over the air entrance. This is asking for trouble . Consider what a bird entering that could do to your oil temp if it went in there. Have you checked the cooler for any obstructions ?. This might be the source of your high temp. Put a screen cover over that air entrance ..
Something still isn't right as far as flow in the cowl because despite the change, the #4 is still at 295 on the CHT after leveling off with the others 336-345.
Dan , the pressure was 75 psi on cruise now it's around 65 psi ,its quite amazing I think that it's been such a dramatic improvement on my oil cooling , one would think that fitting a 13 row cooler over a 7 row would do the job but the pressure adjustment has done the job.
Dan Correct me, if I'm mistaken...Can someone explain why this would be as it seems counter intuitive.
Dan Correct me, if I'm mistaken...
By lowering the oil pressure, I believe you give the oil more time in the cooler, to transfer its heat to the moving mass of air.
Thanks Carl, everything I learned about this stuff in school many years ago, I have forgotten!The oil pump is a positive displacement pump. So the pump output volume is for all practical aspects independent of system pressure (for our closed systems) and constant. I offer that since oil is not a prefect fluid the heat generated by the pumping action might add a marginal amount of heat at a slightly higher pressure - but I'd estimate the additional pumping heat between 65 and 75 psig would be hard to measure.
Oil cooler heat rejection is a function of pounds mass of air and air temp rise across the cooler. Bigger cooler - more heat transfer area and better airflow (pounds mass of air). Better cooler then higher air temp rise across the cooler. Better air pressure drop across the cooler (and everything else constant), more pounds mass of air.
Carl
The oil does collect air to about 5-8%. Right on the pressure, with that increase the pumping loss would be higher but with 95% efficiency already, marginal, and the total flow would also incrementally be lowered, although the various paths to the sump will change. Nothing jumps out as to why it would have such a pronounced effect on the oil temps. Unless a baffle seal was pushed back into place in the process.The oil pump is a positive displacement pump. So the pump output volume is for all practical aspects independent of system pressure (for our closed systems) and constant. I offer that since oil is not a prefect fluid the heat generated by the pumping action might add a marginal amount of heat at a slightly higher pressure - but I'd estimate the additional pumping heat between 65 and 75 psig would be hard to measure.
Oil cooler heat rejection is a function of pounds mass of air and air temp rise across the cooler. Bigger cooler - more heat transfer area and better airflow (pounds mass of air). Better cooler then higher air temp rise across the cooler. Better air pressure drop across the cooler (and everything else constant), more pounds mass of air.
Carl
Just for the record , I have an enclosed plenum, 4inch scat to 13 row cooler, 25' timing . As said previously nothing has changed the temps as dramatically as winding down the oil pressure. I would not have posted my results if it was possibly something else .
I have a theory, something I've been kicking around a while. At s&f on a cell phone, more later
The cooled oil is either going to go through the galleys and hot parts of the engine or is going to be dumped back into the sump to recirculate.
All the oil goes to the hot parts after the pump. None can bypass the hot parts.
It is possible to bypass the cooler but all the oil will go through the filter and then to hot parts.
The oil bypass relief that dumps excess oil back to the crankcase once it exceeds set pressure - is that routing before, or after the cooler? If most of the oil is bypassing right there it never sees the cooler, right?
Bret im not sure whether the oil pressure is in front of or behind the vernatherm but it did cross my mind that it may be lifting it.