Ed Cesnalis Posted October 30, 2013 Report Share Posted October 30, 2013 I know this has been discussed by my searches fail to find it. As my CHT to Oil Temp differential grows I tend to believe my CHT and doubt my Oil Temp even more. Oil now runs 40F hotter than CHT. This morning's flight was below freezing temps with one strip of tape across the bottom, not quite end to end. On the ground CHT was 30F higher than Oil Temp but by the time I was leaving the pattern oil was 35F higher than CHT. I was climbing slowly at 12,000' and Oil Temp got to 250F and CHT to 210. Level I went down to 235 and 190. My confirming thermometer gets here in a week which will have to go in the oil tank but if it is cooler than my Oil Temp gauge I will know the gauge is high. What is your differential? Link to comment Share on other sites More sharing options...
Anticept Posted October 30, 2013 Report Share Posted October 30, 2013 You should probably specify that you do not have a thermostat. My aircraft, oil is usually cooler than CHT. I'll look later and report back. Link to comment Share on other sites More sharing options...
S3flyer Posted October 30, 2013 Report Share Posted October 30, 2013 20-25 degrees. Link to comment Share on other sites More sharing options...
chanik Posted October 30, 2013 Report Share Posted October 30, 2013 Unless there is a fire burning in the engine cowl, it is pretty much impossible for oil to be hotter than CHT Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted October 30, 2013 Author Report Share Posted October 30, 2013 Unless there is a fire burning in the engine cowl, it is pretty much impossible for oil to be hotter than CHT Kurt, please explain why Link to comment Share on other sites More sharing options...
Roger Lee Posted October 30, 2013 Report Share Posted October 30, 2013 Hi Kurt, For us with a Rotax not completely true. First we have to look at where the oil temp gets it's signal. Our oil temp readings come after the oil has gone through the cooler as it enters the oil pump. So this is the coolest our oil gets. Our head temps are coolant cooled, but the oil isn't. The oil then can have a line restriction that slows the flow and allows the temps to rise. Oil in the Rotax is almost always hotter than the CHT. My oil is always 20F+/- hotter than my CHT's. Ed, All this is going to be guessing and could go for years until you remove the fire sleeve on those two hoses and get the engine hot to see if they reduce their radius. Diagnostics is about ruling possible cause in or out even if you think there is only a slim chance. Or you can re-route the return oil hose off the bottom in two ways to keep any radius reduction out. Most also make the oil hose coming out the top right side of the oil cooler that swings 180 degrees back to the oil pump too short. When it gets hot it can reduce its radius at about the mid hose point. Your temp differential isn't out of the ball park, but a little wide spread. With those cool temps the oil temp should be down. I never see over 235F on an 85F day and loaded to the hilt. 15 flap 60 knot take off to 800' agl then zero flaps and 75-80 knots to how ever high I choose to go. Another thing I would seriously consider doing is removing the radiator. Flush and blow out the outside fins, but I would flush the inside of the oil cooler with a solvent and follow it up with air 2-3 times. I flushed the outside fins today with a pressure sprayer on a CT and they were loaded with oil, dirt and bugs. Call me. I would bet if we talk and you do the few things above you high oil temps will reduce. The three things above would take me about 2 hours to do and how long have you been chasing this problem? Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted October 30, 2013 Author Report Share Posted October 30, 2013 I think in our CT world we use gauges that are labeled CHT when they are actually measuring coolant temperature. The CHT idiot light for a Corvair was set to 475F CHT and coolant temps are in different ranges. Roger, I'm on my 3rd set of hoses and a recent inspection also been there done that on the coolers. The one thing I haven't done is confirm the high oil readings. After that I can look at my oil hoses again. The digital thermometer confirmation was your idea too. Link to comment Share on other sites More sharing options...
Roger Lee Posted October 30, 2013 Report Share Posted October 30, 2013 The CHT only reads metal temp out on the edge of the heads. It is not in contact with any coolant. Coolant and metal head temp should be within several degrees of each other. The new 912is engine actually has ports drilled and tapped for coolant probes, but don't come from the factory with them. So your oil cooler has been flushed and blown out? Give me a few minutes and I'll post a pic of a better oil hose route. I have to download it off the camera first. The blue Parker oil hose even though meant for high temps can collapse a little easier than the original hose so if some lengths get cut the same as the original they can reduce radius on you if bent a little too far. Link to comment Share on other sites More sharing options...
Ed Cesnalis Posted October 30, 2013 Author Report Share Posted October 30, 2013 The CHT only reads metal temp out on the edge of the heads. It is not in contact with any coolant. Thanks for the correction. Interesting that my CHT remains so cool. We spent a day flushing and blowing out the coolers to perfect condition and they remain clean. Link to comment Share on other sites More sharing options...
Roger Lee Posted October 30, 2013 Report Share Posted October 30, 2013 Here is the bottom engine return oil hose that goes back to the tank. It has the hottest oil and has not been cooled. This return line normally snakes around back up behind the engine and FD tries to use a straight fitting into the tank. later they changed it to look like this. You rotate the banjo bolt on the bottom so it aims straight out to the left side of the engine. The hose end gets changed from a straight fitting to a 90 degree. The hose is now nice a straight with a sweeping curve. No chance for a reduced radius. the other way to do this with the straight fitting is to rotate the banjo bolt on the bottom to aim more to the back right side of the engine. Attach a new slightly longer hose and bring it back behind the engine again, but this time there are no sharp turns. just a nice sweeping arch. This hose is a major offender in slowing the oil and causing higher temps. I should have taken a picture of the hose that comes out of the cooler on the top right and back to the oil pump, but I forgot. Link to comment Share on other sites More sharing options...
Jacques Posted October 30, 2013 Report Share Posted October 30, 2013 which cylinder head do you take the CHT reading ? #3 or # 1 or both .. if so ..are they the same ? Link to comment Share on other sites More sharing options...
Roger Lee Posted October 31, 2013 Report Share Posted October 31, 2013 The Dynon's are #2 & #3 CHT. My CHT's within 10F of each other. EGT's are #3 & #4 unless you have a Flydat then all 4. My EGT's 5F-40F difference depending on throttle setting. Link to comment Share on other sites More sharing options...
Jacques Posted October 31, 2013 Report Share Posted October 31, 2013 I should have taken a picture of the hose that comes out of the cooler on the top right and back to the oil pump, but I forgot. here we go Roger took that picture while visiting you remember the reason for the head removal..? Link to comment Share on other sites More sharing options...
Roger Lee Posted October 31, 2013 Report Share Posted October 31, 2013 Hi Jacques, That is a perfect picture for Ed to see that right side hose. I do not remember why the head removal. Too many hose changes are damaging brain cells. CHT's are left front #2 and the right rear #3. 1 & 3 are on the same right side. Link to comment Share on other sites More sharing options...
Jacques Posted October 31, 2013 Report Share Posted October 31, 2013 sure 2 and 3 of course the head removal was for a tie wrap the plane wasn't yours but 537.. Link to comment Share on other sites More sharing options...
Roger Lee Posted October 31, 2013 Report Share Posted October 31, 2013 I remember now. Link to comment Share on other sites More sharing options...
Runtoeat Posted October 31, 2013 Report Share Posted October 31, 2013 Roger, instead of replacing with longer hoses, would installing a spring inside the current oil hoses keep these from kinking - similar to what is done with coolant hoses? Link to comment Share on other sites More sharing options...
Roger Lee Posted October 31, 2013 Report Share Posted October 31, 2013 Hi Dick, I don't see why not, but I haven't tried it. Just use as thin a spring as possible and no longer than needed so as not to restrict flow. Too beefy a spring could slow flow. Then on a test flight watch the oil temp closely and if it's good so are you. I use springs all the time in coolant hoses, even the 1" when necessary. FD has them in 1-2 coolant hoses. Link to comment Share on other sites More sharing options...
FastEddieB Posted October 31, 2013 Report Share Posted October 31, 2013 As an option to an internal spring... ...in the past I've taken a piece of slightly larger diameter hose, slit it, slid it over the problematic kink-prone area and ty-wrapped it in place. Mostly done it on garden hoses, but I don't see a reason why it might not work here. Link to comment Share on other sites More sharing options...
207WF Posted November 16, 2013 Report Share Posted November 16, 2013 It is not uncommon for me to see 195-200 CHT and 235-240 on the oil, similar spread as Ed is seeing. WF Link to comment Share on other sites More sharing options...
suntheman Posted June 3, 2014 Report Share Posted June 3, 2014 The Dynon's are #2 & #3 CHT. My CHT's within 10F of each other. Is it normal roger? How much differential be tolerated? Dhony Link to comment Share on other sites More sharing options...
Roger Lee Posted June 4, 2014 Report Share Posted June 4, 2014 Perfectly normal. 5-10F is normal. If I started to see a 20F+ difference I may start looking around, but wouldn't be alarmed. If it went to 40F then there is an issue. It may be a wire, a probe or a real cooling or oil issue. The CHT only measures metal temps on most of our engines. The new engine with new style heads actually have the probe in the coolant and the probe is on top of the cyl.. These new cylinders are interchangeable with our cylinder heads. One thing to keep in mind. If you have one wacky reading it could be false because it should affect something else. So look for trends and other readings being affected if you think you have a problem. If you have a real problem and not just a wire or bad sensor then you should see some other reading being affected. (this isn't 100%, but most of the time) Link to comment Share on other sites More sharing options...
suntheman Posted June 5, 2014 Report Share Posted June 5, 2014 I see, everything normal except CHT Thanks Link to comment Share on other sites More sharing options...
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