Oil temp and Oil Pressure

Oil temp and Oil Pressure

I have a  Cessna 172F with 280 smoh. I resently installed a F&M oil filter kit and started using Aero Shell 15-50. In the summer my oil temp using Aero Shell 100 sets the oil temp gauge to near red line, and keeps around 40 psi oil pressure. Now with Aero Shell 15-50 and the new oil filter kit my oil temp  is operating at about 180f and the oil pressure has dropped to 30 psi, and at idle after hot flying day the oil pressure is near red line on the oil pressure gauge. If I make more that 3 touch and goes with outside temp. 95 degress or higher the oil pressure will get about 1/8 of an inch above 25 psi inwhich I would say that it is near 30 psi. Continental states oil pressure for this engine is 30-40 psi.  Help me as Next I will go the adding a washer to the spring to gain some oil pressure. My mechanic says fly the thing and don't worry with the oil pressure at 30 psi as this heat is really hard on the engines.

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Re: Oil temp and Oil Pressure

I saw that Aeroshell makes 120W.  I always wondered what guys from Arizona did as I use 100W here in Chicago and on a hot day the oil is like water.  See if there is an oil distributor in town that can get the stuff for you.  Even if you know the manager at a Shell station, he can get it for you.

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Re: Oil temp and Oil Pressure

I have some thoughts and wanted to share them.  Maybe it will trigger some other ideas.

What would produce the lower temperatures and pressures? 

Reviewing the continental design in the service manual, it looks like a lower temperatures result from 1) a higher oil flow rate through the engine passages; 2) lower engine operating temperature;

Have you done anything to improve engine operating temperature such as repair baffleing to get better air flow around the engine? Have you changed how you set the fuel mixture control? 

I really don't see how adding an oil filter has any real immediate  influence on the oil pressure. Especially lowering the oil pressure and certainly has no affect on tempreature. If designed correctly, the pressure loss should be minimal.

The most significant change I see is the change in oil viscosity.  Is the new viscosity appropriate for these extreme temperatures?  the lower viscocity oil is a significant factor in the system oil pressure.  It may be a sign that it's too low. 

As for a lower pressure, another possibility is that the setpoint on the oil releif valve has changed.  Temperature can influence on relief valve settings. This might be a stretch.

The continental design shows that with tan oil filter, the oil temperature element is on the suction side of the pump versus the discharge side without a filter.  Has a new temperature element been installed?  Was the location of the discharge lines temperature element in a hotter environment?

What kind of oil pump does continental use? 

I have more questions than answers.....

Bottom line though, is the engine being lubricated properly?  You can't change what happened before, but you need to assure yourself of the margin in low pressure versus adequate lubrication. If I remember correctly, the bearing and journal clearances require a certain oil pressure to be properly lubricated.

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Re: Oil temp and Oil Pressure

Barry,
1. The baffleing is in good condition and in this heat I leave the mixture full rich untill reaching cooler air.

2. You are right adding the filter kit shouldn't have a lick to do with oil pressure. I did experience on a Continental 0200 engine on my cessna 150 that during the winter months that the engine would not get oil pressure for approx. 2 minutes with the oil filter kit on. I removed it and got oil pressure within 15-25 sec. I remove the filter kit. But this is another chapter.

3. The Aero Shell 15-50 lets the engine oil temp run some cooler as when I am fully loaded with family the oil temp with 50w climbs to very near red line on temp. But hold around 40psi. Egt around 1350 and Cht 355. With 15-50 aero shell egt is 1250 and 325 cht. But the oil pressure drops about 10 psi and still is in the green but on the low side. At idle it shows redline or very little oil pressure.

4 No new temp element has been installed.

5. Don't really know what type of pump other that it is gear driven in the assessories case.

6. Thank you for all your questions and help. I did do the add a washer in the relief valve area. This O300 had 3 washers under the spring when I took it apart last night - I called my mechanic and he said that I should add one washer to the exsisting 3 and see what it would do for the oil pressure. I did and now I have 35 psi or better at 2500rpm after reaching operating temp. and at Idle I have 10-15 psi after running engine for an hr in 98 degree outside temp. I did ad another qt of oil to make it at the full 8 qt limit on the dip stick. I normally only run 7 as this engine usually blows out the one quart. Yes the 7 qt on the dip stick is really now 8 qt due to the extra volume for the filter. Any thing else that would be of help please write Thank you Barry and all.

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Re: Oil temp and Oil Pressure

George,
If adding washers under the spring does not make noticable increases in pressure, then inspect the ball and seat for FOD or other imperfections. We had a Baron recently; same symtoms, added washers with very small increase. Then inspected the seat and noticed a slight burr. Polished smooth and had a very good and acceptable increase in pressure.
Del.

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Re: Oil temp and Oil Pressure

I believe Del is correct.  Relief valves can operate premature when they get dirty or don't seat properly due to imperfections.  Also, they tend to weep (leak) when system pressure gets to within 10% of the setpoint.  That tends to put wear and tear on the ball - seat fit.  Even though we are dealing with very low pressure, they can chatter and damage the seat or get dirt on the seat.  So it's good to operate in the green and low in the band to keep the relief from having oil flow past the seat. The washer fix assumes the spring has weakened due to age.  But how weak?  And how did you confirm it?  I don't think you bench tested it.


I want to preface this before I go on, I have no experience with the continental engines.  I based my previous response on the system flow diagram in the service manual and my experince in similar system operation.  The system diamgram in the manual is a "cartoon" of what is really happening.  From this diagram, and textual description, I assumed that the relief valve does not normally operate to maintain pressure.  It only operates to protect the system from pressure getting too high.  If that is wrong, then I would not have said what follows.

Here's the downside of this success story.  How do you know the relief valve is set to operate at the correct pressure?  The added washer set the pressure higher due to the additional force on the spring, which closes the valve tighter.  This can "smash" (technically speaking) the dirt and reseat the relief.  Like closing the bathroom faucet tigher when it drips.  That works to the point you damage the seat.  In the case of the relief valve, if or when outside temperature drops and the oil viscosity increases, the system pressure will increase substantially.  If the pressure goes off scale then you probably have the setpoint too High.  That's why Del's advice is good with one change I would suggest. 

Now that you know the relief valve was operating at a lower than correct setting for the current oil, I would think it preferrable to take Del's advice and just clean the components without changing the spring setting.  See if makes a difference.  If not then you have just a little more confidence that it's the set pressure.  But it could be mal-operation of the relief. It is very hard to see imperfections in tiny ball or seat.  With the previous 100W oil the valve was operating, probably full open maintaining pressure.  But now if you put the 100w oil in the pressure it will control at a higher pressure.  Maybe too high?  How much, depends on the setpoint change from a single washer.

I've seen a small valve like this in a hydraulic system keep a power plant down for over two days due to leakage past the seat.  The system engineer couldn't see anything wrong with the small ball so he just reinstalled it.  However, I was sure the relief was the problem because the sound of the leak changed as the setpoint on the relief was changed.  this valve should not have had any flow through it.  It was there to limit peak pressure.  The moral of the story is it is very difficult to see imperfections in tiny relief valve balls.  The best thing I can think of, if money isn't a problem, is to replace the relief valve with a new one set and tested to the proper setting.  Then try it again.  Oh, in that power plant the system hydraulic pressure was much higher ~2000 psig.  But the principle is the same.

my 2 cents...

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Re: Oil temp and Oil Pressure

Yes I do understand many aspects of the powerplant as I have worked in and around powerplants for 30 yrs. I work for an electrical cooperative in Fayetteville Ar. As far as the bal and seat I cleaned it and it looked i good shape. Now if I stay with the aeroshell 15-50w I truly believe the pressure will be fine in winter and summer now. But if I switch to 100w then oil pressure in the winter may become a problem with toooo much pressure. Especially on cold day.  Thanks
George

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Re: Oil temp and Oil Pressure

Del,
Did you remove the washer after you cleaned the ball and seat?
How much pressure did you increase?
I did clean the ball/cylinder and added 1 small washer to increase the pressure maybe 5-lbs. But this small increase gave me 10-15 psi on the low end at idle inwhich on 95 degree days the oil pressure was showing in the red at idle after flight with aero shell 15w-50w. Now I show 10-15 psi at idle and about 35- 40 psi in the green at operating rpm.
thanks George

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Re: Oil temp and Oil Pressure

George,
Initially we added 1 washer, there was allready 1. No increase. Then we removed the added washer, cleaned and polished the seat. Best I recall we got about 15 PSI increase. Further evidence that keeping your balls and seat clean do make a difference in the longevity of your engine.
Regards, Del

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