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Oil Pressure

decathlon737

decathlon737

Well Known Member
Benefactor
Help guys, I have too much oil pressure. I have a freshly rebuilt IO360 A1B that I started for the first time yesterday. The vans gauge showed 110 lbs at idle, I ran it for a few minutes thinking it was fresh oil and cold and would come down when warm or possibly a bad gauge or sender. Today I put a manual oil pressure gauge in line to verify vans gauge and also showed 110 lbs.I screwed the oil pressure adjuster out to decrease pressure until it was at the end of it's limit. I removed it, inspected and replaced, every thing looked good. I managed to get the pressure down to around 95 lbs at idle but immediately goes back to 110 lbs when throttle is applied. I warmed the oil to 180 degrees but pressure stayed at 110 lbs. The ball and spring mechanism looked good. Oil pressure is being taken from port right above right Mag. Any ideas?
Thanks,
 
Bill,

They make springs with different compression rates. Check SkyGeeks and order a lighter spring.
 
Bill,

On the right side of your engine, above and behind the #3 cylinder, you'll find the oil pressure relief valve. It is a large fitting, somewhat cylinder shaped, and will be saftied to the engine block.

Pull the relief valve and you'll find a spring and a ball bearing. There may be some washers in there too. How it works is that the spring holds the ball bearing in place until you reach a pressure limit, then the oil pushes the ball bearing out of the way and relieves the oil pressure.

After you pull the valve, there are at least two options for changing your pressure relief setting. First, if there are washers serving as spacers in the assembly, each washer you remove removes about 5 lbs of oil pressure before the relief valve opens. If you don't have washers serving as spacers, you will need to order a new, softer spring. My understanding is that Lycoming sells at least 3 different springs. I have also heard that there are adjustable relief valves, but would not know one unless I saw it.

If you want, I could swing by the airport tomorrow at lunch and we could look at it. If you're interested - 770-722-4084.
 
Thanks guys, I wasn't aware they made softer springs. Kyle, airplane is still at my home but thanks anyway.
 
Kyle Boatright said:
... First, if there are washers serving as spacers in the assembly, each washer you remove removes about 5 lbs of oil pressure before the relief valve opens. If you don't have washers serving as spacers, you will need to order a new, softer spring...
Click to expand...
Bill,

My Lycoming manual said that you can put in something like nine, yes nine, washers. My pressure was low so I just put in three washers and it is right where I want it.
 
decathlon737 said:
I managed to get the pressure down to around 95 lbs at idle but immediately goes back to 110 lbs when throttle is applied. I warmed the oil to 180 degrees but pressure stayed at 110 lbs. The ball and spring mechanism looked good. Oil pressure is being taken from port right above right Mag. Any ideas?
Thanks,
Click to expand...

Not sure of the arrangement of pressure ports on your accessory case, but in many instances not using the oil pressure port near the top right engine mount (requires a 90 degree fitting and is nearly impossible to access once the engine is mounted) will result in higher indicated oil pressure.

Kyle's suggestion of adjusting the washers in the relief valve might also get the pressure down to where you want to see it.
 
Oddly, lycoming made two different oil pressure relief mechanisims. One you use washers to shim the spring to the desired tension, the other you turn a screw at the end of it. Sounds like you have the screw kind. I'd go with the lighter tension spring myself, but if this doesn't solve it, could it be the wrong size bearings on your crankshaft? I've heard of people installing a non-ground crank with oversize bearings, resulting in a higher oil pressure. I doubt this is the case, but if the lighter spring doesn't work you might look into it.
 
High Oil Pressure

You want to remove the washers to lower the oil pressure. The washers go on top of the spring so that the more you add, the more compressed the spring becomes. This compression is what holds the ball in place. The higher the compression of the spring, the more oil pressure you have to have open the relief. When the engine is cold, this relief valve is what controls the oil pressure from going too high. My book says the washers are # 10 plain washers with up to 9 washers in place. Be sure to put anti-seize compound on the threads of the oil relief valve plug housing. It is aluminum on aluminum. If it galls you are in trouble. Ask me how I know. Mine is now the wrench adjustable kind that does not require removal.

Jerry Isler
Donalsonville, GA
RV-4 N455J
Cessna C140A N9641A
 
I have the screw adjustable type and it has NO washers. It is screwed out to the end out it's limits to lower pressure but still pressure remains at 110 lbs. I will check into the lighter forced springs. Thanks for the input.
 
How about consulting with the person or company that did the overhaul before touching or removing anything. Did they do an engine run up after the overhaul? Either way, it probably is a good idea to talk to the rebuilder before taking tools to your engine. Hope this helps:)
 
Bill, if discussion with your overhauler doesn't yield any good results, give me a call and I will give you a few things to check.
Good Luck,
Mahlon
1-800-624-6680 ext. 305

?The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
oil pressure

Is your oil cooler connected properly?
do you have a oil fiilter? does it have a by-pass valve that might
be defective?
just a couple thoughts.
Good luck
 
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