Loss of Oil Pressure? A-series 1275

[SomethingNew71]

Hey everyone!

I have been encountering a pretty large drop in oil pressure on my motor the past couple weeks.  Normally my car runs at a solid 80-100 PSI depending on the load however recently its been idling at around 25-30psi and maxing out at 60-65psi.  I have removed the relief valve and cleaned it multiple times as well as changed the oil and filter in the car twice.  I am still seeing the very low (in my opnion) pressures and its really concerning me.  I have noticed under throttle load the pressure is lower than when I am at speed(lets say 45-50) and I am in gear with no throttle.  When I and just coasting down the road in gear I have a higher pressure. 

Now I have talked with Jedduh on this forum who is a friend of mine outside the forum and who's opinion I trust very much.  He suggested perhaps the oil pressure sender line is blocked in some way or perhaps there is just a lot of crap in the oil system.  I did want to open the question to everyone else here as well though.  Anyone have any additional ideas?  Oil pump is about a year old and all the engine(cam, crank, etc) bearings were replaced during a fast cam upgrade about 1.5 years ago. 

[94touring]

On my who knows how old 998, after its up to temperature I see 25 at idle and 60 under power. 

[MPlayle]

The last I knew (may be out-of date or slightly erroneous by now), 25 at warm/hot idle and 60-65 at speed was pretty much normal.  As the oil warms it thins slightly, thus the drop from 80+ cold idle/load.

The 25/60 readings are what I am used to at least.

The pressure dropping when under acceleration/load and increasing on cruise seems unusual, but I have no suggestions.  (Or is it the increase is during engine braking  - coming off throttle and letting the engine "drag" slow the car?)  Either way, I would think the pressure would be closely related to engine rpm only versus load/no-load at a given rpm.

[SomethingNew71]

The last I knew (may be out-of date or slightly erroneous by now), 25 at warm/hot idle and 60-65 at speed was pretty much normal.  As the oil warms it thins slightly, thus the drop from 80+ cold idle/load.

The 25/60 readings are what I am used to at least.

The pressure dropping when under acceleration/load and increasing on cruise seems unusual, but I have no suggestions.  (Or is it the increase is during engine braking  - coming off throttle and letting the engine "drag" slow the car?)  Either way, I would think the pressure would be closely related to engine rpm only versus load/no-load at a given rpm.

I was struggling with explaining that but yes that's exactly right the pressure is higher when it's "dragging" or engine braking.

[MtyMous]

My old 998 had about 30k miles on it and it would idle around 25-30 psi when at op temp and then around 70psi when under load. I think it's just the nature of these engines. With the oil pump being rpm driven and the oil thinning out at higher temps. Now, if you start getting pressures consistently lower than 25, and the load pressure doesn't go back up quickly, I would be concerned that the oil pump or bearings are losing its tolerances or the plunger on the pressure regulator is getting hung up. I had issues with he plunger on my pressure regulator for a while and finally ended up just buffing and polishing the thing to a really high gloss finish and that kept it operating well until I sold the whole lump.

It's worth noting that I had some weird cooling issues as well with mine. I was running pretty hot temps in the summer and so I experimented with water and oil cooling. I noticed that I could get my water temps to lower with an additional radiator, but my oil pressure was not affected much by this. And honestly, my water temps were a little hot, but that wasn't my biggest concern. I was concerned with the oil temps and oil pressure getting really low. So I removed the second radiator and put in an oil cooler. My oil temps went back to normal levels and my oil pressure was significantly improved. I got a bunch of flak from the purists and others saying that the oil cooler was just a bandaid, and I had real problems elsewhere. After tearing into the engine I found that my bearings were fine (except a roller bearing in the transmission which is not oil fed) and my pump was good, too. It really was just the hot temps thinning out the oil too much.

I know this may not be your exact situation especially with it being winter, but I can only share my first hand experiences. Hope that is a little food for thought.

[MiniDave]

The last I knew (may be out-of date or slightly erroneous by now), 25 at warm/hot idle and 60-65 at speed was pretty much normal.  As the oil warms it thins slightly, thus the drop from 80+ cold idle/load.

The 25/60 readings are what I am used to at least.

The pressure dropping when under acceleration/load and increasing on cruise seems unusual, but I have no suggestions.  (Or is it the increase is during engine braking  - coming off throttle and letting the engine "drag" slow the car?)  Either way, I would think the pressure would be closely related to engine rpm only versus load/no-load at a given rpm.

I was struggling with explaining that but yes that's exactly right the pressure is higher when it's "dragging" or engine braking.

That sounds like a tolerance of something opening up under load and closing down under coast.....I'll have to think about what in the engine could do that.....

[MPlayle]

That sounds like a tolerance of something opening up under load and closing down under coast.....I'll have to think about what in the engine could do that.....

Change in case pressure?  Under load, too much draw from the carb pulling case pressure low through the breathers and under engine braking the case pressure goes back up?

[MiniDave]

Interesting thought, but I would think that would cause it to burn or leak oil.....

[SomethingNew71]

That sounds like a tolerance of something opening up under load and closing down under coast.....I'll have to think about what in the engine could do that.....

Change in case pressure?  Under load, too much draw from the carb pulling case pressure low through the breathers and under engine braking the case pressure goes back up?

Would it do that even with a PCV valve present?

[SomethingNew71]

Generally what I am reading here is that I may be worrying without merit.  It sounds like my oil pressures currently are correct and I shouldnt be worrying.

25-30 psi at 1000rpm
40-50 psi at 4000rpm
60-65 psi any higher rpm's

Thank you so much guys for the info.  The only thing that is left concerning is the higher pressure when my car is engine braking or dragging on the motor.  It only goes up from 40psi to about 55-60psi on engine brake. 

[MiniDave]

That sounds like a tolerance of something opening up under load and closing down under coast.....I'll have to think about what in the engine could do that.....

Change in case pressure?  Under load, too much draw from the carb pulling case pressure low through the breathers and under engine braking the case pressure goes back up?

Would it do that even with a PCV valve present?

What year is this car? None of the pre-injected cars had PCV valves that I recall.....

[SomethingNew71]

The car is 1960 however the motor is a 1275 from an austin america (mid 70s) I added the PCV valve to reduce fumage in the car. 

[Nicholasupton]

That sounds like a tolerance of something opening up under load and closing down under coast.....I'll have to think about what in the engine could do that.....

Change in case pressure?  Under load, too much draw from the carb pulling case pressure low through the breathers and under engine braking the case pressure goes back up?

Would it do that even with a PCV valve present?

What year is this car? None of the pre-injected cars had PCV valves that I recall.....

Yes all late twin carb cars had a PCV valves pulling from the rear tappet cover http://www.7ent.com/products/pcv-valve-smiths-13h5191.html

No Idea on the oil pressure issue, as it could be about anything, from thrust washers, cam movement, bearing movement (opening/closing oil hole), to any number of other things. I would just drive it and not worry unless it keeps getting progressively worse.

[jedduh01]

No Idea on the oil pressure issue, as it could be about anything, from thrust washers, cam movement, bearing movement (opening/closing oil hole), to any number of other things. I would just drive it and not worry unless it keeps getting progressively worse.
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[MiniDave]

You know, I remember seeing those on Sprites and Midgets but not Minis.....

[MPlayle]

I recall seeing a few "factory" engine bay pictures with the PCV (aka "gulp valve") on Minis - usually 60's vintage or early 70's.  None of the Minis I've owned had one, but most all of those had been worked on at least once before I got the car.

[jeff10049]

Pressure sounds normal, I wonder if your relief valve had been stuck closed and is now working?

Slight drop under load is normal as you're squeezing more oil out of the clearance area of the mains and pushing the crankshaft down a little opening up the oil feed side a little letting more oil out  . How much change are you seeing?

However any sudden change dose worry one, have you thought about sending out a oil sample for analysis they can check for high levels of wear metals that should not be there and warn of a failure before it becomes a catastrophic side of the road thing. You could also cut open the filter and do a visual inspection for peace of mind.


Jeff

[TJF]

With the oil warmed up when then engine is idling in neutral do you see any change on your oil pressure gauge when you engage/disengage the clutch?

[SomethingNew71]

With the oil warmed up when then engine is idling in neutral do you see any change on your oil pressure gauge when you engage/disengage the clutch?

None whatsoever! :-)

[Spitz]

80-100lb is far too high for a normal running temp IMO.

Even the factory considers 15lb at idle and 60 running as the norm.

I would actually consider that high a pressure as a problem rather that something good.  Perhaps there was a blockage that finally got cleared....(??)

[MiniDave]

Yeah, Buzz will hit 80 when the oil's cold, but once he warms up he runs 55-60, idle pressure is more like 30-40 tho.....20 -30 idle on a really hot day fresh off the highway off ramp.