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Oil Pressure

kam41851

Donation Time
Not sure if this is the correct Forum, but I have a question regarding the 1725 engine oil pressure. What is it typically at idle and at road speed as shown on the Smiths gauge?
 

RootesRacer

Donation Time
Any pressure over 20 psi when the oil is hot and idle is 700 to 900 RPM is fine.
If its lower (perhaps to 15) you are still safe, but it indicates the clearances or pump may be worn.

On the high end, various regulators had different pressure setpoints.
Any pressure above 40psi is fine, most run 45. Some of us have modified the regulators and run 50 to 60 psi for high RPM safety.

When the oil is cold, both idle and running oil pressures will be higher, so dont use that data to make any decisions (unless its really low when cold).
 

kam41851

Donation Time
Thank you for the reply. The acceptable pressure is lower than I thought, but you confirmed my thoughts. I was seeing zero at idle, 20 psi at an elevated rpm with cold oil. I suspected excessive bearing/ pump clearances, and the pressure was a bit lower than I felt comfortable. (Assuming gauge is not reading low, any chance of that?)

Passed that car by for now.Still looking.
 

RootesRacer

Donation Time
Well you may be right on the bearings but here is the kicker, most of the time the pressure is zero at idle and really low at running, the oil pressure relief valve (regulator) is stuck partly open.
I'd lay odds this is the case with the engine you tested.
Even the most worn engines will still run off the relief pressure at RPMs above 2500.

BTW you should buy a sunbeam based on the body, completeness and lack of rust, NOT the engine condition.

HTH

Thank you for the reply. The acceptable pressure is lower than I thought, but you confirmed my thoughts. I was seeing zero at idle, 20 psi at an elevated rpm with cold oil. I suspected excessive bearing/ pump clearances, and the pressure was a bit lower than I felt comfortable. (Assuming gauge is not reading low, any chance of that?)

Passed that car by for now.Still looking.
 

kam41851

Donation Time
I agree completely. The car was 95% "there". But at the asking price, I couldn't justify engine work. I will pass along your words to the seller. Maybe this is salvageable.

What worried me is that the engine was freshly rebuilt.
 

Tom H

Platinum Level Sponsor
Kam, please do pass on to the seller about the Pressure relief valve. They are easy to pull, inpect, clean, and re-inslall to see if that solves the problem. See the photo of a valve stuck part way open in this post:
View attachment 3762
.
 
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Mark B

Donation Time
Kam-

When I start my car cold, I get about 45 to 50 psi, or what I consider about max pressure because of the relief valve, (stock not shimmed). When the car comes up to temp, about 170 degrees on the guage, I get about 15 psi at idle, which is about 1000 rpm, (a touch high). As I accelerate, the pressure tends to spike around 30 to 35 psi at 3000 to 3500 rpm for the first 30 minutes of driving. Over time, as I am driving, or if the car has sat and heat soaked, the pressures seem to wane. This is especially true if the temp creeps up a bit during long idles or sustained runs up a mountain road or incline. Often the idle pressure is at 0 or 5 psi when hot, but jumps quickly when I blip the throttle and peaks around 25 psi at higher rpms. This is true even if the temp comes back down to 170 on the guage after having gone up to 185 or so. It just never really regains pressure once hot.

I write this because it has been this way for 12 years. I rebuilt a different engine in 2000 intending to replace this one as I figured it was worn and would decline and fail on me. That engine still sits in the shed waiting. This one has not experienced the slow decline to failure I expected and has nearly identical pressures to a decade or more ago. I drive it under 2200 miles per year.

This current engine revs well and is not overly noisy, has plenty of compression and fairly even compression numbers. I run it fairly hard but change the oil often and adjust valves frequently. I honestly figured this engine would have packed it in by now and had quite the nagging in the back of my head that I would spin a bearing at high rpm or sieze something because of the low pressure, but over time I have grown to trust the engine and have taken it on 200 mile plus journeys without a concern, including plenty of mountain passes over 9000ft and sustained 12 minute pulls up those passes. I routinely take it to work about 15 miles each way, and keep up with highway traffic, (added an OD), and that means I am not babying it at all. I am trusting that when it really goes it will give me some warning so I am not completely stranded in the middle of nowhere, which might be wishfull thinking.

The bottom line is these are fairly robust little engines when cared for, and most everyone I chat with reluctanly admits to fairly low pressures or having concerns. I run 10w40 in the cooler months and 5w30 in the warmer months.

The simple steps of checking the relief valve is a great place to start and an easy one to fix, at least temporarily, and get a feel for whether the issue is more involved. I have no idea the real milage on the engine I run, and I figure its worn all over, oil pump, bearings, etc... I did make darn sure the top end was getting proper lube and that nothing was clogged or so loose in the valve train that the far ends were not getting oil. I typically run the engine briefly with the valve cover off after adjusting the valves to confirm oil is making its way to all the locations needed.

Longwinded, but hope it helps give you some perspective. I could not agree more with RooteRacer on why you buy an Sunbeam. These engines are suprisingly simple and this group can really help you finesse the details that experience has not provided.

Best,

Mark B
 

Bill Blue

Platinum Level Sponsor
A comment on low oil pressure.

The early Taurus's had computer controlled oil pressure gauges. Initially, the computer was programmed to give an accurate pressure reading. Ford had so many complaints about low oil pressure at idle, they programmed the computer to read normal any time the pressure was above 6psi. That solved all the low oil pressure problems.

Bill
 

Tom H

Platinum Level Sponsor
Mark, Your description of oil pressure is almost spot on how I would describe mine. This, after I rebuilt the engine, and I know I did it right. As you know last Sept I drove it on a 7500 mile trip. One mystery I remain puzzled about is how the pressure would drop when the car got really hot, like when I was waiting to cross the US/ Canada border. And it woud not recover to the normal oil pressure, even after I was back moving and the engine got back to "normal" temp. But once the car was off and cooled overnight, all would be fine. Sometimes the problem was indeed the OPR valve. Over the 7500 miles , I think I pulled the valve out about 7 or 8 times. About 4 times I was able to actually see that it was stuck partly open as in the photo I posted. But even on the times it was not stuck by the time I got it out, it still felt sticky. Each time I would wipe it clean, use a screwdriver to push the piston in/ out a dozen times, wipe it again, and each time it felt smooth when I was done. But 1000 miles later I could pull it and it would be sticky, like there were some fine particles in the bore of the valve.

But this OPR valve issue seemed separate from the heat related low oil pressure as you indicated. It appears that oil can have a Viscosity hystersis. Hey , I just googled Oil Viscosity Hysterisis , there's a lot of articles about it, so i think that explains the oil pressure behavior when the engine overheats! Woohoo! It's real, I'm not crazy! Hysrersis means the oil viscosity is not just dependent on its present temp, but what temp it WAS previously. If you heated oil and measured its viscosity and drew a graph of Viscosity vs Temp, there would be two curves, one as you raised the temp and a different curve as you reduced the temp. From a brief look at the articles it seems that some have figured that you can measure how "worn out" the oil is by measuring the hysterisis. The more hysterisis effect measured indicates a more worn out oil.
Tom
 

RootesRacer

Donation Time
Tom,
I have long suspected such a property of oil. On my own engine if I get the oil really hot with sustained high RPM running, the idle pressure comes way down, and as the oil life ages it gets lower and lower.

I have actually changed the oil when the pressure was unacceptably low after a hard jaunt. The multi-vis oils seem to loose the magic in them with hard life.
Perhaps its better to use single vis oil for that reason (on the alpine).
 

todd reid

Gold Level Sponsor
I agree with all that has been written above. My 2 cents for kam would be to bump up your oil to 10-40 in winter and 20-50 in summer. Also check out the recommended modifications to the oil pressure relief valve. Your thinking that your valve is not opening until 45-50 is logical, but I believe the opening is actually progressive. My 4 banger acted pretty similar to yours, and by doing the mod I saw an improvement at idle as well at at higher RPMs.
 

hartmandm

Moderator
Diamond Level Sponsor
I've always considered the OPRV location as the "side" (right side) of the oil filter block. There is a different part screwed into the front of the oil cooler block.

Mike
 
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DanR

Diamond Level Sponsor
Mark B said "Often the idle pressure is at 0 or 5 psi when hot, but jumps quickly when I blip the throttle ....... "

Could it be the "low" oil pressure at idle is because of the build spec on the bearings having more clearance than stock! A "looser" engine will or should have lower oil pressure at idle?
 

RootesRacer

Donation Time
Mark B said "Often the idle pressure is at 0 or 5 psi when hot, but jumps quickly when I blip the throttle ....... "

Could it be the "low" oil pressure at idle is because of the build spec on the bearings having more clearance than stock! A "looser" engine will or should have lower oil pressure at idle?

That is almost definitely what the issue will be. Major culprits for LOP, more or less in order of likleyhood:

#1 Rod bearing clearances.
#2 Main bearing clearances.
#3 Sticking OPR.
#4 Worn oil pump internals.
#5 Gasoline diluted engine oil (manifests LOP when oil is hot at idle).
#6 Multi-vis oil that has too many miles on it (manifests LOP when oil is hot at idle).
#7 Cam bearing clearances.
#8 Timing chain rubbing block "squirter" missing spring and ball or the tube entirely.
#9 (and to a rather minor extent) worn rockers/shaft or poor clearances between rocker shafts and the rocker oil T fitting.
 

Barry

Diamond Level Sponsor
That is almost definitely what the issue will be. Major culprits for LOP, more or less in order of likleyhood:

#1 Rod bearing clearances.
#2 Main bearing clearances.
#3 Sticking OPR.
#4 Worn oil pump internals.
#5 Gasoline diluted engine oil (manifests LOP when oil is hot at idle).
#6 Multi-vis oil that has too many miles on it (manifests LOP when oil is hot at idle).
#7 Cam bearing clearances.
#8 Timing chain rubbing block "squirter" missing spring and ball or the tube entirely.
#9 (and to a rather minor extent) worn rockers/shaft or poor clearances between rocker shafts and the rocker oil T fitting.



Add connecting rod side clearance to the list of possible excessive clearances. Don't know if Rootes listed a specification, but I would not want to see more than 0.020". Rod side clearance should not be a problem unless the rods have been "reconditioned" incorrectly or the crankshaft rod journals have been reground incorrectly.

Don't forget about leaks / restrictions in the oil pump pickup or tube or leaks / restrictions in the line from the oil pump to the oil filter base.

IME, a lot of low hot idle oil pressure problems are caused by excessive oil temperature. Possible causes include external damage to the oil cooler, insufficient air-flow to the oil cooler, restriction in the oil cooler or hoses and / or a malfunctioning oil cooler by-pass valve.
 
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