Topic: low oil pressure

[mustangluver]

on my 66, while warming up, it stays between like 25-like 50 and after it warms up and gets over like 180/190 it suddenly drops to like 10-25. ive been told it can be my sending unit or my oil pump,  but want a few opinions to be sure. please note that i did a oil change not long ago.

[Tim175]

Try replacing your oil pressure sending unit first. Also what type fof sending unit/gauge are you using? What oil are you running?

[Soaring]

A sending unit either sends or it doesn't.  They are cheap though, so go ahead and replace it along with a factory oil pump. 

[mustangluver]

my gauge i believe is an aftermarket sunco gauge. my oil is a all season grade if i remember right its castrol 5w-30 high mileage full synthetic. is the oil pump fairly easy to replace and how long would it take? i dont always have alot of time to spend with the car.

[Soaring]

It will take a couple of hours to replace the oil pump.  You have to remove the oil pan to get to it. 

[6mustang6]

Ok, we all got to remember that a oil pump doesnt pump pressure but volume. The oil being pushed through the bearings creates the pressure. If your bearings are worn then you are going to have low oil pressure espiacally when its warm. It all honestly every ford i have has low oil pressure at idle when they are warm. Throwing a new oil pump on your engine is unlikely to help any. I swear to you that my 352 in my truck when warmed up and idling has less then 10 psi!! but it doesnt make a noise. Just deal with it i say as long as you are getting oil up to your rockers and they arent making any noise, then you should be getting oil to all your bearings.

[66GTKFB]

There is an oil pressure relief valve built into the oil pump. It is the means to keep oil pressure from getting to high and is, as all mechanical things, subject to failure. It is supposed to "dump" oil over 50 to 80 lbs by use of a spring. It also gets stuck. As it is not serviced, you need to replace the oil pump.
Jim

[Jeff73Mach1]

First gauges are inaccurate!  Verify the actual numbers with a mechanical gauge.

IMHO That is a thin oil for that engine.  You might go to a heavier weight to see if that keeps the pressure a bit higher when warm.

Most likely you have worn main bearings-at least to some extent and the oil pressure is dropping because the oil has excessive space to travel through and can't create back pressure.

if something in the neighborhood of a 15W40 can't keep your pressure at a true15 pounds at idle, you are likely looking at a rebuild.

rule of thumb is a minimum of 10 PSI for every 1000 rpm the engine turns.

so at 2500 rpm, you really should have 25 psi at a minimum and at 5500 rpm 50psi is only okay.

If pressure was good and this is a new development, it could be a sensor or a gauge, but it could also be spun main bearings.

I spun the main bearings in a boat motor last summer and heard a change in the engine note under full throttle before the gauge even registered the drop in oil pressure.  I couldn't explain what I heard to anyone else in the boat, just that it had changed and sure enough I throttled down and the oil pressure dropped to virtually nothing.

I think you just have some wear and too thin of an oil.  5W-30 is designed for modern high tolerance engines.  A 10W-30 or 10-40 or 15-40 will be more appropriate for old iron v-8's, especially with some miles on them.

[mustangluver]

I know i can test the sensor. but no idea where i can go get the tool. and ill be changing the oil out later on next month anyway 

[mustang245]

easiest way to test the sensor would be to get a scan tool. try any tool manufacter or try ebay. you should be able to find one

[mustangluver]

mustang245,
you do realize that a scan tool isnt for a 60s mustang right? if they make one for a 43 yr old car please share with the rest of us.

[6mustang6]

? Im hoping he is talking about a multimeter. lol

[mustang245]

Sorry, forgot this was a classic mustang. A multimeter will help determine if you are getting voltage to the sensor, or if there is a break in the circuit. I would replace both sending unit and pump

[mustangluver]

oh boy  lol theres voltage running to it seeing as how the needle moves.   

[Soaring]

Then you are in luck.  Replace the sending unit 

[mustangluver]

last time you responded you said it was my oil pump. ill go ahead n replace the sending unit first though. correct me if im wrong but i need a special socket dont i?

[66GTKFB]

No.

[mustangluver]

that has got to be the shortest reply i have ever seen on here haha. before i do the repair imma get a mechanical gauge and do a direct check on the oil pressure.

[4thofdmont]

bumped just want to share this picture which has the diagram of the engine parts.



A good starting point for the diagnosis of low oil pressure is an auction. Check the oil level to see who is the right level (not low, nor too full). If low, the engine can burn the oil, leaking oil and / or ignored. Adding oil may temporarily remedy the low oil pressure condition, but unless the oil level is properly maintained by the customer's problem may recur.
If the engine is leaking oil, we recommend new gaskets or seals to fix the leak. If the engine is burning oil, valve guides and seals are more likely to use, but the rings and cylinders might be bad, too. A wet compression test and / or leak test will tell if the valve guides or rings and cylinders are worn. The cheapest solution in the case of the guidelines is used to install new valve guide seals (if possible) without pulling the head. But the best solution would be to take the heads and guides have doubled, knurled, replaced or reamed the valve stems of large size. Worn rings and cylinders requires a complete overhaul.
Also note the condition of the oil and ensure that it is the correct viscosity for application. The heavier viscosity oils such as 20W-50, 30W and 40W may just help maintain the proper oil pressure in hot weather, but they are too thick for cold weather driving and may cause startup problems of lubrication especially in overhead cam engines. Oils with low viscosity, on the other hand, as we have 10W or 5W-20 can improve cold weather starting and lubrication but may be too thin for hot weather driving to maintain good oil pressure. Therefore, most manufacturers now recommend 5W-30 for the entire year of driving in modern engines.
A bad oil pressure sending units are quite common, many of the technicians to replace the unit without checking anything else that takes care of the problem. This approach can save time, but it is risky, because if you measure the oil pressure gauge connected directly to the engine you have no way of knowing if pressure is within specifications or not. Most of the lights come on until the oil pressure is dangerously low (less than 4 or 5 kg.). So, do not assume that the oil pressure warning light is OK, especially if the engine is making noise in the valve or bearings.
If you check the oil pressure reveals unusually low readings, check the filter. And 'possible, the filter can be connected with Gunk. Ask the customer when was the last oil and filter changed. Or replace the filter and see if it makes a difference.
The next step would be to drop the oil pan and check the oil pump pickup screen. If the screen is clogged with debris, you've found the problem. In addition, make sure the pickup tube is properly installed and positioned, firmly attached to the oil pump (losses) and is easily accessible.
If the oil pump is mounted inside the housing, the next step would be to remove and inspect the pump. Open the pump cover and authorization measure. Also, check for scoring or other damage. A broken pump drive would tell you something entered and jammed the pump. If the pump is worn or damaged, it is the only option.
If the pump seems fine, the next step would be to measure the shaft and bearing clearances. Check the free space on the main bearing closest to the pump (because it has the greatest effect on pressure) and clearances in the connecting rod bearing away (as shown by the greater wear). If the bearings are worn, they must be replaced. But before doing so, carefully inspect and measure the crankshaft bearings for wear, scoring extra-round and conical. If newspapers are in need of attention, the crank will also have to be sharpened or replaced.
Other checks might include camshaft end play, and/or pulling a valve cover or the intake manifold to check the cam bearings and lifters. Remember, excessive clearances or leaks anywhere in the engine's oil supply system can contribute to low oil pressure.