Oil Pressure

Barry53

Barry53

Junior Member
I have finally got my 39 pickup on the road. It has a 81A engine. on start up from cold the oil pressure gauges reads about 15lbs, after warming up the pressure drops to about 5-10lbs then when hot 2-3lbs. The engine temperature does not get above mid range on the gauge. Is this any thing to worry about.
 
Flatheads are amazingly resilient engines that don't need the perceived high oil pressures to operate satisfactorily for years. That said, you would do well to verify the 'correct' oil pressure via a known mechanical gauge. Same for the engine operating temp. A lot of owners have overheating problems, not running too cool, I suggest you verify the readings before you place too much faith in what the original gauges are telling you.
Just as an example, there are two differing oil pressure sender units; one is calibrated for 80 lbs pressure, the other for 50 lbs. Use an 80 lb sender unit in conjunction with a 50 lb gauge, the gauge will always indicate lower oil pressure!
Enjoy your flathead!
 
I'm running an 8BA in a 38 PU. Original gauges fitted. With the oil pressure sender as fitted to 8BA normally shows around 15 psi when hot. Once it was showing lower. removed sender unit and cleaned out to sensor. Now again shows 15 psi which i believe is ok.
Was not aware of different prssure ranges in sensors.
Phil NZ
 
Phil, I'm not 100% sure, but I think you will find that all the 80PSI ones are marked "80" on one of the flats of the square bit of the (original) sender. The earlier ones (which are a bit hard to buy) are marked "50" or not marked at all. I can't remember about the part numbers.
Point being, as Brian said, if you have an 8BA era sender and your gauge is an early one, You will have a low reading, so checking with a capillary tube type gauge. It might give you a pleasant surprise. I hope for your sake, that is the result.
 
Consider removing the sender and screwing a mechanical gauge into the block where the sender went. Then start the engine. That will give a direct, correct reading. Once you know that number you can evaluate your electric gauge.
 
How miles on the engine, is old and worn out? As was said, install a regular guage right on the back of the block and see just what the pressure is. If that's what it is use some heavy oil 15-40 20-50 it won't hurt it. Walt
 
Berry, I just finshed a 40 todor with an 8BA, new everything! Cold it runs 10-20 at idle, after it warms up 0- 5lbs. It has been this way for over 3000 miles. My theory is, if it doesn't make any noise, it must have enough oil pressure. If it not boiling over, the heat is ok. It has two oil pressure gauges, and two temp gauges. I think we worry too much, Chuck S.
 
Barry53 said:
I have finally got my 39 pickup on the road. It has a 81A engine. on start up from cold the oil pressure gauges reads about 15lbs, after warming up the pressure drops to about 5-10lbs then when hot 2-3lbs. The engine temperature does not get above mid range on the gauge. Is this any thing to worry about.
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What weight oil? Most people find Castrol 20/50 helps increase oil pressure
a little. Most low oil pressure is from a weak spring in the oil bypass valve.
There is one in front under the intake manifold, up in the front under the large hex nut. There could also be one in the oil pump if a later pump was installed. After running these valves can start to dump oil back into the
pan dropping pressure to the engine. Remove the intake manifold, screw
a mechanical gauge into the oil fitting on the bell housing at the rear of
the engine on the drivers side. Remove the spark plugs and put a small amount of oil in all cylinders. WITH 12 VOLTS to the starter the oil
pressure you see with 12 VOLTS is what it will be driving at 45 MPH.
To increase the pressure remove the hex plug in front of the valve
valley, pull out the spring and valve. You will notice the ball of the
valve has a flat spot to allow some oil to drip on the timing gears at
all times. This oil also lubricates the water pumps on your engine. To
increase oil pressure make a shim about 1/4" thick out of 1/8" steel or
brass pipe. Put this on top of the spring and do the test again. Adjust
the thickness of the shim to the oil pressure wanted. I set mine a 55
lbs and they run at 45 after warm up. These pumps will put out close
to 100 lbs. If the pump has a bypass oil that can dump oil and you will
still have low oil pressure. You don't want two bypass valve and you
can't adjust the pump valve without a test fixture so screw the
adjustment in on the later pump so the valley valve which can be
adjusted controls the oil pressure. G.M.
 
As per GM's recommendation, I would check the spring that's forward under the intake manifold... Could be broken or weak...

I am running a 59AB with both pressure reliefs, for me it's all about oil flow. I hold with the opinion that about 30lb. is all you need. If the engine holds that at hot idle you've got tight bearing clearances, anything more than that- running down the road- does not help.

Mine holds about 62-3 lb. @ 3K RPM, hot. Idles at 35+ hot.

Karl
 
I did not think that 8ba's had the spring in the front of the eng. under the intake. he said he is running an 8ba, in a '38 with original gauges, not original eng.
 
Ditto on this suggestion. Mechanical gauge are not that expensive and will give you a more accurate reading.

As far as the water temp, if you are worried about it start the engine w/o the cap and warm it up to where the gauge reads normally and stick a thermometer in the radiator.

41LjH said:
Consider removing the sender and screwing a mechanical gauge into the block where the sender went. Then start the engine. That will give a direct, correct reading. Once you know that number you can evaluate your electric gauge.
Click to expand...
 
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The oil being used is 20w/50. not sure what mileage the engine has done, brought it as is. Have had heads off, some wear in bores nothing major. Have just done a 180km(112miles) trip with no problem. But for my own piece of mind will look at installing a another pressure gauge. Where the oil pressure sender is there is blanked off hole which I presume I can hook the gauge into.
 
The blanked off hole is likely where the head mounted canister filter should feed from. Tap that with a direct reading gauge. Keep in mind, you only need about 10 psi per 1000 rpm so around 5 psi at idle and you're good.

Lonnie
 
"Consider removing the sender and screwing a mechanical gauge into the block where the sender went. Then start the engine. That will give a direct, correct reading. Once you know that number you can evaluate your electric gauge."

X's 2. I run both gauges.
 
49-53 Note: As someone noted, the later 49-53 engines do not have a pressure relief system in the front of the block - it was moved to the oil-pump. As he said he has an 81A engine, then he will have the front pressure relief system.

As said by others - first use a quality mechanical gauge to validate the pressure readings - then you'll know what to do next. It could be a faulty pressure spring, it could be incorrect bearings/clearances . . . it could be a bad pump . . . or it could just be the dang electric sender or gauge
 
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