Oil pressure mystery

flathead 39

flathead 39

Member
In climbing a 6% grade on the freeway @ 55mph, my oil pressure dropped to 0. Later i discovered that it would drop even on slight grades If i accelerated. If I keep the speed down to 40 or so there's no problem.

The dip stick reads full. I' wondering if I may have the wrong dip stick and maybe not carrying enough oil. Where is the oil pick up located in an 8ba pan? Anybody else ever see anything similar? thanks in advance.
 
Don't know what oil pressure gauge you are using and depending on to give you correct readings. But it is suspect also.
 
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Next oil change , add the correct amount as per the manual and mark your dipstick with a file slash
 
Measure how much comes out on the oil change.

I'm a believer that flatheads traditionally have accumulated sludge in the upper and lower areas that can displace oil.

Knowing how much comes out related to your current dipstick level may be educational.
 
Using a piece of appox. 1/8"-3/16" stiff wire or tubing that is long enough, insert into the dipstick hole all the way to the oil pan floor to see what the oil level is from the oil pan floor.
 
I'm going to offer a completely different theory. I say the baffle has been removed from the oil pan.
 
All good points made above. Another point not made as yet is the level of oil relative to the rotating mass, which should determine a correct quantity, rather than any other factor which may be variable due to a mismatch of dipsticks and/or oil pans and oil pump pickups, as well as the depth of any accumulated sludge present at the bottom of the pan. For the poster of the question, I’d say your issue is serious enough to warrant removal of your pan for inspection.
 
Try this: With your engine oil warm, rev your engine to about 1500 rpm and hold it steady. Observe the oil pressure, then goose the throttle while observing the pressure, then let off the throttle and immediately observe the pressure. You can do this driving, too. Let me know how the pressure reacts.
 
Thanks for all your suggestions. Got my work cut out for me. Easiest will be an oil change so I'll start there & see what's in there.. but, I'm not sure about the capacity. The dipstick that came with the car is for an 8rt. If that is the pan, would that be 5qt capacity? No filter.
 
40cpe said:
Try this: With your engine oil warm, rev your engine to about 1500 rpm and hold it steady. Observe the oil pressure, then goose the throttle while observing the pressure, then let off the throttle and immediately observe the pressure. You can do this driving, too. Let me know how the pressure reacts.
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I don't have a tach but I did drive at around 35 mph (oil pressure 50-60psi) then accelerate to 50-55 and the oil pressure dropped to nearly 0 and returned to normal when I let up on the gas. I can cruise at 55-60mph with no problem until I hit an upgrade. also if I keep the speed down to 40-45 & don't accelerate quickly there's no problem.
 
I was thinking maybe loose mains, but if you have that much oil pressure it doesn't sound like it.
 
Some good suggestion listed in the above posts. My bet is sludge buildup restricting the oil pump intake, causing cavitation in the pump, or incorrect oil level, not allowing enough "drain down" to keep the pump in oil. Also, page 285 of the Green Bible lists the dipsticks as "Indicator (oil level).
 
It was on a Mercedes, but same issue, uphill and heavy acceleration oil pressure would go away ---the oil pump had sucked up a bolt cut it in 1/2, pushed a piece out of the pump side, as long as the pump was submersed pressure was good, I have also seen loose oil pickup bolts causing problems similar
 
I had the same on my 41 pickup truck with a 59A. There was a mismatch between the dipstick, the tube and the pan. I filled with 4 litres and remarked the stick. I probably only had 2 litres in there when it was at the bottom of the safe driving range on the stick.

I showed it in a video.

https://youtu.be/1r51WFrUgMs?t=897

Mart.
 
My engine reportedly is out of a 53 Merc, so I looked up the specs on oil capacity for that engine & found that it required 5 qts in the pan + one for the filter. I know there have been arguments back and forth about this for years right here in the Barn, but enough opinions call for 5 qts in the pan that I'm going to give that a shot after I drain whats in there to see whats what...
 
flathead 39 said:
My engine reportedly is out of a 53 Merc, so I looked up the specs on oil capacity for that engine & found that it required 5 qts in the pan + one for the filter. I know there have been arguments back and forth about this for years right here in the Barn, but enough opinions call for 5 qts in the pan that I'm going to give that a shot after I drain whats in there to see whats what...
Click to expand...

Just noticed this post and I'm surprised that the type of oil hasn't been mentioned yet. I've been searching this topic since I bought my '35 and settled with Castrol 20/50 oil, 5 qts at change. At first I was putting 6 qts of oil at change going by the dip stick, but after reading all the info here I changed to 5 qts and re-marked the dip stick as stated. My '35 starts out with great oil pressure but after warm up, expecially going down the highway, it drops to 9-10 lbs and at idle, hot, it will even get lower. The engine sounds and runs great without any issues, especially for the Florida heat! As stated in some of the post' I've read on this forum, any pressure is good! So far I've put almost 4,000 miles since purchased in early Dec. '20. So it's not sitting still, LOL. Good Luck and enjoy the ride!
 
51 MERC-CT said:
Using a piece of appox. 1/8"-3/16" stiff wire or tubing that is long enough, insert into the dipstick hole all the way to the oil pan floor to see what the oil level is from the oil pan floor.
Click to expand...
Great suggestion, what would be a good level from the oil pan floor? I am using a none original dip stick so would like to check it. I have a clean new engine so can check with next oil change too. But, for older engines with sludge build up this would be great gage to go by.

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