Oil Pressure

[MarkAubuchon]

All, not sure what to think.  After driving my 49 about 70 miles, varing speeds up to a max of 60 in OD. When I slowed down to stop at a red light, Oil pressure dropped to 0 then eased back up, Driving home it varied from 40 to 10. This car has always run at a solid 35-40 #'s.  Recently pulled the motor for new seals and timing chain, but nothing on the bearings. Have put about 300 miles on it since these repairs. Fresh oil, a little low  straight 30W.  No knocking, temp is 160.

[Don Coatney]

How low was your oil level? You might drop the oil pan and inspect your floating oil pump pick up screen. If it is stuck in the uppermost position and your oil level is a bit low it could starve the oil pump.

[dpollo]

I think Don is right.  When the oil is down a quart or more,  corners and sudden stops will cause the oil pickup to suck air.

 

In the old days, I watched for this condition before adding oil.  Too lazy to pull the stick, I guess.

[MarkAubuchon]

I will give that a try

[VFFFrank]

IMHO, it's not a bearing issue.....at least, not yet, and I'll agree that it sounds like an air leak on the inlet side of the pump. I'm guessing from an earlier reply that they used a "Floto-Screen" or similar type floating pick-up device, The pivot point, in my experience, is a poorly sealed joint that isn't a problem as long as it stays submerged. I could be wrong here but I think it becomes exposed to air before the level drops so far that the inlet point (the actual opening of the pick-up tube) is no longer submerged. This could present an air leak even though the pick-up tube end is still submerged. I've added an o-ring at that joint in the Hudson pressure-lubed engines but one must be careful that it still moves freely. I've always questioned the value of the floating screen device anyway. No advantage in my opinion.

I've got a 218 basket case here and I guess I should have a look again so that I'm familiarized with such details.

Frank       (who?)

[Don Coatney]

This is the floating assembly on a Desoto engine.

 

[Plymouthy Adams]

actually at speed and good pressure/flow sudden drop of speed will find that oil is yet in the upper portion and not yet dripped back to the pan..really a problem for OHV engines than the flathead but still a time factor for return, could be your bounce time to return to 10.    As for 10 at idle, that is considered good per the manual...rule of thumb is 10lbs per 1000 rpm....this low allowance is very much prevalent in the later big block engines..

[MarkAubuchon]

Well, that's good to know.  But the car has always held steady at 35-40#.. Will park it on a flat surface and fill it up.  What are the odds of draining the oil and sticking something thru the oil drain and try and unstick the float?

[Plymouthy Adams]

Well, that's good to know.  But the car has always held steady at 35-40#.. Will park it on a flat surface and fill it up.  What are the odds of draining the oil and sticking something thru the oil drain and try and unstick the float?

first off you just speculating this in the problem....when you did your rebuild/oil change did you indeed check that the fill level coincided with the actual amount of oil required?  In other words, do you have the correct dip stick in your engine? 

[meadowbrook]

Isnt the floating oil pickup an attempt to make up for sludge accumulation? As it piled up the pickup rises?

[Plymouthy Adams]

it is designed to flat near the top of the oil level to assure clean oil pickup...and yet deep enough not to gather foaming

[greg g]

how is the line to the oil pressure gauge?  any leakage???  Might check the condition of the pressure relief spring also though problems there usually lead to overly high pressure.

Edited April 11, 2016 by greg g

[MarkAubuchon]

Dipstick shows correct level after oil changes, had the relief valve out moved freely, flexible line seems good. Spoke with George Asche as well. He too thinks its the pickup. But also said to remove the flexible line and see if it pumps oil, or even lightly back flush in the event something is clogging the oil line.  Wont know anymore until tonight

[Niel Hoback]

I think the float is designed to pick up oil from the top to keep from picking up the dirty stuff on the bottom. They were primarily run on non-detergent oil.

[VFFFrank]

The floating pick-up device floats in the oil and isn't pushed up by sludge accumulation.....at least it sure as heck shouldn't be.

I took a look at my 218 stuff and found the "Floto-Screen to be the same as Don's Desoto image...and the same as those I've encountered in the Hudsons. It was also evident that with the oil level low enough to leave the float hanging at it's low point, the joint where it rotates is probably not submerged. So, have a look at the possibility of an air leak there while you are checking stuff.

If it held 35-40 before, it should still hold that. Something has changed.

Frank

[dpollo]

I had a very strange but similar pressure problem with a worn out sludger of an engine.

 

The oil screen in the float had become plugged. Suction then pulls the screen away from the cover so the hole in the middle will allow oil to pass through.  Anyone who has had the cover off the float will have seen this bypass hole but it is not visible otherwise.

This made for some wild variations in oil pressure.

[Dodgeb4ya]

I recently had to adjust the float in a Chrysler "8" a few months ago...Oil pressure dropped on turns and stop/starts.

[Jeff Balazs]

It seems to me that this could be caused by a bit of debris in or around the the pressure relief valve too. Maybe it acts like it is  stuck in the open position?

[MarkAubuchon]

Well, it was an easy fix.  Low on oil.  I guess I cleaned it up too much. Oil sloshes around.  I have driven this car thousands of miles, they all burn oil  but have never had a low pressure issue.. Goes to show, you learn new stuff every day.  Thanks for all your help

[Don Coatney]

How low was it? My engine uses very little oil and I probably dont check it as often as I should.