1940 L8 low oil pressure

[Narve N]

My 1940 NewYorker is supposed to have an overhauled engine (auction company claim), but the oil pressure is steadily dropping when hot to below 20 lbs at idle and not more than 25-30 lbs at normal speeds. When cold the pressure is steady at 45 lbs. Is this a sign of a worn oil pump or something else wrong, or is it supposed to be like this? The car burns 1L oil every 1000km (A quart pr 600 miles) but does not smoke and will run all day at 60 mph+ and climb 1 in 4 gradients (pictured)

 

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[Spinneyhill]

What oil are you using?

[Narve N]

Straight 40 weight, better oil pressure that the 20-50 I tried first.

[Spinneyhill]

Hmmm. I was running a 20W-50 in my Dodge 8 and the oil pressure was lousy and variable like yours. I changed to a 5W-40 and it is much more consistent and undexpectedly higher. If you use a low first number like 5 or 10W, it behaves like that SAE viscosity at low temperature and your warmup will be easier with less wear (thinner oil is easier to pump so proper lubrication is achieved sooner at startup). Your car was probably made for "30 weight" oil so something like 30 or 40 for the second number would be good.

Edited October 11, 2016 by Spinneyhill (see edit history)

[normanpitkin]

I had the same problem on my 48 New Yorker ,it was the oil pressure relief valve ,try taking it out and really cleaning it .I mean really clean it to a high polish ,reinstall and adjust ,might be worth a try.

 

[Narve N]

Much appreciate inputs, thank you both. A thorough clean of the oil relief valve sounds like a sensible first step for a long Winter coming up.

[Narve N]

Have now run the oil pressure relief valve in a sonic cleaner, resulting in much quicker pressure build up (and quicker drop off at off throttle). The valve is now working as intended, but I continue to get pressure dropping off when hot so issue is not solved yet.

 

Especially worrying is the drop to 10 lbs or less (have seen zero reading) when turning the car to the right with engine at idle (sharp bend with off-throttle). This is similar to a car running low on oil with the pick-up not being able to suck any in when cornering. When straightening the car out, pressure returns. Question: When this occur with oil levels topped up, is it an indication of wrong oil pump, oil pump pick-up being bent away from proper position, or something else? Should I pull the pan and look for anything out of place?

 

[c49er]

The car has a floating pick up. I had the same issue and had to pull the pan to fix the sudden loss of oil pressure on turns and or a sudden stop.

There is a metal tang that you bend on the PU tube to adjust max oil float PU float height.

With absolutely no bottom end knocking or rattle on start up and running...... maybe Worn Cam bearings are your issue.

Low oil pressure and burning a quart of oil every 600 miles.......... engine rebuild time IMO.

I have several Chrysler 323 eight cylinder cars been there and done most all of it!.

Edited May 19, 2017 by c49er (see edit history)

[Narve N]

Thank you Bob,

I will pull the pan and check for tangs/tabs restricting the downward movement of the pick-up. I do assume with annual oil change intervals and few miles in between, the risk of dirty oil at the bottom of pan is less than when the cars were new.

As for the need for an engine rebuild, I must admit the oil consumption baffled me as there are no visible leaks. I will run a compression check later on to see if there are further indications of a worn engine.

[c49er]

Here is a 323 Chrysler 323 1950 straight eight Town and Country PU....I hope your 40 is the same!

There is a upper and lower limit tang that can be bent to control how far down and up the floating PU can travel.