Oli pressure

[Guest Californiagates]

I have a 1929 Desoto 6 what kind of oil pressure should I have when car is cold at idle and hot at idle

[Coley]

What does it have now?

[Guest Californiagates]

Well cold it's 30 -40 hot it's 5-10 at idle I have 2050 oil

[ply33]

Your owners manual ("instruction book") should say for sure. But that was before Chrysler started putting a shut off on the return from the bypass oil filter if the pressure dropped too low. So hot idle will have a bit lower pressure than for engines built starting, for Plymouth, in late 1933.

Your engine is a bit older technology than for my 1933, but for what it is worth the DeLuxe Plymouth Six Instruction Book for 1933 says 30 to 40 pounds "at normal driving speeds". It also says to check the flow through the bypass filter when the oil pressure is 10 pounds by removing the return fitting and checking for "a steady flow of clean oil".

My take-away on that is 30-40 pounds when running 30 MPH or so. And down to 10 or so pounds at hot idle. And that is pretty much what my 1933 Plymouth does with 20w-50 oil.

[Guest Jim_Edwards]

Well cold it's 30 -40 hot it's 5-10 at idle I have 2050 oil

You may be getting lower readings than would be normal because of the oil you are using. 20W-50 may get too thick and and too hard for the oil pump to push once the engine is at operating temp. Personally, I'd forget multi-viscosity grades of oil and just put SAE 30 HD in the crankcase or maybe 10W-30 if you live in a climate that will be seeing freezing temperatures.

[Guest Californiagates]

Engine sounds good when cold, when engine gets warmed up oil pressure drops to 1 or 2 psi engine starts to knock.let engine sit for two hours starts fine engine sounds good till it's warmed up,change oil to 50 weight took longer for oil psi to drop to 1 psi.I drop oil pan plastic gauge rods measure .002 mains .002 bearing show a little wear not bad.

[Guest De Soto Frank]

Is the knock at idle, or when you let off the throttle between up-shifts ?

Your bearing clearances sound fairly reasonable.

[Guest Jim_Edwards]

Engine sounds good when cold, when engine gets warmed up oil pressure drops to 1 or 2 psi engine starts to knock.let engine sit for two hours starts fine engine sounds good till it's warmed up,change oil to 50 weight took longer for oil psi to drop to 1 psi.I drop oil pan plastic gauge rods measure .002 mains .002 bearing show a little wear not bad.

In the assumption you are saying the knock appears to be rods knocking I'd be getting that 20W-50 out of there ASAP before you screw the crankshaft up. It seems rather obvious once the oil thickens to 50 weight it just isn't flowing to places it should. The fact allowing the engine to cool a bit and then restarting things seem to be fine until normal operating temp is reached seems to confirm, which means the oil has once again become thick enough to not flow as it is needed to flow and the knock reappears.

What was the logic of using 20W-50 anyway? What did you perceive would be improved?

[Guest Californiagates]

The knock would be at idle and when running the engine up,as far as the thicker oil goes I read a post thicker oil would rase the oil pressure,it seemed to help but than the pressure drops to 1 to 3 psi after driving 2 to 3 miles

[ply33]

The knock would be at idle and when running the engine up,as far as the thicker oil goes I read a post thicker oil would rase the oil pressure,it seemed to help but than the pressure drops to 1 to 3 psi after driving 2 to 3 miles

In that distance the oil should not be thinned very much so something might well be wrong.

I'd look into the easy stuff first. Like is the pressure relief valve stuck? Is the bypass oil filter (if so equipped) defective and allowing too much oil flow. Is the oil pump worn (cover can be flattened, or shims on the cover removed perhaps)?

[Guest Californiagates]

I removed the cover on the oil pump no gasket could see marks on cover,flipped gear around and cover too,not running a oil filter

[Guest Jim_Edwards]

The knock would be at idle and when running the engine up,as far as the thicker oil goes I read a post thicker oil would rase the oil pressure,it seemed to help but than the pressure drops to 1 to 3 psi after driving 2 to 3 miles

First of all it is not unusual for oil pressure to vary more than 1-3 psi with any engine. Oil pressure is not a constant and may vary several psi with given driving conditions.

So let's get to the issue of the knock and momentarily forget oil pressure unless it is dropping to below 10 psi and stays there or drops to virtually zero under load.

Does the engine begin to knock immediately on starting cold or does the knocking begin only after engine has warmed to or near normal operating temperature? Does the intensity of the knock become greater under load such as going up a hill and with increase acceleration? Is the "knocking" more like a "rapping" noise or more like a "whomping" noise.

[Guest Californiagates]

Thank's for the replay,when engine is cold oil psi is 50 no knock,when driving car oil psi keeps dropping slowly as temp goes up no engine knock,than oil psi drops to zero psi at idle engine starts to knock when driving engine is rapping oil psi goes up to 5-10 psi when car sits for four hours it all starts over again.

[Guest Jim_Edwards]

The one and only time I have had an engine doing what yours is doing the culprit was a spun bearing. The end result was a chewed up crankshaft. Wasn't that big of an issue as I was going to replace the engine anyway for other reasons, not the least of which was 300,000 hard miles. Your situation is obviously not as easily solved as dropping in a fresh 5.0L Ford engine.

I candidly have no solution to offer beyond saying I'd pull the engine and at minimum replace all the rod and main bearings whether poured Babbitt or insert in nature. I would consider it too risky to just hope something is going to change or a quick fix is around the corner. Probably not exactly easy to come up with a new crankshaft for a 72 year old engine.

I am still curious as to whether the problem started with the use of 20W50 oil. FYI, a oil that becomes thicker with or as an engine is reaching operating temperature will only have minor effect in restoring compression in an engine with worn rings or tapered cylinder walls, nothing else. Another way of saying heavier grade engine oil is not a cure all for an engine needing an overhaul which might include a need for boring to bring cylinder walls to a true diameter.

Edited October 27, 2011 by Jim_Edwards (see edit history)

[Guest Californiagates]

Jim thank's for all your help,I think you are right I need to tear apart the engine and dig deeper your the best Mitch

[Guest willeys41]

willeys41 here,trying to get a answer from someone that knows what a fair price for a good deSoto 6cly eng is worth????