No oil pressure

[Jeff Wit]

I'm trying to get my 1952 300 back on the road after sitting in my garage for several years (don't ask). As part of the process I drained the oil and did not refill it for a few days. Now when I turn it over (with plugs out) I am not getting any oil pressure. I've tried applying a few psi air pressure to the crankcase by putting a few psi of shop air into the oil dip stick tube and modulating pressure relieve via the breather hole in the top of the valve cover. Did not help. Then I opened the oil filter and found it dry. I then got the idea to remove the pressure relief spring/valve on the oil filter housing and feeding fresh oil down the hole into the oil pump in an attempt to prime it. I added about one pint this way. Still no pressure when I turn it over. It seems the oil pressure gauge is working since it does move a bit when I apply the air pressure at the oil dip stick tube. Any suggestions? How long should I need to crank (with plugs out) see oil pressure? I really do not want to remove the oil pan. Thanks .

[dobrodan]

You might want to remove the valve cover and pour some oil on the cam and valve train to lubricate it a bit while you're trying to get the oil pressure up. I think your oil pump and distributor are drive by the same gear, so pulling the distributor cap to see if the shaft rotates while turning the motor over would tell you if the pump is turning. If so you could pull the distributor and run the pump with a drill turning in the same direction as the distributor is turning. It should be fairly simple to rig up something to put in the drill to turn the pump. With the engine sitting for so long it could take a few minutes of cranking to produce oil pressure.

[97 SL320]

Originally Posted by Jeff Wit

I'm trying to get my 1952 300 back on the road after sitting in my garage for several years (don't ask). As part of the process I drained the oil and did not refill it for a few days. Now when I turn it over (with plugs out) I am not getting any oil pressure. I've tried applying a few psi air pressure to the crankcase by putting a few psi of shop air into the oil dip stick tube and modulating pressure relieve via the breather hole in the top of the valve cover. Did not help.

You have the right idea however, there needs somewhere for the oil to go outside of the crankcase. Disconnect the oil pressure line / sender then do the pressure in the crankcase again while cranking the engine. This will fill the pump and filter.

Find out what filter this engine has, either it will be full flow ( all oil through the filter ) or bypass ( oil goes from pump directly to bearings with some oil bled through the filter ) Bypass filters take a while to fill due to a small bleed orifice.

Originally Posted by Jeff Wit

Any suggestions? How long should I need to crank (with plugs out) see oil pressure? I really do not want to remove the oil pan. Thanks .

Usually 30 sec is long enough of a crank.

[ejboyd5]

Don't remember if the filter canister is horizontal or vertical. If vertical make sure it is filled with oil before cranking.

[rbtoj]

You mentioned that the car was park for several years. It could be that the oil pickup tube got clogged up with sludge. When you did the oil change, did you noticed any sludge coming out?

[97 SL320]

Originally Posted by ejboyd5

Don't remember if the filter canister is horizontal or vertical. If vertical make sure it is filled with oil before cranking.

I used to fill oil filters ( on all brands ) but have found that increases the time to build oil pressure if the pump has lost prime.

When the filter is full, there is a greater head of pressure for the pump to push against. I do wet the element to prevent blow out when oil hits dry paper.

[ejboyd5]

Originally Posted by 97 SL320

I used to fill oil filters ( on all brands ) but have found that increases the time to build oil pressure if the pump has lost prime.
When the filter is full, there is a greater head of pressure for the pump to push against. I do wet the element to prevent blow out when oil hits dry paper.

An anecdotal allegation that counters years of accepted practice - fill the filter.

[97 SL320]

Not really.

If a pump has lost it's prime, the oil pump will push air lots easier than pushing oil. Leaving the oil filter off when cranking gives zero head of pressure for the pump to push against, however this gets messy when oil stats to move.

The next best thing is to leave an air pocket, in this case an empty filter will act as an accumulator. This allows air after the pump to go somewhere, by this time the pump is now drawing oil and has regained prime.

If the filter is filled with oil, the accumulator effect is lost and now the pump must push against the entire oiling system. The pump might not prime at this point especially at cranking speeds.

If the pump has not lost it's prime, filling the filter may result in faster pressure build, however, pressurized oil systems are mainly used for high load conditions , areas where splash lubrication isn't possible. In other words, the amount of oil left on bearings is sufficient for idle operation. If an engine knocks at start up before oil pressure builds, the engine is already worn out.

Some engines have a prelube system, this is to reduce long term wear from start up where engines are huge $ to replace. Some used an external motorized pump, others use a pump on the back of the starter motor where the starter is spun but the drive isn't engaged. Once oil pressure is built up, the motor stops and regular start sequence is initiated.

In my 40+ years of building engines, I've seen enough stuff drive for a few miles without any oil pressure and suffer zero to way less damage than you would think.