Oil Pressure Drops, more since oil change?

[Pete]

My CD31 has a Univ. M25. The engine runs great, easy starts, etc.

The only "bother some event", is what happens to my oil pressure. As the engine runs and gets hot, the oil pressure indicator drops. When the engine is cold, the pressure is about mid-way on the gauge. After a two hour run, the needle shows almost zero. Prior to the oil change, the pressure never went below 15% of the guage (compared with 50% range on engine cold running level).

Background:
- New Oil Filter and Oil replaced three weeks (4 engine hours) ago.
- Checked level of oil, at top of mark on dip stick.
- Engine is not running any hotter than I have seen before.

?? Is this a normal event??
?? If not, then what have other seen / done??

Thanks, Pete

[Oswego John]

Hi Pete ,

There are several things that could cause this drop. We have had good results by adding LUCAS Heavy Duty oil stabilizer to the crankcase. It has been known to be almost miraculous in how it helps Diesels, old and new.

It's well worth trying. About $7.00 in most auto supply stores. Read the label first and believe.

Good luck,
O J

[Reed]

Oil pump is feeding oil to the crankshaft bearings. As the bearings wear down with age and use the space the oil is pushing into widens and the oil flows into the wider spade with less resistance. Oil thickeners or heavier oil will increase the pressure for a while. Your engine is probably telling you it's time for a re-build.

Best of Luck, Reed CD31 #51 Mary Alice

[Mark Yashinsky]

Like using a lighter weight oil (viscosity)? If you had been using a SAE 40 and this time used a SAE 30 or went to a multi viscosity, like 15w-30, the oil is thinner and will get around the worn areas easier (see Reed's comment above!). Another thought, if the oil pressure suddenly is much lower and everything else is the same, something might have worn and broken in the lubrication circuit (the oil path in the engine, not the oil pressure sender/gauge), and is now allowing the oil a much easier path back to the pan (again, see Reed's comment above!). One thought, confirm the oil pressure readings shown on the gauge).
How many hours on the engine???

[Pete]

The weight of the oil is the same, SAE40. The engine has 650 hrs on her. Not having any experience with diesel engines, how can I confirm the oil pressure?

Pete

[Reed]

At 650 hours (since rebuild? Or new?) it shouldn't need rebuild. Could it be a faulty sensor? Diesel mechanic could probably hook up a mechanical guage somewhere and confirm pressure. Faulty oil pump is another possibility. Worn bearings seems unlikely.

Keep on Sleuthing, Reed

[bill 2]

Pete

When oil pressure drops after an oil change a very likely place to start looking is the oil itself. ie:

1> Engines with spark plug ignition have two letter specs that start with an "S_" to designate Spark ignition. Diesel engine specs call for a two letter spec starting with a "C_" for compression ignition. ( At the local auto shop you can now find oil marked for gas engines only Hence spec'd "S_".) So you should be using a "C_" spec oil.

2> A sudden ( after oil change ) drop in pressure is very likely due to a lower viscosity (SAE 40 weight to SAE 30 weight ) oil or quality. The lower the viscosity the lower the temp range the oil is designed for or the tighter the manufacturer has made the internal clearances and therefore the "finer" the oil needs to be but they usually offset this by spec'ing multigrade ( SAE 15/40) .

3> VW/MB and such are now also spec'ing straight synthetic for diesel though older CD's should not require this.

So if it was me , I would check the engine manufacturer ( Universal ) spec's and try ANOTHER oil change with a different and quality oil for a quick first remedy.

Bon Chance

[Stan W.]

A lot of after-market filters are of poor quality compared to o.e.m. and it is not unheard of to get a defective filter. There is also a remote chance you used the wrong part. To establish a base-line, I would try another filter, make it o.e.m. and make sure the part number matches up.

[Pete]

I will replace the old, recheck the specs, etc. and see what happens. If that doesn't do it, then it may be time for my mechanic to take a check. BTW, I only use OEM filters (from marinedieseldirect ). I could have gotten a bad filter, given the low cost might be worth a change just in case.

Thank you to all...

Pc

[Pete]

I pulled the "new" oil out and replaced it with a heavy weight SAE30 mix (per specs from Universial book). The pressure started around 40, then dropped to half that after she was hot. I will continue to monitor. My best guess is the oil was just not the correct viscosity.

Thanks, Pc

[Boyd]

I experience a slight reduction in idle speed oil pressure when the engine is hot after an oil change. The oil increases in viscosity on some engines due to the increase in carbon from ring blowby. This is why your oil goes black almost immediately after an oil change. The hot idle readings rise slowly as the hours on the oil increase. A mechanic told me once that as long as there was some oil pressure reading at idle things were ok. It was good judgement to change the oil again and confirm that the viscosity was as recommended. The wrong viscosity can be disastrous.

Several years ago my oil pressure gauge began to give oscillating readings. The needle bounced around a 10 psi range in a regular pattern as the engine ran at constant speed. I replaced the sending unit and the readings returned to normal.

I tried the Lucas product several years ago and all it did was make the engine hard to start and didn't stabilize the oil pressure readings. Seems like the increase in viscosity was too much for the starter motor.

Boyd
s/v TERN
CD30 MkII
Fort Lauderdale, Fla.

[Cappy]

I have been using both these additives for many years now and can only say good things about them. Up here in New England the winters are severe. When used in the right proportion Lucas never gave me any problem with hard starting on any of my equipment. As a matter of fact Lucas will increase compression on a loose engine to help starting. Im surprised that the oil would get so thick down in Florida that it would effect the starter. What was the reason you added Lucas?Maybe there was other reasons to try a oil additive.
A multi viscosity oil-10w30 or 5w20 has two weights. It starts up using the lighter oil and as the engine warms up it becomes the thicker weight. Most engine wear comes from starting. Lucas and Marvel Mystery Oil plate surfaces so when you start, you dont run dry until the oil pressure comes up. The upper end stays lubricated and engine life is extended. Cappy

[Boyd]

Hi Cappy:

I was having some smoke and hard starting problems with my engine. It was at this time I also experienced the aberrant oil pressure readings. Figured trying an oil additive was the cheapest way to fix the problem.

I added Lucas to the next oil change and the engine just got harder to start. It cranked even slower than before making the starts even longer. The smoking continued and the oil pressure was up a bit. Seems my engine is still pretty tight.

I have a Westerbeke which has about 200 hours on it since the last rebuild. The recommended oil is straight weight 30. Westerbeke specifically does not recommend multiweight oils for this engine.

After the lack success with Lucas, I took an oil sample for analysis and it came back with excessive sodium. This indicates either salt water or glycol in the oil.

Subsequent replacememt of the multipart exhaust manifold with a new single part casting and a new oil pressure sensor has cured all problems. My oil now tests normal for sodium.

Lucas may help some things but not all. It was an interesting diagnostic tool however.

Boyd
s/v TERN
CD30 MkII
Fort Lauderdale, Fla.