Low oil pressure reading after oil change

[REHolder]

Just changed oil and filter using STP 10w-40. Now, oil pressure gauge is reading low. Took five minutes idle for idiot light to go off but still reads half of what it did before the change. I have heard that the Veglia gauges are unreliable but can anyone explain why an oil change would cause this to occur? Is the sender more likely to fail after an oil change?

[18Fiatsandcounting]

It can take a few seconds for the oil pump to fill a new (empty) oil filter and then start pressurizing, but not 5 minutes. That indicates something is wrong. Check your oil level to make sure you have enough.

The Veglia gauges are pretty good, but the sending units go bad after a couple decades. If you haven't changed the oil pressure switch and the gauge sending unit, now is the time.

What kind of filter did you use? Could also be the wrong oil filter. By the way, I pre-fill the oil filter before installing. Dribble new oil into the filter, let it burp for a few minutes, top it off, then spin it on.

As to why the idiot light didn't come on before? My guess is that the old oil was actually thicker due to having a lot of crud in it. Not good of course.

-Bryan

[REHolder]

Filter was a NAPA 1189 Gold and it was pre-filled before installation. Don't know if the service tech burped it but if I had to guess I would say he did.

[Nut124]

Do you know what oil was in the pan?

I'm thinking you oil pump is bad, has hard time priming after draining the oil. The idiot light should turn off within 5 seconds or so.

[18Fiatsandcounting]

Don't know if the service tech burped it but if I had to guess I would say he did.

Wait, service tech? You had the oil changed at a shop? Almost all shops are honest, but there are crooked shops that charge for one type of filter and oil and use much cheaper substitutes. You can verify the oil filter by looking at it, but if it were me, I'd change the oil again and verify that you do indeed have good quality 10W-40.

If the issue persists, I'd start with replacing the two sending units.

By the way, the reason I change my own oil is not because I don't trust them, but because they simply don't have the time to allow the oil to fully drain. I open up the drain plug and remove the filter, let it drain overnight sometimes two if I don't need the car, and then refill the next day. Shops don't have that kind of time. An extra cup or two of old oil can drain out if you wait long enough.

-Bryan

[bdinardo]

May also be a good idea to try and prime the oil system. Copied from another forum discussion, "Disconnect the ignition, carefully take the oil filter off, put a something under the oil pump housing, and turn it over until you see oil coming out of the filter mount. Put the filter back on and start it. Pressure should be there."

[REHolder]

I provided the filter and saw the oil going in. The drain plug was out for over 20 minutes while they procured the STP 10w-40. I've decided to drain 2 quarts and replace with Castrol 20w-50. I'll let you know if thickening the oil helps.

[REHolder]

Took BDinardo's suggestion. Removed filter and turned motor over. Plenty of oil squirted out, so I removed 2 quarts of the 10w-40 replacing with Castrol 20w-50. Careful to put new oil in filter and burp. Pressure now reading 50 which it is back to normal for this car. I still think I have a defective or dirty sender as the needle fluctuates a lot more than it did before the oil change.

[18Fiatsandcounting]

Good to hear! Replace the sending units (both idiot light switch and gauge sending unit). 90% of "low oil pressure" problems are just issues with these two old parts slowly failing.

-Bryan