We had the oil pump and it's siphon replaced on our 1992 Dodge Shadow about two months ago. The car has been running good until this morning when the oil light came back on as if the oil pressure was gone again. I went back out about a half hour later, started the car and the light was off. I drove the car to town and back and still - no oil light. The engine has plenty of oil in it and this has just happend once, but I didn't want to take any chances. The oil pump and siphon were purchased from AutoZone.
I read the reply to the "tffisher" Email asked on November 13, 2010, and would like to know if our oil pump could be occasionally loosing prime also - or could it be something worse.
We greatly appreciate your time and any thoughts or suggestions on this problem.
When oil pumps lose their prime, it happens when sitting and the oil runs out of the pump and passages, not while the engine is running. A common cause is from using an oil filter without a built in check valve. Normally that makes an engine knocking sound for a couple of seconds after start-up and it's fine after that. That happened to one customer with a Shadow that had a Fram oil filter. He had been using that brand for years with no problem. It made that noise at every stat-up until he next used a Mopar filter and the noise went away.
If your warning light comes on while driving but there is no valve noise, it's more likely the sending unit is the problem. What you would have to do is replace it with a temporary mechanical gauge so you can see exactly what is happening while you're driving, particularly at idle. If the pressure really is low, it is typically caused by worn crankshaft and connecting rod bearings. They can often be replaced if that is done before damage to the crankshaft journals occurs.
April, 28, 2011 AT 7:57 PM
Thanks for all the great info. I just wanted to add, that I cranked the car and noticed that as long as the engine idled a bit high the light stayed off, but when the idle slowed down low - the light came back on. I don't know if this means anything much or not.
Thanks again for all the help
April, 29, 2011 AT 4:04 AM
That is the way worn bearings will act but it is also common for sending units to do that as well as worn oil pumps. Worn bearings let the oil run out too fast and at low engine speeds the oil pump can't keep up the volume so the pressure drops. A worn pump also can't keep up the volume normally required so again, the pressure drops at lower speeds. Since you already replaced the pump, it's pretty safe to eliminate that as a possible cause of low pressure. Both of these things will cause the light to turn on more often after the engine has warmed up because warm oil thins out and runs out of the bearings faster.
If you have a new sending unit, install it to see if the problem persists. If you don't already have one, have the pressure measured first when the engine is warm so you'll know exactly what the pressure is. We can decide on the next plan of action once we know that.