Oil pressure issue

[BobT]

2001 Chrysler 2.7L V6

120,000 miles

Earlier this spring I blew the head gasket and contaminated my crankcase with engine coolant.

After it was repaired I had a problem where once the engine was warmed up the oil light would illuminate when the engine was idling in gear. I figured the pressure sensor got contaminated and needed replacing. I returned it to the mechanic so he could run a few tests to make sure everything else was okay. He said he ran it quite a bit so the oil could get well warmed and everything tested okay so he replaced the pressure sensor.

After that everything seemed to be okay until the first time I took it on the Interstate. Now, every time I run in excess of 55mph for any length of time, the oil light will illuminate when I am at idle rpm. All I have to do is touch the throttle and the light goes out. Sometimes just putting it in neutral so I’m not idling in gear will extinguish the light so I must be just on the edge of minimum pressure. If I slow down and drive 55 for as little as a mile, then everything seems normal again.

Is it possible that at high speed (70mph) the oil is getting just a little warmer than at low speed (55mph) and the pressure is dropping a bit? The only explanation I can figure is that when the oil got contaminated with anti-freeze the oil pump was damaged just enough that it can no longer maintain pressure when the oil gets a little thinner.

Any other thoughts on why interstate highway speeds might cause this?

[Jeremy airjer W]

The 2.7 and 3.5 are no strangers to lack of oil pressure. Chrysler issued a tsb a year or so ago not to use oil friction modifiers anymore because they starve the pump and then grenade the engine.

There may be some sludge in the pan that is starving the pump, the engine is on its way out, or you may have a bad switch.

[theoilman]

When you blew the head gasket and had coolant in the oil, you likely broke loose some sludge that at higher engine speed is clogging the oil pickup screen. An engine flush may help (my guess less than 50% chance), my educated guess is the oil pan needs to be dropped and cleaned.

[BobT]

They ran a solvent through the system to clean it but I suppose there could be more gunk coming loose. I'm nearing my next oil change so I've been thinking of running a cleaning agent through it first. I was thinking of maybe using Seafoam.

[98prosport]

the coolant has damaged the rod and or main bearings. You might get away with replacing them in the car. The way to test would include dropping the pan and inspecting for wear, and plastigauging. just my 0.02

[Scott K]

the coolant has damaged the rod and or main bearings. You might get away with replacing them in the car. The way to test would include dropping the pan and inspecting for wear, and plastigauging. just my 0.02

These are my thoughts as well, very common on some model vehicles, if there is any coolant in the oil.