* Weak or failing oil pump: This is the most probable cause. The pump may be worn, allowing it to struggle to maintain pressure at low RPMs when the engine's demand for oil is reduced (during idle or deceleration). Revving the engine increases the pump's speed, thus restoring pressure.
* Clogged or restricted oil pick-up tube: The tube that draws oil from the sump might be clogged with sludge or debris. This restricts the oil flow to the pump, especially at low engine speeds.
* Blocked oil filter: A severely clogged oil filter will restrict oil flow, leading to low pressure at low RPMs. This is less likely to completely drop to 0, but it's worth checking.
* Low oil level: While seemingly obvious, low oil level can cause pressure to drop dramatically when the pump is not fully submerged. Check your dipstick immediately.
* Worn or damaged crankshaft bearings: If the bearings are excessively worn, they might leak oil, reducing the overall oil pressure, particularly under low RPM conditions. This is a more serious problem.
* Leaking oil cooler: A leak in the oil cooler could cause a pressure drop, but less likely to drop to zero.
What to do:
1. Check the oil level immediately. Add oil if needed but only to the correct level. Overfilling can cause just as many problems.
2. Inspect the oil filter. If it's old or visibly damaged, replace it.
3. Check for obvious leaks: Look carefully around the engine for any signs of oil leaks.
4. Have the oil pressure tested by a mechanic. They can use a gauge to measure the pressure accurately at different RPMs and identify the problem more precisely. They can also assess the condition of the oil pump, bearings and the oil pick-up tube.
Ignoring this problem is dangerous. Low oil pressure can lead to catastrophic engine damage. Do not continue driving the van until the issue is diagnosed and resolved. The sooner you address this, the better the chances of avoiding a costly engine repair or replacement.
