Low Oil Pressure

"Imagine a small construction company in Minneapolis, MN USA. One winter morning you attempt to start the engine of a dozer that has been sitting outside for several days. Since last running the engine, outside temperatures have slowly dropped to a temperature near -25C (-13F).

The dozer's motor oil viscosity is SAE 10W-30. The engine cranks slowly but still starts. However, the oil pressure is very low and stays low.

What might have caused this? What risks or damage to the engine can result? What is the solution to the problem? What lubricant physical properties tests might have revealed this problem? What contaminants in diesel crankcase oil can compound the problem?"

Winning answer by John Pavlovic, Rental Fleet Service, Finning Canada:

a. The high viscosity of the engine oil did not allow oil pressure to build quickly, and may also have caused the system to go into bypass, thus the low oil pressure.

b. Possible engine damage may include; scored engine oil pump - damaged lead/tin overlay of crankshaft bearings (mains and rods) - damage to camshaft bearings - damage to lifters - damaged small end bearings of connecting rods - damage to bearings of engine timing/idler/accessory drive gear train

c. Solution would be to change engine oil and filter. Install a multi-viscosity oil such as 0W-30 or 5W-30, or install a low wattage engine oil pan heater (stick on or magnetic)

d. Lube oil tests that show the viscosity at 40°C and 100°C would indicate that oil has degraded from new. Soot loading would be high. Oxidation and sulphur would also read high.

e. In this unit (diesel engine), soot loading would be the primary factor for the increase in viscosity. Soot loading also increase the oxidation rate of the oil, which in turn increase the viscosity. Sulphur in the oil (from fuel) could also be high, either from extended oil change intervals, or, from the engine running too cold (cooling system problem or short operating cycles). Condensation (and the rise in acid formation) would also be a factor in a cold running engine. All of these, combined, would lead to a severely degraded oil, with high viscosity, in a short period of time.

Editor's Note: We received a LOT of responses this week. Below are just a few that we received:

Air Binding Could Be the Problem
The cranking problem is due to too high a viscosity of the oil at low temperatures. The low oil pressure could be due to an air binding effect at the oil screen/pick up, where the oil is too viscous to flow into the void around the pick up and air is actually pulled into the oil pump.

This would be expected to correct itself as the oil warmed. In the mean time, damage to the upper end of the engine, particularly the valve train, cam bearings, etc., could occur due to an oil starvation condition. The solution to the problem is using an oil with a lower low-temperature viscosity, perhaps an SAE 5W-30 during the winter.

Physical property tests that may have revealed this problem are cold-cranking simulator and Brookfield viscosity at low temperatures. A typical contaminant of diesel engine oil is soot, which increases the oil's viscosity and would exacerbate the problem. Don Smolenski, Program Manager, General Motors WFG

Flush Engine and Refill with Better Oil
The 10W30 viscosity is not suitable with this kind of freezing temperature of -25C. Certainly a lower viscosity oil of 5W30 will be a good choice. The risk or damage on the engine could be broken Piston Rings, plugged filters and failure of oil pump. The solution of the problem is the engine flush and then refill with fresh SAE 5W30 CH4 or better Engine Oil formulated with Group II base stock or better stock.

Also Oil Filters should be replaced with new filters. The air filter is also recommended for inspection. Following lubricant properties might have revealed this problem: high viscosity on low winter side, high cloud/pour point, and poor or no-dispersant .

Please note that 10W30 is mostly formulated with Group I base Stock and the Group I basestock oil has a higher cloud point (indicating a less refined product with greater wax content) than Group II base stock. In the cold-start situations, the cold oil in the coolers had a tendency to cause large pressure drops across the filters.

The contaminants like wax crystals and varnishes compound, have promoted this problem. The wax crystal can cause base-oil congelation at low temperatures and forms an interlocking structure to restrict flow. Khalid Malik, Technical Engineer/Officer, Ontario Power Generation

Use Synthetic Oil
At that temperature, I would not go outside to start a dozer. I would stay inside next to the fireplace where it is warm. But, if I had a boss that insisted, I would shut down the dozer immediately because starting an engine at temperatures below the point that the oil will flow will seriously damage the engine because of lack of lubrication. I would sample the oil in the crank case and check it for Borderline Pumping temperature ASTM D3829, Pour Point ASTM D97, and CCS Viscosity @-25 C.

These three test would tell me if the oil was too viscous at the prevailing temperature to effectively lubricate the engine. If the test showed that the oil still had a reasonable viscosity and a lower Borderline Pumping temperature such as a -40 C, then the engine has mechanically failed or failing.

I would tow it to the repair facility. If the oil was just to viscous due to age, use, or improper viscosity selection, I would heat the sump with a heating pad, torch, kerosene heater, or heated garage to warm the engine enough to start it with reasonable oil pressure. At operating temperature,

I would drain the oil and use a synthetic Diesel 5W - 30 oil as a replacement. Also I would try to remember to plug in the block heater if the equipment was equipped the next time I shut it down. Gerald Cessac, consultant, Cessac Enterprises

Amount and Type of Pour Point Depressant
I would say that we are looking at a air binding failure in the oil pump causing inadequate lubrication to the engine bearings,rings ect-catastrophic failure can occur. A 10W-30 is checked for cold cranking at -25 deg C and for pumping at -30 deg C so I would expect that the vis grade should have been OK. I would check to see if the proper amount and type of pour point depressant was utilized. Testing that will pick up this type of failure: MRV,TP1/ gellation index/ scanning brookfield/ pour point. Soot can cause the oil to have directionally poorer low temperature properties. John Cannella, formulation chemist, American Refining Group Inc.

Thick Oil, Poor Pumpability
Low oil pressure in cold temperatures is due to the oil becoming too thick causing poor pumpability of the lubricant. This property is measured with the Mini-Rotary Viscometer (MRV). It determines the borderline pumping temperature of a lubricant.

Soot contamination from diesel fuel combustion can compound the problem. In addition, old oil will have worse cold temperature performance than new oil because oxidation thickens the oil and evaporation of the light components leaves the heavy thick components behind.

Poor cold temperature performance such as this will result in oil starvation, causing rapid wear of the bearings, pistons, cylinders, and rings. There are several solutions to this problem: 1) Change to a 5W-30 or better yet, a 0W-30 oil 2) Use quality synthetic oil like AMSOIL 3) Park the vehicle in a heated garage 4) Keep sheet on the motor, plug it in, etc. Alan Amatuzio, vice president, AMSOIL INC.

Oil Turns "Gel-Like"
Low oil pressure Likely causes are invariably related to the lubricants inability to flow normally under cold start and cold soaked conditions. Severe damage can result to the engine from lack of lubrication, for example seizure of main and connecting rod bearings, piston scuffing/seizure.

Solution to the problem - well we don't have experience with these conditions in Australia; we do have one small alpine region where it never gets as cold as - 25 Deg C .(only about - 6 deg C ! ) Better storage of the machine exposed to these severe low temperatures would be directionally of help; covering the engine with insulating material or raising entire machine temperature with space heaters within a tent type cover before attempting to start the engine would assist.

If starting in such low temperatures is envisaged using a lower viscosity oil may help eg 5W-30; the oil needs to be replaced before the winter season not at the time the cold starting is attempted.

Cold starting should not be attempted unless the oil will "flow" off the engine dipstick, and this is a quick simple visual test. One first needs to determine if the in-service lubricant has the ability to provide proper cold start performance at this starting temperature. According to SAE J300, the borderline pumping temperature for an SAE 10W- xx oil is - 25 Deg C.

The specific 10W-30 lube oil in this engine may have a marginal pass when subjected to the Cold Crank Simulator (CCS) tests prescribed by SAE J300 to measure oil flow characteristics under low temperature conditions. It is the lubricant suppliers responsibility to ensure that lubricant performance is measured against the relevant SAE performance standards it is claimed to meet.

Regarding contaminants in the diesel crankcase oil; diesel fuel in the lube oil may alter the lubricants bulk properties and hence its ability to flow under cold start conditions. The nature of the crude that the diesel fuel was refined from can have an effect, when even small quantities of diesel are present in the lube oil. Diesel refined from paraffinic crude stocks may form waxes at low temperatures.

The thixotropic nature of these waxes may then limit the ability of the engine oil pump to move the "gel -like" fluid. The wax structure may be modified by the shearing action of the oil pump and hence present the engine oiling system with a semi-fluid like substance. Air may also enter the oil pump pick up as the thick fluid will not flow properly.

Air entrained in the engine oil further reduces its ability to provide proper lubrication.This would help explain the oil pressure being low. If some time after starting oil pressure remains low, this could indicate that bearing damage has occurred (increased bearing clearances from lack of lubrication damage) The engine oil filter should be inspected for signs of bearing material and source of this material investigated if present. Steve Bliss, Technical Service Engineer, Hastings Deering (Aust) Ltd

Oil Cooling Slowly For Extended Period
The oil has gelled. Even multi-grade oils with pour point depressants can gel under extreme cold conditions. There is a phenomenon that occurs with these oils when the oil cools slowly over an extended period. The oil under the right circumstances forms a gel. The oil in and around the pickup tube is drawn into the engine and warmed back into a fluid state however since the entire sump is gelled the areas not in the immediate turbulent zone remain in a gelled state.

The engine is starved for lubricant and the pump is drawing air in with the oil with a resulting low oil pressure. The equipment should be shut down immediately and the entire sump should warmed slowly to a temperature where the oil returns to a fluid state before further operation is attempted. Clyde Hughes, Lube Tech, Harmony LLC