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,
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
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
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
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
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,
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
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
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
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