Technical notes of interest to Marine Engineers
Voltage in engine coolant
Authored by: Caterpillar
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Engine destruction due to excessive voltage in engine's coolant
It has become apparent that many preventive engine failures, due to problems noted in the cooling system. Problems caused by an electrical current passing through the coolant from an electrical ground problem and generation of static electricity elsewhere on the equipment. This can destroy an engine in 24.000 miles regardless of the cooling system maintenance. The only way it can be stopped is to correct the electrical problem causing the current.
The enclosed maintenance tests were developed with the help of fleet maintenance superintendents, port engineers, and several people workings in equipment maintenance. To correct this potential for engine destruction we recommend it be incorporated in any preventive maintenance program. Examples of problems noted in the field that led to this test procedure are enclosed for your convenience.
Engine damage from an electrical current will be illustrated by pitted liners, all coolers, radiators, extreme aluminum corrosion, and abnormal water pump and head gasket failure. Aluminum corrosion, products will stop the flow of coolant through the oil cooler causing severe ring and bearing wear due to improperly cooled engine oil. Copper will plate out onto the iron components causing iron destruction. One may also notice abnormal rusting of cabs and other sections of equipment.
Field Problems That Led To This Test Procedure
1. Copper injector shells in a truck engine were being destroyed in 3D days because a broken cab ground strap allowed the electrical current to ground through the coolant.
2. A twelve cylinder marine engine was destroyed by liner pitting. As indicated by our laboratory testing of the coolant, the overhauled engine was again damaged. The starter, which was starting the engine with no apparent problem to the operator, was causing a 12 volt current to ground through the coolant.
Pitting destroyed engine blocks in a large towboat. The pitting was, caused by an electrical current due to two defective electrical switches on the after cooler systems and one switch on the air conditioning unit in the captain's cabin.
4. The aluminum top tanks of truck radiators were pitting on a new fleet of trucks equipped with rubber air bag suspension an the rear ends. The rear ends were generating a current, which passed up the drive shaft to the cooling system. Grounding the rear ends and transmissions stopped the problem before the engines were destroyed.
5. A large fleet of trucks made up of half tankers and half flatbeds, using the same brand of engines and trucks, lost sixty engines in one year. Fifty-four engines failed in the flatbeds while only six engines failed in the tankers. Tankers have a bonded ground system while flatbeds do not. The nine to one ratio indicates the potential for damage.
6. A truck hauling plastic pipe was losing the engine every 100,000 miles. The operator noted the load was glowing because of static electricity due to air brushing down the open-ended pipes. The operator covered the pipe with a tarp and the engine lasted over 300,000 miles,
7. Newer model electronic controlled engines, head gaskets, water pumps, radiators, oil cooler, and transmissions were being damaged. Capacitors in the computers were allowing a stored electrical current to enter the coolant when the engines where turned off or starting after a period when the engine was in not in use. The electrical current has been present even with the batteries removed from the unit.
8. Grounding systems with the computer grounded direct to the batteries are beginning to be used by several manufacturers. Contact your manufacturer service-engineering department if a current is noted.
Electrical Test for Voltage in A Cooling System
Dry Land and Marine Equipment
Multimeter or voltmeter capable of reading both AC and DC currents is required. The meter needs to read 0 to the maximum voltage of the system being tested in tenths of a volt. The meter leads must be long enough to reach between the coolant and the groundside of the battery. We do not recommend a digital voltmeter.
Test Procedure for dry land machinery;
1. Attach the proper meter lead to the groundside side of the battery, negative-to-negative or positive-to-positive.
2. Install the second lead in the coolant touching the coolant only.
3. Read the DC and AC voltage with all systems off. If a block heater is present, also take a reading with the heater turned on. If on automatic battery charger is present, as in a stand-by system, also take a reading with the system running. Turn engine off and read DC and AC voltage,
4. Read the DC and AC voltage with the electrical &tatter engaged,
5. Read the DC and AC voltage with the engine running and all systems turned on; lights, heaters, air conditioning, two-way radio, and the radio on both stand by and transmit.
6. Remove the lead from the coolant and repeat the AC and DC voltage test with the lead touching the top radiator tank metal hose connection.
7. Remove the lead from the coolant and repeat the DC and AC voltage tests with the lead touching the outside of the engine block.
The above procedure will test a complete system except for an electrical current, which can be generated by the rear end and transmission. This is particularly true with air bag suspensions, rubber pad suspensions, and rubber mounted transmissions. Any current generated will travel up the drive shaft to ground through the engine coolant. We recommend grounding rear end and transmissions to the frame rail that the battery is grounded to.
Test Procedure for marine equipment
1. Test each engine as outlined in steps one through four.
2. Test DC and AC voltage of each engine coolant with all lights, electronics, air conditioning, and every electrical item turned on, Stand-by generators and main engine props should be running for this test.
3. Also, test from the outside of the engine block to the groundside of the battery.
1. 0 to .3 volt is normal in a coolant of a cast iron engine. .5 volts will destroy a cast iron engine with time and engine manufacturers are reporting .15 volts will damage an aluminum engine with time.
2. The current will be AC if the problem is due to static electricity or a diode problem in the alternator.
3. If the coolant Shows an electrical problem with all the equipment turned on, turn off one system at a time until you finally turn off the system that stops the electrical current, When the current stops this will indicate the electrical system causing the problem.
4. Be particularly careful of starters. They can cause as much damage to an engine as a direct connection to an arc welder. This is due to the amperage present.
5. Always change the coolant if a current is detected. The electrical current will destroy the iron protecting chemicals in a property-inhibited coolant.
6. If aluminum damage has occurred, check the oil cooler and radiator to be sure they are not stopped up with aluminum oxide corrosion products. This can lead to liner scoring and cause engine failure.
7. If a current is present with the engine turned off, battery disconnected, and reverse& direction it usually indicates capacitor problems in the computer. See field problem number eight.
This problem as it pertains to Caterpillar Engines
Summed up by Doug Hunsicker
Modified Stray Current Test
The standard test for stray current measures the current (AC & DC) from
(a) coolant to ground of battery (b) from top of radiator, near clamp, to battery ground (c) the outside of the engine block to the battery ground.
This is done under the following conditions.
1) The engine, and all accessories off. 2) The starter engaged -- accessories off.
3) All accessories turned on.
If there is a stray current only when more than one accessory is turned on, turn off the accessories sequentially until the stray current disappears. This will indicate the source of the stray current. This test, as designed, will determine a normal stray current (positive for a negative ground system & negative for a positive ground system) where the battery ground is the system ground for all component systems.
It has recently become apparent that there is no common ground in many of our power generation applications involving 3400 and 3500 engines. This allows the possibility (with these floating grounds) of a positive or negative stray current (with respect to either the engine ground, the radiator ground, or a true earth ground). If a positive stray current exists (normal stray current condition), the metal acts as an anode and serious corrosion occurs at the anode. If a negative stray current exists (if the all normal negative grounds were tied together this. condition would be impossible), the metal would -act as a cathode and no corrosion would occur -- but the reduction of the nitrite and nitrate in the coolant could occur - enabling the production of ammonia. This would quickly attack all copper components in contact with the engine coolant causing failures in- these components (e.g. radiators and oil coolers).
It is now necessary to check the voltage on the coolant with respect to the battery ground, the earth ground, and the block and to note whether the current is positive or negative. It is also necessary to check for any potential difference between the block, the radiator, the battery ground, and the earth ground.
It appears that 3500 series engine gen-sets may be prone to the negative stray current, causing the production of ammonia. This ammonia can destroy the radiator, oil coolers cores, or any other copper alloy component it contacts in short order. We have seen formation of ammonia on 3500 gen-sets in Australia and East Peoria and in Australia the presence of a negative stray current was confirmed. We have also noted a number of problems with iron corrosion in the cooling systems of 3400 gen-sets where the condition of the coolant does not appear to warrant the corrosion present. It may be a positive stray current that is causing this problem. Problems have been noted with a number of 3400 gen-sets at Powell, Hewitt, and Toromont and Ron Wclde, has noted @ problem with some 3400 gen-sets in CACO.