Date: Fri, 1 May 1998 12:59:56 -0700
Reply-To: Rick Stevens <rstevens@ISLANDNET.COM>
Sender: Vanagon Mailing List <Vanagon@vanagon.com>
From: Rick Stevens <rstevens@ISLANDNET.COM>
Subject: Cavitation corrosion/erosion
Content-Type: text/enriched; charset="us-ascii"
I was watching <italic>ShadeTree Mechanic</italic> on TNN a couple of
Saturdays ago and they were doing a major service on I believe a fairly
new Kenworth with a Cummins Diesel. What caught my attention was when
they were changing the cooling system filter which is precharged with
some kind conditioner. At the same time they talking about a situation
which is apparently common in wet sleeve diesel engines, known as
<underline>cavitation</underline>
<underline>corrosion/erosion</underline> which causes sleeve pitting. This precharged filter available from Fleetguard, Cummins Diesel maintenance products division apparently controls this problem, and they also have test kits to check the coolant condition. And I figure a big company like Cummins must know what they are talking about as they service a pretty big commercial market and they have to spend a lot of time and money on R&D.
What got me really thinking was there a possible connection with this situation and the Waterboxer cylinder head corrosion problem. I don't think this will fix leaking heads but may be a great preventative maintenance idea.
BTW these Fleetguard products, if your interested, are apparently available at most Truck Service Centres in North America and are very reasonable. They also have a new Tech Line - 1-800-223-4583. Call them, they were very helpful and are sending me more info. Also check out their Website @ www.cummins.com or www.fleetguard.com
So I figured, I'll give it a try and I picked up a:
CC2602A DCA Test Strip Kit(4 pack) @ $5.72Cdn
FLG/DCA0L DCA-4 Liquid (16oz) @ $4.37Cdn
I have included in this posting the full text of a Service Bulletin I picked up at a local Western Star Truck dealer who is also a Fleetguard dealer.
<underline>
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</underline>
<center><bold><underline><bigger>DIESEL ENGINE LINER PITTING
</bigger></underline></bold><underline><bigger>ITS CAUSES AND HOW TO PREVENT IT
</bigger></underline></center><underline><bigger>
</bigger></underline><bigger>CAVITATION CORROSION/EROSION
LINER PITTING
Modern high speed diesel engines contain cast iron replaceable cylinder liners that are subject to accelerated corrosion due to a process commonly known as liner pitting. When plain water is used as a coolant, liners can be penetrated in a matter of 500 hours of operation when conditions are severe. It is important to understand the causes of this liner pitting and how to prevent it.
Cylinder liners are installed in a press fit with the engine block. Gaskets, called crevice seals, are used to seal the lube oil system from the cooling system across the liner.
The pistons strike the liners as they travel up and down due to the side thrust imparted by the connecting rods as the power is translated from the linear up and down motion of the piston to the rotary motion of the crankshaft.
The clearance between the piston and the liner and the liner and the block allows this piston slap to be translated into a high frequency vibration, much like the vibration of a bell when it is struck.
The side of the liner in contact with the coolant moves first toward the coolant and then away from it. This rapid movement can cause small vapor bubbles to form as the liner moves away, and to collapse or implode as the liner moves back. Very large forces are generated in very small areas as this happens. This is known as cavitation corrosion/erosion.
The violent shock waves caused by bubble collapse hammer the liner surface. The resulting bare liner surface has been highly stressed and is very active. The resulting corrosion/erosion is localized and effectively drills small verticle holes in the liner wall. If allowed to progress, these holes will penetrate the wall and oil will flow into the coolant when the engine is running and coolant into the oil when the engine is shut down.
Liner pitting can occur anywhere on the cylinder liner. Most frequently it is found on the side of the liner where the piston strikes just after the cylinder fires, and to a lesser degree on the opposite side where the cylinder strikes on the up stroke. However, it can occur anywhere on the liner where the highest level of vibration occurs. Because of variations from cylinder to cylinder and engine to engine, no two liners will appear the same.
THE EFFECT OF ENGINE
CONDITIONS ON LINER PITTING
The formation of bubbles in coolant during cavitation corrosion/erosion is very similar to the way bubbles are formed when boiling water. Remember how water in a pressure cooker boils at a higher temperature because of the higher pressure? In the same way, anything that affects the local pressure or the local temperature around the liners will impact on the ease with which bubbles are formed and will effect the potential for liner pitting.
Incorrect plumbing of the cooling system can cause local hot spots or local low pressure areas near the liners making them more susceptible to liner pitting.
Air leaks in the cooling system can cause local hot spots because of the insulating properties of air. In addition, when air is present in the coolant, more oxygen is available to accelerate corrosion in general.
HOW TO PREVENT LINER PITTING
Since the early days of high speed diesels, supplemental coolant additives [SCAs] have been used to prevent liner pitting. In the early years, sodium chromate was used. Around 1969, borate/nitrate was introduced. In 1984, Fleetguard introduced a state-of-the-art SCA containing phosphate/molybdate under the trade name of DCA4.
All of these SCAs were effective in preventing liner pitting when used in the cooling system in the recommended concentrations. Basically, they all work by the same mechanism. They form a protective microscopic film on the coolant side of the liner by transforming the ferric oxide [rust], which is very soft, into Fe3O5, which is very hard.
This very hard film resists damage from the implosion of air bubbles. As long as the concentration of SCA is high enough any damage to the protective coating will be healed.
Borate/nitrate SCAs are still commonly used, however, they rely on nitrite for their protection against liner pitting. High concentrations of nitrite are aggressive against the solder in the radiator. These inhibitors also rely on large amounts of silicate to protect against aluminum corrosion. Silicate is already present in large amounts in many commercial antifreezes. The combined silicate can cause silica get to form a "green goo" that plugs coolant passages.
DCA4 contains 30-40% as much nitrite as the borate/nitrite SCAs. Fleetguard discovered that a mixture of nitrite and molybdate provides better liner pitting protection that nitrite alone. This lower level of nitrite also allows DCA4 to provide better protection against solder corrosion that borate/nitrite SCAs.
THE RECOMMENDED CONCENTRATION LEVEL OF DCA4 IS ONE UNIT PER GALLON OF COOLANT. THE LEVEL MUST NEVER EXCEED TWO UNITS PER GALLON OR DROP BELOW ONE HALF UNIT PER GALLON OF COOLANT.
PREVENTATIVE MAINTENANCE
SCA is added to the coolant to provide necessary protection against liner pitting and scale. Most often, the SCA is contained in a coolant filter which serves the dual purpose of keeping the cooling system clean of debris and providing a convenient way to add the necessary make-up SCA at the same time other filters are changed. Sounds simple, but lots can go wrong.
There is frequent confusion regarding the initial SCA charge of a cooling system versus the service dose used to maintain the concentration. The required recharge dose is three to four times the amount added at the service interval. If maintenance personnel do not understand the need to precharge, the SCA concentration is never sufficient to protect the cooling system.
The issue of precharging is further complicated because to do it right, cooling system capacity must be know...information that is not always readily available. In a large over-the-road fleet with many different vehicles, the cooling system capacity can range from 8-18 gallons. The same amount of SCA can adequately precharge the 8 gallon system, but leave the 18 gallon system marginally treated at best. The problem only gets worse in construction/mining fleets where cooling system capacities can very from 5 to over 100 gallons.
Coolant leakage can really cause a problem when using automotive antifreeze plus SCA. Typically, the system is topped off with antifreeze and water, and no thought is given to the SCA concentration. If a vehicle loses more that 2 gallons of coolant in a service interval [15-18,000 miles], changing the coolant filter or adding a pint of liquid SCA 'WILL NOT' maintain liner pitting protection.
The complications of precharge versus service, and how to deal with coolant leaks, causes many cooling systems to get out of control. When the SCA is under-treated, you can expect liner pitting.
There are two ways to maintain proper SCA concentration on a vehicle with a leaky cooling system. You can resort to frequent coolant testing, or use Fleetguard's Compleat antifreeze for the initial fill and subsequent topping off of the system. Compleat contains DCA4 and eliminates much of the complexity involved in cooling system preventative maintenance.
TROUBLESHOOTING WHEN A PITTED LINER IS FOUND
Review maintenance records to see if the proper amount of chemical has been maintained in the system. The addition of large amounts of make-up water should be a signal that more than likely SCA was not added every time water was.
Review maintenance practices. Are radiators topped off above the fill neck? If so, there is no expansion area remaining in the top tank, and when the engine warms up, coolant will be forced out of the system. This leads to dilution of the SCA unless more SCA is added every time the radiator is filled.
Look at the liners. If there is a coating of any kind, most likely the level of SCA was not adequate. The SCA in the proper amount will protect against the formation of scale or oil coatings. The microscopic protective coating of ferrous oxide is invisible and will not be seen by the naked eye.
Review oil analysis records, if available, for traces of potassium which indicate leakage of coolant into the oil and oil into the coolant.
COOLANT TESTING
The level of protective DCA4 chemicals can easily be determined using Fleetguard Coolant Test Kit CC2626. This is the most effective field test kit for heavy duty engines available today. It will measure SCA protection levels, even if the system contains the old borate-nitrite based SCA, DCA4, or any mixture of the two.
In addition, Fleetguard offers Monitor-C [CC2700], a laboratory analysis service for monitoring or troubleshooting diesel engine cooling systems. In addition to measuring SCA levels, Monitor C provides information on freeze protection and the level of corrosion products. Analysis of fresh water samples is also available to measure sulfate, chloride, and total hardness levels.
NEED HELP ON A COOLING SYSTEM RELATED PROBLEM? USE THE FLEETGUARD U.S. COOLANT HOTLINE NUMBER 1-800-521-4005.
<bold><underline>______________________________________________________________________________________________
</underline></bold></bigger>
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<bold>Rick Stevens VE7SMR _____ '91 VW Westfalia
Victoria, BC Canada /_][_]|_____ '86 VW Transporter
Crew-Cab
Phone:(250) 474-6329 ||_|---|-----| '79 VW Convertible
Fax: (250) 474-3576 ` (+)=====(+)=
rstevens@islandnet.com </bold>
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