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HD Diesel Engine
Coolants for RVs




Unlike your typical passenger vehicle, heavy duty diesel engines have some unique requirements when it comes to coolants. Many RV owners who have diesel engines are unaware of just what kind of maintenance they need to perform. For this reason I'll detail some of my thoughts regarding coolants as they apply to diesel engines used in RVs. I'll give you a bit of background on why they have unique needs so that you can better understand. This is supplementary information and you always need to follow your factory recommended cooling system service schedule. However, these schedules are matched not only to the particular engine in your RV but also to the coolant used in that engine as shipped from the factory. If you choose to upgrade your coolant to the new organic acid technology, chances are that your schedule may change.

If you would like to print this review it probably won't work that well. The pictures and text on the far right will probably get clipped. If you want to print this review, Click Here for a Print Ready Version.

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Mark Quasius - "Cruzer"




Cylinder Liners

Before we even get into coolants we first have to understand why diesels have special needs. It's all because of the cylinder liners.

Engine blocks used in lighter duty automotive applications are cast and the cylinders are machined into them. If you score a cylinder or wear it out you have the engine bored out to a larger diameter, then fit it with oversize pistons. Engines can be bored out .010", .030", or even .060" oversize. Of course when the walls get bored out, the wall thickness gets thinner. But, automotive engines don't rack up that many miles so it's not that often that this needs to be done.

Heavy duty diesel engines, as used in trucks, aren't in the same class. For one thing, they can rack up many more miles so the odds of them requiring a rebuild is much greater. Also they are subject to more stress and thinner cylinder walls just aren't the answer to longevity. Also, their engine blocks are large and expensive and replacing them is not an option and removing them from a vehicle to be machined is also a costly alternative. Therefore heavy duty diesel engines use replaceable cylinder liners. If an overhaul is needed the engine can remain in the truck frame and the cylinder liners are removed with a puller tool and replaced with new ones. Your RV may not rack up the same kind of miles as a truck but the engine is still in the heavy duty class so it's construction will be similar.

Cylinder liners come in two designs - dry sleeved and wet sleeved. A dry sleeve is inserted into the engine block. The engine block has outer walls that contain the coolant around the cylinder so the dry sleeve slides inside that bore and the coolant never actually touches the cylinder liner itself. A wet sleeve is inserted into a block that does not have any outer cylinder wall. The coolant in the cylinder cooling jackets actually touches the cylinder liner itself. The liner has flanges and counterbores on it's outside diameter that are used to hold o-ring seals so that the coolant stays in the engine's water jackets and doesn't leak down into the engine's oil sump.

Typically dry sleeves are used on smaller engines while wet sleeves are used on larger engines. The reason for this is that larger engines create more heat and the wet sleeve does better job of conducting that cylinder heat to the coolant because the wet sleeve is in direct contact with the coolant. Engines like the 5.90 liter Cummins ISB and 7.2 liter Cat C7 use a dry sleeve while larger engines, like the 9 liter Cat C9 series and up, or the 8.3 liter Cummins ISC, 8.9 liter Cummins ISL, etc all use wet sleeves. Dry sleeves don't have as specific a need as the wet sleeve engines when it comes to coolants so if you have a Cummins ISB or CAt C7, you won't have to read any farther unless you're curious. The rest of this information applies to any RV owner with a wet sleeved diesel engine.


Cylinder Liners and Pitting

pitted cylinder liner

As you can see in the above image, there are some serious pits in this liner's cylinder wall. These pinholes will allow coolant to pass into the combustion chamber and you'll find your coolant level going down and white smoke coming from your exhaust. This is when it's time to pull the engine apart and spend some money. In addition the hot combustion gasses will pass into the coolant and you'll have very high temps real quick. So, where do these pinholes come from and how can we stop them?

Pitting is a result of something best described as "cavitation". Wet cylinder liners are held in place in the engine block with o-ring seals and the clamping pressure of the cylinder head upon the upper flange of the liner. As the piston moves up and down there is also side to side force being exerted on the cylinder due to the throw of the crankshaft. This sideways forces causes these liners to vibrate back and forth. When the cylinder moves in one direction it moves away from the coolant, creating a small air bubble in it's wake. Eventually this air bubble bursts and the coolant, which is under pressure, bursts through and impacts the cylinder liner. This sudden jet of high pressure coolant can pit the liner, and if allowed to continue, will create a pinhole through it. Think of this action as giving you the same results as if you fired a pressure washer's meanest cleaning tip to your wooden sided house at point blank range. The results would be equally disastrous except all of this happens in microseconds in a diesel engine running at high RPM and it doesn't stop until you switch off the key.

Regular coolants just can't handle the effects of cavitation. They're fine for gasoline powered engines but then gasoline engines don't have the cavitation issue to deal with either so don't go stick Dexcool into your large diesel. Keep it for your passenger car or light truck. Cavitation needs the high compression ratios of a diesel engine with wet cylinder liners to begin. It's even greater on a cold engine because the increased slap creates more vibration. It's also greater at lower RPMs when lugging your engine that it is in a diesel engine that's revving. In order to counteract the effects of cavitation we need to use special coolants designed for wet sleeved diesel engines.


Heavy Duty Coolants


There are a number of heavy duty coolants available for diesel engines and each have their own specific requirements. Couple this with the fact that Cat and Freightliner have their own private labeled coolants and things get really confusing for the average RVer. The biggest thing that separates the heavy duty diesel coolants from the automotive stuff is the presence of special additives in the coolant to deal with cavitation. Some coolants use a Borate and Nitrite salt additive package to coat the surface of the liner. This coating reduces the surface tension of the coolant and also forms a coating on the liner. Some other coolants use a Phosphate/Molybdate based inhibitor package so it's important to use the correct stuff and never to intermix them. These coatings are gradually eroded by the pinging caused by cavitation but the additives continually replenish this coating so everything remains in balance. The problems begin when these additives begin to deplete themselves from the coolant.

Because the additives are continually trying to "plate" the surface of the liner, they will eventually run out. There are a number of circumstances that determine just how fast this will happen but the most critical is the quality of the coolant - in other word's, how good is your water. A cooling system with good fresh coolant starts out with a high additive concentration. Eventually, scale and lime can begin to form in the coolant. The various metals in the engine can react with your coolant to modify it's mineral content and reduce it's effectiveness. Add in the fact that your additives are depleting simply by the constant bonding action to the liner wall and you can see why coolant has a given length of time to do it's job. But, the biggest detractor to this is the water that is used in your cooling system. For best cooling and best freeze protection a mixture of about half water and half coolant is ideal. Too much water and you'll run the risk of damage from freeze ups while too much coolant will reduce it's effectiveness at cooling off the engine. Regular tap water is full of minerals and stuff that you really don't need in your cooling system. It's best to use distilled or deionized water when filling your system with coolant. If you can keep that stuff out right away you're coolant will have a better chance at surviving longer. You can now buy premixed coolant which is already reduced with deionized water. That's a very foolproof method of keeping contaminants out.


Replenishing Your Additives

test strips and refractometer

In order to test your coolant you will require more than just a hydrometer or refractometer. These devices measure specific gravity so that you will know when your coolant has dropped below it's freeze protection level. Hydrometers function by squeezing the bulb until the center unit floats and they need to be compensated for various coolant temperatures. A spectrometer is a better choice because even cold coolant can be accurately tested, plus you can also use it to test the specific gravity of your flooded batteries as well. But they won't tell you the condition or chemical composition of your coolant. That is best done with test strips. The test strips are litmus based paper strips that you dip into your coolant. It will report the various mineral content and additive levels in your system by changing colors. A color reference card is included and is then used to convert these readings into real numbers. If your additive levels are too low you don't have to replace the coolant. All you really have to do is add some more additives. These additives are referred to as Supplemental Coolant Additives, or SCAs. When your SCA level readings are low you need to add some more SCAs. They come in a can but be sure you know which can. If your coolant uses a Borate/Nitrite based inhibitor package you'll want to use the DCA2 style of additive because the DCA4 style is only used for Phosphate/Molybdate based coolants. You'll need to first verify exactly which coolant is in your engine, then check out which SCA additive product is designed to work with that coolant. If you really aren't sure which coolant is in your RV you may want to just consider dumping it out and starting over with something that you know and can easily obtain. Chances are it'll have to be dumped soon enough anyway. Even "long life" coolant doesn't last forever.

Judging a coolant by it's color isn't the easiest any more. In the past everything was the green Ethylene Glycol coolant for a long time until the extended life coolants, such as Dexcool became available. These were colored pink to help differentiate from the old green stuff. Eventually everyone got into the coolant specifying business and each brand had their own special coolant that they felt was best. Coolant manufacturers then countered with extended life coolants that tried to meet all of these requirements and before you know it there were a bunch of different colored coolants out there. Some multi-use coolants were even gold but they would take on the characteristics and color of any existing coolant they were added to. The heavy duty industry also had a bit of a coolant revolution as the old green stuff gradually became replaced with heavy duty coolants designed to minimize liner cavitation on the newer engines. That stuff too, was available in a number of colors so just because your diesel came with pink coolant doesn't mean that you can pout any pink coolant into it. Fleetguard, a division of Cummins, recently had a pink extended life coolant, a green heavy duty coolant, a blue ES Compleat coolant (that confusingly looked very much like windshield washer fluid), as well as an orange Optimax OAT coolant. You really need to know what's in your coach so that you can monitor it with the proper test strips and use the correct additives. Each coolant may have different service schedules as well so you may be replacing one coolant every 2 years while another goes 5 years. You really need to know what you have. If in doubt, throw it out. Then start over and keep records. Remember, if you don't keep your SCA levels up there or mix up the wrong stuff, you'll cause liner damage and that gets very expensive.

Some of the older RVs used coolant filters. If you have a filter be sure that you are replacing it with the correct filter. Many of these are not filters at all. They look like filters but in reality they are SCA dispensing agents that are designed to dispense SCAs over time to keep your SCA levels up so that you don't have to add them from cans every now and then. Again, be sure to check these SCA levels with test strips every 6 months to be sure that the "filter" is still working. If you have converted over to the newer OAT coolants you should not add any SCAs to them. In that case you can probably get a plain old filter without any additives and spin that on instead.

There are a number of popular coolants on the market. Daimler, who owns Freightliner, markets the Alliance brand of coolant. Peak Antifreeze offers a number of coolants, including the Fleetcharge antifreeze so popular with heavy duty diesels. Old World Industries offers the Final Charge extended life coolant, which is also handled by Peak. The Fleetguard division of Cummins, known for their high quality filters, makes a number of coolants as well, especially the new ES Compleat OAT extended life coolant.


OAT Coolants

test strips and spectrometer

The latest generation of coolants has much to offer. These coolants use Organic Acid Technology (OAT) to eliminate the constant monitoring of SCA levels. In addition to this low maintenance approach, they are longer lasting, and a far better coolant. The final benefit is that various brands are compatible with each other. Finally, the coolant industry has gotten it right. OAT coolants do not use nitrite/borate salts or phosphate/molybdate additives as SCAs. Instead they utilize carboxcylic/fatty acids to handle those needs. The largest benefit is that the coolant is good for 6 years or 600,000 miles - whichever comes first. The only maintenance requirement is that you must add a can of extender at 3 years or 300,000 miles to replenish the additives. You do not have to monitor SCA levels any more because there are none so throw away those test strips. You should not add any SCA additives to an OAT coolant either so do not do that. Spartan has been using the Final Charge OAT coolant on their chassis in recent years and places a warning decal right by the filler explaining that you should not add any SCAs. If you are converting an older coach over to the OAT based coolant, be sure to remove and SCA laden water filters. Either disconnect them or else replace it with a plain old water filter and leave it alone. Many of these coolants are being marketed as Extended Life Coolants, or ELC.

But OAT coolants have many other benefits as well. Organic Acids are kind to aluminum. Traditional coolants tend to eat away at aluminum and you'll find corrosion and deposits in water pump housings after a while. Radiators, as well as their solder joints, are much better off with OAT coolants as well. Your generator set has lots of aluminum in it's engine and OAT coolants will keep that system much cleaner and efficient than a non-OAT coolant. Finally, the fatty acids are actually good for your water pump and help keep it lubricated, which is just the opposite of the traditional coolants which rely on short term additives in the coolant to accomplish this. That's why it's not a real good idea to "extend" an extended life coolant because the additives do drop off as the coolant ages with use. OAT coolants don't have that issue and just need a quick shot of extender at 3 years to keep your RV's cooling system up to snuff.

OAT coolants are compatible with just about anything so you can use the same stuff for your engine as well as your generator. They are also cross-brand compatible. Peak's Final Charge coolant is an organic acid coolant and is currently used by Spartan in their chassis. Cummins' Fleetguard Division originally made an OAT coolant called Optimax but this has now been rebranded as ES Compleat OAT extended life coolant. Caterpillar offers it's own Cat ELC coolant, which also uses hybrid OAT technology. All four of these are 100% compatible. If you can't find Final Charge wherever you are, you can go into any truck dealership and pick up some ES Compleat OAT or Cat ELC at the parts counter. The majority of the OAT coolants are orange in color, although this can vary, so color alone won't determine OAT status. Shell's Rotella ELC coolant is more of a red in color. It too is an extended life coolant that can go 600,000 miles. However, it is not a true OAT coolant so don't go mixing this with any of the other brands of OAT coolants.

I highly recommend changing your existing coolant and converting over to OAT coolants. The benefits are many - you'll have more time on your hands from not having to check the SCA levels, it will last a long time, and it's better for your engine. Converting isn't all that hard. You just drain out the old coolant and dump in the new OAT coolant. Chances are you won't get all of the old coolant out but the OAT coolant is somewhat compatible with the older coolants. The biggest thing is how much is still in there and what were the SCA levels of the old coolant. OAT coolant doesn't mind non-OAT coolant but it doesn't get along that well with old coolant that has high SCA levels remaining in it. If 25% or less of your coolant is old, you'll be fine but if you can't get 75% of your old coolant removed, then you can get a converter product to help neutralize the effects of the remaining SCAs in the system. If your old coolant's SCA levels are way down it probably won't even be an issue. The converter bottle basically adds a bunch of CTAs (Contamination Tolerant Additives) to the system to prevent the old SCAs from messing up the OAT additives imbedded in the new coolant.



Antifreezes and cooling system maintenance isn't all that bad once you understand how things work and why. Hopefully the above information will help you determine the best course of action for your RV. In my case, my last Allegro Bus came with Final Charge OAT coolant so I didn't have to convert this one. But I did convert the Onan generator set over so that I had one common coolant and also the benefits of the OAT in my Onan's engine. Now I just have to wait for 3 years to pass before I do anything else, other than check the level.



©Copyright 2008 Mark Quasius All Rights Reserved
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