Choosing the right coolant is important for all Diesel trucks and for your 7.3L Power Stroke Diesel choosing and maintaining the right coolant is necessary to ensure the longevity of your engine and cooling system components. For this we consider not only what Ford recommends but also what Navistar International, the engine manufacturer, recommends as well.
What Coolant to Choose
The Ford Factory Recommended Standard on coolant calls for low silicate conventional coolant (Ethylene Glycol), often referred to as green coolant, with Supplemental Coolant Additives. The OEM coolant is Ford / Motorcraft VC-5, but any high quality brand of diesel rated coolants will work if it meets or exceeds fords OEM specifications. Whatever coolant you choose it needs to meet ASTM D4985 standards and will require the addition of Supplemental Coolant Additives (SCA) initially and then additional SCA supplementation at 15,000 miles or 600 hours of operation to ensure the coolant remains in spec. You may also choose a pre-charged conventional coolant, often pink or purple in color, if it meets ASTM D6210 standards. A pre-charged coolant does not require an initial dose of SCA but still requires the same 15,000 mile SCA supplementation as above.
Although not mentioned by Ford, we recommend routinely testing your coolant to ensure it is in spec. It is good practice to test your coolant on a schedule, perhaps as often as every oil change or more frequently towards the end of its life cycle (every 1,000 miles) with 3-way Coolant Test Strips such as Fleetguard brand to check that the level of supplemental coolant additives (SCA) or nitrite levels in your coolant are in the optimum rage above 1.2 and below 2.0 per gallon, with a good target number being 1.5 per gallon. Too much SCA (above 2.0) starts to put stress on the water pump and anything below 1.2 per gallon can lead to conditions favorable to cavitation and pitting. Otherwise 800 parts per million is the number to stay above. Knowing your coolant is up to spec is important for the longevity of your 7.3 PSD.
When choosing a coolant a few things to note, DO NOT USE Dexcool, All Makes – All Models, or Universal coolants because they are meant for gasoline engines, be sure to choose a coolant that meets the needs of diesel engines.
We mention the common color for coolant types but take note that the color of a coolant is not a 100% identifier of the type. it is important to know what coolant you have and that it meets OEM recommended spec or better and not guess.
Supplemental Coolant Additives
The Factory SCA recommendation is to use Ford/Motorcraft VC-8 Diesel Engine Coolant Additive but there are other brands that are compatible. The two types of cavitation inhibitors in SCA’s are DCA-2 (nitrite-only based) and DCA-4 (molybdate/nitrite based). Nitrite being the most effective inhibitor. DCA-2 is free of phosphate and usually contains potassium buffers and is the original inhibitor type and remains the most popular. DCA-2 can be tested with any test strip that shows Nitrite levels (2-way or 3-way test strips). DCA-4 uses a synergy between Molybdate and Nitrite as its inhibitor and has sodium buffers and phosphates, it is harder to find and needs to be tested with 3 way test strips.
RMI-25 is an additive that claims to clean your cooling systems metal surfaces and increase protection. RMI-25 is said to consist of a cleaner, pH Stabilizer for acid/alkaline balance, an Oxygen Scavenger to prevent cavitation/pitting and corrosion, and a lubricant for seals, hoses, and water pumps. It is hard to find definite information on using RMI-25 as a coolant additive. It mentions that it is compatible with any coolant and SCA but we are unsure if it is safe to use in place of SCA’s. One though though is that because it has cleaning agents what is cleaned from within the system has to go somewhere and therefore the addition of a coolant filtration system would be best if planning to use this product.
Why Flush and Change Conventional Coolant
With conventional coolant the cooling system needs be flushed and replaced every 30,000 miles or as needed if earlier to protect against pitting and cavitation inside your engine. We have a PDF of Gooch’s Coolant Flush Procedure (open or save) found on a multitude of ford and power stroke forums that helps make easy work of a proper flush.
To best protect your engine and radiator your coolant should be flushed as part of routine maintenance or before you change coolant types such as switching form conventional to extended life coolant. As coolant ages and breaks down silicate drop out becomes more of a a problem and a reason for routine maintenance coolant flushing. When thinking about why Silicate is bad, note that Silica is sand. As coolant ages silicates become insoluble and become microscopic abrasives, this is known as silicate drop out, that cause premature wear and damage especially the water pump and water pump seal which is constantly exposed to the coolant. Also with age the break down of phosphate in the coolant can become abrasive as well when mixed with water.
Water is the Weakest Link
Without water all of the issues surrounding diesel cooling systems goes away. Unfortunately conventional coolant which is based on Ethylene Glycol cannot be run at 100% coolant as it looses all freeze protection, water is necessary to lower the freezing point and a pressurized system is necessary to raise its boiling point. The optimum mixture is 50/50, and at the coldest conditions 60/40 but at 70/30 the coolant falls below usable tolerance specifications. When picking fluid it is best to use Concentrated Coolant and Distilled Water. Even the best tap water has undesired minerals and is not pH neutral so it reduces the effectiveness of the cooling system and the life of the coolant. Distilled water is preferred because it is generally more pH neutral. In the end, coolant mixed with distilled water will always outperform and out last coolant mixed with tap water.
After a flush or for initial fill from empty be sure to use Concentrate Coolant combined with the appropriate amount of distilled water instead of 50/50 mixtures because there will be residual water remaining in the system from the flush which further dilutes the overall solution.
Using Heavy Duty Extended Life Coolant
The Ford owners manual does state not to use Extended Life Coolant (ELC). Heavy Duty Extended Life Coolant comes pre-charged with carboxylate inhibitors and require no testing or maintenance. They offer superior protection combined with a super long life (750,000 miles with Chevron Delo HD ELC) but these coolants do come come at a much higher cost. These coolants are silicate free, and often free of phosphate, borate, amine, and nitrate.
After research, Navistar International found ELC to be problematic in the long term for early 1999 and older 7.3L PSD engines (pre SN 940614). Navistar International (who manufactures Ford’s 7.3 PSD engines) found some compatibility issues during testing with the older injector cup material (the sealant used on install) and other silicon based engine seals when using newer coolant based on Organic Acid Technology (OAT). So for 7.3L engines manufactured before February 2nd, 1999 with OEM injector cups there may be long term risks of internal issues because of the OAT in extended life coolant. Simply put OAT coolant can eat the seals and sealants used in older motors.
Navistar International does recommend and uses HD ELC in their 7.3L models for engines built after Feb 2nd 1999 (SN 940614+). There are many HD ELC to choose from for your 7.3L PSD such as International Fleetrite ELC, Shell Rotella HD ELC, CAT HD ELC, Chevron/Texaco/Delo ELC, Prestone Heavy Duty ELC, and Zerex Extreme HD ELC. These coolants are usually Red in color.
If your engine is newer you may choose to use HD ELC which can save you time on maintenance and give you piece of mind with better protection and cooling performance. If your engine is older stay away from OAT and follow Ford’s recommendation on coolant. We recommend you find a coolant that meets or exceeds Catepillars EC-1 performance specification. Delo ELC seems to take the cake with a 750k/8 year lifespan that can be extended with an extender supplement to 1 million miles. Fleetrite HD ELC and Rotella HD ELC are the same thing and are what Navistar International uses in their 7.3L vehicles from the factory. Ultimately it is your engine and your choice, but make sure what choice of coolant you make is not going to decrease the life of your engine.
Gold Coolant
Although it works if your vehicle can run an OAT coolant, and in some cases Ford may recommend it. However, we are not fans of using G-05 gold colored coolant in your 7.3L PSD because it ultimately is not much better than conventional green coolant with the exception that it does have a longer life span. Gold coolant is not an Extended Life Coolant. It is actually a universal hybrid coolant primarily used in cars and still contains components that conventional coolants have such as silicate. Gold coolant still requires SCA’s and we recommending testing it regularly just like conventional coolant. If you want better than conventional coolant see if you can switch to a proper HD ELC coolant meeting CAT EC-1 specification.
Propylene Glycol
Propylene Glycol (PG) is another type of coolant that is non toxic and bio degradable but often confused with Extended Life Coolant, however, it is not extended life coolant. The jury may still be out on whether or not PG coolant is OK to use in diesels, but there are those doing it. If you want to look into PG coolant ensure that is tested or provides information for use in diesel engines and that it is low silicate. Evans High Performance Waterless Engine Coolant is one option that they have rated to include light duty diesel engines. Here is a PDF article from Evans on Rethinking Diesel Coolant. All things considered with Evans PG waterless coolant, with no water all the issues that come with water go away (think corrosion and cavitation), so if the PG coolant meets the other specs then you may have an alternative that lasts longer and requires no SCA maintenance or testing. If you choose to try this route note that running PG requires prep ensure the system is purged of old coolant and water. Also once you go PG waterless you can only top off as needed with PG waterless coolant, if any SCA’s, water, or other fluids are introduced to the system it will need to be flushed and replaced. Evans recommends a coolant filter setup on systems that have switched from conventional to PG as well.