I was reading online and found a few people saying you should never add concentrated anti-freeze to a cooling system. you should only dilute what you already have in there with water and only add anti-freeze when doing a flush, is this correct?

7 Answers 7


The reason adding straight anti-freeze to a nearly full system is not recommended is because you will have no idea of the actual concentration. Most manufacturers recommend a 50/50 mix of antifreeze concentrate to water. Mixtures with too much water may not provide adequate boil over or freeze protection. Mixtures with too much antifreeze concentrate may actually cause over heating. This is due to the fact that the antifreeze alone is not very efficient at absorbing the heat from the engine with out water mixed with it.


In the modern world, it is easy to find premixed bottles of 50/50 antifreeze and water. Unlike a bottle of concentrate, you are fine to top off from a premixed container. It is essentially impossible to make the ratios worse in the radiator when adding a dollop of the correct mixture. So, if someone is lecturing you about what you should / should not put in your car, make sure that you're talking about the same product.


2007 6.0 powerstroke diesel ford e 350 van No water just pure concentrated antifreeze I drove this diesel 70 miles per hour in 112 degree weather across the Arizona desert Towing a 10,000 pound trailer It don't get no worse than that folks My temperature stayed right at 180 degrees and never fluctuated the cooling fan only came on when I pushed it above 75 miles per hour. Again I'm towing a 10000 pound trailer. I will never put water back in this engine again Always remember manufacturers want to sell new vehicles if they last forever they go out of business


No, 50~70% dilution with water total. If you flush with water then there is 100% water in the engine block which is hard to drain on most vehicles., then you have to calculate how much pure AF to add to make remaining water 50~70% AF, then add add additional 50~70% AF to top off. Its better to have a little too much AF than too little.


Maybe I'm misinterpreting what you're asking but here is always the goal (unless your house is an igloo): Whatever you add to your cooling system should always be mixed with 50% antifreeze and 50% distilled water. Whether you've done a cooling system flush or you're tapping off the level, it should be a mix. The ONLY exception to this is if you're adding, and what's already in the system is pure antifreeze, then you'll want to dilute it as close to 50/50 as possible with only distilled water (or vise versa). You want your system to have a 50/50 mixture to gain the perfect compromise of freezing point and boiling point, maximize heat absorption, and the 50% antifreeze (ethylene glycol) will have have corrosion inhibitors in it that help to keep the parts and engine from rusting/corrosion. One of the reasons that flushing the system is necessary for maintenance is that the corrosion inhibitors wear out or get 'used up'. Things will then start to rust. But the bottom line is that your question depends on what's already in there. If it's 100% antifreeze, then yes, add water to dilute as close to half and half as possible. If you've already got a mix in there, you should add 50/50 to maintain the balance. Hope that helps.


If you know the volume and concentration of what is in there, then you can do some calculations to work out how much straight anti-freeze to add to get to the mixture you want.

Also, if you add straight anti-freeze then it is a good idea to run the engine sufficiently to enable proper mixing ie hot until the cooling fans come on.


I run straight antifreeze. And it works great. I check it each fall before winter and tests at 20 below zero. Green and clean year after year. Water pump and hoses don't wear out. Radiator stays clean.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .