How much coolant is not enough?

[Vilan]

Gave my '94 Geo Metro a much overdue coolant change last night. The manual says it holds 4.1 L of coolant, but when I drained the rad I only got about 2 L out so I assume the rest was in the engine. I refilled it with water, idled for about 5 minutes (had heat set on maximum inside), let it cool, then drained the water. Did 3 rinses total... after the 3rd, the water wasn't totally clear but it was just very slightly green so I figured I'd gotten most of the old coolant out of the engine.

Here's the question. I refilled the rad with about 70/30 antifreeze/water. After some thought though, if what's in the engine after those flushes is close to pure water, and the engine holds as much as the rad (2 L each), I'm going to end up with around 35/65 after it all mixes together, or maybe 40/60 if we assume there's still a little coolant in the engine. That seems pretty low, I was aiming for 50/50. Am I in trouble? It rarely goes below freezing here so reduced low temperature protection is no big worry, but I may regret not having all the anticorrosion etc stuff from the coolant. No big deal? Or should I get more antifreeze in there? I'm using some lovely bright green Motomaster 8 Metal "advanced silicone silicate formulation" coolant.

 

[Big Jim]

You would have been OK with straight coolant for your top off since roughly half of the capacity was occupied by something that was very nearly water.

I try to stay above 40% coolant no matter what. Most of the time I run colse to 60% even in my mild climate.

 

[jmacmaster]

Since the whole system (engine + radiator) holds 4.1 L and you figure you drained about 2 L out of the radiator, if you're worried that you did not put enough antifreeze in, then, if you drain a L out of the radiator and replace it with a L of straight antifreeze, you will, with just the antifreeze you put in, have a mix of at least 25/75, which, with the antifreeze that's in the 3 L that are left after you drain a L out of the radiator, should get you up to at least a 40/60 mix, which will be ok. The antifreeze probably has a chart on the back of the container that will give you the below 0 protection of a given mixture. You can use that, and the coldest it gets in your area, to decide on the mix. The back of the container probably also gives you the minimim % of antifreeze that should be in the coolant. If you go to any service station or service shop, they can test your coolant and tell you how low a temp its good for. You can then, working backwards and using the chart on the back of the antifreeze container, find out the percentage of antifreeze that is in the coolant. For example, if the coolant tests out at good for -40F, since most antifreeze charts specify a 50/50 mix to get to -40F, you know you have a 50/50 mix.

 

[Vilan]

My antifreeze jug only lists down to 50/50, so I thought Bad Things Would Happen if I went below that. But I found a website listing various mixing ratios and it looks like I should be good down to at least 0 F, which should be OK but I may drain a bit and top it up with some pure coolant as suggested to be safe. We'll see.

The jug instructions confused me since they say to flush out the system with water and then just fill it up with 50/50. Guess that's assuming the engine isn't holding any water. Wonder how many people end up with a smoking radiator each year because of overly dilute coolant from that assumption.

Thanks all!

 

[jmacmaster]

Your flushing technique is a common one. Drain radiator, fill radiator with distilled water, run engine till it heats up so that what you put in radiator mixes with what's in engine block, shut off engine, let radiator cool a bit, repeat above process a few times. The last time you fill radiator check owner's manual to see how much coolant the system holds and then put in radiator enough antifreeze to get you to the cold weather protection level that you need. If you have 50% of the coolant in the radiator, then each time you drain the radiator you drain 50% of the antifreeze left in the system after the prior drain. So four drain cycles would result in your having only 6 1/4% of the old antifreeze left. I go 5 drain cycles myself, resulting in only
3 1/8% of the old antifreeze left (again, assuming that about half the coolant is in the radiator and about half is in the engine block). On the 5th drain the coolant coming out of the radiator is running clear. Be sure to use distilled water each time you fill up the radiator. Tap water has minerals in it that can be bad for the coolant system.