1999 Mustang V6, Engine Coolant Issue

deeplist said:

I have a 1999 Mustang with the V6 engine. It is having a slight problem with the engine collant system. For some reason, it doesn't fully warm up all the way. The temp gauge still registers in the "normal" range, but when opperating, it's slightly cooler than it's supposed to be.

First thing that comes to mind would be, perhaps the thermostat is stuck open? No, I already replaced it. Secondly, the heater core may be blocked? No, I already replaced that also (a real ***** might I add). Thirdly, perhaps there's a blockage in one of the hoses or somewhere? Nope, I already completely flushed the system.

What else could cause this?

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deeplist said:

The only thing that leads me to believe there may be a problem is that the heater doesn't blow as hot as it used to. I would consider it to be "just warm". I talked to a friend of mine and he said maybe the sending unit was faulty that tells the electric fan when to turn on and off. I will check that out this weekend to see if it's not acting right.

It's not a big deal since summer is coming and of course it's better to have the car run slightly cooler than hotter. But things like this bother me until I get them resolved. And if it actually is the gauge itself, and it's slightly off, then I will always have the fear that my engine MAY be hot, but it will only show it as being normal.

This may be an ignorant question, but does the mix of coolant vs water have an impact on the temperature in which it is heated or runs at? I know it's supposed to be roughly 50/50 but when I flushed the system, I put too much antifreeze in. I would say its probably more like 70/30 or 80/20. I just couldn't justify dumping it for no reason. Also, while we're talking about coolant, is tap water okay to put in there? I heard from somebody that you're only supposed to put distilled water inside.

Thanks for all the help.

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