coolant change question

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HI all... three questions regarding how I've been changing my coolant on my 95 Maxima.

The owners manual and factory service manual differ a bit in what to do before draining. The owners manual says to simply set the heat to high temp before opening radiator drain plug and engine block drains. The FSM has a somewhat more complicated procedure that I honestly don't know what it does - it involves turning ignition on while pressing certain buttons on the automatic temp control till a certain number is displayed.

1. Does anyone know what this does? (The manual does call for opening engine drain plugs which I never do - perhaps this has something to do with it). During my coolant change today when I also replaced the hoses, I forgot to perform the automatic temp control step but performed it after draining the radiator. I hope that was OK.

After very slowly filling the radiator again with my funnel (the FSM says to fill slowly as to not trap air), I start the engine with heat on high and blower fan on and watch the coolant level and keep an eye on the temp gauge over the next hour while the car idles. Eventually, I can sort of see a flow in the neck of the radiator and the hoses get quite warm telling me the thermostat has opened up now allowing flow through the radiator.

2. I read on some DIY sites to just have the heat temp on high but no blower on during the warm-up step. The only reason I can figure out for that it probably delays opening of the the thermostat as engine heat is being bled off through the heater. therefore prolonging circulation of coolant through the radiator for cooling. Correct?

3. The FSM says to wait till radiator fans turn on before shutting down the engine. I assume the fans turn on when additional cooling is needed but the thermostat is probably nearly or full open before that, right?

I then watch the coolant level over the next few days and in fact upon the first cool down, I find some coolant is now missing from the reservoir tank.
 
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Originally Posted by NissanMaxima

The owners manual says to simply set the heat to high temp before opening radiator drain plug and engine block drains.

Does anyone know what this does? .


It sounds like there is a valve in the heater line that gets opened. I would make sure to follow that step.
 
You do not need to open the drain plugs in the engine, and even if you wanted to, you wouldn't be able to anyway since they always get stuck. They call them freeze plugs because they're frozen
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I would suggest you buy the Lisle coolant funnel. It is an extra large funnel that lets you fill the funnel well above the highest point in the cooling system/radiator, and it makes it very easy to see when you get all the air out
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Hondas are the cars where you don't want to turn the blower on because they dissipate heat so well they will never warm up when you're trying to bleed them
 
Thanks folks. Regarding waiting till the coolant fans turn on before shutting things down, the thermostat should have been at least partially to even fully open even before the fans cycle right? I suspect so as the coolant in the neck was quite warm as was the bottom return hose.

Also, am I correct that having the blower fan on high (with temp on high) would probably delay the burping process as the heat is dissipated through the heater core for quite some time till it eventually gets hot enough to cause the thermostat to open and start cooling via radiator heat exchange process.
 
It depends. I know in some cars the heat adjustment will mechanically open up the heater core if you turn it to a higher setting. With a setup like that one could turn it all the way up with the ignition off and it will open up the heater core. But a lot of newer cars it's really something that electronically controls how much the heater core opens. I got very little out of my wife's car because I thought I could just turn it, even thous the dial feels really soft and can't possibly be a mechanical control. I looked at the owners manual again, and it said that the engine needed to be run for a few seconds.

I think the procedure you're seeing is probably to open up the heater core so as much coolant can be drained as possible. But really the most important thing with most coolant drains these days is to get out some of the old coolant and put in some new coolant with fresh corrosion inhibitors to replace what's been depleted. Especially when a lot of manufacturer recommendations are for 10-11 years for the first coolant change. If you feel you didn't remove enough, you could probably just do more often drain and fills.

I always wondered why once can just take out a little bit of coolant and just introduce concentrated corrosion inhibitors. However, it's probably a good idea to remove some of the depleted inhibitors and replace them with about as much fresh corrosion inhibitor.
 
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