Coolant System - How to check etc.

[FD3UK]

I have seen several threads on MRC regarding the coolant system; I have written the following which I believe explains its operation correctly, to try and clarify any confusion. Please feel free to correct me on any errors so that I can edit post.

Hopefully it can be made a sticky.


There is only one coolant system on the RX7 which maintains the correct temperature for the engine and standard twin turbo setup. The filling point for the system is via the cap to the left of the alternator (only when cold of course). This can be filled to the brim with a water and antifreeze mix.

While the coolant is circulating around the engine and radiator, any air bubbles and excess pressure are released through the cap at the top of AST (air separation tank) to the expansion tank. When the engine cools the coolant system draws back any necessary coolant back from the expansion tank via the AST.

The expansion tank does need to be checked for the correct amount of water and antifreeze mix which can be done using the plastic level indicator incorporated into the lid.

The cap on the AST only needs to be removed to check its condition as this is what maintains the correct pressure in the coolant system. This is the first thing to replace if you suspect any cooling system problems.

[Glenn Butcher]

Made sticky for you - if there are any other comments from anyone, please post.

[evildave]

Ive heard it's possible to run without a AST. what are the pros and cons of this? My air pumps already been removed and battery relocated to the boot and i'm running a single turbo so the engine bay is getting nice and empty allowing plenty of air flow.

[the lemster]

what is the correct level of coolant to have in the expansion tank when the car is cold?... if any....

am I stupid asking this or not?...

and I assume everyone knows to use distilled water to stop mineral buildup in the coolant systems?... ( distilled or deionised )

[RobbieRX-7]

i think they are both the same distilled/de ironised..i just use clean filtered rainwater collected in my butt..oops i mean water butt :chat

[probedb]

Sorry for a late addition to this but why does the owner's manual tell you to fill the expansion tank? Or is that just for checking? Quite difficult trying to judge from pictures in a Japanese Efini manual :)

[NurburgRob]

Probably raising an old dead thread here but I'm a newbie, so give me a break!

I've got a 96 FD and what would appear to be the AST (located near the intercooler?) has a cap on it that say 'Do not ever remove this'? so I guess this means I only need to check the expansion tank and rad cap by the alternator.

The coolant level under the rad cap is about an inch or two down from the cap, the level in the expansion tank is about two maybe three inches from the bottom of the measuring thingy.

So, should I add some coolant to the expansion tank? or as the rad cap level looks okay should I just leave alone?

Another thing - the car had a mahoosive service at Rotechniks in Oct/Nov last year when it had antifreeze. What worries me is that the coolant is pink and I've read on here that we should be using blue or green? surely Rotechniks would put the right coolant in? (and don't call me shirley :))

[Andrew Harper]

The AST Cap is usually only really removed to fill up the coolant system when replacing the fluids. There's nothing wrong with removing it is you want to check the levels. Just don't do it when the engine's hot!

The coolant levels are normally nearly to the top of the engine coolant cap (the one by the alternator). and the expansion tank is normally about half way between min and max. You can have the level a little higher if you like.

Sorry can't remember about the coolant issue. It was a chemical that can attack the o rings I think. But it was in special coolant that didn't require water (you put it in undiluted). So you should be fine.

I'm sure someone will correct me if I'm wrong!

[chippy68]

Hi just changed my rx engine and i am having problems even getting what i think is any sort of water into the system have filled it where everyone says to have done the usual squeezing hoses etc but have no water reading at all in the expansion tank on the white dip in reader any ideas !

[Grizzly]

Hi just changed my rx engine and i am having problems even getting what i think is any sort of water into the system have filled it where everyone says to have done the usual squeezing hoses etc but have no water reading at all in the expansion tank on the white dip in reader any ideas !
In what respect do you mean your having problems getting water into the System?

Do you mean it water locks and overflows without much finding its way into the engine? Or it fills up then the level drops so you top it up and it drops again?

[Grizzly]

I found a good way of finding water leaks is to use the Blue Antifreeze, run it for a while so it gets well throught the system (may be even carefully run it for a week if the weaks not too bad) then look for Blue stains around the lower part of the engine/Rad/Water hoses then you can follow the stain back to the leak :)

[Joeh]

Is it ok to run 60%-75% antifreeze & 25-40% water mix?

Thats what is in my car right now, but if its bad then I'll drain some and top it up with water.

Oh, opinions on castrol antifreeze? first time for me using this stuff, anyone used it and think this stuff is any good?

Thanks
Joeh

[Rixio]

I reckon thats too much...you dont need so much Antifreeze. A 60/40 Water/Coolant would be better but you defo dont need 75% Coolant (unless you live on the north pole :p)

I run a 80% Water 20% Coolant...but atm im only using water :)

HTH

Rixio :Thumbs-up

[JohnnyP]

I have replaced my coolant (50/50 antifreeze water) and did it slowly squeezing rad hose to burp the system, but the strange thing is when I take the cap off the water level is near the top but then drops and each time I top it up it drops again! The expansion tank level is on the 'F' and after switching off I get the gurgling boiling noise. Why does the level drop?

[robedwards99]

A second question.

I check my fluids regularly.

Usually when I check the rad and ast caps they are near full, yet when I check the expansion dipstick it is often low.

I tend to top up ithe expansion tank as it worries me that fluid is low on the dip-stick.

comments???

[Joeh]

LOLOL!! You are not ment to touch the expansion tank. The reason the expansion tank is there is if the coolant pressure is above the 1.3bar or 0.9 (depending on the cap you have), boiling water will be pushed into there... temporarly, usually sucked back in once the car has cooled down.

You shouldn't ever need to touch the dipstick of the expansion tank.

Any help?

[ro284]

You shouldn't ever need to touch the dipstick of the expansion tank.
LOLOL Of course you should check the Expansion tank! That's why there is a Dipstick in it! to check it with

[Grizzly]

LOLOL Of course you should check the Expansion tank! That's why there is a Dipstick in it! to check it with
There is wires crossed Here, If you refill an Empty System you should fill from the engine and Not take the AST tank top off (so there is no water going into the Overflow)

On day to day Driving you should not take the Engine or AST top of unless the buzzer goes off (but some people check it once a Month to be on the safe side) BUT!!! you should mark the Dipper in the Tank (Drivers wheel well) and keep a good eye on that (Check it often) and make sure it does'nt rise or fall from where its Marked.

[koolance]

Is there any way of draining the overflow? If the systems been topped up when it was only sitting at its level but then filled to the to a few times, then the waters been forced into the overflow.

[Grizzly]

the easyest way is to take it off but you can drop the level by getting a peice of hose pipe about 12" long with two clean cut ends then dip it in the tank and block off the end with your thumb whilst the pipe is touching the bottom of the tank , lift it out and take your thumb off the end. This way you can drop the level but if you need to take alot out it may take some time.