Coolant/Overheating help

[PaulDeb&Freda]

Hi folks,

just flushed out my engine and replaced the coolant. I followed the very helpful videos on youtube on the bleeding process (very handy) and went through the whole process (t/stat opened) and once all bubbles had virtually gone all was ok. Went for a test run about 6 miles and all well.
Stopped for a cup of tea and it sat for around 20-30 mins. Went for another short run and within a mile the temp gauge rocketed up and coolant was coming from expansion bottle hose!!!

Any thoughts folks? Your help & advice is much appreciated

Regards
Paul.

[bigdaddycain]

It sounds like their is air still in the system! if she's cooled down now, remove the cap slowly, is there an air rushing sound or any gurgling?

[PaulDeb&Freda]

There was some gurling right enough!

Also the heater went cold at this stage too.

So my option is to let it cool overnight and repeat process but take even more time to get all the air out?

thanks
Paul

[bigdaddycain]

What's the level in the header tank now? Can you see any coolant?

[bigdaddycain]

Cold heater is a classic airlock symptom.

[PaulDeb&Freda]

There was a fair bit of pressure as I got coolant coming out as I tried and release the header tank cap. it was still hot so don't want to open it right up.

So does this sound like I have not bled it enough then?

Update - Things cooled and cap of it looks like the tank is pretty empty now!

[bigdaddycain]

I'd give it a half hour, then twist the cap EVER SO SLOWLY with a tea towel wrapped around your hand just in case. Don't stand "in the firing line" if the coolant does decide to pop up to say hello. You can help to relieve the pressure by twisting the cap till you can hear it just about to hiss/gurgle... leave the cap that way as a temporary pressure release for now.

[bigdaddycain]

There was a fair bit of pressure as I got coolant coming out as I tried and release the header tank cap. it was still hot so don't want to open it right up.

So does this sound like I have not bled it enough then?

Update - Things cooled and cap of it looks like the tank is pretty empty now!

Ok, have you any pre mixed coolant?

[PaulDeb&Freda]

Ok cap off ok, no pressure now and the tank looks empty!!

So it looks like I have not bled the sytem enough?

The heaters were pumping out fine hot air when out on the first run? I guess the air has moved around the system?

Thanks for the help.

[bigdaddycain]

Hmm... Unusual to get hot heaters, then an airlock, then cold heaters.... Was you getting equal good heat from both front AND rear heaters? Good solid heat is a good indicator of a relatively air free system. Could you use a measuring jug to re-top off the coolant up to the full mark please? Try to note roughly how much coolant she takes on.

[bigdaddycain]

Pour slowly please! The less air introduced the better!

[PaulDeb&Freda]

I can't access the rear heaters as they are behind the conversions units so was unable to check the hot air from it.

I topped up the tank and it took 2ltrs. I also removed the radiator cap as I did this and it overflowed when I poured in the water

[mikeonb4c]

Hmm... Unusual to get hot heaters, then an airlock, then cold heaters.... Was you getting equal good heat from both front AND rear heaters? Good solid heat is a good indicator of a relatively air free system. Could you use a measuring jug to re-top off the coolant up to the full mark please? Try to note roughly how much coolant she takes on.

I agree. I've followed the workshop manual instructions (there are other methods that work equally well, in the factsheet on here) and done the job twice with no bother (I don't bother draining the rear heater mind you, which makes the process simpler). Could there be any other issues like a tired thermostat that is not opening as quickly or well as it should - this could possibly make the bleeding a little more finnicky I imagine (although provided the bottom hose is hot some would argue that you have full flow around the system, so critical stat problem unlikely )? Worth replacing a thermostat anyway (with a genuine Mazda one) whilst changing coolant if there is any doubt over the stats age. Easy enough to do on a 2WD - a bit trickier on a 4WD but doable.

Good luck - keep us posted.

[bigdaddycain]

I can't access the rear heaters as they are behind the conversions units so was unable to check the hot air from it.

I topped up the tank and it took 2ltrs. I also removed the radiator cap as I did this and it overflowed when I poured in the water

When the heaters are going full belt up front, can you gauge if there is any airflow/heat coming from the vents high up just behind your head? This is of course if they are switched on hot and blow. Do you have climate control or manual heaters?

Yellow cap on the header?, red cap on the rad?

[PaulDeb&Freda]

Cant really feel any airflow from top vents behind my head.

I think it's a manual system although it does have a button marked "auto"

Caps are as you mention.