Coolant/heater line issue of some sort.....

Hey all so today I decided I'd do a coolant flush and clean of the radiator just using some radiator flush stuff. I followed all the steps in the workshop manual properly and had my dad was helping me as well(I'm only 18 and this is my first car 😬)

We drained all the water that was in it (bought it from someone who appears to not have taken care of it properly) filled it back up bleed the whole system and then started my mgf to get it up to temp and to the point where the radiator fan turned on.

We let it sit running for a little bit like that just to get everything going through then I look behind me and see a huge amount of steam coming up from around the engine cover/t bar area. Turned the car off took the cover off everything's fine push the passenger seat forward and a heap of water had pooled there (was a tiny bit on the driver's side but hardly any) we then looked under the car and an absolute massive puddle of water had appeared and was dripping out of the bottom of the car.

I had a look in the center console area where the heater lines seem to run(may be wrong correct me if I am) and the water hadn't come from there, it was bone dry. So we pull back some of the carpet and the sound deading and it seems to possibly have come from around the fuel tank area but we're not sure as we didn't have a chance to get the metal plate off today to check.

We have no clue how this happened as it hasn't happened the past few times I've driven it before or anything like that(mind you I haven't used the heater) and when we opened the expansion tank after it cooled down there was absolutely no liquid left in it. Does anyone have any idea why this might have happened and what I can do about it?? Not sure if it's too important but its a 1997 mk1 vvc mgf.

Any help or ideas at all would be a huge help!!

When you say you bled the cooling system, you did bleed it at all three bleed points?
However your problem may just be that the flush washed away the rust, dirt and stubborn under stains holding hands that was keeping the cooling system together.
In fact there may’ve been some miracle cooling system muck put in the system to “fix “ a leaking system and the flushing agent has washed this shit away.
Once you find the problem fix it properly….. no amount of miracle elixir snake oil will ever give a permanent and satisfactory result.

The best way to tell is do a pressure test, and getting under and all about the cooling system whilst it’s under pressure.
To do this you need a cooling system pressure test kit such as this one: One of these

You pump up the pressure and you can safely search for the leak without the hazard of scalding yourself with boiling water or worrying about damaging the engine.
Pity that you’re on the other side of the Tasman sea and not in Melbourne otherwise I’d be able to pop over and test it for you.

Can we assume that the condition of the coolant flow and return pipes under the car and the rubber pipes and plastic connectors up to and from the pressure relief thermostat have been eliminated from your enquiries?
There is at least one connector that has a tendency to fail under pressure due to age.

I wasn't aware that there were three bleed points!! The workshop manual only showed me the radiator and heater bleed points however I may have missed it! I'll have a look into doing a pressure test like you say as that'll probably be the easiest way to find and diagnose it I'll have to have a look on some of the nz tool sites to see if I can find something like that!

I haven't been able to entirely eliminate all the piping just yet but I would assume so as it wasn't over heating the few times I drove it before and they were for an hour or so where this was more like 20-40 minutes however as Cobber suggested the process of draining and then filling and the short time it may have been circulating could have loosened up a bunch of gunk/rust or whatever and caused a blockage and build up of pressure and maybe a hose split or something but I haven't had the time just yet to look into it much further... This connecter that you say has a tendency to fail under pressure whereabouts is this located and I'll make sure to have a close look in and around it!

Another thing is that it wasn't coming from the two coolant pipes that are exposed when you go under the car as the water was dripping/pouring down from above them as in the floor/bottom of the car and out of two holes either side of the piping

Hoverbob wrote:

Another thing is that it wasn't coming from the two coolant pipes that are exposed when you go under the car as the water was dripping/pouring down from above them as in the floor/bottom of the car and out of two holes either side of the piping

The leaking water you describe here; was it leaking from the holes in the chassis, like this?


This was a couple of years ago. Mine is a 2004 MG TF. This leak occurred about 10 minutes after a decent drive and a fair amount leaked out. I had a large part of the interior out searching for the source of the leak. By reaching back into the tunnel from under the armrest cubby, I could feel wetness around the end of the heater pipes and the hoses that pass through the bulkhead. A mechanic who does some work on my car said he hadn't seen this before. He did a pressure test that produced no leak. We eventually decided that it could be a problem with excess pressure build-up. I replaced the pressure release thermostat (PRT) and it seems to have been OK ever since. Your MGF may not have a PRT but the cause could be similar.

I've read this a few times and to me if the water is in the cabin surely it has to be the heater pipes where else could the water come from?
Cobber is right regarding a pressure test being the best bet but make sure the heater is set to hot, if it's leaking out of sight and pooling behind the seats which appears to be the case, then some interior stripping may also be needed.

Hey y'all haven't been on the forum for a while as I decided to just bypass the heater lines for now and plan to come back to this issue which I suspect as a few have said that it's either the heater matrix or the heater pipes. Decided this was the best course of action as I was really just trying to get it road legal and had other more important issues to fix..... Like front subframe rust and all my suspension needed to be replaced 😭😭. But thanks again for all the advice and help!!