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mg_zs
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Discussion Starter #1
Does anyone have any ideas how to find where the coolant system is sucking air from on a 2004 MG TF 135?
The story so far.... On a road trip of over 130 miles the HEATER BYPASS 4 way Tee split and caused the car to overheat.
Ordered a new one online. Had it fitted by the garage but unfortunately after getting the car back I had issues with overheating and then cool down again if it was revved hard for a couple of minutes. Took it back to the garage as they said it is probably due to an air lock. Sure enough they bled all three points and air bubbled out of the heater matrix. Car was fine again for about 10 miles or so then same again so I bled it again and sure enough it got me home no problem. Left the car overnight and test drove the next day same issue again re-bled matrix and fine again. The garage then pressure filled the cars coolant system again but same issue. Bled it again ran until warm and heat was coming out of the heater then left overnight. Drove next morning it was fine pressure was still up no coolant loss and car drove fine for 10 miles.
To cut the story short the car has now had a new PRT fitted same issue, New Expansion cap (old one works fine on my ZS 120 so not that) same issue. New Rad black plastic bleed cap replaced for one with bleed valve (just in case it was the crap plastic one) but same issue.
Both myself and the garage mechanics are now at a loss as to how to find the air leak other than change every single hose/connector/pipe/component one piece at a time to find it. As there is no coolant traces to identify the source.(too expensive an option as this would also mean changing the heater matrix and radiator).
Symptoms are heater stops passing warm air. One matrix pipe stays hot the other is cool to touch bleed the matrix and the other one starts to warm up and heater works again. Matrix disconnected and flushed even back flushed but nothing blocking it.
There is no loss of coolant (which is strange) and the expansion bottle pressure is holding. It is always fine after bleeding the heater matrix. Could it just be a pin prick air leak in the matrix? If so why is there no coolant leakage as the pressure build up is immense?
It has been bled on ramps it has had coolant flush and always the same thing air lock build up in the heater matrix. Could this be the matrix bleed nipple leaking air? but if so why does it not leak coolant?
Any advice appreciated on this one as I really don't want to have to swap out every hose/pipe/connector one by one. Now at a loss and I haven't been able to take advantage of the nice weather lately.
 

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mg_tf
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You should also check the heater control valve. These have a tendency to leak behind the lower dash and go un-noticed. Check under the driver side carpet for any moisture as it tends to pool on that side.
 

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I am a little surprised that a pressurised system (even if only semi pressurised) can suck air in. If no loss of coolant, then I would suggest that it could be that the hoses have been incorrectly connected the engine end. This happened to me once by someone who should have known better. Kept overheating during a 200-mile journey back home unless the heater was on all the time; got home and then got under the car to find that two hoses had been transposed, totally messing up the coolant circulation; fixed it and no problems since.

I would carefully check the routing of all hoses to ensure a silly mistake like this has not happened to you. Use the workshop manual and systematically tick each hose connection off.
 

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mg_zs
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Discussion Starter #5
You should also check the heater control valve. These have a tendency to leak behind the lower dash and go un-noticed. Check under the driver side carpet for any moisture as it tends to pool on that side.
Checked and it is fine also turned it on with pipes off.. bad idea !! now also have a wet patch on the carpet too... Thanks for the tip though.
 

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mg_zs
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Discussion Starter #6
Check the water pump
There is no leak around the pump and when revved it pushed the air lock through for a while. Also took the one of the pipes off and the more revs I give it the more powerfully the water spurts out so I think that is working ok. Or could I be wrong, is there any other way of testing it?
 

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mg_zs
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Discussion Starter #7
I am a little surprised that a pressurised system (even if only semi pressurised) can suck air in. If no loss of coolant, then I would suggest that it could be that the hoses have been incorrectly connected the engine end. This happened to me once by someone who should have known better. Kept overheating during a 200-mile journey back home unless the heater was on all the time; got home and then got under the car to find that two hoses had been transposed, totally messing up the coolant circulation; fixed it and no problems since.

I would carefully check the routing of all hoses to ensure a silly mistake like this has not happened to you. Use the workshop manual and systematically tick each hose connection off.
From what I can see this is correct.
135527

As this all started after the 4 way gave out I am now wondering if I have a faulty replacement one. Are they just a straight through 4 way or is there some sort of one way valve or something inside?
 

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Discussion Starter #8
From what I can see this is correct. View attachment 135527
As this all started after the 4 way gave out I am now wondering if I have a faulty replacement one. Are they just a straight through 4 way or is there some sort of one way valve or something inside?
Looking at the diagram above I know the heater knob pipe is correct as that one is hot to touch, I know the PRT is fine as that is also a new one. So then when the fault occurs it is the pipe to the y-connector that is only getting hot after a bleed of the Matrix so realistically it can only be a fault at the Matrix. Looks like I am going to have to strip the car out and replace the matrix. But even so I agree with you that being a pressurised system I should also be losing coolant so I don't understand why there is no leakage in either the passenger or drivers footwell which brings me back to my first thought of the matrix bleed valve maybe the nipple is stopping coolant leak but allowing air in ie.. one way valve system or the leak is so fine it is not noticeable under the bonnet. Maybe if I talcum powder the valve and matrix hoses then take it for a run maybe it will reveal itself. Sounds like my next step tomorrow.
 

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The mistake made on my car was that the two pipes to/from the engine leading to the radiator had been transposed (at the engine end where they join to the 'steel underbody pipes' on your diagram).In fact, right close to the PRT - which tells me than when fitting the new PRT, the mechanic may well have transposed these two pipes.

If you turn the heater off, does the temperature of the coolant rise?

Replacing every pipe one by one is not the answer!
 

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The transposed hose suggestion makes sense.

It could be a leaking heater matrix but so small that the coolant is evaporating. When the engine is off and cooling down, air is sucked into the coolant system. I'd suggest adding a UV dye to the coolant. I used this method to find coolant leaks on my F,
I've attached a couple pictures showing coolant leaking from a failed head gasket.
SAM_3695.JPG
SAM_3697.JPG
 

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mg_zs
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Discussion Starter #11
The mistake made on my car was that the two pipes to/from the engine leading to the radiator had been transposed (at the engine end where they join to the 'steel underbody pipes' on your diagram).In fact, right close to the PRT - which tells me than when fitting the new PRT, the mechanic may well have transposed these two pipes.

If you turn the heater off, does the temperature of the coolant rise?

Replacing every pipe one by one is not the answer!
No the temp doesn't rise unless I bleed the matrix again. Also when I took the Heater valve pipe off and opened the valve to check it functioned correctly that was hot water that came out whilst the other pipe was still cold.
I actually fitted the PRT myself so that was a single pipe disconnection at the PRT end as I drained the coolant from the Rad end (had it on axle stands at the back to get to it easier).
Ordered one of the UV Coolant dye and light sets though from flea-bay as that suggestion may be my only way to find any leaks other than the process of elimination method of one pipe at a time, plus rad and matrix replacement.
Carried out another quick check too, and found that once the matrix is bled and the heater works again the warm/hot water comes out of all three bleed points as expected.
It is looking more and more like a matrix replacement every time I try to figure it out. That is the one single point of failure of heat passing around the circuit. That may well be that it is just the highest point of the coolant system. I may have to raise the engine on axle stands/ramps to ensure the expansion tank becomes the high point to see if the air works its way back to there.
 

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mg_zs
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Discussion Starter #12
The transposed hose suggestion makes sense.

It could be a leaking heater matrix but so small that the coolant is evaporating. When the engine is off and cooling down, air is sucked into the coolant system. I'd suggest adding a UV dye to the coolant. I used this method to find coolant leaks on my F,
I've attached a couple pictures showing coolant leaking from a failed head gasket. View attachment 135528 View attachment 135529
Thanks for the suggestion, I will give this a go. As I cannot get it into the mechanic for a couple of weeks (booked up now), I have ordered a kit and will update everyone once I have tested/checked it.
 

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Discussion Starter #13
Whoop Whoop.... I finally managed to fix it. She is running sweet as ..... now. No temperature issues and covered over 200miles so far. Plus the heater is working spot on again.🙂
Just to recap....
The story so far.... On a road trip of over 130 miles the HEATER BYPASS 4 way Tee split and caused the car to overheat.
Ordered a new one online. Had it fitted by the garage but unfortunately after getting the car back I had issues with overheating and an air lock appeared in the heater matrix (highest part of the forward coolant system).
Well after all the suggestions (thanks again everyone) I inserted a dye but no water leak, bought a combustion test kit (eliminate dreaded HG) no issues with HG either. As you may recall the heater matrix was back flushed all hoses tested pressure at 100%, PRT changed still the same.
So I went back to basics .. ie when did this start? "When the HEATER BYPASS 4 way Tee split" and I had the garage replace it.
I went back to the initial fault and asked around on other sites too... One suggestion was that there may be different 4 way T-Pipes or Maybe mine was faulty in some way. Therefore, reluctantly I purchased another 4 way but this time I fitted it myself. Low and behold once I fitted it the car worked fine again...
So after close inspection I found they looked exactly the same and the hoses on the old one were fine (so didn't need the new ones that came with the new part) but this one actually worked. So why the other one did not I do not know it appears with the new one that there is some sort of plastic movable part inside but the old one doesn't seem to have one. I can only presume that there are possibly different types of them, possibly the first one was missing this or was actually faulty when purchased (even though it was a brand new OEM part). So all good again...🙂
Down side is that now the TF is fixed my ZS 120 has just developed the dreaded HG issue @105k. I also have another job I have been putting off on my ZS 180.. she needs an Air intake manifold (rattling like a good un) so I now need to spend even more money.😢
Once again thanks for all the help guys and sorry it took so long for me to actually update this thread, but I am also doing alterations and refurb to the house at the moment so other things have taken priority.
 

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Well done! There was a very recent thread (last few weeks?) on a similar problem and it turns out (from memory) that the 4-way T-pipes have a plastic restrictor orifice inside one of the branches. The thread was from someone who couldn't remember what branch the restrictor went in after taking the 4-way T pipe off and having it fall out.

IIRC he tried it without the restrictor but found it worked much better with it in, once he figured out where it went.
 

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Well done! There was a very recent thread (last few weeks?) on a similar problem and it turns out (from memory) that the 4-way T-pipes have a plastic restrictor orifice inside one of the branches. The thread was from someone who couldn't remember what branch the restrictor went in after taking the 4-way T pipe off and having it fall out.

IIRC he tried it without the restrictor but found it worked much better with it in, once he figured out where it went.
This thread: Coolant Restrictor
 
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