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ZT 1.8-T Coolant system pressurising

16K views 25 replies 10 participants last post by  T-Cut 
#1 ·
Asking on behalf of a friend.

2005 ZT 160 1.8-Turbo

Car was driving fine with no problems. Then just lately the coolant system has started presurising. Temp guage will hit the red then drop back down again to half way, stay there for a few more miles then shoot back up to red again and so on.

No oil or coolant loss. Coolant system has not been touched so cant figure out how it seams to have gotten an airlock in it?

Any idea's?
 
#2 ·
The gauge on MGR cars is legendary for being unreliable! On the 1.8T I think I'm right in saying it only moves when the engine temp hits 115C which is symptomatic of losing fluid.

If you're certain there's no mayo in the filler cap or rising levels in your dipstick I'd try loosening the bleed valve and top up with a correct % OAT anti-freeze just in case.
 
#3 ·
I think you are mistaken. There will be coolant loss. If the system has been building excessive pressure, it will have lost fluid.
How are you checking? It has to be done with the engine cold, on level surface, the water level in the expansion tank has to be above the MIN mark, with a maximum at MAX.
Don't overfill.
It has not developed an air lock, it has simply lost water. There are a number of prime candidates for that, T-piece cracking, can be difficult to spot, replace with metal!!! inlet manifold gasket, replace! water pump, replace, rotten hoses, replace, expansion bottle cap, replace: check for any other leak.!!!

The only other realistic option for what you are seeing, is a stuck thermostat, and that is much less likely in my view.


So tell you friend to check the water level, daily!
 
#4 ·
What he said ^

Missed the point about it being a friend's car. Tell them they MUST check the water level properly. Looking into the expansion tank when cold, the Min/Max level indicators are right at the bottom of the tank and only about 5mm apart.

Overheating serious enough to move the temperature gauge into the red MUSt be investigated, it's just not a normal phenomenon!
 
#5 · (Edited)
Cause needs to be identified before more serious overheating causes damage to the engine. As in kaiser's list, the first thing I'd check is the Coolant Bottle Pressure Cap ~ they do not last forever and are not expensive so replace anyway. Get the genuine MG-R one ideally. If that doesn't improve things, water pump next suspect.... another prime suspect for coolant loss is the inlet manifold gasket although, I'm only familiar with those on the normally aspirated K-Series ~ the Turbocharged may have a different arrangement to cope with the boost pressure in the plenum chamber...

We have and have had K-Series engines in the family for close on twenty years. In a healthy engine, the needle on the temperature gauge reads just below halfway ~ if it goes noticeably above halfway, something needs investigating...

In a healthy engine, the cooling system runs at a higher pressure once the engine warms up. If there's a leak ( split hose or worn water pump for instance ) in the cooling sysyem, that normal running pressure is never reached and so the coolant can boil prematurely.
 
#6 ·
To be honest guys im a qualifed mechanic. I know how to check a coolant level and its not dropped. Its still just under max where it always has been. This is whats confusing me

Coolant has not been topped up. Its more than likely still on the coolant it left the factory with.

I've also owned over 30 different MG-R's all with k-series fitted apart from 3 L-series and i've always done my own work on them, everything from minor issues to full engine rebuilds. But i've never come across this problem before thats why im asking the question on here.
 
#7 ·
Its more than likely still on the coolant it left the factory with.
If that's a possibility, to be on the safe side, drain all the coolant and fill with fresh .... as recommended by all manufacturers.

You with your experience may already know that, but others searching with similar problems finding this thread may not.

That way we all can learn.

..;)

Fluctuation of the K-Series temperature gauge needle in the way you describe I'd bet a few quid means there's air in the system where it should not be.
 
#9 ·
Hi all, I'm a newby so go easy on me! Apologies in advance!
Sorry to cut in on this subject, but I too have the exact problems with my ZT 160 T. I've replaced in the last week .... headgasket, waterpump, radiator, t piece (top of rad), thermostat and ALL gaskets..... and still I have pressurised pipes and overheating. Also, I experience a cold rad and the fans do kick in. The only thing I haven't changed is the PRT. Could the PRT be the cause of the fault? I should add that i think there may be air in the system as when I start her up, I hear a water type splash behind the dash.
Any help or advise would be appreciated as I'm close to cutting my wrists!!!
 
#13 ·
Thanks for the reply MGJohn. Is this the technique you use.....

Take out the bleed screw on coolant rail.
one of the secrets of bleeding the K-series is to slowly trickle the coolant into the expansion bottle, not jug it in and hope for the best.
You want the heater temp control knob set to max heat, if you don't do this you will have air-locked in the heater matrix.
When nothing but coolant is streaming out, replace the bleed screw, keep slowly filling the tank until at correct level. Give the hoses a good squeezing. Top up cap on, and start engine, within a few minutes, the heater with the fan on should be throwing out ever warming air, getting hotter by the minute......................... assuming you didn't have a bit of a furred up heater matrix to start with.
If not, stop engine and get squeezing the hoses some more, and check the bleed screw in case there is more air in the coolant rail.
The above is the normal approach.................

This is a superior method, supplied by ASHY.
I've done it a good few times now and never had a problem with airlocks. Slow and continuous filling is the key. No good just filling a jug up, pouring that in and then filling it up again as that's how air gets trapped.
My method is to use a syphon. I use a fishtank syphon, about £3-£4, as I don't want to get any in my mouth, but any old bit of hose pipe will do, just don't suck it into your mouth.
Fill a bucket or bowl with the right amount of coolant/water mix and then put one end of the tube in the coolant tank and one end in the bucket. Undo bleed screw and then just wait until a good flow of liquid comes through.
Run the engine for a bit without the expansion tank cap on and then switch off and allow to cool.
Bleed again and then take the car for a run and then a final bleed when cool.
I don't usually get any air on the second bleed with this technique.
I will add that he assumes that anybody reading this, would have the bleedscrew out as above method and would have their heater set to hot............... and run the car with the heater on, as a warning of air-lock.
 
#14 ·
Thanks for the reply MGJohn. Is this the technique you use.....

Take out the bleed screw on coolant rail.
one of the secrets of bleeding the K-series is to slowly trickle the coolant into the expansion bottle, not jug it in and hope for the best.
You want the heater temp control knob set to max heat, if you don't do this you will have air-locked in the heater matrix.
When nothing but coolant is streaming out, replace the bleed screw, keep slowly filling the tank until at correct level. Give the hoses a good squeezing. Top up cap on, and start engine, within a few minutes, the heater with the fan on should be throwing out ever warming air, getting hotter by the minute......................... assuming you didn't have a bit of a furred up heater matrix to start with.
If not, stop engine and get squeezing the hoses some more, and check the bleed screw in case there is more air in the coolant rail.
The above is the normal approach.................

This is a superior method, supplied by ASHY.
I've done it a good few times now and never had a problem with airlocks. Slow and continuous filling is the key. No good just filling a jug up, pouring that in and then filling it up again as that's how air gets trapped.
My method is to use a syphon. I use a fishtank syphon, about £3-£4, as I don't want to get any in my mouth, but any old bit of hose pipe will do, just don't suck it into your mouth.
Fill a bucket or bowl with the right amount of coolant/water mix and then put one end of the tube in the coolant tank and one end in the bucket. Undo bleed screw and then just wait until a good flow of liquid comes through.
Run the engine for a bit without the expansion tank cap on and then switch off and allow to cool.
Bleed again and then take the car for a run and then a final bleed when cool.
I don't usually get any air on the second bleed with this technique.
I will add that he assumes that anybody reading this, would have the bleedscrew out as above method and would have their heater set to hot............... and run the car with the heater on, as a warning of air-lock.
The first description is close to the method I use. Alternate squeezing of the top and bottom radiator hoses for a minute or two whilst the engine is running ( be careful ) does the trick for me with the K-Series.
 
#16 ·
#25 ·
I am having the same problem with my ZT 190 kv6. Was leaking from the stat and causing air locks so had it replaced but now the system is over pressurising both top hose and bottom bulging and no matter how many times I bleed it come back to it the next day and will have air in it again. What's confusing me is that mine is not overheating and the heaters are running hot. put a obd on it and was going up to 103 then dropping back down when the fans kicked in. Had nothing but trouble with it so far :( only drove it a total of 20 miles since I bought it.
 
#26 · (Edited)
The maximum pressure that the cooling system can develop is controlled by the relief pressure of the filler cap. This is nominally 22psi. A system running near this pressure will have very hard/pumped up hoses and is normal for a hot engine. If something causes a pressure increase (a severe overheat due to coolant loss/exhaust pumping due to HGF) then the excess pressure will cause the relief valve to open. This may be accompanied by the ejection of hot coolant. Air locks will cause pressure increases since gases expand faster than liquids. Since it can't increase in volume, the pressure goes up.

TC
 
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