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MGZT coolant problems

8K views 55 replies 10 participants last post by  philiptrak 
#1 ·
Hi Guy's i am a new member so bare with me, but need some advice with my 1.8 K Series MGZT 120+. My car is an 04 plate with 98,000 on the clock and with the usual issues all fixed head gasket, fuel filter, all this has been done over the life span of the car and all seemed well, but over the last few weeks my car has started loosing coolant through the expansion tank cap and is doing the same through a brand new genuine rover one as i thought it might be the old one had failed. The interior heater is working as it should, the car is not overheating only when it has lost most of the coolant and then the fan kicks in as it should, i immediately stop let it cool and fill the system back up. I check the water level every day, the level stays fairly constant but under pressure sometimes when cold and overflowing from the expansion tank when i remove the cap after the car has stood all day which i know is not normal, the problem usually starts when i am in slow moving traffic. I have had a mate who is a mechanic look at it but the car fails to play up every time he has it for a day so both of us scratching our heads, i really don't want to get rid of it as this is the best car i have ever had and i am hoping it is something simple any ideas?
 
#2 ·
The signs point to another HGF in progress I'm afraid. Repeatedly allowing coolant to get so low as to cause red light overheating is only exacerbating the situation. When the warning pops on, it's often too late to prevent damage, however small. That's why many of us with 1.8 models fit proper temperature gauges.

TC
 
#3 ·
Thanks it was an uprated head gasket that was fitted, and so far no mayo on the oil stick or the oil filler cap, recently had an MOT and the exhaust test all came back normal car running fine so really confused as to what is causing the pressure problem as i said the interior heater is working fine it has only overheated twice but it is difficult to know the car is losing coolant as it does it when driving through the expansion tank cap.
 
#4 · (Edited)
Assuming the pressure relief cap is in working condition, the only way that coolant can be ejected is for the cooling system pressure to exceed 22psi. Over-filling can cause hydraulic lock ejection, but that doesn't seem to apply from what you've said. Over-pressure can happen if there's an excessive overheat (to around 128-130°C) which will raise the vapour pressure in excess of the relief pressure, or for exhaust gases to be pumped into the cooling jacket via a fissure in the head gasket. This can happen by failure of the gasket material, if the head surface is untrue, the liner protrusion is too small for the gasket system in place or lack of tightness in the head clamping bolts. Another cause could be a crack in a cylinder liner.

TC
 
#5 ·
When the engines up to operating temperature squeeze the top hose.
If its hard, you have a problem.

It could still be head gasket related.

Since it would be most likely getting combustion pressure in order for it to overpressurise (rather than the engine over heating)
A sniffer test on the coolant would work.

It might be that its leaking coolant from somewhere.
This would lead to air in the system which expands and pushes water out.

You need to decide which case it is
 
#7 ·
One other thought, how full are you filling the expansion tank? The MAX/MIN level indicators are actually right at the bottom of the tank below the fins, anything above this is likely to be expelled when the engine reaches the correct operating temperature. If you are overfilling it may be the engine is just finding it's own level and you have nothing to worry about.

 
#9 ·
I don't want to hijack this thread, but my ZT-T 1.8 Turbo is showing similar symptoms. I've had 2 hoses burst in the last two months. The first, back at the end of July caused the needle to top out and the overheating warning to flash up on the dash. The second was better managed, and only saw a brief, slight rise in temp. Since then I've continually had to top up the coolant - not sure of quantities, but I've started to monitor it now. No mayo, and there's always pressure when I take the cap off, even after a couple of days of no use. The fan only kicks in occasionally when stuck in traffic for an extended period. Heater works fine.

Never having noticed the "Max" mark in the expansion tank because it's usually covered by coolant (nice bit of design genius there!), I've often over-filled it (but no more!). Is it worth changing the cap, and/or should I be worried about hgf?
 
#10 ·
Don't be fooled by the level of water, i went several days without topping up always making sure the water level was just below the fins in the expansion tank, and then for some reason i lost the lot again! out of the pressure cap and that lead to overheating. I stopped the car immediately let it cool and then topped up the water it took quite a lot before it found a level again so it is really difficult to know how much to keep adding. You probably already do this but keep plenty of water on board and check the expansion tank every day. My car is being looked at over the next couple of days with various tests will keep you posted.
 
#11 ·
Well, I'm not sure if I noticed a new symptom today or not. Cold morning and a very steamy exhaust, although it did seem to clear up after the engine warmed up. I suspect I'm just being paranoid because coolant loss is on my mind, but it did seem a lot steamier than any other car around me. It was very noticeable when sitting in traffic, but less so once moving. Haven't checked the coolant level yet, but will pop down at lunchtime and see how much it's gone down since last week.
 
#12 ·
Excessive steam production can be a sign of inlet manifold seal failure. This is common in the 1.8 engines and leads to coolant loss with no outward signs. The coolant will usually get into cylinders 1 and/or 4 causing their spark plugs to look 'washed' and get a pink stain. The fix for this is a new seal. The best option is the later Viton version (black). The original seals are in a less robust blue coloured rubber.

Viton Seal: http://www.rimmerbros.co.uk/Item--i-LKJ101110
 
#13 ·
Excessive steam production can be a sign of inlet manifold seal failure. This is common in the 1.8 engines and leads to coolant loss with no outward signs. The coolant will usually get into cylinders 1 and/or 4 causing their spark plugs to look 'washed' and get a pink stain. The fix for this is a new seal. The best option is the later Viton version (black). The original seals are in a less robust blue coloured rubber.

Viton Seal: http://www.rimmerbros.co.uk/Item--i-LKJ101110
Well, I've just ordered both a new expansion tank cap, and a new IMG. Give me something to do at the weekend...
 
#16 ·
Had a test done to find out if there was gases in the water and all clear so no HGF, and cylinder head also ok, but still no answer to the pressure build up in the expansion tank when it has been left cold. At least it behaved itself this morning in heavy traffic no loss of coolant through the cap so still head scratching at the moment .
 
#18 ·
Well after doing a gas test and all came back ok, the last few days the car has run perfectly fine. Maybe this is a tip for anyone else with a similar problem, the last time i took the expansion cap off when the engine was cold and the coolant came straight to the top and overflowed i kept pumping the top hose with my hand forcing more coolant out until the level settled just above the max, maybe doing this helped force some air, i really don't know, and i hope it's that simple, but i have been stuck in traffic, done some heavy motoring and no coolant loss through the cap and keeping a constant water level in the expansion tank, fingers crossed, and thanks for all the help and suggestions will keep you posted. cheers
 
#19 · (Edited)
Well after doing a gas test and all came back ok, the last few days the car has run perfectly fine. Maybe this is a tip for anyone else with a similar problem, the last time i took the expansion cap off when the engine was cold and the coolant came straight to the top and overflowed i kept pumping the top hose with my hand forcing more coolant out until the level settled just above the max, maybe doing this helped force some air, i really don't know, and i hope it's that simple, but i have been stuck in traffic, done some heavy motoring and no coolant loss through the cap and keeping a constant water level in the expansion tank, fingers crossed, and thanks for all the help and suggestions will keep you posted. cheers
Hmm, well, I put a new cap on yesterday, and although I've only done 4 short (~4 miles) trips since, the coolant has dropped by about 1/4 pint. Also, there was no pressure when I took the cap off ths morning - is that right or wrong? It also seemed a bit lumpy on start-up from cold, so I'm definitely thinking inlet manifold gasket. New Viton one turned up on Weds, so I'll get that fitted overthe weekend and see if that sorts it.

{Edit} Anyone got a spare inlet manifold nut? :-(
 
#20 ·
JensenHealey;6082378]Hmm, well, I put a new cap on yesterday, and although I've only done 4 short (~4 miles) trips since, the coolant has dropped by about 1/4 pint. Also, there was no pressure when I took the cap off ths morning - is that right or wrong? It also seemed a bit lumpy on start-up from cold, so I'm definitely thinking inlet manifold gasket. New Viton one turned up on Weds, so I'll get that fitted overthe weekend and see if that sorts it.


{Edit} Anyone got a spare inlet manifold nut? :-(
 
#21 ·
A rule to follow. If you check the level cold but there's pressure after driving the car and allowing it to completely cool down again, something's wrong. That can only be due to exhaust being pumped into the cooling system. Air getting in from leakage will not cause cold system pressure.

TC
 
#22 ·
A rule to follow. If you check the level cold but there's pressure after driving the car and allowing it to completely cool down again, something's wrong. That can only be due to exhaust being pumped into the cooling system. Air getting in from leakage will not cause cold system pressure.

TC
Strangely, while I've been checking it for the last few weeks it's always had pressure first thing in the morning which is when I usually check it. After putting a new cap on, when I checked it yesterday and today, no pressure...
 
#24 · (Edited)
Well, an update - having had the new IMG and expansion tank cap fitted for nearly a week, I kept topping up each morning, but less and less, until Weds/Thurs it didn't need any - presume little air pockets working out of the system. No residual pressure each morning either. Yesterday, however, I got stuck in nightmare traffic on the way home, and although there was no sign of overheating (needle stayed bang on normal), I lost coolant through the expansion tank. (As evidenced by the embarrassing clouds of steam!). I've heard the fan cutting in over the last few days, but only to a normal extent when stuck in traffic - it would cut in for 20-30 seconds once or twice if I was queueing for more than a few minutes. Last night, however, I didn't hear it at all. Is this a new problem with the fan?

OP - how are you getting along with yours? (As I seem to have hijacked this thread fairly comprehensively! )

EDIT - just to say, I only lost about 1/4 - 1/2 pint of coolant.
 
#25 ·
I got stuck in nightmare traffic on the way home, and although there was no sign of overheating (needle stayed bang on normal), I lost coolant through the expansion tank. (As evidenced by the embarrassing clouds of steam!). I've heard the fan cutting in over the last few days, but only to a normal extent when stuck in traffic - it would cut in for 20-30 seconds once or twice if I was queueing for more than a few minutes. Last night, however, I didn't hear it at all. Is this a new problem with the fan?
OK, do NOT rely on the temp gauge to indicate overheating, they are useless and only move when the engine is already well on the way to being cooked. Far better to use the digital display which will tell you the engine temp to the degree.
 
#30 ·
So, the temp stays between 90 and 95, unless I'm stuck in traffic or looking for a space in a car park. Waiting for a space today and I noticed it went up to 100, and although I didn't see any steam, I could smell it when I got out of the car. When I got home I simulated crawling in traffic by doing short hops up and down the drive. Temp crept up to 110 and then it boiled and vented. The fan only came on AFTER I switched off! That may have been a coincidence, and it may have been about to come on anyway. It then cooled fairly quickly back down into the 90's.

My guess is therefore whatever is controlling the fan. Is it the Cooling System Temperature Sensor on the coolant outlet elbow next to the rad top hose connection? Is it possible to test this, or should I just swap it out?

Any other suggestions as to the problem?
 
#31 · (Edited)
The typical running temperature for the 1.8 engines is in the 90-100°C range.

Temp crept up to 110 and then it boiled and vented. The fan only came on AFTER I switched off!
Clearly you have a cooling fan problem.The 1.8s have a 2-speed fan, which first trips on at around 104°C to cool the engine to about 97°C. The high speed running after engine off is due to heat soak from the head. It comes on around 112°C till about 105°C. It can run for up to five minutes max. It really shouldn't cause pressure cap ejection unless you over-filled it.

My guess is therefore whatever is controlling the fan. Is it the Cooling System Temperature Sensor on the coolant outlet elbow next to the rad top hose connection? Is it possible to test this, or should I just swap it out?
It's a problem with the fan itself, not the control system. It depends on the year whether it's easy/cheap or more complex/expensive to fix.


Any other suggestions as to the problem?
You can prove the slow speed failure by running the standard Demist test.
The demist test is discussed more than any other fan issue.

TC
 
#34 ·
I'd say the slow speed resistor has failed. it's virtually inevitable and when they say 'they all do that', it's actually true. You can get uprated resistor on eBay. It means taking the front end off to replace and will fix the slow speed.

TC
Yeah, just looked in the Haynes manual - looks a horrible job! I'll do the demist test tomorrow, then order the gold resistor.
 
#36 ·
This might explain why my old 1.8T Mk2 MG ZT is doing this, my dad said it keeps using coolant but no visible leaks, head gasket has been done, inlet has been done etc.

I know the fan is faulty so the resistor needs fixing! Will have to order one and fit it. I believe mines the easier one as you can see the resistor on the fan through the grille?
 
#37 ·
This might explain why my old 1.8T Mk2 MG ZT is doing this, my dad said it keeps using coolant but no visible leaks, head gasket has been done, inlet has been done etc.

I know the fan is faulty so the resistor needs fixing! Will have to order one and fit it. I believe mines the easier one as you can see the resistor on the fan through the grille?
Sounds possible, but there should be some evidence of the leak via steam/smell when it boils over. "Easier" is a relative term - it will still involve removing the bumper!
 
#40 ·
Hi guys i haven't been on for a while, still trying to sort my overheating and fan problem. At the moment the fan comes on at normal temperature within 5 minutes of normal driving then the Temp needle creeps up but i am not losing water from the expansion cap any more, it looks like it is not getting round the engine and the water pump is working. So last resort
another gas check plus a vacum check to get rid of any air locks and a new thermostat which by the way isn't a normal looking one which i have on my MGB this is the big white grenade looking thing with 3 hoses off it at the lower part of the engine, if that doesn't work i am afraid she may have to go, 9 years and 100,000 miles still the best car i have had fingers crossed the new thermo might be the answer.
 
#45 ·
- - - a new thermostat which by the way isn't a normal looking one which I have on my MGB this is the big white grenade looking thing with 3 hoses off it at the lower part of the engine - - -
It's a Pressure Relief Thermostat (PRT) that's fitted to the late 1.8 engines. It fits into the cooling hoses just behind the bottom of the radiator.



A thought about your overheating issue. Are you sure there isn't a standard thermostat fitted at the usual place? It's a fairly common mistake by garages unfamiliar with these engines. If there's an upper end stat and a PRT, the engine will constantly overheat.
 
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