75ZT Community

On the 13th March I discovered I had a leak from the thermostat on my MG ZT 190 I noticed this as the coolant in the header tank was low, so I checked in the V of the engine and sure enough I could see the red coolant not much but enough to have to remove and replace the thermostat.

Below is how I removed and fitted the thermostat I hope this helps some other members if they have to do the same job, remover the under tray before starting the task,the thermostat I removed had only been fitted for 2 years with limited mileage of about 3.700miles.

First remove the engine cover two 8mm bolts Fig 1
1

Remove the cover and put it in a safe place with the bolts Fig 2
2

Using a torch and shinning it through the gap in the manifold I can see the leak Fig 3
3

The next step is to remove the air filter box from the engine bay, loosen the hose clip on the throttle body inlet hose Fig 4
4

Pull off the small air induct hose pipe Fig 5/6
5

6

Next you can pull up the air box it may be stiff as it sits in the holes and is held in by the lugs under the box Fig 7/8
7

8

You now need to release the Shannon tube from the air box Fig 9/10
9

10

Air box removed put it safe with the engine cover in the boot of the car Fig 11
11

You may see a little oil in the air induct hose this is normal and can be cleaned out before re-fitting Fig 12
12

There may also be a little oil in the throttle body again do not worry Fig 13
13

You can now see the three hoses that are connected to the thermostat and the bleed screw Fig 14
14

Later you will also need to remove the bottom hose that is the reason for removing the under tray before starting the task. Fig 15
15

The next parts to remove are the breather hoses, the first one is the one connected to the vis motor & throttle body and the front Fig 16/17/18/19
16

17

18

19

These hoses are removed by depressing the red locking collars Fig 20/21
20

21

You will have to use a screw driver to depress the locking collar connected to the vis motor Fig 22/23
22

23

The last locking collar on the top breather pipe is connected to the top of the throttle body and is black an again a screwdriver may be used Fig 24/25
24

25

You can now pull back the engine bracket and feed the hose past it Fig 26/27
26

27

With the hose removed again put it in the boot for safety Fig 28
28

You can now remove the second breather hose Fig 29
29

Start at the front cylinder head again depress the collar Fig 30/31
30

31

Them move to the collar on the manifold Fig 32/33
32

33

The last part of this hose to be removed is the T piece, this is held in by a white collar Fig 34
34

This white collar needs to be pressed in at both ends and twisted to release the hose Fig 35
35

Once remove inspect it and make sure it is in good order no cracks or splits and put it in the boot Fig 36
36

Next step disconnect the vacuum hose from the idle control valve Fig 37
37

Place this hose to one side for now Fig 38
38

You can now unplug wiring plug from the throttle body Fig 39/40
39

40

unclip the next plug underneath by depressing the metal spring clip Fig 41/42/43
41

42

43

With the two wiring plugs removed set them out of the way Fig 44
44

Next we turn our attention to the throttle cable Fig 45
45

lift the throttle lever and remove the cable 46/47
46

47

We now need to remove the throttle body it's self which is secured to the manifold by four torx 30mm bolts two above and two below Fig 48/49/50
48

49

50

You will need to use a long reach socket and ratchet with 30mm torx start with left top bolt Fig 51
51

Next bottom left Fig 52
52

Bottom right Fig 53
53

Last top right Fig 54
54

Once removed inspect and clean up with a bit of WD 40 and in the boot with it Fig 55
55

You can now put a container under the bottom radiator hose and remove it to let out the coolant Fig 56/57
56

57

This hose with the bleed screw in it will be removed once the coolant as be drained off Fig 58
58

I then tied back the breather hose so it would not be in my way later Fig 59
59

The next step is to remove part of the thin header tank hose again for more access later Fig 60
60

To help get to the hose above better remove the lead of spark plug 61
61

With the lead removed you can use some grips to open the hose clip and set it back Fig 62
62

You can now pull out the T junction as here fig 63
63

We now need to remove the right hand side of the header tank hose from the T joint Fig 64
64

As before release the hose clip with some long nose grips or mole grips and remove the hose Fig 65
65

The hose can now be moved to the front of the engine out of the way Fig 66
66

The other part of the hose can be tied back with the breather pipe with the white collar from before Fig 67
67

Now that the thin header tank hose is out of the way you will see there is some wiring also that will need to be lifted later, but as you can see another breather hose is lying over the top of it this will also have to be removed Fig 68
68

To remove this last breather pipe again as before press the red collar and it will release Fig 69/70
69

70

Breather pipe pulled out Fig 71
71

Removed from the engine put it safe in the boot with the others Fig 72
72

Now with most of the item out of the way we can see the thermostat and the hoses connected to it Fig 73
73

You can now check the header tank it should be empty Fig 74
74

Also check at the bottom hose & rad to see if the coolant as stopped coming out Fig 75
75

We are now ready to remove the large hose with the bleed screw attached to it again use long nose grip if you have some if not mole grips will do or pliers Fig 76
76

Once removed from the car put it safe Fig 77
77

With the first hose removed we can then turn our attention to the other two Fig 78
78/79

79

Now release the clip from the next large hose and pull it backward Fig 80/81/82
80

81

82

This hose is connected to the top of the radiator Fig 83
83

With the clip released you can now pull off the hose expect a little more coolant to drain out Fig 84
84

You can now tie this hose out of the way Fig 85
85

Before you carry on mop or soak up the split coolant Fig86/87
86

87

We are now ready to remove the last hose from the middle the smaller of the hoses Fig 88/89
88

89

Now that the middle hose as been removed and tied back to the other one, we can turn our attention to removing the 10mm bolt which holds the thermostat in place to the engine block, you will need a thin long reach socket with a knuckle on the end to do this through alloy manifold Fig 90
90

Pass the socket through the gap in the manifold as here Fig 91
91

Once you have the socket through make sure it is seated on the bolts head properly Fig 92
92

Get a good grip and turn the ratchet socket slowly to break the joint on the bolts and it will them release quite easy Fig 93/94
93

94

Once you have the bolts to the end of its thread and still sitting in the elbow joint you will need a telescopic magnet to remove it if not you will be fishing for it later in the V of the engine Fig 95/96/97
95

96

97

You are now ready to prise out the thermostat housing first try twisting and lifting the elbow bend if no joy prise the housing up it's self as here Fig 98
98

You will now get some more coolant flow into the V of the engine this can be cleaned up later when al the hosing as been removed and before re-fitting the new housing.

If you are still finding it difficult to remove the housing use the long nosed grips to help as here Fig 99
99

remove if you are going to re-use the housing maybe because only the seals have give way then set to one side safe Fig 100
100

With the main thermostat housing body remove it will leave the straight piece and the elbow bend in place you can now remove these Fig 101/102
101

102

Those should remove easy now you can clean up inside the V of the engine Fig 103/104
103

104

I also hoovered some coolant out of the openings which the thermostat fits into so it did not over flow when replacing later.Fig 105
105

Part three to be continued

Part Three refitting the new thermostat.

With all the thermostat parts in front you straight piece, housing, and the bend start by fitting the straight piece into the housing.

Straight piece with Fig 106
106

The bend Fig 107
107

The housing with the straight piece fitted into it, this you need to do first before you offer and fir the housing and straight piece back into the engine Fig 108
108

Now you have the housing and straight piece together feed thin into the V of the engine you can and should smear the ends of the straight piece and the hosing with a lubricant Vaseline etc, make sure you push home the straight pipe and then push the thermostat housing down and in Fig 109
109

Double check the straight piece by looking through the manifold holes into the V with a touch as here Fig 110
110

And also at the housing end as here Fig 111
111

Next check the housing it's self is pushed home and seated right, this housing as lugs and only allows the housing to be pushed home as much as it should be Fig 112
112

The next step is to fit the bend again making sure the end is lubricated to help it being pushed home with ease Fig 113
113

Look through the holes in the manifold again with a torch and make sure you have lined up the adjoining holes in the housing and the bend then offer the bolt to it carefully through the hole in the manifold using the socket and ratchet you remove it with Fig 114
114

After fitting the bolt which holds the bend and housing in place double check the straight piece in still in place Fig 115
115

Now you are satisfied that the thermostat is fitted correct you can start adding the hose to the housing pipe work do the small middle one first Fig 116/117
116

117

Next fit the large one which fits on to the bend Fig 118/119
118

119

You can now fit the hose with the bleed screw in it to the main thermostat housing Fig 120
120

And fit the hose also to the bottom of the radiator Fig 121
121

With all hose fitted and jubilee clips tightened up make sure the bleed screw is hand tight as you will need to undo this at a later date when bleeding the system. Fig 122
122

Fit all the wiring and throttle body with breather pipes back into place Fig 123
123

Making sure you fit the throttle cable Fig 124
124

If you are working on your own as I was you need to find something to raise the header tank up as far as it will go to refill it slowly, as you can see here I used a short plank of wood Fig 125
125

I rested the locating pegs on to the rad housing as here Fig 126/127
126

127

I filled the header tank slowly at the same time I undid the bleed screw and carried on filling until the water came out of the bleed screw then I screwed in back in making sure the coolant never dropped below the minimum level when filling, thus trying my best to avoid an air lock Fig 128
128

Once happy i ran the engine with the header tank still raised and kept my eye on the coolant once I saw is rising I added the coolant cap and let the car get up to temperature 91 turned the engine off and let it cool a bit, at this time I again checked in the V to see all was ok and not leaking Fig 129
129

I then checked the level in the header tank all seemed ok ran the engine again this time up to 101 and waited for the n to kick in and bring the temp down to 95 I did this a few times and turned the engine off, I cleaned up all my tools and put them away, I went and ate my tea by the time I had finished an hour had passed and I again checked into the V for leaks etc it was bone dry Fig 130/131
130

131

Also checked at the housing connections Fig 132
132

The next morning I again checked the coolant in the header tank and it was spot on with the max mark Fig 133
133

Steve thats a great how to and will no doubt come in useful to me one day, when is the second episode ?

Trebor wrote:Steve thats a great how to and will no doubt come in useful to me one day, when is the second episode ?

Hi Rob.
Funny I have just thought I will have a stint at the second part as it too is going to be long

Two years passed now since I replaced the thermostat and all is good so hopefully the thermostat with the lugs is doing it's job pics to be added later Arctic.