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MG ZR ZS ZT Technical - ZS 120 ... Temperature gauge rapidly reaches ...

.... a 'normal' reading after start-up.

I don't drive my new ZS 120 very often as it's the family runabout. However, one thing I've always noticed when I do drive it is the rapid way the needle on the temperature gauge reaches the 'normal' position within say half a mile of a cold start. Surely the engine cannot be fully warmed up to best temperature so soon even in the hot weather we've had since I got the car..??

Fast long distance motorway work or stop-start traffic conditions makes no difference to that 'normal' reading, just below the half way mark in the middle.

Since making this observation I've been thinking that the temperature sensor must be located in an area which heats up very rapidly whilst other areas of the engine still would not be up to ideal working temperatures. Using all performance as soon as the needle reaches 'normal' could lead to problems if the engine isn't fully warmed up ....

Haven't given this much further thought until yesterday. Whilst removing bits from a Rover M16 engine in the local breakers, got talking to a guy who'd put a K series 1.8 (VVC? - cant remember) in a midget which his daughter uses for track days. He told me he had relocated the thermostat in his conversion as it's original position was not ideal for the K series. I have not seen this engine of course but from his description, could see what he was getting at. With my ZS's rapidity to reach 'normal' reading (false?), I think he has revealed something interesting here. IIRC he said his daughter's name was Tamsin Fischer (?spelling) and he does read these BBS threads sometimes.

If anyone knows of such a successful and beneficial thermostat relocation for the K series engines, or indeed if the chap I spoke to yesterday reads this, I'd really appreciate more information on this subject ..... who knows, may reduce or even eliminate the dreaded HGFs in the K series.

Definitely worth more discussion and I'd welcome anyone's views on this subject.

Finally a question for other ZS 120 drivers .... How quickly does your temperature gauge reach a normal reading after start up. Mine does within half a mile.

John McFeely

Was not aware of all these HGFs in the K series;surely MGR should by now have found the reason (or is your idea too simple?).
With such problems was it wise to launch a turbo version?


There are several K series in our family. So far no problems. We tend to hear on this BBS only about those that do have problems. There could be some idiot proof answer to the problem that some cars/owners have. For that reason alone it's worth further investigation and something simple like a different location for the thermostat could be that answer.....

John McFeely

As the K Series engine only holds about 1.5 litres of water (internally) I'd expect a rapid warm-up.

Nothing to worry about.

I know of a friend whose head gasket went on his Rover 416 at 35k miles (approx 4years old. Whether this was the result of design, or the fact that he drove 1 mile to work and back each day, without warming the engine up before revving hard up the hill, I don't know. My neighbour has just experienced the same problem on his 416 as my wife's 214, which is the failure of the inlet manifold gasket. The gasket is a 10 item, but a labour intensive fitment. Now the garage that did my neighbour's car reckons it is a poor design on the K.
I have also heard from several sources that regualar coolant replacement on the K series can help avoid the problem (my neighbour had been topping his system up with water). I wonder how many gasket failures on cars such as teh MGF etc are down to budget motorists skimping on the servicing?

John, I have followed a discussion elsewhere about the rapid water warm-up and the resulting temperature differential with the oil in the sump. I would allow the engine a good 5-10mile run before even starting to use the revs properly as the indicated temp on the guage is going to be a lot different to the oil. Alternatively, to partly alleviate this problem run a Mobil 1 0W40 instead of the semi-synth 10W40. This will offer a thinner oil when warming up and should be less of a problem. But wait until 10k miles before the fully synth oil goes in.


The K series in the MGF has a separate oil temperature gauge. This is a far better way of indicating whether the engine is up to temperature. When I was driving the F the water temperature got to 'normal' within a couple of miles. The oil did not reach 90 degrees, which is the temperature that I required before I used the full capability of the car, for another 5 - 10 miles. By allowing the engine to reach a proper working temperature I managed to avoid the HGF, which is so prevalent on early MGFs, until the water pump failed at 83K miles. Later MGFs are fitted with steel location dowels for the head, which seems to have reduced the occurance of HGFs.

I would think that you would be able to source an oil gauge and sensor from an F to fit to your ZS.



This thread was discussed between 25/08/2003 and 26/08/2003

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