Maintenance: diagnosis and prevention of HGF
Look at the coolant expansion tank. Is there any coolant left? Is it boiling? Is it Green?
If yes, then the steam erruption is likely to be due to a failure of the coolant cap. To confirm, perform the following checks:
Visual checks for evidence of a HGF
Thanks to Jon Fredheim for the picture of the failed head gasket (D).
(c)2001, Jon Fredheim
|In the event of a head gasket failure, do not attempt to drive the car any further. Arrange transportation to an MG/Rover dealership or specialist for replacement.|
The most likely cause of a failure of this type is the malfunction of the ECU temperature sensor or its electrical connection to the engine management system. To check, open the engine inspection lid, and examine the following parts. A replacement sensor (part # GTR206) costs less than 11 GBP including VAT, so replacement is a sensible precaustion.
Replacement of ECU temp sensor
A: location of sensor at front left corner of engine cylinder head (arrowed)
B: close up of sensor (brown coloured, arrowed).
C: what the sensor looks like (part #GTR206)
D: removing the wiring loom requires release of a circlip- careful not to loose!
Similar faults can occur with the dashboard temperature guage making it under-read coolant temperature. Its location is immediately below the ECU temp sensor mounted in the verticle plane.
Preventative Maintanence to avoid HGF
|There are three bleed nipples in the cooling system of
the MGF. One is located by the radiator (A), the heater (located on the front bulk head
behind the bonnet shroud, B) and in the engine bay, on the header rail, pictured from two
different angles (C, with filter removed observed from the luggage compartment & D
from inside the engine bay with inspection cover removed. The latter provides the easier
To bleed the system of air, keep the resevoir topped up with coolant (50:50 water and Unipart Super3 antifreeze) and individually remove the bleed screws one by one to release any trapped air. Drive the car a short distance, and repeat again once the engine is cold.
Location of the Bleed Nipples
A potential solution to the HGF problem?
Another potential cause of the HGF problem has come to light as a
result of MGF related motorsports. Basically, from what I gather, the problem is as
already been highlighted on the MGF BBS, namely that due to the remote nature of the
radiator causing larger than 'normal' [than that found in FWD applications] changes in
coolant temperature entering the engine. This causes the standard type thermostat to
occasionally be fooled and close when the engine is actually hot, thus allowing localised
'micro' overheating. This phenomena, over a period of time, may weaken the perfectly good
head gasket leading to failure.
The common solution, apparently, is to drill four equi-spaced 6 mm holes in the thermostat ring. This mod allows the cooling system to continue to function in a normal fashion, but crucially also some circulation when the thermostat is shut. Thus, when the thermostat is inappropriately shut, some cooling circulation continues avoiding the excess oscillations of temperature caused by a negative-feedback system such as this with a remote effector system.
There is a draw back- the warm up time is increased. It has been suggested to me that a compromise for a road car would be one (or possibly two) 6 mm holes- which would result in a slower warm-up time, but still adequate closed-thermostat circultion to prevent a temperature peaks causing head gasket failure.
Thermostat modification: see Dieter's thermostat site.
If your MGF has ever suffered from a head gasket failure, we would very much appreciate it if you could enter as many details as possible into our HGF listing. From this we hope to learn more about the causes of the HGF, and help prevent them occuring in the future- thankyou. Enter http://www.shame.4mg.com here.