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MG MGF Technical - Coolant loss

HGF 3 weeks ago, no overheating, kept coolant in tank, water leaking from HG onto manifold, lots of steam.

HG replaced by local mg workshop, skim, new bolts, camshaft seals, gaskets coolant etc.

Over the following 2 weeks and 640 km I have lost0.9 litres of coolant of evidenced by a small patch of coolant under the middle of the engine on my garage floor mast mornings.

Pressure tested system both cold and hot and found no leaks. MG workshop found the expansion tank cap "Cross threaded" and not sealing properly.

Is this a common problem? One would think that a coarse thread cap would be hard, if not impossible to cross thread.
Phil Stafford

Phil,

Not heard of caps becoming 'cross threaded'. Caps have been known to fail in the past and I believe that this was due to a bad batch on early cars. The failure showed as leaking from around the cap leading to a loss of pressure which in turn led to localised boiling in the cylinder head and then head gasket failure. I speak from bitter experience. Newer caps were then marked with a white dot of paint on the top to show that they were from a later lot but this practice may have discontinued.

As you say, the thread is really coarse and somebody must have been really determined/careless to get the threads crossed! As you have pressure tested your system and had no signs of leakage I would guess that your system/engine is OK as the pressure loss was not great. But if a new cap does not stop the loss of coolant around the cap then this indicates that the pressure inside is rising beyond the limits. The cap is designed to blow off (release pressure) at a certain limit otherwise your hoses might explode. Excessive pressure build up could be from gases getting into the cooling system from the engine, say through a leaking head gasket? Keep an eye on the situation.

Bruce

Bruce
Bruce Caldwell

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

MG MGF Technical index

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