Mayo at Christmas time

Posted on December 3rd, 2012 by Rob Marshall

Mayo at Christmas timeAt this time of year, GEM Motoring Assist’s technical team receive more enquiries than ever from members, who feel that their car’s cylinder head gasket has failed. Their concern is justified. A garage prognosis of ‘the head gasket’s gone’ is often followed by a quotation of at least several hundred pounds. With this in mind, a certain amount of paranoia can set in.

One of the commonest ways of identifying whether or not a head gasket is failing is to remove the oil filler cap and take a look inside. The sight of white mayonnaise-like gunk, within the opening, leads many people to make an immediate and pessimistic diagnosis. While it is true that a failed head gasket might allow the water and oil to mix together, creating the white emulsification that forms beneath the oil filler cap, normal condensation from within the engine can cause the symptom, especially during wintertime. If the car is not driven on long journeys regularly, the water cannot evaporate and the ‘mayo’ build-up increases.

Often, worried owners presume that this is an indication of cylinder head gasket failure but it is not always the case and additional checks should be made, before arriving at a snap diagnosis. If more than several of the following points are noticed as well, then it is more likely that the gasket has failed and further advice should be sought, before driving the car any further.

1.   Pull out the dipstick and inspect its end for any evidence of water.

2.   Check that the coolant level has not fallen to below the ‘minimum’ mark.

3.   Ensure that the engine does not seem down on power or overheating.

4.   Open the coolant cap, with the engine cold, and inspect the expansion bottle’s insides for white or oily scum.

5.   With the coolant cap removed and the engine running, check for air bubbles emanating from the coolant. A ‘sniff’ test, performed on the cooling system by specialised equipment, can determine whether or not combustion gases are leaking into the cooling system.

6.   Ask a garage to perform a compression test.

Prior to thinking that a cylinder head gasket has failed, investigate the issue a little further, before committing yourself to what could be an avoidable major repair.