I have heard that certain engine blocks made of aluminum alloy - especially foreign makes, utilize antifreeze that is specifically low-silicate for the purpose of low abrasion in the water jacket. If you have a head gasket leak, and you have one of these types of engine bolocks, it may prove to be detrimental to add silicates to the coolant. If the situation is desparate, such as being stranded without mechanic support or without resources to accomplish a repair and transportation is vital, I suppose you have no other choice. Otherwise with low risk situations, it is better to go to the nearest auto parts store, purchase a Haynes or Chiltons repair manual, study it, and buy the parts to effect a head-gasket repair. Like any other event , weigh expense of self or mechanic repair versus loss of money by not having the transportation available. If you are mechanically handy, then you might justify the expenditure for extra tools which may be used for other jobs in the future, or be able to be written off in taxes if you have your own registered business.