Dramatic Rise In Fuel Usage

I drive a 1990 Civic EF9 with a B16A DOHC VTEC engine. I face these problems:

1. The radiator cover cracked last month and I changed to a new one and flushed the radiator system. But after a few weeks, my reserve tank keeps decreasing dramatically. Normally, it takes me at least two weeks to refill the tank, but now I have to do it once a week. I found no leakage on the hoses or water-pump failure in the cooling system..

2. I bought a second-hand sports extractor which still has its two O2 sensors. I installed the extractor together with the O2 sensors but fuel consumption becomes higher than normal. I used to get 200km plus with RM30 of fuel but now I get only around 140-160km. Is there any failure on the O2 sensors although it is not indicated by the "check engine" light? Should I re-install my original sensors (from the OEM extractor)?

Reply:
1. If you are sure the coolant is not venting out somewhere, then the other possibility is the radiator cap. The radiator cap is supposed to vent off excess coolant ito the expansion tank and allow coolant to flow back into the engine when there is needed, such as when the engine cools and a partial vacum is formed in the engine. If the cap is venting to the atmosphere then you are loosing the coolant through evaporation and the coolant levels will come down. The radiator cap has two seals and if the upper seal is leaking or not contacting the lip of the radiator filler neck, coolant will vent off. You may also want to check if the cap is of the correct pressure for you car. If the pressure setting is too low, it will venting off too early and you will lose coolant also.

2. Yes, the obvious thing to do is to replace the original O2 sensors because the ones that came with the extractor may be of a different specification or even faulty and that may be causing the heavy fuel consumption. Also you should remember that the extractor may be improving your gas flow and giving better performance and you may also driving the car harder, resulting in heavier consumption.