Home UOA Kit Gas In Oil

May 25, 2005
In the past I've often thought I had fuel contamination as "verified" by smelling the oil. Wrong! Every time my nose was wrong, with the UOA proving it. I no longer trust the "sniff" test (at least with my "sniffer"). If cost of doing a UOA is a factor, your local NAPA store sells a test kit for $14, part number 4077. This is will tell you if you really do have fuel contamination. I am unaware of any home chemistry experiment which will directly tell if you have fuel in your oil. However, it might be possible to infer indirectly. If you have a lot of fuel in your oil, it will affect viscosity. You could put a sample of virgin oil in the freezer along with a sample of used oil. After they are well chilled, see if there is a difference in their ability to pour. If the used sample pours faster than the virgin sample, it could indicate excess fuel in your oil. The cause of fuel contamination can be leaking injectors, and misfires. Defective or misadjusted carburetors are also a problem. Does your car misfire a lot? The misfires could be causing fuel contamination. One way to test for leaking injectors is to attach a fuel pressure gauge to the fuel rail. There is usually a Schrader valve on the rail which allows you to easily do this. Check the fuel pressure with the engine running. Look for excess pressure. Make sure the vacuum line attached to the pressure regulator is not cracked or missing. If you have excess pressure it could cause injector leaks. Next, shut down the engine. Leave the pressure gauge attached. The pressure should hold for a considerable length of time. If you come back an hour later and the fuel pressure has dropped considerably, then you might have leaking injectors. Some drop in pressure is normal. It depends on the car. A drop of 10 or 15 percent after an hour probably would not be a cause for concern. Check you shop manual for more information.