That liquid is normally dark blue. It turns yellow in the presence of combustion gases from a leaking head gasket as you suspect, but if it turned brighter yellow after the engine stopped running, that suggests you were picking up exhaust gas that floated over from the tail pipe or an exhaust leak near the engine. The other symptoms you described don't sound like head gasket issues. They suggest misfires or fuel pressure problems. I wouldn't jump on head gaskets yet until other potential causes are ruled out.
You may also want to have the charging system professionally load-tested. If you find the generator can only produce exactly one third of its design value for current, which is commonly 90 amps, and "ripple" is very high, we will discuss that further if necessary.
Tuesday, April 30th, 2013 AT 2:28 PM