Also worked on the VF500 Interceptor.
I had two incidents over the last few months where it would puke a little coolant out of the overflow bottle. Once after a long highway trip, and once after a short hop across town. Never, EVER did it run hot.
Did some investigating and decided to try and "burp" the system again. Within seconds of cranking, the coolant was at the top of the filler neck. I let it run for ~8-10 minutes and it got HOT. Like, really hot....hotter than I've ever seen on the street. Puked coolant from the filler neck all over the driveway. I got nervous and cut it off.
I did notice that the fan never came on. I had tested the fan earlier, and it tested good now. That means that the thermo switch must be bad. I was advised to replace the cap as well. Yep, the old one was definitely sagging a bit.
I drained the system again. This time I removed and tested the thermostat and flushed the entire system/engine and not just the radiator.
Found a thermo switch at AutoZone ( for a ~'84 Honda Accord) that is slightly longer but fits and, as a bonus, it comes on 10-15 degrees cooler than the VF switch. Plus, it was less than $20 vs. ~$55 for the "correct" switch.
Bled the system again, this time using the drain plug on the water pump as well as the filler neck. The fan kicked on as intended, just as the needle got into the "fat" part of the gauge. Woo-Hoo! Love it when stuff works like it's supposed to!